LOPEZ-FORMENT, Marta, Museum of Paleontology and Dept. of Integrative Biology, University of California ,Berkeley, CA 94720-4780; and BONILLA, Hector Reyes, Universidad Autonoma de Baja California Sur, La Paz, Mexico
Fungia distorta is a common mushroom coral throughout the Indo-Pacific, from East Africa to the Americas. It occurs at various places along the west coast of Mexico, reaching the northeastern limit of its biogeographic range in the Gulf of California. We studied its ecology, population density, growth rate, age structure and mortality rate in 49 quadrants on the SW side of Isla San José. There a dense bed of F. distorta coexists with algae and other animals. The corals are strongly aggregated, occurring in groups from 18 to 119 individuals/m2, which is equal to a nearly 100% coverage of the substrate. This is one of the highest values ever registered for a coral population in the Gulf of California. Associated algae and invertebrates, including Herbestia pubescens, Tylodina fungina, Columbella fuscata and Acanthaster plancii, are dispersed as aggregates among the Fungia. The invertebrates live very close to the algae or at the borders of Fungia clusters. Fungia distorta is abundant, and even dominates the marine biota, in certain areas near the end of its geographic range in the Gulf of California, unlike it does in much of the Indo-Pacific, where it lives more dispersed. The mushroom corals showed annual growth bands, and therefore we calculated growth rate by counting the number of pairs of light and dark bands. The average yearly growth rate was 5.11mm, which is low if compared to other corals like Montastrea annularis, whose rate is 8.5mm/year. The age structure of the F. distorta population was calculated with the growth information. Age distribution is skewed towards the younger ages, with the maximum number at 3 years. The oldest individual was 6.5 years. We then calculated the mortality with the declining section of the age structure, and we found that the mortality rate is 37% per year. This is not so high if we consider that they reach up to 100% coverage/m2 quadrant.
Comparison of molecular and morphological information between other populations in the Indo-Pacific with the Gulf of California and fossil populations at selected locations (well within its Indo-Pacific range) may indicate the historical biogeography, evolutionary history and relationships between the 17 existing species in the group. The modern distribution of F. distorta corresponds to many Indo-Pacific taxa in a variety of groups; hence these data are useful in inferring the geologic and evolutionary history of this biota.