S. Mayfield et al., Determining prey availability for rock lobsters, jasus lalandii: diver-sampling versus monochrome video photography, MARINE BIOL, 135(2), 1999, pp. 347-352
Accurate determination of diet is important in ecological studies. Many mac
robenthic predators fragment their prey so finely that identification of co
mponent organisms is difficult. Knowledge of the food available to masticat
ory predators such as lobsters can help in determining potential prey and e
nhance the accuracy of dietary assessments. With SCUBA divers limited by de
pth and submersion time, benthic analyses are becoming increasingly reliant
on camera systems. Here, based on paired samples, we assess the relative m
erits of using removal-sampling by divers Versus monochrome video photograp
hy to determine the prey spectrum available to macrobenthic predators. We a
lso relate the results to the gut contents of rock lobsters (Jasus lalandii
) that were collected simultaneously. Diver samples took on average four ti
mes longer to collect and process than video-image samples. No significant
differences were evident between the number of species identified in diver
samples and video-image samples (n = 21 paired samples, Student's t = 0.233
, P > 0.1), although an analysis of similarity (ANOSIM) test revealed that
the results obtained from the two sampling methods were significantly diffe
rent in terms of species composition (global R = 0.203, P < 0.01). Cluster
analysis based on Bray-Curtis similarity to compare diver and video-image s
amples revealed four clusters of samples with <35% similarity, confirming t
hat the two techniques do sample different assemblages of species. Video im
ages detected and allowed identification of all species of prey recorded in
the rock lobsters' stomach contents, probably because rock lobsters prey m
ainly on relatively large prey which are readily detected by video. Diver-s
ampling underestimated or failed to detect two important prey types, namely
small barnacles and encrusting coralline algae. We concluded that the came
ra system employed was adequate for assessing the prey assemblages availabl
e to macrobenthic predators such as lobsters, and that it was considerably
more economical than using divers.