Fish larvae settling in seagrass: do they discriminate between beds of different leaf density?

Abstract

A field experiment was designed to test the hypothesis that settling fishes do not discriminate between artificial seagrass units (ASUs) with dense and sparse leaves, but do occur in greater numbers in any type of ASU than on bare sandy substratum. The experiment also tested for the effects of excluding predators on the outcome of settlement patterns. A total of 2360 fishes, from 29 species, settled on the experimental units. Only one species, Achoerodus viridis (Richardson) (Labridae), settled in great numbers. A. viridis did not discriminate between dense and sparse ASUs or between shelter in the form of seagrass and shelter in the form of a cage alone, but did discriminate between shelter (ASUs, cages, or both together) and no shelter (bare sand). Postsettlement prédation was insignificant. Patterns of settlement for all other species combined were similar to those for A. viridis. We conclude that abundances of juvenile fishes in isolated ASUs were not due to settlement preferences based on physical complexity of seagrass, or postsettlement predation. Rather, they were due to availability of larvae prepared to settle indiscriminately into any shelter.