INTRODUCTION TO TROPICAL EASTERN PACIFIC
1. THE TROPICAL EASTERN PACIFIC (TEP)
Fig 1. The Tropical Eastern Pacific
1.1 Terrestrial and Marine Topography: Geographically the TEP is fairly simple, consisting of a relatively straight and uncomplicated continental shoreline that is oriented roughly north-south, plus a few small, isolated islands and archipelagos (Figs 1 & 2). Habitat available to shorefishes in different parts of the TEP is determined by variation in the extent of shallow (<200m deep) continental and insular shelves. Unlike the Caribbean on the eastern side of the Central American Isthmus, those shelves are quite narrow in most parts of the region averaging about ~ 25 km wide and broadening to about 150 km in only three places, the head of the Gulf of California, the Gulf of Panama and the Gulf of Guayaquil (Ecuador) (Fig 3). The ocean island also have small (Galapagos) to very small insular shelves (the rest of the islands), due to their recent volcanic origins
Fig 2. Continental topography of the TEP (Source NASA).
Fig 3. Submarine topography of the Tropical Eastern Pacific (NASA).
The Gulf of California, which constitutes the subtropical part of the region, offers a complex and dynamic set of environmental conditions (Castro-Aguirre et al. 1995). The range of sea surface temperatures increases greatly towards the northern Gulf (to as much as 28 °C), where the tidal range also is much more extreme than at the mouth of the Gulf. The separation of the areas with different temperature regimes in the upper and central Gulf is enhanced by a zone of permanently cold water around the islands. Sea temperature regimes differ on the two sides of the Gulf, with sites on the east coast having higher temperatures than sites at similar latitudes on the west coast of the Gulf (e.g. 22-28 °C at Mazatlán vs 14-26 °C at La Paz). During spring and summer sea surface temperatures in the Gulf are about 10 °C higher than at locations at the same latitude on the Pacific coast of Baja. Conditions at the tip of Baja are sufficiently tropical (the temperature range is only 9 °C) for it to provide a small outpost of coral development, with many tropical fishes found there but nowhere else in the Gulf of California. Geographically the Gulf is complex with many nearshore islands along the western coast, and a group of islands straddling the junction between the upper and lower Gulf. There are localized upwelling areas on both east and west coasts. Salinities of estuaries ranges from high in the north to more variable in the south where they are fed by flowing rivers (the Colorado estuary at the northern limit of the Gulf is no longer river fed). The strong environmental gradients within the Gulf are reflected in differences in the distribution of shorefishes within the Gulf that are sufficiently large for ichthyologists to have delimited distinct biogeographic subdivisions of the Cortez Province (Walker 1960, Thomson et al. 1979).
Most of the TEP's continental coastline north of Costa Rica is relatively dry (Figs 4 & 5) , although there are some small areas with moderate rainfall, such as that in southern Mexico and Guatemala and around Puerto Vallarta, at the extreme SE corner of the Gulf of California. The highest rainfall is in a band between ~30-100N, extending from the Pacific watershed of Colombia far out into the W Pacific, and encompassing Cocos and Clipperton Islands. This band runs along the center of the seasonally changing position of the Intertropical Convergence Zone (Fig 6), a wet zone or rising air where the tradewinds of the northern and southern hemispheres meet. In fact the Pacific coast of Colombia is one of the wettest places on earth, with parts of the watershed of the Rio San Juan receiving up to 11m of rain per year (Restrepo et al 2002).
Fig 4. Regional rainfall
Fig 5. Regional Rainfall on Land (R-HydroNET)
Because the primary mountain chain that extends through north and south America runs along the western edge of both continents, and the western side of the widest parts of the central American isthmus (see Fig 2). Thus river watersheds that feed into the TEP are all small relative to those that feed into the Greater Caribbean (see Fig 7). The TEPs largest estuarine systems with high freshwater outflows are in the Gulf of San Miguel (eastern Panama), the San Juan River (Colombia, see Restrepo et al 2002) and in the Gulf of Guayaquil (Ecuador). The remaining two large estuaries, in the Gulf of Fonseca (shared by El Salvador, Honduras and Nicaragua), and that of the Colorado River at the head of the Gulf of California, are high-salinity systems draining low-rainfall areas. In addition, almost all of the flow of the Colorado has been diverted to agriculture, with the result that it now has little influence on salinity in the Gulf of California.
Fig 7. River watersheds of the neotropics (R-HydroNET)
As we discuss in the section on the effects of the El Niño cycle (ENSO), the extremes of this cycle have strong effects on the distribution of maximum and minimum temperatures throughout the TEP, but particularly southern edge of the region. During El Niño event temperatures increase throughout the region and the Peru current shuts down. During the opposite extreme of the ENSO cycle (La Niña state) the Peru current flows very strongly and temperatures are particularly low along the equator.
Fig 8. Seasonal extremes of surface temperatures in the TEP: the northern winter (March) and the northern summer (September)
Fig 9. Global distribution of average wind speed (NASA)
Fig 10. Neotropical patterns of winter and summer average wind levels (NASA)
Fig. 12 Hurricane passing near the Revillagigedo Islands in 2008
Fig. 13 Global tidal regimes (Modified after Wikipedia)
Seasonal variation in TEP tidal regimes includes variation in the amplitude of spring and neap tides, in the occurrence of diurnal tides, and in the relative sizes of the 2 semidiurnal high tides of the same day in the northern part of the region.
Fig. 14 Global variation in the strength of the M2 semilunar tidal component (Wikipedia)
Fig 15. Surface ocean currents and oceanographic provinces of the TEP.(RSMAS)
Fig 16. Global variation in average salinity
Fig 17. Short-term variation in surface salinity in the TEP (Aquarius, NASA).
Animation at: http://www.youtube.com/watch?v=zUZHMbZuWVQ
Fig 18. Upwelling systems in the Tropical Eastern Pacific
Fig 19. Global variation in surface pH of the ocean (Courtesy S Doney, WHOI)
El Niño events, which occur at ~ 4-9 year intervals (Fig 20) greatly change conditions in the TEP. During such events the NECC strengthens and widens, and produces a surge of relatively hot water from the central Pacific that first hits the Galapagos and the equatorial part of the TEP. That surge then spreads northwards and, especially, southwards along the continental shore, and can affect virtually the entire TEP, as well as the temperate regions to the north and south of the TEP. During El Niño events the upwelling along the coast of Peru virtually disappears. In contrast during La Niña conditions, which are the reverse of those during El Niños, the west-bound SECC is much stronger and colder (at the surface) than normal (Fig 21).
Fig 20. ENSO index variation since the 1950s
Fig 21. Changes in superficial currents and SST during the ENSO cycle.
Fig 22. Areas with primarily soft (sand and mud) shorelines.
