Habitat Selection by Demersal Nekton: Analysis of Videotape Data

Abstract

ln the past, analysis of habitat choice by marine nekton has been hampered by limited access to its environment. We suggest a method to facilitate study of habitat choice, using data gathered from videotapes. The aims of this study were (a) to identify members of a particular nekton assemblage, and (b) to identify environmental variables important to the assemblage as a whole. Data on species and environmental variables came from Videotapes of a sandy-bottom shelf area (60m depth) in the Gulf of Mexico off Pensacola, Florida, taken by a remote-controlled submersible travelling along defined transects. We analyzed these Videotapes to derive Information on habitat use of several species of fishes and large invertebrates. We divided the transects into sections which were homo· geneaus for bottom type and algal coverage, and in each section measured habitat variables and abundances of the most common and reliably identifiable species of demersal nekton. Factor analysis of species' means for environmental variables identified patterns of habitat use among these species. The analysis identified these patterns by generating axes that represented environmental gradients. The patterns of habitat use by these species related to their preferences for different amounts of three·dimensional structure, algae, and infaunal and epifaunal organisms. We compared species distributions and habitat distributions on these axes to find which environmental gradients were of most importance in habitat selection by these species. We found that more species selected habitats on the basis of particular amounts of structure, fewer selected on the basis of algal coverage and infaunal organisms. Only one species seemed to select habitats on the basis of types or abundances of epifaunal organisms. Thus, amount of three-dimensional structure seemed an important variable to the sandy·bottom assemblage overall, followed by amount of algal coverage and types of infaunal organisms.