Trophic models for investigation of fishing effect on coral reef ecosystems

A comparison was made using general trophic models of three coral reef slopes in the Mexican Caribbean. Two reef slopes are in semi-protected areas (Boca Paila, Tampalam) and the third is subject to more intense exploitation (Mahahual). The mass-balanced models of the three reef slopes were derived from fish biomass density data obtained directly from field measurements (fish census). Other trophic groups were derived from published sources. Initial parameters for the three reef slopes were calculated using the Ecopath with Ecosim software. Comparisons of model outputs were done to establish differences between reef slope systems that are semi-protected and unprotected from fishing activities. The most significant results include: partition of production was always lowest for the unprotected reef slope; net primary production was three times higher for the semi-protected slopes than for the unprotected one; total catch in the unprotected reef slope was three and eight times higher than the two semi-protected reef slopes; food chain length increased as total catch increased; the calculated trophic level of the catch was relatively lower in the unprotected reef slope; and catch per net primary production (gross efficiency) was higher in the unprotected reef slope than the semi-protected reef slopes. It is concluded that trophic macrodescriptors can serve as a guide to the hard-to-detect negative effects of coral reef management, aid in decision-making, and emphasize the effects that structural descriptors, (e.g. total fish biomass, diversity indices) do not detect.