The foraging ecology of the Gulf of Mexico stone crab Menippe adina (Williams et Felder)

Abstract

Laboratory experiments were used to study prey species and size selection by the Gulf of Mexico stone crab Menippe adina (Williams et Felder) on oysters, i.e., Crassostrea virginica Gmelin and southern oyster drills Stramonita ( Thais) haemastoma Grey. Stone crabs select smaller rather than larger oyster drills, and smaller rather than larger oysters. Two results support the idea that size selection in this crab is more the result of mechanical limitations to feeding on large prey than active choice for smaller prey. First, differences in size selection disappear when feeding rates are weighted by differences in handling times, which increase with prey size. Second, an estimate of prey value (tissue dry mass divided by handling time) does not differ dramatically with prey type or size, suggesting large variations in handling time obscure differences in prey energy content. Stone crabs select small oysters over small oyster drills. Stone crabs attack larger oyster drills more frequently than small oyster drills, and persist longer before rejecting them as prey. Neither attack frequency nor persistence increase significantly with increasing oyster size. We also studied aggressive interactions between stone crabs provided with oysters as prey and found that larger stone crabs had greater feeding rates than smaller crabs, and exhibited higher frequencies of dominant behaviors. Our results suggest that the relative importance of active choice vs. mechanical limitations in determining prey selection varies with the specific crab predator-prey system. Gulf of Mexico stone crabs may also affect oyster and oyster drill populations by selectively removing smaller individuals. Finally, smaller stone crabs may be forced to forage in suboptimal habitats, or at suboptimal times, by larger, more aggressive conspecifics.