Fig 23. Major mangrove areas
The 5 oceanic islands and archipelagos (Revillagigedos, Clipperton, Cocos, Malpelo and Galapagos) rise abruptly out of deep water and contain little or no sand and mud shoreline habitats. Only the Galapagos have a significant area of shelf (less than 200 m deep) bottom habitat and that archipelago provides ~97% of the insular shelf habitats in the TEP. Further, habitats and environments within the Galapagos are particularly diverse, ranging from tropical at the tiny northern islands to temperate at the western and southern edges of the group, and subtropical in the center between those extremes. Those three areas exhibit strong differences in the composition of their shore-fish faunas and other components of the Galapagos biota.
Fig 24. Areas with primarily hard (rocky) shoreline
4.3.1Coral Reef in the TEP
Opportunities for coral reef development in the TEP are limited, by generally unfavorable conditions in the narrow coastal zone that result from sedimentation and freshwater input from river runoff, and coastal upwelling with cold water, reduced pH, and nutrient enrichment that affect large sections of the coast. In addition the regular impact of El Niño events probably represent the strongest limiting factor on coral reef development in the TEP. El Niños occur at 4-9 year intervals, and at intervals of about 1-3 centuries there is an intense event like that of 1982-83, which produced mass coral mortality throughout much of the TEP. Those stresses are the reason why the TEP has only a few, small structural coral reefs, which occupy a total area of ~ 25 km2, or only about 0.1% of the area of continental shelf that potentially could support coral reef growth). Hence the overwhelming majority of reef habitat in the TEP consists of rocky reefs. The TEP coral fauna also is small (~ 47 species) that includes only a handful of endemic species.
The only significant coral reef in the entire TEP is at Clipperton Atoll, a 4 km2 reef 1,100 km offshore from the Mexican coast, well away from coastal influences, at the fringe of the zone of greatest impact from ENSO-produced high water temperatures, and out of the zone of hurricane impact. On the mainland, structural coral reefs are concentrated in the equatorial part of the region, particularly around Panama, and primarily in the Gulf of Chiriqui, in western Panama. This area is not subjected to cold seasonal upwellings, unlike the nearby Gulf of Panama where coral reefs are more poorly developed. Because of the more stable thermal regime there is extensive development of certain hermatypic corals to depths of about 10 m. Coral reefs in the TEP are constructed by handful of species of Pocillopora, Porites and Pavona. Tiny Clipperton, the only atoll in the eastern Pacific, is the only site in the entire TEP that consists exclusively of coral reef habitat (~ 4 km2 of it). There is no other place within the TEP whose habitats and fish fauna closely resemble those of Clipperton.
5 THE SHOREFISH FAUNA OF THE TEP CARIBBEAN
This information system covers 1,358 species (in 521 genera and 156 families) of shallow-living (found above 100 m depth) coastal and near-shore pelagic species known from the TEP.
5.1 A short history of taxonomic studies of the regional fauna:There is a rich history of ichthyological exploration in the TEP dating back to Charles Darwin's voyage to the Galapagos aboard the Beagle. Fishes from this expedition were described by Jenyns in 1842. Since that time a number of major works have been published, primarily by US authors. An extensive listing (over 1000 titles) of relevant material is presented in the library of this system. Several are worth mentioning here, because of their considerable depth and overall contribution to our knowledge of the region's fish fauna. Jordan (1885) was the first to assemble a list of the TEP shorefishes. The four volume work of Jordan and Evermann (1896-1900), The Fishes of North and Middle America, presented an invaluable synopsis of the known fauna as it stood at the turn of the 20th century. This was a solid foundation upon which Jordan, his colleagues, and their students continued to build during the early part of the twentieth century. Charles H. Gilbert, a collaborator of Jordan's, also had a considerable impact. He made large collections in Mexico and Panama, and along with Edwin C. Starks (1904) produced The Fishes of Panama Bay. Other landmark publications were Meek and Hildebrand's (1923-1928) The Marine Fishes of Panama and Hildebrand's (1946) A Descriptive Catalog of the Shore Fishes of Peru. Besides these larger works there exists a considerable taxonomic literature devoted to different components of the region's fish fauna. For the most part these consist of either new species descriptions or generic revisions. The Scripps Institution of Oceanography (SIO) at La Jolla, California, the Los Angeles County Museum (Los Angeles, California) and the California Academy of Sciences (San Francisco, California) have earned reputations as leading center for studies on tropical eastern Pacific fishes. The reputation of SIO is largely a result of the work of the late Carl Hubbs, and Richard Rosenblatt, and their many students. The Institute maintains a large collection of regional fishes and many important publications are based on this material.
5.2 Major modern guides to TEP shorefishes:Until recently there was only one comprehensive illustrated guide that treated a large part of the tropical eastern Pacific's fish fauna: Reef Fishes of the Sea of Cortez, by Thomson, Findley & Kerstich. (1979), a revised edition of which was published in 2000. This book provides good coverage of the Gulf of California and served as a proxy for a regional guide for 15 years. Chirichigno's (1974) guide to the fishes of Peru, (a revised edition of which was published by Chirichigno & Vélez (1998): Clave para identifica los peces marinos del Perú), also functioned partly as a regional guide for the TEP because about a third of the fauna we consider here occurs in northern Peru. Recently two truly regional guides were published: Fishes of the tropical eastern Pacific, by Allen and Robertson (1994), and the multi-authored 3 volume Guía para la indentificación de especies para los fines de la Pesca: Pacífico Centro-Oriental (1995), by FAO (the UN Food and Agriculture Organization). The FAO volumes are in Spanish and a Spanish edition of Allen and Robertson's book, Peces del Pacífico Oriental Tropical, was published in 1998. In addition Grove and Lavenberg released the long awaited Fishes of the Galápagos Islands in 1997, a book that comprehensively treats the entire fish fauna of that island group. Humann & Deloach published a popular photographic guide to reef fishes of that archipelago, Reef fish identification: Galápagos, in 1993 and, in 2004, Reef fish identification: Baja to Panama. Other guides with limited geographic coverage include Garrison's (2000) bilingual Los Peces de Isla del Coco (revised 2nd edition in 2006) and the spanish language Peces de la Isla Gorgona (1987, revised edition 2000) by Rubio et al. Peces demersales y pelágicos costeros del Pacífico de Centro America Meridional: Guia Ilustrada(1993) a bilingual guide by Bussing and Lopez focuses on marine species trawled from soft bottoms off Costa Rica.
5.3 Global online resources about shorefishes:Major online resources that effectively cover different aspects of the region's fishes via information on individual species, include William Eschmeyer's Catalog of Fishes, at www.calacademy.org/research/icthyology/catalog , which provides comprehensive up to date information on the systematics of fishes and FishBase [ www.fishbase.org ], which summarizes information from other sources on a variety of aspects of the biology of fishes; the International Taxonomic Information System, ITIS (http://www.itis.gov ), which covers the scientific names of fishes. Both OBIS, the International Biogeographic Information System (http://www.iobis.org ) and GBIF, the Global Biodiversity Information Facility ( www.gbif.org ) aggregate and make available information on georeferenced databases of collection records of fishes from individual museums and research organizations.
