Reef fishes of St. Paul’s Rocks: new records and notes on biology and zoogeography

St. Paul’s Rocks is a very small group of rocky islands located on the mid-Atlantic Ridge just north of the Equator, about 1000 km from the Brazilian coast. The aim of this work is to add new information on the abundance, biology, zoogeography and taxonomy of its reef fishes. In the course of four expeditions the fish fauna was surveyed in tide pools and over reefs at depths down to 62 m using a number of different methodologies. Seventy-five fish species (25 new records) were found, of which 58 were reef inhabitants and only 17 were pelagic. The most speciose families were Muraenidae (seven species), Carangidae (five), Pomacentridae (five), Labridae (four), Serranidae (three), and Scaridae (three). Stegastes sanctipauli (Pomacentridae), Chromis multilineata (Pomacentridae), Melichthys niger (Balistidae) and Caranx lugubris (Carangidae) were the most visually abundant fishes. Carcharhinus galapagensis and Anthias salmopunctatus) recorded in prior surveys, were not observed by our team. It was found that 60.3% of the reef fish species are carnivores, 15.5% planktivores, 8.6% omnivores, 8.6% territorial herbivores, and 6.9% non-territorial herbivores. Of the 58 reef fishes recorded, four are endemic to St. Paul’s Rocks and about 80% also occur off the coast of Brazil. It is thought therefore that St. Paul’s Rocks should be regarded as an impoverished outpost of the Brazilian province. Resumo O Arquipélago de São Pedro e São Paulo é um conjunto muito pequeno de ilhotas rochosas localizado logo acima do Equador, distante cerca de 1000 km da costa brasileira. O objetivo do presente estudo foi adicionar novas informações acerca da abundância, biologia, zoogeografia e taxonomia dos seus peixes recifais. Durante quatro expedições, a ictiofauna foi levantada em poças de maré e em recifes até 62 m de profundidade através de várias metodologias. Setenta e cinco espécies de peixes (25 novos registros) foram encontradas na área, das quais 58 são habitantes dos recifes e 17 são pelágicos. As famílias mais ricas quanto ao número de espécies foram Muraenidae (sete espécies), Carangidae (cinco), Pomacentridae (cinco), Labridae (quatro), Serranidae (três), and Scaridae (três). Stegastes sanctipauli, Chromis multilineata, Melichthys niger e Caranx lugubris foram os peixes visualmente mais abundantes. Carcharhinus galapagensis e Anthias salmopunctatus, registrados em levantamentos anteriores, não foram observadas pela nossa equipe. Foi constatado que 60,3% das espécies de peixes recifais são carnívoras, 15,5% planctívoras, 8,6% onívoras, 8,6% herbívoras territoriais e 6,9% herbívoras não territoriais. Dos 58 peixes recifais registrados, quatro são edêmicos do Arquipélago São Pedro e São Paulo e cerca de 80% ocorrem também na costa do Brasil continental. Acredita-se, portanto, que o Arquipélago de São Pedro e São Paulo deve ser considerado como um ponto externo empobrecido da Província brasileira. Zusammenfassung Die St.Paul’s Rocks sind eine sehr kleine Gruppe felsinger Inseln, die entlang der mittelatlantischen Kammlinie – nur wenig nördilich des Äquators , etwa 1000 km vor der brasilianischen Küste, liegen. Der Zweck dieser Untersuchung war die Erfassung neuer Reef fishes of St. Paul’s Rocks: new records and notes on biology and zoogeography 62 aqua vol. 7 no. 2 2003 Informationen über Artenreichtum, Biologie, Zoogeografie und Taxonomie ihrer Riffische. Im Verlaufe von vier Expeditioner wurden die entsprechenden Einzelhein der Fischfauna in Tidentümpeln sowie ubre den Rifen, bis hinuter zu Tiefen von 62 m, mit verschiedenartiger Methodik erfasst. Fünfudsiebzig Fischarten (25 davon als Neuaufzeichnungen) wurden verzeichnet. Davon warem 58 Arten Riffbewohner und 17 arten kamen pelasisch vor. Die artenreichsten Familien waren: Muraenidae (7 arten), Carangidae (5 arten), Pomacentridae (5 arten), Labridae (4 arten), Serranidae (3 arten). Stegastes sanctipauli (Pomacentridae), Chromis multilineata (Pomacentridae) und Melichthys niger (Balistidae) waren die am