Aggressive Predation Drives Assembly of Adriatic Fish Communities

Abstract

We performed over 19,000 lure-assisted, underwater visual fish census transects at over 140 shallow coastal sampling locations in the mid- eastern Adriatic sea of the Croatian mainland and islands, recording all fish taxa observed, their predatory behavior in response to the lure, and the cover of benthic habitats with which they were associated. We hypothesized that prey habitat preference was a learned or selected response to aggressive behavior by piscivorous mesopredators, and predicted that mobile prey would be spatially segregated from aggressive predators into different benthic habitats within local sampling sites. We found that aggressive piscivores were primarily wait-chase or cruise-chase mesopredators that preferentially foraged along heterogeneous habitat edges within juxtapositions of rock, unconsolidated sediment, macroalgae (Cystoseira spp.) and seagrass (usually Posidonia oceanica). Prey species and less aggressive piscivores avoided these heterogeneous habitats and preferred more homogeneous habitats that the aggressive predators in turn avoided. We found strong and consistent spatial segregation between aggressive predators on the one hand, and less aggressive predators and prey on the other hand. These results are consistent with the hypothesis that aggressive behavior by piscivorous species is the primary organizing force shaping assembly of fish communities at our study sites, driving preference and occupancy of heterogeneous and homogeneous benthic habitats. Management of shallow benthic resources should recognize the value of complementarity in habitats allowing coexistence of predators and prey through contrasting habitat preferences.

A review of fish diversity in Mediterranean seagrass habitats, with a focus on functional traits

“…Research carried out on fish communities from vegetated and unvegetated habitats in eastern Adriatic Sea showed that prey and predators resulted negatively associated in various habitats and this negative correlation was as much stronger as predators were more aggressive. In this geographic area prey showed a positive association with C. nodosa and P. oceanica, besides unconsolidated sediments, in agreement with our analysis (Kruschel and Schultz 2020).…”

“…Our results are drawn from a high number of heterogeneous studies applying different sampling methods in different seasons, taking into consideration only seagrass habitats without bare substrates, and skipping details on predation mode. As stated in dedicated studies, local environment may play a main role in producing different patterns of prey/predator association through habitat patchiness, interspecific interactions, fishing activities and many other variables (Kruschel and Schultz 2020). Nevertheless, the signal of segregation between aggressive predators that are associated with P. oceanica and C. nodosa and their putative prey, that tend to occupy other seagrass habitats, seems to be strong enough to be recorded by our broad analyses at the whole basin scale.…”

“…However, predators too may benefit from such habitats due to either the high prey density, if they are transient species, or the many hideaways if they are ambushing residents. Therefore, predation risk is not fixed for each habitat but depends largely on both the relative abundance of predators and their mode of searching and catching (Kruschel and Schultz 2020). The differential predation risk associated with different predation modes will in the end select or train prey to choose the habitat that better balances their foraging needs with the protection against the most frequent kind of predators.…”

European native oyster reef ecosystems are universally Collapsed

“…Coexistence with C. gigas (Staglicic et al 2020). Listed as present in Novigrad and Karin Seas, but no further mention (Kruschel et al 2011). Cyprus no no O. edulis present in species list (Fischer 1997).…”

Predators as Agents of Selection and Diversification

“…This is a clear example of the complex interplay between predator ecological constraints and prey adaptation in response to varying selective pressures. Kruschel and Schultz [61] censused Adriatic fish communities and found that aggressive predators appear to drive prey species to habitats where less aggressive predators are found, changing both the types of predators that they encounter and the ecological context in which they encounter these predators. This work shows how some predators indirectly affect the evolution of prey traits through other selective agents.…”