5.4 Systematic order in which fishes are arranged:The fishes are presented in phylogenetic or systematic order by family (the scientific names of which end in -idae); with the most primitive fishes presented first followed by more recently evolved forms. We follow the classification and sequence of families presented in J.S Nelson's 4th edition (2006) of Fishes of the World. Within each family genus pages and species pages within genus pages appear alphabetically by scientific name. The Systematic Tree in The Fishes section indicates each species position in a simplified systematic hierarchy that includes only 3 levels: Family, Genus and Species.
5.5 Names of Fishes:
Scientific names: Many of the fishes found in the TEP were given their names by ichthyologists in the latter half of the 19th century or the first half of the twentieth century. In some cases the same fish was given a different scientific name by different researchers. By the Law of Priority, the oldest name is the accepted one, provided it is binomial, was accompanied by a description, and was published at the scientific work that started our current system of biological nomenclature (on or after 1758 with the 10th edition of Carl Linnaeus' Systema Naturae). Subsequent, invalid names for previously described organisms are called synonyms. Most of the problems involving synonyms have been sorted out, but some older names are still being discovered, which means they must replace names in current usage. The Catalog of Fishes by William Eschmeyer of the California Academy of Sciences provides excellent coverage of this aspect for our fishes and we only occasionally mention synonyms. Here we follow names as presented in ITIS, The International Taxonomic Information System which provides information that supplements that in the Catalog of Fishes, and makes decisions about valid names. The scientific name is the name in two (rarely three, in the case of subspecies) parts, the first being the genus name and the second the species name. This is immediately followed by the name of the author(s) who gave the fish its scientific name and the year in which the description was published. If the author's name is in parentheses, it indicates that the fish was originally placed in a genus that is different from the one that is currently accepted. A few species treated here still lack scientific names, because they have not been formally described; these are indicated by "species A, B etc", following the genus name.
Common names: The common names of fishes used here have been taken from a variety of sources. In many cases they are names that have been previously published in other books, for example Reef fishes of the Sea of Cortez (Thomson, et al., 1979). Unfortunately, there is a scarcity of popular fish literature for the TEP, hence many of the smaller and more cryptic reef fishes previously lacked a common name. In these case we have introduced a name, often after consultation with appopriate family specialists. We have revised the names used in Fishes of the tropical eastern Pacific (1994) and Peces del Pacífico oriental tropical (1998) to bring them into conformity with names used in the FAO volumes for our region (1995, edited by Fischer et al), in Bussing and Lopez (1994) book on Costa Rican fishes - Demersal and pelagic inshore fishes of the Pacific coast of lower central America, those used in FishBase. ITIS and the American Fisheries Society’s Special Publication 29 (2012, 6th edition4): Common and scientific names of Fishes from the United States and Mexico. Sometimes multiple common names are given for a species, genus or family The first common name we use for a species is one that is most widely used and is intended to be the principal common name, which is not shared with any other species. Fishes common names vary greatly from one country to the next, and even within different parts of the same country. No attempt has been made to fully cover this variation.
6 BIOLOGY AND ECOLOGY OF TEP SHOREFISHES
6.1 Use of environments and habitats:The fishes included here are very largely (90.3%) restricted to inshore environments, including not only rocky and coral reefs and there immediate surroundings, but also soft (sand and mud) habitats in estuaries and beaches as well as in water extending well down the continental shelf. Species found on either reefs or soft bottoms exhibit precise habitat preferences that are dictated by a combination of factors including the availability of food and shelter, and various physical parameters such as salinity, depth, water clarity, currents, and wave action, as well as the precise nature of the bottom.
6.2 Reef-associated fishes: The majority of inshore fishes in the region likely to be encountered by divers and anglers are associated with what can be broadly defined reef habitats. These include rocky shores and submerged rock reefs as well as coral reefs. About 44 % of the regional fauna comprises bottom living fishes found in association with reefs. Rock outcrops and ledges provide necessary shelter and a source of benthic invertebrates and algal growth, important dietary components for many reef fishes. Rocky reefs often have a dense covering of various types of seaweed, which provides additional shelter for a variety of small fishes. Some of the more prominent families found on rocky reefs include moray eels, snappers, grunts, damselfishes, wrasses, parrotfishes, blennies (three families), gobies, and surgeonfishes.
6.3 Soft-bottom fishes:Another large and important segment of the TEP fish fauna is associated with soft bottom habitats, which range from clean white sand in clear waters to soft thick mud, characteristic of turbid bays and estuaries, to mangroves. Although this habitat is often considered to be low in fish diversity, about 40% of the species treated here live in such habitats. The soft bottom community includes such fishes as rays, snake eels, catfishes, lizardfishes, croakers, sand stargazers, and flatfishes.
6.4 Water-column fishes:The third most important group of fishes live in the water column above the substratum, over shallow reefs and soft-bottoms as well as the open ocean. These species constitute about 17% of the species included here. These include jacks, anchovies, herrings, and silversides, flyingfishes, tunas and billfishes, as well as a smattering of members from many other families.
6.5 Use of environments of differing salinities:Almost 66% of the shorefish fauna comprise species that are found only in marine (i.e. full salinity) environments, while another 27% occur in estuarine (reduced salinity) as well as marine situations. Only 7% are non-marine species (which do not enter full salinity environments), and only 9.5% enter freshwater. A few of the fishes included here (3%) are basically freshwater fishes that occasionally enter brackish water, or whose juveniles are encountered in brackish water.
6.6 Depth distribution patterns: Most of the regional fauna considered here lives in fairly shallow water - 41% of species reach the surface, the depth ranges of 73% extend to within 5 m of the surface, and only 4% do not come above about 50 m. The lower limit of the depth ranges of 50% of the species terminate at about 30 m, with only 32% occurring down to 50 m and 19% below 100 m.
6.7 Fishes dietary groupings:The great majority of TEP shorefishes are carnivores of one type or another: 81% of the species have such a diet, which includes items ranging from tiny benthic mollusks, worms and crustaceans to sharks, whales and marine birds. The next most abundant group comprises species that consume plankton (either exclusively or with a mix of non-planktonic animals): 25% of the fauna. Bottom feeding omnivores and herbivore/detritivores are relatively uncommon, constituting only about 5% and 4% of the fauna, respectively.
6.8 Modes of reproduction:The diversity of shore fishes found in the TEP is reflected in a wide variety of reproductive habits. The great majority of shorefishes treated here are egg layers that employ external fertilisation. Relatively few species (10% of those included here) bear live young that are prepared to fend for themselves at birth. These include most of the sharks and rays, but very few of the bony fishes: the brotulas and two genera of weed blennies.