meisten gesehenen Fischarten. Die in früheren Berichten angeführten Arten Carcharhinus galapagensis und Anthias salmopunctatus, wurden von unserem Team nicht gefunden. Es wurde beobachtet, dass unter den Fischarten dieser Inseln 60.3% Fleischfresser, 15.5% Planktonfresser, 8.5% Allesfresser, 8.6% territoriale Pflanzenflesser und 6.9% nicht-territoriale Pflanzenfresser sind. Von den 58 erfassten Riffischarten waren vier für die St.Paul’s Rocks endemisch; etwa 80% kommen ebenfalls entlang der brasilianischen Küste vor. Daher ist es zu vermuten dass man die St.Paul’s Rocks als einen fischartenverarmten Vorposten der brasilianischen Provinz betrachten sollte. Resumé St Paul’s Rocks est un minuscule groupe d’îles rocheuses sises sur la dorsale médiane de l’Atlantique, juste au nord de l’Equateur, à environ 1000 km de la côte brésilienne. L’objectif de ce travail es de fournir des informations nouvelles sur l’abondance, la biologie, la zoogéographie et la taxonomie de ses poissons de récifs. Au long de quatre expéditions, la faune piscicole a été relevée dans les mares tidales et sur les récifs jusqu’à des profoundeurs de 62 m. en utilisant plusieurs méthodologies. Soixante-quinze espèces de poissons ont été collectées (25 sont nouvelles), don’t 58 inféodées aux récifs et 17 pélagiques. Les familles comprenant le plus d’espèces étaient les Muraenidae (sept espeses), les Carangidae (cinq), les Pomacentridae (cinq), les Labridae (quatre), les Serranidae (trois) et les Scaridae (trois). Stegastes sanctipauli (Pomacentridae), Chromis multilineata (Pomacentridae), Melichthys niger (Balistidae) et Caranx lugubris (Carangidae) étaient lês espèces les plus souvent visibles. Malgré leur présence dans des releves précédents, Carcharhinus galapagensis et Anthias salmopunctatus n’ont pas été observées par notre equipe. L’analyse a revele que 60,3% des espèces récifales sont carnivores, 15,5% planctonivores, 8,6% omnivores, 8,6% herbivores territoriales et 6,9% herbivores non territoriales. Sur les 58 poissons récifaux collectés, quatre sont endémiques à St.Paul’s Rocks et 80% environ figurent aussi au large du Brésil. D’où la conclusion que St Paul’s Rocks devrait éter considéré comme un poste avancé plus pauvre en espeses de la province brésilienne. Sommario St. Paul’s Rocks è un piccolo gruppo di isole rocciose localizzate lungo la dorsale Atlántica, a nord dell’equatore e a 1000 km dalla costa del Brasile. Lo scopo di questo lavoro è quello di fornire nuovi dati sull’abbondanza, la biología, la zoogeografía e la tassonomia dei pesci che abitano le coste di queste isole. Nel corso di quattro spedizioni, utilizando diverse metodologie, è stata censita la fauna ittica marina delle zone costiere dalla fascia delle maree alla barriera fino alla profondità di 62 m. Sono state registrate complessivamente 75 specie (incluse 25 nuove segnalazioni), 58 delle quali sono pesci di barriera, mentre 17 sono pelagici. Le famiglie presenti con il maggior numero di specie sono quelle dei Muraenidae (7 specie), dei Carangidae (5), Pomacentridae (5), Labridae (4), Serranidae (3) e Scaridae (3). Stegastes sanctipauli (Pomacentridae), Chromis multilineata (Pomacentridae), Melichthys niger (Balistidae) e Caranx lugubris (Carangidae) erano le specie più abbondanti. Malgrado fossero state Registrate in precedenti spedizioni, le due specie Carcharhinus galapagensis e Anthias salmopunctatus non sono invece state osservate in questo studio. Dal censimento eseguido risulta Che il 60,3% delle specie di barriera sono carnivore, il 15,5% planctivore, l’8,6% omnivore, l’8,6% erbivore territoriali e il 6,9% erbivore non territoriali. Delle 58 specie di barriera registrate, quattro sono endemiche a St. Paul’s Rocks, mentre circa l’80% sono presenti anche lungo le coste del Brasile. Si ritiene pertanto che St. Paul’s Rocks debba essere considerato un avamposto impoverito della regione brasiliana. Introduction St. Paul’s Rocks (Arquipélago de São Pedro e São Paulo) is a very small group of rocky islands located on the mid-Atlantic Ridge, just north of the Equator (00o55’N; 