Relevance of Cryptic Fishes in Biodiversity Assessments: A Case Study at Buck Island Reef National Monument, St. Croix

Smith-Vaniz, William; Jelks, Howard; Rocha, Luiz

Because cryptic fishes are difficult to accurately survey, they are undersampled components of coral reef habitats, and their ecological roles have been generally ignored. Fifty-eight enclosed stations were sampled in shoreline, nearshore reef, lagoon, backreef, forereef, and bank/shelf habitats with an ichthyocide (rotenone) at Buck Island Reef National Monument, St. Croix, U.S. Virgin Islands. Our samples included 55 families and 228 species, 60 previously unreported from St. Croix. Fish assemblages varied across habitat zones with the shoreline assemblage the most distinct. Only 8% of the species were present in all habitats. Multi-dimensional scaling plots of habitat characteristics and Bray-Curtis similarities of fish assemblages revealed similar patterns. Dominant and rare taxa are enumerated for each habitat sampled. Rotenone and visual census data are compared. While visual surveys accumulated more species per unit of effort, rotenone samples accumulated more species by area. Only 36% of the 228 species sampled with rotenone were visually detected, while 70% of the 115 species visually detected were also collected with rotenone. The use of rotenone is controversial but important for obtaining reasonably complete inventories of reef fishes. Misconceptions about rotenone and the advantages and limitations of alternative biodiversity assessment methods are discussed. Managers of marine protected areas (MPAs) generally recognize the importance of fish biodiversity in reef ecosystems, yet a reasonably complete picture of that biodiversity is frequently lacking. Coral reef ecosystems are so structurally and biologically complex, and reef-fish life histories and behavior so diverse, no single assessment technique can provide resource managers and scientists with unbiased qualitative or quantitative estimates of reef-fish assemblages (Sale and Douglas, 1981; Bortone et al., 1986; Ackerman and Bellwood, 2000). Nevertheless, a reasonably complete baseline inventory is desirable for estimating biodiversity, comparing the composition of ichthyofaunas at different locations, and evaluating the success of future management actions and the impacts of threats (e.g., overfishing, pollution). Census techniques routinely used to detect highly mobile or easily observable species will likely miss or significantly underestimate morphologically or behaviorally cryptic species that are usually hidden among intricate substrata. Both readily observable and cryptic fishes have complex ecological and behavioral interrelationships, and human and natural events that alter coral reefs impact the entire fish community. By supplementing data obtained from studies of visible fauna with collections of cryptic organisms, a more complete assessment can be achieved. The use of ichthyocides to investigate coral reef fish communities is controversial because some reef biologists consider it to be an unnecessarily consumptive sampling method. The objectives of this paper are to: (1) present a base-line inventory of cryptic reef and shoreline fishes inhabiting shallow-water habitats at Buck Island Reef National Monument; (2) compare fish distributions and relative abundance patterns among the sampled habitats; (3) compare the results of ichthyocide (rotenone) sampling with independently conducted underwater visual censuses (UVC); and (4) discuss misconceptions about rotenone and suggest guidelines for its use in marine habitats.

Relevance of Cryptic Fishes in Biodiversity Assessments: A Case Study at Buck Island Reef National Monument, St. Croix

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