Recruitment of Aurelia aurita (Cnidaria: Scyphozoa) larvae is position-dependent, and independent of conspecific density, within a settling surface

Abstract

Aggregated settlement patterns in marine invertebrates are often assumed to result from larval preference for the presence of conspecifics ('gregarious' behaviour). These patterns might also result from larval selection of, or deposition in, particular rnicrohabitats. On smooth, homogeneous surfaces habitat heterogeneity may be produced by the interaction between moving water and a submerged surface. Settlement is aggregated for the larvae of the jellyfish Aurelia aurita. I used removal experiments and reciprocal transplants to test whether recruitment occurred as a function of the position of the settlement site within a submerged surface or as a function of the density of conspecifics present. Position determined recruitment rates. The distribution of larvae may be attributable to reductions in local shear stress and increased thickness of the boundary layer. Planulae metamorphose into polyps after settlement, producing patches of varying density. Polyps may grow larger or bud to form clones. Budding rates were not a function of density, but growth rates did decline as density increased. However. hgh density areas maintained a greater polyp surface area over time than less dense regions, suggesting that food may be as unevenly distributed as larvae within a surface. Thus, position may confound the effect of density on growth and survivorship.