Coral Reefs of the Southern Gulf of Mexico by Tunnell John W.;Chávez Ernesto A.;Withers Kim;

Author:Tunnell, John W.;Chávez, Ernesto A.;Withers, Kim;
Language: eng
Format: epub
Publisher: Texas A&M University Press
Published: 2007-08-15T00:00:00+00:00

Trophic Structure

Despite the similarities of fish communities observed among these reefs, we can observe some differences in the way trophic webs are organized, as indicated by the changes in relative abundance of dominant species at each reef, and in some particularly striking differences in fish densities. Relative abundance of fishes differs among reefs to such a degree as to suggest important quantitative and qualitative changes in the structure of trophic webs. Trophic structure comparisons indicate striking differences among coral reefs in guild composition as well as abundance.

Planktivores perform a critical function in the cycling of energy on coral reefs. Much of the energy flowing into coral reef systems comes in the form of nutrients released by large numbers of planktivorous fish living on the upper reefs (Hammer et al. 1988). Planktivorous fish glean energy and nutrients from the water column and deposit it on the reef in the form of detritus. Energy and nutrients are then available to a host of reef resident detritivores and plants, which in turn become food for other reef species.

The most abundant planktivorous fish, C. multilineata, was found at all reefs. The fish assemblage of zooplankton feeders in the Campeche Bank is quite similar to that at Flower Garden Banks, where C. multilineata, T. bifasciatum, and creole wrasse (Clepticus parrae) are dominant species grouped in mixed feeding schools at midwater with I. vittata and O. chrysurus.

Although found on all reefs along the western Gulf of Mexico, planktivores are not the most abundant fishes at all reefs. Cayos Arcas and Cayo Arenas reefs seem to support large numbers of piscivorous fish, such as the serranid groupers red hind (Epinephelus guttatus), rock hind (E. adscensionis), black grouper (Mycteroperca bonaci), and tiger grouper (Mycteroperca tigris) and S. barracuda.

Reef-fish assemblages are loosely structured (Sale 1982; Sale and Douglas 1984), with variation caused by differences in habitat heterogeneity. Reef size may lead to the expression of a higher diversity of habitats as in Alacrán Reef, allowing the possibility of a wider variety of niches to be exploited by fish.

Seasonal influence of freshwater runoff from the continent over the reefs at Veracruz and the west Campeche Bank, and the presence of a seasonal upwelling along the Campeche slope, result in water masses that cause changes in trophic pathways. Freshwater runoff most likely affects the reefs of the Veracruz Reef System and the southwestern portion of the Campeche Bank, while upwelling along the Yucatán Channel is more likely to influence Alacrán Reef. The influence of freshwater runoff in these areas seems to support the idea that because trophic structures respond to similar environmental influences in predictable ways, reefs displaying highly similar trophic structures may be influenced by similar environmental pressures.

Despite their limitations, available data may still provide a general view of reef-fish abundance, species distribution, and fish-community structure. Although differences in relative abundance were observed at each reef, it is evident that, as commonly occurs in natural communities, a few species exhibit strong dominance. A comparison of the number of species per trophic levels suggests there are some differences in trophic structure between reefs.

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