coral reef fishes

Atlantic and Gulf Rapid Reef Assessment

Coral reef fishes

Fish populations are characterized in AGRRA in order to infer the effects of any overharvesting by humans or changes in community dynamics due to natural or anthropogenic causes. Visual fish censuses of all types have been conducted throughout the Caribbean and Gulf of Mexico, but few usually are comparable because of the various methodologies used (Sale 1997). The AGRRA approach includes two distinct survey methods that provide different types of data and should both be applied at each site.

The first is a 2-m wide belt transect, chosen because this distance is small enough for accurate estimation while swimming with a T-bar. Abundance and size data (used for biomass estimations) are recorded for SELECTED Caribbean predators, herbivores, and “indicator” species, many of which are commercially significant. The list of fish species to assess was adapted to include fish of interest in the western Atlantic (Appendix 4). Focusing on a restricted number of species allows a relatively consistent search image to be used, enhancing precision of the collected information. The Reef Environmental Education Foundation (REEF) rover diver surveys (Schmitt et al. 1998) are used in the second method to measure species composition and density of all observed fish species which can be used to investigate the relationship between species distribution, abundance and fishing pressure. Together these two data sets provide a baseline on the status of local fish assemblages, and the extent to which they are likely to have been affected by human activities.

Fish communities respond to disturbance in various ways, depending on the type and degree of perturbation. Large fish kills have occurred as a result of shifts in ocean currents, abrupt changes in water temperature, outbreaks of red tide, and volcanic activity. Accumulations of dead fish along the beaches have been reported following hurricanes and large storms (Robins 1957), and although we readily recognize the immediate impact on the architectural complexity of the reef, it is still unclear what the long-term effect of these natural disturbances are on fish community structure. Connell’s (1978) theory of ‘intermediate disturbance’ suggests that diversity increases as a result of intermediate levels of disturbance, since more species can coexist under the conditions of reduced competition and environmental harshness. While this theory has been widely applied to patterns in coral diversity, studies of reef fishes response to disturbance have largely been empirical, without testing of models to predict the response of fish community to changes in habitat structure (Jones and Syms 1998). Intense fishing directly affects a fish population by eliminating organisms, resulting in a change in abundance and a reduction of large-sized individuals. Removing large-sized individuals decreases spawning potential and has the indirect effect of reducing larval recruitment. Fishers are often driven to use destructive fishing methods as catch-per-effort yields decrease. The use of explosives or poisons reduce the habitat complexity of reefs, and are reflected in declines in species diversity and abundance, especially for species that are directly dependent on the substratum for food (e.g. obligate corallivores) (Samoilys 1988, Chiappone 2000). Intense fishing may also be reflected in a shift of predator-prey dominance (Roberts and Polunin 1991) with subsequent consequences on overall community stability (Goeden 1982).

Reef fish, as predators or grazers, play an important role in the community dynamics of coral reefs through their interactions with corals, algae and other herbivores. Various combinations of commercial, subsistence and recreational fishing, particularly of herbivores, are one of the most widespread and greatest anthropogenic impacts on coral reefs (Roberts 1995). The loss of fish species, especially certain indicator species and guilds, cause both direct and indirect shifts in the structure of fish communities as well as other components of coral communities (Munro and Williams 1985, Munro et al. 1987, McClanahan and Muthiga 1988, Hughes 1993, 1994). Disruption in the balance of reef fish assemblages can decrease coral cover and increase algal abundance (Roberts 1995, 1996, McClanahan 1996).

More overview:

General overview
Coral condition
Bleaching
Disease
Algae and Diadema

Robert N. Ginsburg
Atlantic and Gulf Rapid Reef Assessment
MGG-RSMAS, University of Miami
4600 Rickenbacker Causeway
Miami, FL 33149
USA Telephone: (305) 421-4664
Email: info@agrra.org
Send data to: data@agrra.org
URL: http://www.agrra.org