Helgol Mar Res (2006) 60:287–305 DOI 10.1007/s10152-006-0045-4 ORIGINAL ARTICLE Reef fish community structure in the Tropical Eastern Pacific (Panama´): living on a relatively stable rocky reef environment Arturo Dominici-Arosemena Æ Matthias Wolff Received: 12 September 2005 / Revised: 2 May 2006 / Accepted: 3 May 2006 / Published online: 14 June 2006 Ó Springer-Verlag and AWI 2006 Abstract We compared the community structure of and structural complexity. Species diversity increases reef fish over different physical complexities in 12 with habitat complexity and benthic diversity. It seems study zones of Bahı´a Honda, Gulf of Chiriquı´ (BH- that water current strength, tides and waves which se- GCH), Tropical Eastern Pacific (TEP), Panama, aim- lect for swimming, play an important role in the com- ing at an analysis of the importance of the physical munity organization. The study region has been structure provided by corals, rocks and benthic sessile proposed as a refuge-centre in the TEP, where reef organisms. This was the first region that emerged in the fishes that evolved on coral reefs have shifted their Isthmus of Panama; it exhibits the oldest benthic fauna distribution onto rocky reef habitats. and has constant conditions in terms of temperature and salinity. Two hundred and eighty-eight visual fish Keywords Fish diversity Æ Distribution Æ Trophic censuses were conducted on 48 benthic transects from groups Æ Rocky reef Æ Tropical Eastern Pacific February to July 2003. One hundred and twenty-six fish species of 44 families were found. Plankton feeding pomacentrids and labrids along with haemulids that Introduction feed on mobile invertebrates were the most abundant, particularly in shallow areas. Fourteen species showed Ocean basins may promote speciation within a region size-segregations between zones, suggesting ontoge- during periods of low sea levels, and extensive shallow netic migrations (smaller fishes in shallow high-com- habitats can reduce faunal losses by acting as a refuge plexity zones, larger-sized fishes in deeper habitats). or centre of accumulation (Springer and Williams 1994; Highly mobile and site-attached genera were abundant Paulay 1996; Wilson and Rosen 1998; Palumbi 1997; in most shallow, wave-exposed zones particularly on Bellwood and Hughes 2001). It has been suggested that exposed rocky substrates. Planktivores were the most reef fish have evolved along with the coral communi- abundant, followed by carnivores, feeders on mobile ties they are associated with, but that their ancestors invertebrate and piscivores. Herbivores and feeders on have existed even prior to the coral reefs (Bellwood sessile invertebrate were lower in abundance. Species and Wainwright 2002). Thus, the recent reef dwellers richness exceeds that of any other studied region close would represent derived forms, with ancestors which to the mainland in the TEP and correlates with sub- would have occupied non-reef habitats (Bellwood and strate diversity, increasing size-heterogeneity of holes Wainwright 2002). In this respect, it should be con- sidered that tropical reef fishes indeed occupy non- coral built habitats such as rocky shores that are pre- Communicated by H.-D. Franke dominant in the Tropical Eastern Pacific (TEP). The fish fauna in this region has a north–south division, and & A. Dominici-Arosemena ( ) Æ M. Wolff subdivisions can be based on the highly localized Centre for Tropical Marine Ecology (ZMT), Fahrenheitstrasse 6, 28359 Bremen, Germany endemism of small benthic rocky reef-associated fishes e-mail: [email protected] (Hastings and Robertson 2001). In the Central American 123 288 Helgol Mar Res (2006) 60:287–305 Isthmus, besides the Golfo Dulce in Costa Rica, a Gasparini 2000). However, the available information fiord-like tropical embayment with anoxic deep waters on the TEP does not allow for the determination of (Quesada-Alpı´zar and Morales-Ramı´rez 2004; Wolff gradients in fish diversity in the Mesoamerican region et al. 1996) and low coral development (Corte´s 1990), and for the verification of the basic assumption of the first uplifted region where new reef development higher diversity of reef fish in the TWA compared to started is the open area of the Gulf of Chiriquı´ (GCH). the TEP. Here are the oldest corals of modern reefs in the TEP The main objective of the present study was thus to displaying maximum thickness and accretion rates characterise the fish assemblages of Bahı´a Honda (BH- (Corte´s 1993, 1997). This region comprises the largest GCH, TEP) along spatial scales and gradients of sub- archipelago of rocky islands in the TEP (Kwiecinski strate complexity. and Chial 1983; Glynn and Mate´ 1997). Due to its It is hypothesized that due to its environmental inaccessibility, detailed biological studies are still stability (as compared to other TEP regions), its rel- lacking. The fish community structure of this region is ative old age and great habitat diversity, a