Habitat Associations and Co-Occurrence Patterns of Two Estuarine-Dependent Predatory Fishes

Estuarine-dependent fishes experience a wide range of environmental conditions, and most species exhibit distinct associations with particular habitats. However, similar species or multiple conspecifics often overlap spatiotemporally, which can result in ecological interactions that have consequences for behaviors that can shape the structure and function of ecosystems. We used a long-term gill-net data set (2001–2015) to investigate the habitat associations and cooccurrence patterns of two estuarine-dependent predatory fishes, Red Drum Sciaenops ocellatus and Spotted Seatrout Cynoscion nebulosus, in coastal Alabama, USA. Both species were associated with similar environmental conditions, primarily low dissolved oxygen and low salinity, especially when temperature was low. However, differences emerged between the species with respect to the effects of interacting environmental variables on their habitat use patterns, which were likely driven by physiological, biological, and ecological dissimilarities between them. Concerning their biogenic habitat use, extensive submerged aquatic vegetation (SAV) was an important habitat for both species, but Spotted Seatrout appeared to prefer high-salinity SAV beds, while Red Drum associated with SAV regardless of salinity. Spotted Seatrout were associated with extensive emergent marsh edges, and the positive relationship between Red Drum and SAV was diminished when marsh edge was abundant. Co-occurrence was observed primarily in habitats with which both species were associated, most frequently in shallow, prey-rich marsh edges and high-salinity seagrass beds. These observed habitat use patterns elucidate the subtle differences in resource use that allow these species to coexist and suggest potential areas where interactions between them may shape their roles as predators

Reversing a Tyranny of Cascading Shoreline-Protection Decisions Driving Coastal Habitat Loss

Abstract Shoreline hardening is a major driver of biodiversity and habitat loss in coastal ecosystems yet remains a common approach to coastal management globally. Using surveys of waterfront residents in North Carolina, USA, we sought to identify factors influencing individual shore‐protection decisions and ultimately impacting coastal ecosystems, particularly coastal wetlands. We found that neighboring shore condition was the best predictor of respondent shore condition. Respondents with hardened shorelines were more likely to have neighbors with hardened shorelines, and to report that neighbors influenced their shore‐protection choices than respondents with natural shorelines. Further, respondents who expressed climate‐change skepticism and preference for shoreline hardening were opposed to shoreline‐hardening restrictions. Despite preferring hardening, respondents ranked wetlands as highly valuable for storm protection and other ecosystem services, suggesting a disconnect between the ecological knowledge of individuals and social norms of shore‐protection decisions. However, our results also suggest that efforts to increase the installation of living shorelines have the potential to conserve and restore important coastal habitats and support biodiversity along shorelines that may otherwise be degraded by hardening. Further, encouraging waterfront‐property owners who have adopted living shorelines to recommend them to neighbors may be an effective strategy to initiate and reinforce pro‐conservation social norms

Ecological Dynamics and Connectivity Within an Assemblage of Predatory Fishes in Coastal Texas

Predators shape ecosystem function through direct and indirect effects on prey populations and other predators. Furthermore, co-occurrence of multiple predators is common in most ecosystems and interactions between them can result in far-reaching ecological implications. However, resource partitioning is expected to occur among sympatric predator species to alleviate competitive pressures. This study employed multiple methodologies to examine the habitat use, movements and feeding ecology of an assemblage of estuarine and coastal predators in a Texas estuary and the larger northwestern Gulf of Mexico (nwGOM). Four primary species were chosen to exemplify the diversity of life histories of estuarine predators in this region: Spotted Seatrout (Cynoscion nebulosus), Black Drum (Pogonias cromis), Bull Shark (Carcharhinus leucas), and Alligator Gar (Atractosteus spatula). These species co-occur in estuaries but vary in their degree of freshwater habitat use and differ morphologically and physiologically. In Chapter II, habitat suitability modeling revealed seasonal shifts in the habitat use and spatiotemporal overlap patterns of each predator and four potential prey species, suggesting the potential for seasonality in predator-prey and predator-predator interactions. Acoustic telemetry was employed in Chapter III to further examine habitat use, the results of which primarily aligned with Chapter II but added greater seasonal detail, exposed differences in core use area, and documented long-distance movements outside the estuary. Variation in isotopic niche breadth and trophic position was observed among these predators using stable isotope analysis in Chapter IV, which elucidated the degree of trophic overlap and partitioning between them. Additionally, five shark species were chosen to expand the scope of the study into the coastal and pelagic nwGOM: Bull, Bonnethead (Sphyrna tiburo), Blacktip (C. limbatus), Spinner (C. brevipinna), and Shortfin Mako Sharks (Isurus oxyrinchus). In Chapter V, elemental tracers in each species’ vertebrae cartilage were examined across ontogeny, providing insight into the co-occurrence patterns of these sharks throughout their lifespans. Together, these four chapters described the trophic and habitat overlap and partitioning of estuarine, coastal, and oceanic predators in the nwGOM. Understanding the circumstances in which these predators co-occur with one another allows for inferences into how they coexist in a shared ecosystem