COLONY FISSION INCREASES PARTICLE CAPTURE RATES OF A SOFT CORAL - ADVANTAGES OF BEING A SMALL COLONY

The rate at which a passive suspension feeder captures food particles depends on the rate at which ambient currents bring particles into contact with its feeding apparatus. This flux of particles is controlled in part by the turbulence and velocity of water as it moves over a surface of a given topography, and is thus strongly influenced by the size and shape of an organism, and by the size and spatial distribution of neighboring individuals. The effects of (1) colony size and (2) the presence of conspecific neighbors on particle captures rates were quantified in laboratory experiments conducted with colonies of an undescribed species of alcyonacean soft coral. Soft coral colonies were observed feeding in a recirculating flow tank at freestream flow speeds ranging from 0.04 - 0.51 m/s. At all experimental flow speeds, per polyp particle capture rates decreased as colony size increased. At low flow speeds, colonies had lower particle capture rate when surrounded by neighboring colonies than when neighbors were absent; however, at high flow speeds, particle capture rates were enhanced slightly in the presence of neighboring colonies. These alcyonacean colonies, as well as other colonial organisms in diverse taxa, undergo continual asexual fission as they grow, thereby forming aggregations of small, physiologically discrete daughter colonies. The results obtained here suggest that this growth strategy may be an effective means of maximizing nutrient intake (hence growth rate and sexual reproductive potential) per unit biomass of the genotype. The experimental results can be used to predict the size at which a colony should undergo fission in a given flow environment in the absence of other selective forces acting on colony size.