No abstract

We evaluated the effects of competition for space between mixed turf algae (MTA) and the hermatypic coral Montastraea faveolata Ellis and Solander (1786) using reciprocal transplantation of 17 cm 2 cores and by measuring the response of some biological parameters of the coral: zooxanthellae density, mitotic index, chlorophyll a (Chl a) concentration, and tissue thickness. Mitotic index and Chl a zooxanthellae Ϫ1 were not significantly affected by the competition, but zooxanthellae density, Chl a cm Ϫ2 , and tissue thickness were reduced in M. faveolata tissue surrounded by algae. Lower values have been reported for these three biological parameters of scleractinian corals subjected to stress conditions. Stressed M. faveolata surrounded by MTA were completely overgrown in 6-9 months. MTA frequently formed unattached cushions before the algae were attached to the coral skeleton. The cushions could be affecting M. faveolata by shading the coral tissue beneath the algae and probably causing stress to the tissue. Trapped sediments in the cushions may also be affecting M. faveolata by trapping sediments that cause smothering or burial of coral tissue. This is the first demonstration that algae directly stress a coral species and that MTA can be superior competitors than M. faveolata under experimental conditions. M. faveolata is sensitive to algae and bacteria, and the outlook for this coral species is poor if deleterious conditions act together in the Caribbean Sea.

Epiphytic algae from Bajo Pepito, Isla Mujeres, Quintana Roo, México. A total of 96 epiphytic algae species were identified from Bajo Pepito, Quintana Roo, México. 60.4% (58) belonged to the Rhodophyta, 19.79% (19) to the Phaeophyta, 16.6% (16) to the Chlorophyta and 3.1% (3) to the Cyanophyta; 49 species (50.5%) were found only in one month, while Heterosiphonia crispella was found in all of the sampled months. That species provided the largest contribution to the biomass of epiphytes. During January we registered the greater biommass and richness of epiphytes species, coincidently with high values of host species cover and rainfall.

No abstract

Mangroves occur in coastal areas and are therefore vulnerable to anthropogenic disturbance and exhibit high rates of deforestation. Mexico is among the countries with the highest degree of mangrove deforestation in America; however, precise data on national mangrove coverage in Mexico is incomplete, making it impossible to accurately ascertain the rate of mangrove loss over time. Precise information is necessary to assess changes at local and regional scales to detect the magnitude, trends, and drivers of the transformation. This study aimed to estimate the loss of mangrove cover in the area of Mahahual-Xcalak (Quintana Roo, Mexico) between 1995 and 2007, to calculate the annual deforestation rate and to identify the drivers of deforestation. Landsat TM and ETM+ images from 1995 and 2007 were used to estimate the loss of mangrove cover using a multitemporal analysis. Semi-structured interviews with local residents of Mahahual and Xcalak were undertaken to identify and validate the drivers of deforestation. The image analysis for the 12-year period showed that 1070 ha of mangrove forest have been lost, with an annual deforestation rate of 0.85%—a relatively high value compared with other mangrove regions in Mexico. The main factor that has triggered the reduction of mangrove coverage is the expansion of anthropogenic land uses (e.g., settlements and roads). This study concludes that conservation and rehabilitation programs need to be implemented so that the Mahahual-Xcalak mangrove environment can continue to provide key ecosystem services.