Most shorefishes use one of two patterns of egg-laying reproduction. Females of many fishes, including the highly visible wrasses and parrotfishes, scatter relatively large numbers of small, positively buoyant eggs into open water where they are summarily fertilized by the male. Fifty-eight percent of the species included here reproduce in this manner.
The spawning event is typically preceded by nuptial chasing, temporary color changes, and courtship displays in which fins are erected. This behavior is generally concentrated into a short period of the day, often at sundown or shortly afterwards, or is related to the stage of the tidal cycle. This pattern is seen in diverse groups such as lizardfishes, angelfishes, wrasses, parrotfishes, and boxfishes. Typically either pair or group spawning (the latter involving a single female and multiple males) occurs in which the participants make a rapid dash towards the surface, releasing their gonadal products at the apex of the ascent. The fertilised eggs float near the surface and are dispersed by waves, winds, and currents. Hatching occurs within a few days and the young larvae are similarly at the mercy of the elements. Older larvae, however, are good swimmers and have considerable control over their movements. Recent studies of the daily growth rings found on the ear bones (otoliths) of reef fishes indicate that the larval stage generally varies from about 1-8 weeks depending on the species involved. The extended pelagic larval period accounts for the wide dispersal of many reef species. A few of species found in the TEP extend their ranges all the way to Africa (Robertson et al, 2004).
The second major reproductive pattern (exhibited by 29% of shorefish species in the TEP fauna) involves fishes that lay their eggs on the bottom, frequently in rocky crevices, empty shells, sandy depressions, or on the surface of invertebrates such as sponges, corals, or gorgonians. These include the skates and a few of the sharks, which produce large benthic eggs in horny egg cases. Among the best known fishes in this category are the damselfishes, blennies, gobies, and triggerfishes. These fishes often prepare the surface prior to egg deposition by cleaning away detritus and algal growth. Bottom spawners also exhibit elaborate courtship rituals which involve much aggressive chasing and displaying. This behavior has probably been best studied amongst the damselfishes. In addition, one or both parents may exhibit a certain degree of nest-guarding behavior in which the eggs are kept free of debris and guarded from potential egg feeders such as wrasses and butterflyfishes.
A more specialized mode of parental care is seen in cardinalfishes and sea-catfishes, in which the male broods the egg mass in its mouth. Similarly, male pipefishes and seahorses brood their eggs on a highly vascularised region of the belly or underside of the tail. Only 4% of our region's fishes reproduce using brooded eggs. As a rule the eggs of benthic nesting and oral-brooding fishes are less numerous, larger, have a longer incubation period, and are at a more advanced developmental stage when hatched, compared to the eggs and larvae of pelagic spawning fishes.
6.9 Longevity and size:There is little information on the longevity of most eastern Pacific reef fishes. Perhaps one of the longest life spans is that of the Lemon Shark, Negaprion brevirostris, which may reach 50 years or more. Most of the larger reef sharks probably live at least to an age of 20-30 years. In general the larger reef fishes such as groupers and snappers tend to live longer than smaller species in the same family or genus. However, small snappers can live as long as much larger groupers. Otolith aging techniques indicate that groupers, both large and relatively small, may live at least 25 years (Craig et al 1999), and some snappers up to 30 years. However, small species of TEP damselfishes also reach ages of more than 30 years (Ruttenberg 2005, Meekan et al 2001).
Whatever information is available on the maximum size of each species, from the literature as well as our personal experience, is distilled to maximum known total length in both the text and database. A few data is also presented (in the text descriptions of species) on maximum total weights when that is known.
Most of the species in the shorefish fauna are small: 22% are 10 cm or less and 47% 25 cm or less. Large species of fishes are uncommon: only 13% are 1 m or longer, and only 5% are 2 m or longer.
7 MARINE BIOGEOGRAPHY OF TEP SHOREFISHES
7.1 Scientific studies of TEP zoogeography:Charles Darwin's name inevitably appears in any historical account of marine zoogeography. In The origin of species by means of natural selection (Darwin, 1872, p 279) he briefly discussed two key topics of modern debate: (i) the close relationships between fishes on the two sides of the isthmus of Panama, and (ii) the significance as a barrier of the 4,000-7,000 km wide expanse of ocean separating the west coast of the Americas from the islands of the central Pacific, a barrier that we know as the Eastern Pacific Barrier (EPB). Early works on global patterns of marine zoogeography [ Zoogeography of the Sea by Ekman (1953), and Marine Zoogeography by Briggs (1974)] emphasized the importance of isolation produced by the EPB, as have studies of the TEP's shorefishes (Briggs 1961, Rosenblatt 1967, Rosenblatt et al. 1972, Bernardi et al 2003, Robertson et al 2004) and other groups of organisms (e.g. echinoids - Mayr 1954, and molluscs - Vermeij 1987). Springer (1982) examined the zoogeographic affinities of shorefishes found on the Pacific Plate, which extends from the northwestern Pacific to the northern part of the TEP: Clipperton, the Revillagigedos and the Baja Peninsular are situated on the Pacific Plate. Aspects of the biology of the pelagic larval stage of reef fishes that may affect the potential for colonization of the TEP by central Pacific fishes have been addressed by Leis (1984, 1986), Victor (1987), and Victor et al. (2001) and Robertson et al (2004).
Realization of the close relations of the TEP shorefish fauna to that of the tropical western Atlantic began with Gunther (1868) who proposed that the two regions once were connected. Discussion of the evolutionary significance of that relationship has continued ever since - Jordan (1905, 1908), Rosenblatt (1967), Briggs (1970), Thresher (1991), Robertson (1998).
A considerable amount of attention also has been given throughout the past century to the zoogeography of the distributions of endemic species within different parts of the TEP, particularly the relationship of the fish fauna of the Gulf of California to that of the rest of the region - Gilbert and Starks (1904), Meek and Hildebrand (1928), Hubbs (1952, 1953), Briggs (1955), Springer (1959), Walker (1960), Rosenblatt (1963), Rosenblatt and Walker (1962), Stephens (1963), Thomson and Gilligan (1983), Hastings (2000).
Grigg and Hey (1992) assessed the geological history of the EPB, while Veron (1995) and Glynn and Ault (2000) provide modern zoogeographic overviews of coral reef development in the TEP, and the latter incorporate much general information that is relevant to the zoogeography of the region's shorefish fauna.
