PS 43-131
Ontogenetic shifts in foraging habitat utilization of the commercially important striped red mullet, Mullus surmuletus, and its key role in facilitating heterospecific foraging associations
The striped red mullet, Mullus surmuletus, are bottom-feeding goatfishes distributed along the eastern Atlantic and throughout the Mediterranean Sea. They are an economically important species that has been subjected to intense exploitation, mostly via trawling, which disproportionately impacts young fishes. While diet has been studied in this species via gut content analysis, its foraging behavior remains poorly understood. Foraging goatfish disturb the substrate and release invertebrates into the water column, which often attracts follower fishes into heterospecific foraging associations. These associations may decrease both foraging effort and likelihood of predation for either the goatfish or follower species. We conducted habitat surveys and observational studies of both M. surmuletus and potential follower species in Calvi, Corsica, France to address the following questions: (1) Do M. surmuletus utilize habitats for foraging in proportion to habitat availability? (2) Do heterospecific foraging associations have a positive or negative effect on either M. surmuletus or its follower fishes? We restricted our study to juvenile goatfish, which inhabit shallow, coastal regions.
Results/Conclusions
A total of 69 M. surmuletus and 213 follower individuals (5 species) were observed for over 172 minutes. Mullus surmuletus utilize turf algae as a foraging substrate 78% of the time, although this habitat comprises 48% of available foraging substrate in the study area. Further, these goatfish exhibit an ontogenetic shift in utilization of foraging substrate. Smaller goatfish forage primarily on turf algae, while larger individuals utilize a broader range of available substrates. We hypothesize that the shift in foraging substrate usage with size is due either to ontogenetic shifts in prey preference, barbel development, or competitive exclusion of smaller goatfish by larger. Interestingly, species composition of followers differed depending on foraging substrate. This indicates that goatfish do not determine follower habitat, but allow them to reduce energy expended foraging within their preferred habitat. Furthermore, follower species bite rate, used as a proxy for feeding rate, was significantly higher while participating in a foraging association than while foraging alone. Mullus surumuletus bite rate was unaffected by the presence or absence of a foraging association. Since M. surmuletus have a positive impact on follower fishes, excessive removal of this goatfish will have negative implications for the feeding success of follower fishes.