Foraging ecology and behavior of batoids and their influence on coastal sandflats
Australia: Rainforest, Reef, and Cultural Ecology
Mesopredators play an important role in many aquatic ecosystems and understanding their behavior and foraging ecology is crucial for maintaining the function and sustainability of these environments. Batoids are specialized benthic predators that act as ecosystem engineers through their foraging behavior which create depressions in the substrate. The process of making these depressions, or pits, disturbs the sediment and cycles nutrients back into the water column, otherwise known as bioturbation (O’Shea 2012).
Using aerial surveys and isotope analysis, this study examined the feeding behavior and feeding pit morphology of two batoid species, P. ater and H. australis, on a coastal sandflat in northern Queensland. H. australis was observed feeding more often (40.19 pits/hour) and used all six feeding combination methods observed (suction feeding, excavation, and type A) compared to P. ater which was observed feeding less frequently (15.03 pits/hour) and showing no signs of suction feeding behavior. The size of the pits formed by each species varied with feeding type and feeding activity time; H. australis showed high variability in pit size (average ratios of disc width and pit diameter ranging from 0.14 for suction feeding to 0.88 for excavation/type A diameter) with less variance in feeding time (majority <30 seconds>length) whereas P. ater had opposing results (average pit size ratio range <0.36; activity time majority <120 seconds length). Species were observed feeding in two distinct locations on the sandflat, H. australis on the inner sandflat bank and P. ater less concentrated on the south-eastern region of the study area. Isotope analysis of δ13C and δ15N concentrations showed little difference between species, possibly indicating that H. australis and P. ater share similar trophic positions, although future studies should incorporate stomach content analysis for a more comprehensive look at diet. Differences in feeding frequency, feeding type and location might suggest that the two species potentially occupy segregated ecological roles on the sandflat. Mechanisms influencing these results might further be driven by prey preferences and/or resource partitioning between species, which would facilitate the co-existence and reduced competition between the two regionally abundant species. These results might suggest removing either species from the ecosystem would have implications on bioturbation rates and nutrient cycling and should be considered for management and conservation strategies.