Recently, genetic analyses have begun to be applied to zoogeographic questions about the TEP shorefish fauna: the degree of ongoing connections with the central Pacific (Rosenblatt and Waples 1986, Bowen et al. 2001, Colburn et al. 2001, Lessios & Robertson 2006, Craig et al 2007); the history of connections between the TEP and west Atlantic that were broken during the rise of the Isthmus of Panama (Gormon and Kim 1977, Gormon et al. 1976, Vawter et al. 1980, Tringali et al. 1999, Lovejoy and Collette, 2000, Reed et. al., 2001); the history of more recent connections between populations of warm temperate species currently restricted to the north and south of the TEP (Grant and Bowen, 1998); and relationships between geographically separated populations of the same or sister species within the TEP (Lessios et. al. 1995, Muss et. al. 2001, Riginos and Nachman, 2001, Riginos and Victor, 2001, Craig et al 2006).
7.2 Resident and vagrant species in the TEP:About 90% of the species treated here apparently seem to be sufficiently abundant and/or widespread to have resident populations in the TEP. Vagrants mainly (59%) consist of temperate species resident in the Californian and/or Peruvian provinces, although 19% of them are tropical species resident elsewhere in the Indo-Pacific species.The pelagic larvae/juveniles of two at least (the spiny puffer, Cyclichthys spilostylus, and the eel, Anguila marmorata) must have come from the western Pacific, as the former is not known from the central Pacific and the latter spawns in the W Pacific.
7.3 Exotic species introduced from other areas to the TEP:Since 1914 the Panama Canal has provided opportunities for partial reconnection of the shorefish faunas of the TEP and tropical Atlantic, by species that can tolerate the freshwater environment of the canal. However, there have been surprisingly few cases (13 species) in which Caribbean fishes have entered the TEP by this method (McCosker and Dawson, 1975), but only 1-2 species (a pipefish, and, possibly, the W Atlantic tarpon) seem to have successfully spread much beyond the Pacific entrance to the Panama Canal. Of four West Atlantic fishes that were intentionally introduced into the TEP (two silversides, a shad and a corvina), only one or two (the shad, and, possibly, the corvina), seem to have become established.
7.4 The size of the TEP shorefish fauna:Compared to the tropical area in the Indo-Malayan global center of diversity, with several thousand shorefishes, the TEP has a relatively small shorefish fauna. Here we cover 1,358 species; of those 647 are tropical species entirely restricted to the TEP, while another 546 are tropicals that also occur in adjacent temperate areas. The distributions of 165 temperate species that enter the TEP are concentrated in the temperate regions to the north (the California Province – 44.2% of those) and south (Peruvian Province – 41.2%; with the remainder in both provinces. With 965 species of endemic shorefishes the TEP has the highest rate of endemism, 79% of the resident shorefishes, of any major tropical biogeographic region.
The TEP has ~ 25% fewer shorefish species than its sister region, the Greater Caribbean (Robertson 1998, and see Carpenter 2002 for information on the Caribbean fauna). The reasons why the TEP has a relatively small fauna are complex, but several are major contributors. One involves the size of the region. Although the mainland coastline spans nearly 38 degrees of latitude, it is relatively straight and has a fairly narrow continental shelf. Further, there are only a few offshore islands, which, between them, provide less than 5% of shorefish habitat in the region. The largest such island areas (the Revillagigedos and the Galapagos), which together contain 99% of the insular shoreline habitat in the TEP are at the northern and southern limits of the TEP. Hence they have temperate conditions that likely limit the ability of tropical species to survive. Thus the geography of the TEP is fairly simple and the amount of tropical shoreline habitat is relatively small and the vast majority of it is continental. In contrast the sister region of the TEP, the Greater Caribbean, is much more complex geographically, with a much large area of continental shelf and many offshore islands. The abundance and diversity of coral reef habitats in the TEP is also much lower than in not only the remainder of the Indo-Pacific but also the Greater Caribbean. The TEP contains only about 25 km2 of structural coral reef, and only about 45 species of reef building corals are present. Most of the coral reefs are constructed by very few species of corals. In addition there are no extensive sea-grass beds such as those found in association with most areas of coral reef in the Caribbean and some parts of the Indo-west Pacific. In contrast the Greater Caribbean has some 20,000 km2 of coral reefs, about twice the number of species of corals and vast areas of dense shallow seagrass beds, as well as major habit types provided by an abundance of large tree-like soft corals and sponges. Last, but not least, the TEP is isolated by about 4,000-7,000 km of deep water from the reefs and atolls of the Central Pacific, which are the nearest contemporary source of immigrant shorefishes; only about 7% of the shorefishes found in the tropical eastern Pacific seem very likely to have arrived there from the central Pacific in the very recent past. Many of the 88 circumtropical species that occur in the TEP may simply be derived from populations split from those in the Caribbean by the rise of the Central American isthmus. About 20 circumtropical species found on both sides of that isthmus are those most likely to fall into this category, because they are either absent from or rare in the central Pacific.
Impacts of El Niño events on the TEP shore fishes
While El Niño events clearly have strong negative impacts on the coral fauna and coral reef development in the TEP, there is no evidence of similar impacts on the regional fish fauna, except in the Galapagos. In those islands conditions normally range from warm temperate in the south (due to the cold Peru Current) and west (due to a cold upwelling) to equatorial in the north. El Niños produce tropical conditions throughout the islands, with large increases above normal equatorial temperatures. The 1982-83 event produced mass mortality not only of corals but also of certain resident shorefishes and other marine life in the Galapagos(Grove 1984, 1989).. One of the shorefishes that was known only from the Galapagos, the Galapagos damsel, Azurina eupalama, has not been seen in the islands since that event and may have become extinct. Perhaps however, it has a refuge at the coast or offshore islands off Peru to the south of the Galapagos. In addition El Niños also produced influxes to the Galapagos of species from the mainland that normally are rare in the archipelago (Grove 1984, 1989). During the 1997-98 El Niño range extensions were again noted, but this time involving not only mainland species at the Galapagos but also insular species between islands and to the mouth of the Gulf of California at the other end of the region (see Ruttenberg 2000 and Victor et al. 2001). In addition there were increases in the abundances of tropical species already present at the Galapagos (Ruttenberg 2000).
El Niño events have been thought to enhance immigration of shore organisms from the central Pacific to the TEP because the great surge of warm water traveling eastward doubles the velocity of the NECC and cuts in half the time needed to transit the 4,000-7,000 km of open ocean separating the TEP from the central Pacific islands. However, while that surge does bring that transit time to within the range of the duration of the pelagic larval stage of many reef fish species, whether this actually results in enhanced immigration that has permanent effects on the composition of the TEP fish fauna is unclear. In recent years an increasing number of transpacific fishes have been reported in the Galapagos following El Niños. However those sightings may simply reflect increases in the amount of diving activity there during the past 3 decades. At present there is little evidence that El Niño currents do more than bring the odd vagrant of a few species rather than help add new resident species to the TEP shorefish fauna (Robertson et al 2004).
