No abstract

The primary goal of this study was to demonstrate, from field observations and laboratory experiments, some key trophic roles of benthic ctenophores as predators and prey in subtropical communities. We examined individuals of two benthic platyctenid species: Coeloplana waltoni, a minute epibiont on octocorals in exposed, open‐water settings; and Vallicula multiformis, an associate of calm‐water biofouling communities and floating Sargassum spp. Laboratory observations of individuals of both ctenophore species revealed frequent capture and ingestion of diverse zooplankton taxa, especially crustaceans. Laboratory predation trials demonstrated the capture of dolphinfish (Coryphaena hippurus) eggs and larvae by both ctenophore species. Dolphinfish eggs and larvae larger than individuals of C. waltoni were captured but not ingested during 2‐h trial periods. These prey items were sometimes purloined and ingested by polyps of the ctenophore's octocoral host. Ingestion of dolphinfish eggs and larvae by individuals of C. waltoni was observed, however, after longer periods of exposure to prey. In predation trials, dolphinfish eggs and larvae were both captured and ingested by larger individuals of the ctenophore species V. multiformis. Field and laboratory observations revealed diverse invertebrate and fish taxa that prey on both ctenophore species. In the laboratory, the mean daily per capita consumption of individuals of C. waltoni by a pomacanthid fish ranged 0.5–2.8 individuals, and ranged 2.6–3.6 individuals for predation by an ovulid mollusc. Field population densities of these predators ranged 0.1–0.7 individuals per m2 for the pomacanthid, and 0.2–1.1 individuals per m2 for the mollusc. Laboratory feeding observations demonstrated frequent consumption of individuals of V. multiformis by a sea anemone, and by three species of brachyuran crabs. Field observations revealed eight fishes that probably feed incidentally on individuals of V. multiformis. These findings add to the limited knowledge base of predator–prey dynamics in both C. waltoni and V. multiformis.

No abstract

Understanding and ultimately predicting how marine organisms will respond to urbanization is central for effective wildlife conservation and management in the Anthropocene. Sharks are upper trophic level predators in virtually all marine environments, but if and how their behaviors are influenced by coastal urbanization remains understudied. Here, we examined space use and residency patterns of 14 great hammerheads Sphyrna mokarran, 13 bull sharks Carcharhinus leucas, and 25 nurse sharks Ginglymostoma cirratum in proximity to the coastal metropolis of Miami, Florida, using passive acoustic telemetry. Based on the terrestrial urban carnivore literature, we predicted sharks would exhibit avoidance behaviors of areas close to Miami, with residency patterns in these urban areas increasing during periods of lower human activity, such as during nocturnal hours and weekdays, and that dietary specialists (great hammerhead) would exhibit comparatively lower affinity towards highly urbanized areas relative to dietary generalists (bull and nurse shark). However, we did not find empirical support for these predictions. Space use patterns of tracked sharks were consistent with that of ‘urban adapters’ (species that exhibit partial use of urban areas). Modeling also revealed that an unmeasured spatial variable was driving considerable shark residency in areas exposed to high urbanization. We propose several hypotheses that could explain our findings, including food provisioning from shore-based activities that could be attracting sharks to urban areas. Ultimately, the lack of avoidance of urban areas by sharks documented here, as compared to terrestrial carnivores, should motivate future research in the growing field of urban ecology.