relatively particularly interesting from the perspective of popu- rich reef fish community has evolved. Since this and lation biology and biogeography due to its geological other regions of the TEP have been subjected to a history and environmental stability (Kwiecinski and massive decrease in coral diversity due to geological Chial 1983; Glynn and Mate´ 1997). The GCH forms changes, we suspect that reef fish may have evolved part of the Panamic province of the TEP, and there is and diversified on the available rocky substrates with only one recent inventory in the Coiba National Park high benthic diversity and complexity in a similar way by Vega and Villarreal (2003), which includes many as have other reef fish communities on (diverse) coral reef fish with the exception of the cryptic ones (e.g. reefs elsewhere. We thus propose that corals do not gobiids, chaenopsids). Some pioneering studies have play the same reef community-structuring role here as already addressed variations of the reef fish community in the Indo-Pacific and the Caribbean, and we pos- structure in the reef areas in TEP (Zapata and Morales tulate that reef fish communities may just represent 1997; Arburto-Oropeza and Balart 2001; Dominici- species guilds related to hard substrates of diverse Arosemena et al. 2005). Belonging to the lower Mes- complexity. oamerica, this region offers unique opportunities for The TEP region is the most unstable province in the comparative fish community studies (e.g. non-reef vs. whole Pacific where reef communities are adapted to coral reef environments; TEP vs. Tropical Western geological changes, and to temperature decreases due Atlantic, TWA) (Robertson 1998). It is believed that to coastal upwelling. In the non-upwelling GCH this region has a very diverse fish fauna, and that a (where temperatures are higher with relatively low significant component of it is made up of resident seasonality) fishes and benthic fauna that recruit from transpacific fishes that may live on reefs elsewhere in more unstable regions may be adapted to short scale the Pacific (Robertson 1998). There is a sufficient disturbances, particularly warming events (e.g. ENSO; diversity of habitats allowing for meaningful biological for disturbance resistance in corals on this region, see comparisons with the lower Mesoamerican TWA. D¢Croz and Mate´ 2004). Even though research is For comparative purposes we have conducted re- pending in this field, the fishes in GCH, TEP may have cently a similar study on the Caribbean west side of the developed some resistance to environmental changes, Isthmus in Bocas del Toro (Dominici-Arosemena and and suitable habitats should have promoted their spe- Wolff 2005). Both the Caribbean and the Pacific side of ciation and diversification in the region. Western Panama exhibit a rich landscape, and it was The study thus aims at an analysis of the relative these parts, which in geologic times (7–3 million years importance of the physical structure provided by cor- ago) became first interconnected by a shallow shelf als, rocks and benthic sessile organisms for the reef fish (while Eastern Panama was still lacking a shelf area) community organization. when the isthmus started to rise, finally resulting in the Furthermore, we studied the coexistence of subor- fusion of the North and South American continents dinate species with dominant species by differential and the separation of the two oceans (Bermingham habitat use (i.e. different mobility and home range, et al. 1997). size frequencies, territoriality, trophic organization), While the Indo-Pacific regions have been suggested the importance of wave exposure and current regime as evolutionary source of many reef fish species for structuring the community, and the role of reef worldwide (Mora et al. 2003), the TWA is believed to type (i.e. coral reefs vs. rocky reefs) and general be the centre of diversity for both fish and corals in the substrate diversity and complexity for shaping the fish Atlantic Ocean (Briggs 1995; Veron 1995; Floeter and community. 123 Helgol Mar Res (2006) 60:287–305 289 Materials and methods other regions close to the mainland. Coral and rocky reefs are present also off shore on the Canales de Study area Afuera Island, which is part of the Coiba National Park (Cardiel et al. 1997). The Pacific coast of Panama is divided by the Azuero Twelve study zones were classified in terms of depth, Peninsula into two major areas with notable oceano- substrate topography, cover, kind of benthic organisms graphic differences: the upwelling Gulf of Panama to and inorganic substrates. The selection of study zones the East and, protected from northern trade winds by was based on a previous survey aimed at identifying the mountains, the non-upwelling stable GCH to the areas of different but characteristic habitats of the re- West (D¢Croz and Robertson 1997; Glynn and Mate´ gion. 1997). Study sites were located in the latter (7°50¢N, 81°35¢W; Fig.