7.5 Relationships of the TEP shorefish fauna to the faunas of other areas:The TEP shorefish fauna has a strong relationship with the shorefish fauna of the Greater Caribbean, but also significant levels of endemism, particularly at the species level. This pattern is the result of the history of isolation of the region. For perhaps as much as 65 million years (Grigg and Hey 1992) the shoreline biota of the TEP has been isolated from that of the central and western Pacific by the world's largest open ocean barrier to connections between regional shore faunas, the "Eastern Pacific Barrier". That barrier currently is 4,000-7,000 Km wide and apparently has been about as wide as this throughout that period. The slow northward movement of the Line Islands, which brought them into the region of the eastbound NECC about a million years ago, likely has facilitated some eastward immigration of marine shore organisms. Isolation of the region increased with the final closure of the isthmus of Panama, about 3 million years ago (Coates and Obando 1996), although separation of the tropical biotas of the TEP and Greater Caribbean began as much as 10 million years ago as the central American isthmus gradually formed (Lessios 1998). The long-term western barrier and the more recent, and much more complete, eastern barrier have given the fish fauna of the TEP its distinctive characteristics. Rosenblatt (1967) noted that while the shorefish faunas of the TEP and the tropical western Atlantic are both dominated at the genus level by circumtropical genera (over 40% in each case), about 25 % of the genera found in the american tropics occur only on both sides of the Central American Isthmus, and 35% of the eastern Pacific genera are such neotropical genera. Among the 362 TEP genera he considered, 14% are endemic to the region. Our figures for the genera of non-introduced fishes included here are much the same: 44% are circumtropical, 30% are neotropical (or also found in the eastern Atlantic) and 16% are endemic.
At the species level regional endemism is much higher in the TEP than in the Greater Caribbean, presumably because the isthmus rose so relatively recently that new taxa that have arisen have not had sufficient time to accumulate differences that would warrant their classification as new genera, and extinctions need a long time to change the genus level composition of a fauna. Of the 1,358 species included here 71.1% are endemic to the TEP. Most of the remaining species either have circumglobal distributions (6.8 %), or also occur elsewhere in the Indo-central Pacific Transpacific (15.0%). While 107 species occur naturally on both sides of the Central American isthmus, most of those are circumtropical species and only 14 of them are neotropical species. However, the low percentage of species shared with the Western Atlantic is somewhat deceiving as there are numerous species pairs composed of close relatives that occur on either side of the Central American isthmus. The members of these pairs are very similar in appearance and are often referred to as geminate or twin species. The spadefishes of the genus Chaetodipterus present a good example of this phenomenon; C. zonatus of the Pacific is nearly identical to the Atlantic species, C faber. Similarly, the sergeant major Abudefduf troschelii looks virtually identical to its West Atlantic sister, A. saxatilis. Numerous examples of similar twins occur in many other families, and all six members of the snook genus Centropomus found in the TEP are paired with look-alike twins in the Caribbean. The high number of shared genera and occurrence of twin species reflects the common ancestry of the Eastern Pacific and West Atlantic faunas, and their recent separation by final closure of the uplifting Central American landbridge.
As well as being relatively small in size compared to the fauna of the Indo-West Pacific, the shorefish fauna of the Eastern Pacific tropics has a special "flavor" imparted by its large number of endemic species and the unique faunal "mix" of fishes. Many coral reef families that are well represented in the Indo-West Pacific have few species in our region, although the relative abundance of species in major reef-fish families is fairly similar to the relative abundance in the fish fauna of the Caribbean, which is rich in coral reefs (Rosenblatt 1967, Robertson 1998). However, several families found in both those neotropical areas have undergone a tremendous radiation in the eastern Pacific; these include the Sciaenids, with 83 species of primarily soft-bottom fishes, and, to a lesser extent, the Gobiesocids, with 31 species that live mainly in rocky habitats. Our region also has a large indigenous representation among the blennioid families - the reef-dwelling Labrisomidae and Chaenopsidae (45 and 35 species, respectively), and the soft bottom Dactyloscopidae (28 species). All three of those families are well represented in the Greater Caribbean shorefish fauna but absent from the remainder of the vast Indo-central Pacific. In fact the TEP represents a global hotspot of diversity for those five families: 30-50% of the members of each family are endemic to the TEP, and those families collectively provide about a quarter of the TEP's endemic shorefishes.
7.6 Distribution of the fauna in different climate zones: The ranges of the vast majority (82%) of the region's shorefishes include at least part of the equatorial zone between Costa Rica and Ecuador. However, large proportions of the regional fauna also occur in the northern tropical zone between 10-23° N (61%) , and the northern subtropical zone in the Gulf of California (63%). Significant proportions of the TEP fauna have also been recorded in the temperate zones outside our region to the north (40%, including 38% of the TEP endemic fauna) and south (34%, including 31% of the TEP endemic fauna). Many of the occurrences of temperate species in our region and by endemic tropical species in the temperate areas probably are due to traffic by vagrants rather than the occurrence of resident populations in both temperate and tropical areas, with such traffic occurring during El Niño events, when warm water flows from our region into neighboring temperate regions (Chirichigno & Velez 1998, Love et al 2005).
7.7 Variation in species richness and local endemism throughout the TEP:The TEP fauna includes 1,358 known species of shorefishes. As measured by overlap in ranges of different species, the part of the region with the greatest numbers of species (740-760) includes Costa Rica and Panama (Mora & Robertson 2005, a, b). Species richness per section of coastline declines to the north and south of these two countries but slowly - the southern coast of Ecuador and the southern edge of the mouth of the Gulf of California still have about 625 species, as do the tip of Baja California and the south-western corner of the Gulf of California. Even sites near the limits of the region (northern Peru, the central Gulf of California and southern Baja) are included in the ranges of ~ 500 species.
Looking at the pattern of variation in species richness in greater detail we find that the overall pattern, with the greatest richness in the Costa Rica/Panama area, also occurs in many species-rich families (e.g the muraenids, engraulids, clupeids, ariids, batrachoidids, atherinids, sciaenids, blenniids, gobiids, and tetraodontids). Other families follow this same general pattern but with the richest zone spread more widely to the north (to central Mexico) and/or south (to Ecuador) of the Costa Rica/Panama section; these include the urotrygonids, dasyatids, ophichthids, scorpaenids, lutjanids, haemulids, dactyloscopids, and cynoglossids. In a few families (carcharinids, serranids, carangids, and scombrids) richness is spread nearly uniformly throughout the three major provinces, without any obvious concentration. Other families have more idiosyncratic richness distributions: the pomacentrids have slightly greater richness around the mouth of the Gulf of California and at the offshore islands (except Clipperton); in the tripterygiids and labrisomids richness is greatest in the northern part of the region, around the Gulf of California. chaenopsids and gobiesocids have two centers of richness - the Gulf of California and Nicaragua to Panama. However, some apparent centers of richness, eg at the tip of Baja reflect the occurrence of vagrant Californian Province species in the northern edge of the TEP.