29o21’W), 1000 km from the Brazilian coast, and 1890 km from Senegal, Africa (Fig. 1). It is one of the smallest, most isolated groups of oceanic islands in the world. The Rocks are particularly interesting from the population biology and biogeographical perspectives because of their very small size and isolation. They are uniquely influenced by both the Equatorial Undercurrent – facilitating eastward dispersal – and the Southern Equatorial Current – directing flow from the centraleastern Atlantic. The area has been visited by scientific expeditions since 1799 (see Lubbock & Edwards, 1981). In the past, the inhospitable nature and inaccessibility of Bertran M. Feitoza, Luiz A. Rocha, Osmar J. Luiz-Júnior, Sergio R. Floeter and João L. Gasparini aqua vol. 7 no. 2 2003 63 St. Paul’s Rocks had prevented detailed biological studies. However, since the establishment of a scientific station by the Brazilian Navy in July of 1998, ichthyologists have been able to visit the island periodically to reassess the population status of reef fishes (the Rocks, now called ‘Arquipelago’ are permanently inhabited). The present study adds to the knowledge of the biology of the reef fishes of St. Paul’s Rocks obtained by the 1979 Cambridge Expedition (Lubbock & Edwards, 1981). Methods Study area: the Archipelago rises from the 4000 m deep ocean floor close to the mid-Atlantic Ridge, and two putative ages are given to it: 9.5 MYBP (million years before present) if it originated from a nearby ridge, or 35 MYBP if it originated from a farther oceanic ridge (Melson, 1972). It consists of five small rocky islets and four larger islets covering an area of about 16,000 m (Fig. 1). Tide pools are present on most of the islets, which are generally flushed with seawater at high tide (Fig. 2). A small shallow bay (2 to 21 m depth) is formed by the encirclement of three major islets (Fig. 3). Other reef habitats of St. Paul’s Rocks consist almost entirely of nearly vertical cliffs extending beyond 60 m depth (Fig. 4). Robertson (2001) noted that this archipelago has one of the most limited areas of shallows habitats (<50 m deep) among oceanic islands, with less than 0.2 km. Most of the sublittoral zone is dominated by the soft coral Palythoa caribeorum (from 3 to 8 m depth), and the algae Caulerpa sp. (from 3 to about 30 m) (Fig. 5). The hermatipic corals Madracis decatis (Lyman) and Scolymia wellsi Laborel appear where the Caulerpa stops at about 30 m, and occur down to at least 45 m Fig.1. Map of St. Paul’s Rocks. Reef fishes of St. Paul’s Rocks: new records and notes on biology and zoogeography 64 aqua vol. 7 no. 2 2003 Fig. 2. Tide pool at Belmont Islet, it is flushed with fresh seawater at high tide. Photo by B. M. Feitoza. Fig. 3. Bay situated between the Belmont, Challenger and Cabral Islets. Photo by B. M. Feitoza. Bertran M. Feitoza, Luiz A. Rocha, Osmar J. Luiz-Júnior, Sergio R. Floeter and João L. Gasparini aqua vol. 7 no. 2 2003 65 Fig. 4. Vertical cliff, the typical reef habitat of St. Paul’s Rocks. Photo by O. J. Luiz-Junior. Fig. 5. Underwater view at St. Paul’s Rocks, with the green algae Caulerpa sp. Dominating most of the sublittoral zone. Photo by O. J. Luiz-Junior. Reef fishes of St. Paul’s Rocks: new records and notes on biology and zoogeography 66 aqua vol. 7 no. 2 2003 Where they are quite abundant (Amaral, in press). Two black corals (Antipathes spp.) occur from a depth of 45 m to at least 60 m (Edwards & Lubbock, 1983a; Amaral, in press). Edwards & Lubbock (1983a), recorded 14 alga species in their study. Data collection: four expeditions have been undertaken since 1999 (May and November 1999, September 2000, and August 2001) comprising 47 days of fieldwork and about 124 hours of underwater activity (54 scuba dives to depths of 62 m – including two night dives, and 39 snorkelling dives). The water temperature ranged from 23 to 26.5oC and visibility from 12 to 30 m. The fish fauna was surveyed in tide pools and over reefs down to a depth of 62 m, through underwater observations, collections and photographs. Three small clove oils