Land use changes and impact on coral communities along the central Pacific coast of Mexico

The loss of coral coverage from environmental degradation is a progressive phenomenon that occurs in coral communities around the world. However, the consequences of land use changes and its impact on the state of conservation of coral communities are not yet understood. This study compares the impact of coastal land use changes on four coral communities near rural (Isla Faro and El Zapote) and suburban (Caleta de Chon and Playa Manzanillo) sites in the states of Michoacan and Guerrero, along the central Pacific coast of Mexico. Indicators of environmental degradation in coral communities (sediment deposition, water transparency, total suspended solids, and chlorophyll concentration) show that signs of eutrophication are absent from both rural sites in Michoacan. This absence suggests that human impact is not the main cause of the observed degradation (coral Mortality Index MI = 0.85, a high death coral coverage similar to 42% and the lowest species richness). Instead, the 1997-1998 El Nino-Southern Oscillation (ENSO) event (the strongest in the last decade) appears to be the major factor in this coral cover decline, as it occurred in the eastern Pacific and other regions of the world. In contrast, coral communities near the suburban sites in Guerrero are well developed, and their coral coverage and species richness (up to 67.7% and 7 species, respectively) are comparable to other major coral communities in this region. Nonetheless, indicators of human-derived degradation in the Guerrero coastal zone near Caleta de Chon and Playa Manzanillo, including high sediment deposition up to 1.2 kg m(-2) d(-1), low water transparency < 5 m, presence of filamentous algae on dead corals and a coral Mortality Index of MI similar to 0.6 show that human impact is beginning to affect the conservation state of these coral communities, reducing their species richness and coral coverage. Although the ENSO impact on coral communities could be more drastic than the anthropogenic impact, the current study confirms that increased land use changes and coastal erosion are causing progressive coral community degradation. Therefore, land and coastal changes must be rigorously regulated.