Regional patterns of richness among species with different biological attributes often follow the general pattern (greatest richness in Costa Rica/Panama) described above. This occurs for species resident in the TEP (not surprisingly vagrants are concentrated at the edges of the region), those living on sand and mud bottoms, or in the water column; demersal or bottom living species in general; species living inshore and those living offshore; carnivorous and planktivorous species; and non-marine species. Other groups show somewhat different patterns: reef living species and entirely marine species show a broad peak in richness between central Mexico and Colombia; omnivorous species have two peaks (Costa Rica/Panama and the Galapagos). Transpacific fishes display a distinctly different pattern: while there is a peak of richness in Costa Rica and western Panama (144 species), 156 occur at the Galapagos and slightly lower numbers at the other offshore islands (135 at the Revillagigedos, 112 at Clipperton, 130 at Cocos and 118 at Malpelo). In terms of the percentage of the fauna represented by those transpacifics they are much more important components of the island faunas than the continental fauna: while they constitute 19% of the Costa Rica/Panama fauna their percentage representation in the oceanic-island faunas is 68% for Clipperton, 45% for the Revillagigedos, 40% for Cocos, 39% for Malpelo and 35% for the Galapagos.
The general pattern of latitudinal change in species richness described here for the TEP fish fauna (declining richness with increasing latitude) is an example of a general phenomenon for animals and plants in marine and terrestrial environments. For coastal marine organisms this has been ascribed to latitudinal variation in energy supply, as reflected in sea surface temperatures, and nutrient levels due to river inputs and upwellings (see. Macpherson, 2002; Mora & Robertson 2005, a,b).
In the present case we need to consider the extent to which the regional pattern is influenced by differences in sampling effort at various parts of the TEP. While all countries have been sampled there has been a concentration of effort in two areas - the Gulf of California, and Costa Rica to Panamá. Despite the coincidence of these areas of enhanced sampling and species richness it seems likely that the sampling is not the primary factor involved. Those two areas also have a greater diversity of environmental conditions and habitats than other parts of the continental shore, a diversity likely to support rich faunas. This diversity includes large groups of nearshore islands that enhance the local range of turbidity and salinity conditions; large, semi-enclosed bays; large highly active estuarine systems; substantial areas of both rocky shores and soft-bottoms; and areas with varying or different temperature and productivity regimes. In addition, Panama and Costa Rica both have large areas with and without large seasonal upwelling systems.
Finally the distribution of local endemics, species with relatively small geographic ranges, also conforms to the overall distribution of general richness along the continental shore, with a large peak around Costa Rica/Panama and a smaller one in the Gulf of California. Mora and Robertson’s (2005, a, b) analyses of the distribution of richness and endemism was limited to the mainland, and did not include the offshore islands. There are 105 species of shorefishes endemic to the oceanic islands of the TEP, and each of the 5 islands and archipelagos has both its own endemics and multi-island endemics (Robertson and Cramer, 2008). The Galapagos has the greatest number of insular endemics (57 species) and of species endemic exclusively to that archipelago (37 species). Those islands also have 97% of the insular habitat in the TEP and have a far greater diversity of environmental conditions than any of the other 4 islands/archipelagos.
7.8 Zoogeographic subdivisions of the TEP: from the perspective of shorefishes:
7.8.1 Continental and island components of the regional fauna: from the perspective of shorefishes:Shorefishes endemic to the continental shoreline of our region constitute ~57% of the 965 regional endemics and island endemics another ~15%; the remaining ~28% are found on both the continent and at least one island. Cortez Province endemics represent ~13.5% of the 548 continental endemics, Mexican Province endemics ~2.6%, and Panamic Province endemics ~28.8%; ~8.4% are shared by the Cortez and Mexican Provinces and ~9.9% by the Mexican and Panamic Provinces, while ~39.6% occur in all three provinces. Rates of endemism within each province (i.e. the % of the resident inshore fishes represented by local endemics) range from ~2% for the Mexican Province, to ~9% for the Cortez Province and ~18% for the Panamic Province. The level of endemism of each continental province would rise if calculations took into account (i) geographically separated subspecies of a few widespread species (principally of blennioids and gobiesocids), (ii) species that are principally mainland forms and that have been recorded at only one island, often apparently as vagrants, and (iii) species that are common and distributed in one province, but are rarely encountered in a neighboring province.
Fewer of the TEP’s shorefish species are known to occur at the 5 oceanic islands than on the mainland: ~49% of the fauna is known from one or more islands and ~11% only from the islands; for the mainland the equivalent figures are ~88% and ~51%, respectively. While the nature of this difference is not surprising since the islands are tiny compared to the mainland shelf, the islands actually support a disproportionately much larger number of species since they provide < 5% of the region’s shorefish habitat.
The volcanic Galapagos Archipelago, lying 910 km off the coast of Ecuador, is composed of 13 major islands and numerous small islets. The Galapagos shorefish fauna, containing ~ 360 inshore fish species, is a blend of TEP endemics (74%), temperate South America (6%) species, and transpacific species (20%), and there is a significant percentage of endemism among its shallow shorefishes, currently estimated at 37 (~11% of the fauna), while another ~5% of the species are island endemics that also occur on other oceanic islands). The faunal complexity of the Galapagos is partly explained by its relatively large size (shoreline habitats in this island group represent 95% of the shorefish habitat at the region's offshore islands) and diversity of habitats (which include mangroves, extensive sandy areas, rocky reefs, and (prior to the 1982-83 El Niño event) a few small areas of good coral growth. There is also a complex interaction of warm tropical seas, in the northern part of the islands, and cold waters of the Peru or Humboldt Current in the southern part and cold upwelling on the west side of the islands, and intermediate conditions in the central part, which together allow the occurrence of both warm temperate and tropical species.
Malpelo Island is situated 380 km off the Colombian coast and 360 km south of Panama. This rocky outpost is volcanic in origin, largely devoid of vegetation, and rises steeply to an elevation of approximately 450 m. The main island is 2 km long and about 1 km at its widest point. In addition, there are a number of rocky outcrops and pinnacles in the immediately adjacent waters. About 226 species of inshore fishes have been recorded at and around the island, including five endemics (2.2% of the fauna). Most of the fauna is TEP mainland in origin; although 10 species are insular endemics are shared only with the Galapagos and/or Isla del Coco. Malpelo has a very dynamic environment - it is affected by the seasonal upwelling of the Gulf of Panama and lies directly in the path of the eastward El Niño heated water surge.
Cocos Island lies about 650 km northeast of the Galapagos and about 500 km southwest of Costa Rica. It is a small, steep-sided, well vegetated island in a high rainfall area with a land area of about 47 km2. Some 259 shorefishes are known from the island, of which about 75% are TEP endemics, while most of the rest are either Indo-Pacific or circumglobal species. The Cocos fauna includes 12 species of named shallow marine endemics (4.6% of the fauna). plus 20 insular endemics known only from Cocos and other offshore islands. In addition there is one undescribed shallow water endemic, 8 deep-water endemics and 3 freshwater endemics.