stations were conducted aiming to survey cryptic fish not collectable using other methods. Six hours of underwater videos were filmed with a view to investigating fish behaviour. Collected specimens were deposited in the fish col-lections of the following institutions: Universidade Federal da Paraíba, João Pessoa, Paraíba, Brazil (UFPB); and Museu de Biologia Professor Mello Leitão, Santa Tereza, Espírito Santo, Brazil (MBML). Data on voucher specimens is appended. Species list, populational status and abundance data: The species list is based on the fishes observed, photographed and collected during the four expeditions, as well as on data from the literature (Lubbock & Edwards, 1981) and from fisheries run by comercial fishing boats. Bony fishes are listed in the phylogenetic order of families, following Nelson (1994); elasmobranchs are listed following Compagno (1999). Within the families, species are organized in alphabetical order. We have also included the follow-ing information for each species: 1979 population status – a rough indication of relative abundance in 1979, based on Lubbock & Edwards (1981); Current population status – an indication of relative abundance in 1999 – 2001 based on a diver’s likelyhood of observing a species in its normal habitat and depth range on any given dive (adapted from Humman & DeLoach, 2002), where: AB = abundant (at least several sightings of many individuals – at least 50 – can be expected on nearly every dive), VC = very common (at least several sightings can be expected on nearly every dive, but not necessarily of many individuals), CM = common (sightings are frequent, but not necessarily expected on every dive), OC = occasional (sightings are not unusual, but are not expected on a regular basis), UN = uncommon (sightings are unusual), and RA = rare (sightings are exceptional); Habitat – where the species has usually been found (adapted from Edwards & Lubbock, 1983a), where:1 = tide pools (either frequently or infrequently flushed by fresh seawater), 2 = littoral zone (spring-tidal range), 3 = Palythoa and Caulerpa zone (dominated by Palythoa caribeorum, from the bottom of the littoral zone down to 8 m, and by Caulerpa, from 3 to about 30 m), 4 = subCaulerpa zone (from where Caulerpa stops, at about 30 m, to at least 60 m), 5 = slope and bay (gently sloping areas with patches of coarse sand, rubble and isolated loose rocks), and 6 = water column (offshore and over reefs, pelagic habitat); Depth range – range commonly seen in underwater observations; Geographic range of the species; Trophic category – determined from direct behavioural observations and available literature (Randall, 1967; 1996), where: TH = territorial herbivores, NT = nonterritorial herbivores, C = carnivores, P = planktivores, and O = omnivores. Record status – how the species was recorded. We consider ‘reef fishes’ to be species either associated with hard substrate (sensu Thresher, 1991) or epipelagic forms that regularly associate with the reefs (such as carangids, belonids, sharks and pelagic rays). Surveys of the abundance and the occurrence of juveniles and adults of various sizes were used to estimate which members of the fish fauna are residents, i.e. have self-sustaining populations, or vagrants, i.e. exceedingly rare and probably arriving from other sites. Results and discussion New records and population reassessment: Lubbock & Edwards (1981) recorded 50 fish species belonging to 29 families, of which 34 are associated with rocky-reef habitats. Our team recorded a total of 75 fish families (25 new records) belonging to 36 families. Fifty eight species were recorded over reef areas (referred to as “reef fishes”), eleven of which are mid-water species that are regularly observed on reefs, and 47 are dependent on rocky-reef habitats (Table I). Seventeen species are pelagic and are not included in Table I (new records are in bold): Rhincodon typus Smith, 1829; Carcharhinus falciformis (Bibron in Müller & Henle, 1839); Prionace glauca Linnaeus, 1758; Isurus oxyrinchus Rafinesque, 1810; Cypselurus cyanopterus (Valenciennes, 1847); Exocetus volitans Linnaeus, 1758; Paraexocoetus sp.; Remora brachyptera (Lowe, 1839); R. osteochir Cuvier, 1829; Remorina albescens (Temminck & Schlegel, 1845); Coryphaena hippurus Linnaeus, 1758; Acanthocybium solandri (Cuvier, 1832); Scomberomorus cavalla (Cuvier 1829); Thunnus albacares (Bonnaterre, 1788); T. obesus (Lowe, 1839); Makaira nigricans Lacepède, 1802; and Mola sp. Among the 58 reef fishes recorded, the most speciose families were the Muraenidae (seven species), Carangidae (five), Pomacentridae (five), Labridae (four), Serranidae (three), and Scaridae (three). Sixteen species (27.6%) were rare, five (8.6%) uncommon, nine (15.5%) occasional, 13 (22.4%) common, seven (12.1%) very common and six (10.3%) abundant, and (see Table Bertran M. Feitoza, Luiz A. Rocha, Osmar J. Luiz-Júnior, Sergio R. Floeter and João L. Gasparini aqua vol. 7 no. 2 2003 67 I). Nine of the 16 rare species (Cephalopholis fulva, Lutjanus jocu, Stegastes rocasensis, Clepticus brasiliensis, Thalassoma noronhanun, Sparisoma amplum, S. axillare, S. frondosum, and Bathygobius soporator) do not seem to have a self-sustaining population and probably come from other sites where they are commom (e.g. Fernando de Noronha Archipelago). The population status of most of the species between 1999 and 2001 seems to be nearly the same as that observed by Lubbock & Edwards (1981). Two species previously recorded by Lubbock & Edwards (1981) were not observed by our team: the Galapagos shark Carcharhinus galapagensis and the St. Paul’s anthias Anthias salmopunctatus. The abundance of sharks at St. Paul’s Rocks has been noted by most early visitors and partly attributed to the lack of fishing activity (Lubbock & Edwards, 1981). In the past two decades however, fishing pressure has increased greatly, and sharks are now targeted due to the high commercial value of their fins. The pelagic fishes on which sharks feed are also targeted by the fishing industry and this may also have contributed to an apparent population decline of C. galapagensis. Anthias salmopunctatus is endemic to St. Paul’s Rocks and was listed as vulnerable by IUCN (Hilton-Taylor, 2000). This species was common on rock faces below 30 m, as reported by Lubbock & Edwards (1981), but was not seen by our team. The St. Paul’s Gregory Stegastes sanctipauli, the brown chromis Chromis multilineata, the black durgon Melichthys niger and the black jack Caranx lugubris were the most visually abundant fishes in St. Paul’s Rocks and certainly account for the most important part of the fish biomass. The latter two species are usually found up to at least 150 m from the Rocks, forming large aggregations from just below the surface down to about 30 m. Melichthys niger appears to be common around isolated oceanic islands. There are reports of the same abundance for Ascension Island (Lubbock, 1980), Clipperton Atoll (Robertson & Allen, 1996), Trindade Island (Gasparini & Floeter, 2001), and to a minor degree in the vicinity of Rocas Atoll (Rosa & Moura, 1997) and Fernando de Noronha Archipelago (B. M. Feitoza pers.obs.). Almost two thirds (60.3%) of the reef fishes species are carnivores, 15.5% planktivores, 8.6% omnivores, 8.6% territorial herbivores and 6.9% non-territorial herbivores. Stegastes sanctipauli is primarily considered to be a territorial herbivore, but can also be opportunistic, sometimes preying upon fish eggs and small benthic invertebrates. The same appears to be true for the sergeant major Abudefduf saxatilis (primarily treated as a ‘planktivore’) since it has mostly been seen in mid water, clearly feeding on zooplankton. According to Randall (1967), A. saxatilis has one of the most diversified food habits known, and may be observed in aggregations well above reefs, feeding on zooplankton or grazing on benthic algae, or on sessile animal life on the bottom. This feeding flexibility probably enables opportunistic planktivores (e.g. S. sanctipauli and A. saxatilis) and the classic omnivores (e.g. M. niger) to numerically dominate harsh environments around oceanic islands.