Marine and estuarine fish diversity in the inner Gulf of Nicoya , Pacific coast of Costa Rica , Central America

A checklist of the marine and estuarine fishes of the inner part of the Gulf of Nicoya, Pacific coast of Costa Rica, Central America, was compiled by examining a museum fish collection, resulting in 72 families and 274 species. Of these species, 127 (46.4%) were marine species and 147 (53.6%) were estuarine-associated species. In terms of their life history and considering the habitat type classification, 188 (almost 70% of the total) were categorized as species inhabiting softbottom habitats, reflecting the large estuarine environment and rich fish diversity of the Gulf despite its relatively small area in the tropical Eastern Pacific region. Furthermore, the list contains 13 threatened species of IUCN Red List, which need further research to understand their abundance and their exposure to habitat loss in the Gulf. Further detailed studies on its fish fauna and habitat are needed to better understand and conserve biodiversity within the whole Gulf. DOI: 10.15560/10.6.1401 L s t s o f s p e c ie s


Introduction
The Gulf of Nicoya is located on the northwestern coast of Costa Rica (10° N, 85° W) in the Eastern Pacific. It is considered the most important fishing ground for finfish, penaeid shrimp, and shellfish in Costa Rica (Vargas 1995;Vargas and Mata 2004). A number of rivers flow into the Gulf, the most significant of which is the Tempisque River, located at the innermost point of the waterway. The fresh water from these rivers helps to provide a very productive estuarine habitat in the confines of the Gulf (Vargas and Mata 2004;Wehrtmann and Cortés 2009). The Tempisque River creates strong horizontal and vertical salinity gradients in the central region of the upper Gulf, a zone characterized by mangrove forests, sand-and mudflats, and sandy beaches. Bartels et al. (1983) researched the distribution, diversity and abundance of fishes by trawl sampling, and recorded 214 species (composed mainly of fishery species) from the entire Gulf. However, their species list included a number of unidentified species due to the limited taxonomic information at that time, and no data for voucher specimens (e.g., specimen registration number and/or institution) were provided. Basing species lists on voucher specimens is foundational to faunistic and ecological studies because it helps avoid many types of errors such as misidentifications and systematic problems within poorly known taxonomic groups (Biological Survey of Canada 2003). In addition, categorizing each listed species to an ecological niche in a specific geographic Marine and estuarine fish diversity in the inner Gulf of Nicoya, Pacific coast of Costa Rica, Central America River (Vargas and Mata 2004). In order to document the diversity of marine and estuarine fishes in the estuarine habitat of the inner Gulf, this study was restricted to the upper zone of the Gulf from a line connecting the tip of Puntarenas city (9°58′35.399″ N, 84°51′5.400″ W) and the tip of Punta Gigante (9°54′10.440″ N, 84°54′55.799″ W), which combines "Zone B" and "Zone C" of Araya (1984) (Figure 1). The northernmost point of the study area was the first bridge across Tempisque River (10°14′53″ N, 85°14′35″ W).
The specimens collected from within the study area were extracted from collections deposited in the Museo de Zoología of the Universidad de Costa Rica (UCR), and identified following Robertson and Allen (2008). For groups revised since Robertson and Allen (2008), scientific names were determined from the revisionary papers, and these papers are listed in the 'Taxonomic and ecological remarks' below. The size of specimen was usually expressed as standard length (SL), but sometimes as fork length (FL), total length (TL) or disc width (DW). The life history status of each species was determined from ecological information described in Robertson and Allen (2008) and Froese and Pauly (2011) as follows: marine species-living in marine environment and generally not entering estuarine or freshwater habitats; marine-estuarine species-utilizing marine and brackish environments (such as estuaries and river mouths); estuarine species-mainly utilizing estuarine environments (including mangrove areas) as its habitat; freshwater-estuarine species-mainly inhabiting brackish and freshwater environments (not including species sometimes entering rivers); amphidromous speciesutilizing both marine and freshwater environments. The latter four categories are summarized as estuarineassociated species. Furthermore, to better understand the habitat characteristics of the Gulf based on species composition, habitat type was also divided into the following four categories (referring to the same literature as for life history status): soft-bottom species-living on mud and flat bottoms, including estuarine mangrove areas; reef-associated species-mainly inhabiting the reef zone and its adjacent habitat; pelagic species -living and feeding in the open sea (deep water species are also included in this category); multiple habitat speciesutilizing both rocky reef and soft bottom habitats. The IUCN red list (IUCN 2013) was used to categorize the conservation status of each species recorded in this study as follows (in order of threat level): No E, not evaluated; DD, data deficient; LC, least concern; NT, near threatened; VU, vulnerable; EN, endangered; CR, critically endangered. The systematic order followed Nelson (2006) but was alphabetically arranged at species level. All species names recorded in the present study are listed in Table 1, with relevant ecological information as detailed above. All the UCR material examined and designated as vouchers are listed in the appendix, including the number of individuals and their size in mm.

Results
The museum collection survey identified a total of 274 fish species, representing 72 families in 26 orders, from within the inner part of the Gulf of Nicoya (Table  1). The top 25 dominant families in terms of number of species are shown in Table 2. The most speciose family is Sciaenidae (31 species, 11.4% of total) followed by Gobiidae (19, 7.0%), Carangidae (18, 6.6%), Haemulidae (18, 6.6%), Ariidae (14,5.1%), Engraulidae (12, 4.4%), and Serranidae (10, 3.7%); the remaining families are represented by fewer than 10 species each. The dominance of some families such as Sciaenidae and Gobiidae in the inner Gulf corresponds well with the species composition of the whole fish fauna of the Tropical   Table 1. Species list of marine and estuarine fishes recorded from the inner Gulf of Nicoya, Pacific coast of Costa Rica, central America. Numbers in parentheses next to the family name indicate the number of species recorded from that family. Taxonomic and ecological remarks on the species marked with an asterisk were given in the text. Abbreviations for the IUCN Red List are as follows: CR, critically endangered; DD, data deficient; EN, endangered; LC, least concern; No E, not evaluated; NT, near threatened; VU, vulnerable. The Catalog Number of the UCR voucher specimen, and the number of specimens and their size range, were provided in the appendix.

Discussion
Erdman (1971) reported on the occurrence of some fish species in Gulf of Nicoya. Although voucher information was not provided for the vast majority of species in his report, he listed some species from the inner Gulf that were not recorded in the present study. These species were Carcharhinus limbatus, Rhizoprionodon longurio (Carcharinidae), Sphyrna mokarran, S. media (Sphyrnidae), Manta birostris as M. hamiltoni (Myliobatidae), Gobiesox milleri (Gobiesocidae) and Epinephelus quinquefasciatus as E. itajara (Serranidae). Of these species, G. milleri had already been reported from the inner Gulf as its type locality is Caballo Island, Gulf of Nicoya (Briggs 1955), andErdman (1971) described the environment where the holotype of G. milleri was collected. Although no specimen of this species was identified in the UCR collection in the present study, G. milleri was included in the species list of the inner Gulf of Nicoya (Table 1) based on its original description (Briggs 1955).
The present study indicates that the inner part of the Gulf has more than 21% of the total number of shorefish species (almost 1300 according to Robertson and Allen (2008)) from the TEP region. The Gulf of Nicoya has a rich marine biodiversity, despite its small area compared with the entire TEP.