Abstract
ABSTRACTAlpheid shrimp represent an abundant and diverse, but poorly characterized, component of the cryptic biodiversity of coral reefs worldwide. Sponge‐inhabiting alpheids provide a promising model system for exploring patterns of cryptic reef biodiversity because their habitats (hosts) are discrete and qualitatively distinct units. We tabulated data from 14 years of collections at Carrie Bow Cay, Belize to quantify patterns of diversity, host specificity, and dominance among sponge‐dwelling shrimp (Synalpheus), with special attention to eusocial species. From > 600 sampled sponges of 17 species, we recognized at least 36 Synalpheus shrimp species. Of these, 15 (42%) were new to science. Species accumulation curves suggest that we have sampled most of the Synalpheus diversity at Carrie Bow Cay. Diversity of sponge‐dwelling Synalpheus was slightly higher in shallow water, probably because of greater habitat diversity, than in deep water. Host specificity was surprisingly high, with > 50% of all shrimp species found in only a single sponge species each, although some shrimp species used as many as six hosts. Cohabitation of individual sponges by multiple shrimp species was rarer than expected by chance, supporting previous distributional and behavioural evidence that competition for hosts is strong and moulds patterns of host association. The fauna of most well‐sampled sponge species was dominated, both in numbers of individuals and in frequency of occurrence, by eusocial species. Eusocial shrimp species also inhabited a significantly greater number of sponge species than did non‐social shrimp. Consequently, > 65% of shrimp in our quantitative samples belonged to the four eusocial species, and on a per‐species basis, eusocial species were 17 times as abundant as non‐social species. Our data suggest that the highly diverse sponge‐dwelling shrimp assemblage of the Belize Barrier Reef is structured by competition, and that eusociality has allowed a small number of species to dominate the sponge resource.
Highlights
Coral reefs are among the most highly diverse marine ecosystems (Kohn, 1997; Ormond & Roberts, 1997; Reaka-Kudla, 1997)
The island of Carrie Bow Cay (CBC) is part of the Belize barrier reef complex, the longest continuous reef in the Caribbean (Adey, 1977; Rützler & MacIntyre, 1982), and a region known for its high diversity of coral reef fauna
Over the course of 11 collecting trips totalling c. 139 field days and spanning 14 years, at least 36 putative species of Synalpheus shrimp were found inhabiting a total of 17 sponge species (N = 623 sampled fauna-bearing sponges) in the vicinity of CBC, Belize (Table 1)
Summary
Coral reefs are among the most highly diverse marine ecosystems (Kohn, 1997; Ormond & Roberts, 1997; Reaka-Kudla, 1997). While a great deal of this diversity is obvious to the casual observer, much of it is invisible within the reef framework, consisting of a substantial invertebrate cryptofaunal community (Hutchings, 1983; Kensley, 1998) This community is poorly characterized and generally underrepresented in studies of coral reef biodiversity due to logistical difficulties in sampling, a dearth of systematic knowledge for many cryptic taxa, and the high. The high diversity of sponge-dwelling Synalpheus has made these shrimp a model system for study of host-mediated evolution (Duffy, 1996b,c) and sociobiology Sponge-dwelling shrimp might serve as a general model for exploring diversity patterns in other cryptic reef taxa that are difficult to sample quantitatively because of their inaccessible and heterogeneous habitats. These collections provide the opportunity to sketch a quantitative picture of the biodiversity and ecological distribution of one of the most species-rich, but poorly known, components of cryptic coral-reef biodiversity, and to assess indirectly the role of sociality in ecological dominance of the spongedwelling niche
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