Baums, I. B., Miller, M. W., Szmant, A. M.

Ecology of a corallivorous gastropod, Coralliophila abbreviata, on two scleractinian hosts. I: Population structure of snails and corals

2003

Marine Biology

142

1083-1091

"Despite their potential importance in structuring reef communities, invertebrate corallivores and their population structures are poorly understood. We found distinct differences in the population structures (length-frequency distribution and sex ratio) of the corallivorous gastropod Coralliophila abbreviata residing on two coral-host taxa, Montastraea spp. and Acropora palmata, in the Florida Keys. In each of two survey years, around 50 percent of the Montastraea spp. colonies were infested, with a mean snail density of eight snails per infested colony (range 1-45), while around 20 percent of A. palmata colonies harbored three snails per infested colony (range 1-23). Variation in patterns of snail occurrence was also observed within a host taxon. A. palmata occurred in low- and high-density stands (0.4 and 1 colony m super(-2), respectively, at the initial survey) at different sites. Hurricane Georges struck the area in September 1998. When resurveyed in 1999, density of colonies in low-density stands had decreased by 75 percent to 0.1 colonies m super(-2). This decrease was accompanied by a doubling in the proportion of colonies infested with snails (from 19 percent to 46 percent) and an increase in snail density per infested colony (from 3.7 plus or minus 3.3 SD to 5.4 plus or minus 4.6 SD) as snails apparently concentrated on surviving A. palmata. In contrast, sites with high density A. palmata stands (thickets) retained colony densities of about similar to 1 colony m super(-2) among years, while snail infestation increased only from 9 percent to 14 percent of colonies surveyed and snail density essentially remained unchanged (from 2.7 plus or minus 1.8 to 2.9 plus or minus 1.9 snails per infested colony). Snails collected from Montastraea spp. were shorter than those from A. palmata in low-density stands and were longest on A. palmata in thickets. On both host taxa, female snails were longer than males. The sex ratio of snails on Montastraea spp. hosts was even (1-to-1), while that of snails on A. palmata was skewed (70 percent males). Factors that could explain observed differences in size structure and sex ratio between Coralliophila populations on the two coral host taxa include: differential susceptibility to predators, influence of host tissue nutritional quality and/or secondary metabolite content, and genetic differences (cryptic species). The host-specific characteristics of C. abbreviata populations imply that the impact of gastropods on reef communities will vary with the coral species composition."

Sex ratio/Predators/Nutrition/Infestation/Coral reefs/Species composition/Population structure/Predation/Interspecific relationships/ Ecological associations/Coral/Epibionts/Hosts/Marine molluscs/Population density/Population number/Size distribution/Coralliophila abbreviata/Montastraea/Acropora palmata/USA, Florida ASW/USA, Florida, Florida Keys

10.1007/s00227-003-1024-9

FY2002 CRCP Project ID 1055; Project Title: Assessment and Monitoring of Candidate Coral Species; Principal Investigator: Margaret Miller