Akumal's reefs: stony coral communities along the developing Mexican Caribbean coastline

ABSTRACT

Fringing coral reefs along coastlines experiencing rapid development and human population growth have declined worldwide because of human activity and of natural causes.The "Mayan Riviera "in Quintana Roo,México,attracts large numbers of tourists in part because it still retains some of the natural diversity and it is important to obtain baseline information to monitor changes over time in the area.In this paper,the condition of the stony corals in the developing coastline of the Akumal-area fore reefs is characterized at the start of the new millennium at two depths,and along an inferred sedimentation gradient.Transect surveys were conducted in five fringing reefs starting at haphazardly chosen points.with respect to species composition,live cover,colony density,relative exposure to TAS mats and,for one species (Diploria strigosa ,Dana,1848),tissue regression rates in the presence of TAS mats.Fish population density and herbivory rates are also assessed.Data from line intercept transects (n=74)show that live stony coral cover,density and relative peripheral exposure of colonies to turf algal/sediment (TAS)mats were inversely related to an inferred sediment stress gradient at 13m.In 2000, live stony coral cover had decreased by 40-50%at two sites studied in 1990 by Muñoz-Chagín and de la Cruz- Agüero (1993).About half of this loss apparently occurred between 1998 and 2000 during an outbreak of white plague disease that mostly affected Montastraea faveolata ,and M.annularis .At a 13 m site,where inferred sedimentation rates are relatively high,time series photography of tagged Diploria strigosa ,(n=38)showed an average loss of 70 cm 2 of live tissue/coral/year to encroachment by TAS mats during the same period.Whereas densities of carnivorous fishes and herbivores (echinoids,scarids,acanthurids and Microspathodon chrysurus )in 2000 were low in belt transects at 10-19 m (n=106),turf-algal gardening pomacentrids were relatively common on these reefs

RESUMEN

Para conocer el estado de las comunidades coralinas a lo largo de una costa en desarrollo,se realizó inventarios de transectos en cinco arrecifes de borde cerca de Akumal, México,con transectos de intersección (n=74).La cobertura de corales rocosos,la densidad y la exposición periférica relativa de las colonias y masas de algas-sedimentos son inversamente proporcionales a la gradiente de estrés de sedimentación inferida a 13m.En el 2000,la cobertura de corales rocosos vivos había decrecido un 40%en dos de los sitios estudiados por Muñoz-Chagín y de la Cruz-Agüero (1993).Alrededor de la mitad de esta pérdida aparentemente ocurrió entre 1998 y 2000 durante la epidemia de "blanqueo" que afectó principalmente a Montastraea faveolata y a M. annularis .En el sitio de 13m,donde las tasas de sedimentación inferida son relativamente altas,las fotografías en serie temporal de Diploria strigosa marcados (n=38)mostraron un promedio de pérdida de 70 cm2 de tejido vivo/coral/año y el cerco creciente de masas de algas durante el mismo periodo.Aunque las densidades de peces carnívoros y de organismos herbívoros (equinoideos, escáridos,acantúridos y Microspathodon chrysurus )en el 2000 fueron bajas en la franja a 10-19 m (n=106),se vio con frecuencia pomacéntridos que se alimentan de masas de algas