Tiny Clipperton Island is the only true coral atoll in the eastern Pacific and the only site in the TEP at which all habitats are formed by coral reef. This small reef is only about 3 km in diameter and lies about 1,075 km from the mainland, southwest of Acapulco, Mexico, and 940 km south of the Revillagigedo Islands. The 104 species of shorefishes of this remote outpost include a much higher percentage of transpacific species (54%) than any other island in the eastern Pacific, as well as 6 species and 2 subspecies of endemics, plus 7 insular endemics also known from other TEP islands.
The Revillagigedo Islands, consisting of three small volcanic islands and an isolated rock spread 420 km apart on an east/west axis, lie about 400 km south of the tip of Baja California. Although the shorefish fauna has not been throughly investigated, at least 215 species occur there, including 17 endemics (7.9% of the fauna) and 11 other insular endemics shared with other TEP islands. That fauna likely is significantly larger than this figure because these islands offer a larger and more complex set of habitats scattered over wider area than do equally isolated but single islands like Cocos and Malpelo, which have better known and larger faunas.
7.8.2 One, two or three continental provinces?The number and limits of major zoogeographic subdivisions or provinces within the tropical eastern Pacific has been a matter of debate for 50 years (Hubbs 1952, Ekman 1953; Briggs 1955, Springer 1959, Stephens 1963, Briggs 1974, 1995, Hastings 2000, Spalding et al 2007). Hastings (2000) analysed the distributions of species in a single family of reef fishes and concluded, like Springer (1959), Walker (1960), Rosenblatt and Walker (1962), Stephens (1963), Rosenblatt (1967), that there are three major continental provinces, the breakpoints between which are set by the location of two large stretches of soft-bottom shoreline that likely act as barriers to the dispersal of such fishes. In this scenario the northern or Cortez Province includes southern Baja California, and the Gulf of California. The Cortez province is isolated from Mexican Province to the south by the Sinaloan Gap, a ~ 300 km stretch of sand and mud coast between Topolobampo and near Mazatlán. The latter province extends down to the northern edge of Gulf of Tehuantepec, in southern Mexico. Springer (1959) proposed the name "Pacific Central America Faunal Gap" for the area between the Gulf of Tehuantepec and the Gulf of Fonseca. He noted that this 1200km stretch of coast was apparently devoid of rocky reefs, consisting instead of either sand, mud, or mangroves, and that it coincided with the distributional limits of certain species of clinid fishes (now grouped in Labrisomidae). More recent observations show that El Salvador has rocky shore in the Gulf of Fonseca and along its Pacific coastline northwards to around Acajutla, near the border with Guatemala. Hence here we use Acajutla to define the southern edge of the Central American Gap, which reduces that gap to ~ 750 km in width. The southern or Panamic Province extends from El Salvador southward to about Cabo Blanco, in northern Peru. There is not universal agreement about the 3 province scheme of Hastings (2000) and earlier workers. Briggs (1974) considered that there are only two provinces and that most of the Gulf of California represented part of the temperate Californian Province rather than the TEP. Spalding et al (2007) excluded all of Baja and the Gulf of California from the TEP and considered the mainland part of the TEP to constitute a single province.
Robertson and Cramer (2009) analysed the geographic distributions of 1135 TEP resident shorefishes throughout the TEP and immediately adjacent areas. Their analyses (see Fig 25) indicate the following subdivisions of the continental shore, at least from the perspective of these fishes: (i) The northern and southern limits of the TEP are at about Magdalena Bay (25°N,), on the Pacific coast of Baja California, and the southwest shore of the Gulf of Guayaquil (~4°S). These limits are consistent with those suggested in previous, unquantitative, work on such fishes. (ii) The Cortez province, which is composed largely of the Gulf of California, has a subtropical fauna dominated by tropical species (85% of the Cortez fauna) and the entire gulf represents an integral part of the TEP. (iii) The TEP has only two continental provinces, a Cortez province and a Greater Panamic Province. The Cortez Province, which includes southern Pacific Baja, and all of the Gulf of California to about 25 N on the eastern mainland shore, is equivalent to that first described by Springer (1959) and Walker (1960). However, the Mexican Province of those authors evidently is part of a Greater Panamic province, which spans the rest of the TEP continental shore. This 2-province arrangement reflects regional peaks in the abundance of local endemics in the Gulf of California and Costa Rica-Panama, low level of endemism in the “Mexican” area, and sharing of species between that “Mexican” area and the more southern part of the continental shore.
Fig 25. Zoogeographic limits and subdivisions of the TEP
7.8.3 A single ocean-island province.Due to their relatively high level of endemism the Galapagos Islands have sometimes been considered to represent a separate province of the tropical eastern Pacific (e.g. see Rosenblatt & Walker 1962, Walker 1966, Briggs 1974, Spalding et al 2007). The status of the other oceanic islands has been left largely hanging, and they generally have been either ignored or assigned to the nearest continental province without explanation. This focus on the Galapagos is not surprising, given their large size (they contain ~ 95% of the island habitat in the TEP), variety of environments, and abundance of endemics and other species of shorefishes.
Robertson and Cramer (2009) included the faunas of the Galapagos archipelago and the other four oceanic islands and archipelagos in their analysis of biogeographic subdivisions of the TEP. That analysis indicates that the five islands group together in a single Ocean Island province, and have, both singly, and in aggregate, shorefish faunas that are distinctly different from the continental fauna. Each of the five has its own endemics (varying from 2.5-~11 % of its fauna); ~25% of the insular endemics occur on multiple islands; and each island shares a significant number of insular endemics with at least one other island. Further, the density of endemics (no. per Km2 of habitat) is much greater at any of the islands than on the mainland and the percentage of endemics in the fauna of any island and the five islands collectively is at least as great as that at the Mexican Province. The aggregate rate of endemism in the island fauna (insular endemics as a % of the inshore species) is ~20%, a rate of endemism similar to those the two mainland provinces (~9-23%).
Besides their patterns of endemism the faunas of each of the islands have other shared characteristics that imbue the individual and combined island fauna with distinctive characteristics that set it apart from the continental fauna: (i) Transpacific species are much better represented in the islands' faunas than in the continental fauna. (ii) There are fewer soft-bottom and more reef-species species in the insular fauna than on the mainland fauna. Soft-bottom species restricted to the continent represent ~40% of the continental inshore fauna, while the analogous figure for island species is ~4%. The similarities of the faunas of the five islands, the grouping of the Galapagos with one or more of the other ocean islands in various analyses of the entire fauna and its ecological components, and the distinctiveness of all the islands relative to the continent indicate that they together constitute a cohesive zoogeographic unit.