Habitat specialization and the influence of temperature: investigating behavioral plasticity in coral reef fishes
As the ocean warms, the factors that limit the survival and persistence of particular marine species will vary. Declining habitat diversity and availability, driven by climate change, has been shown to cause dramatic losses in coral reef fish abundance and diversity. Further, habitat type and the level of structural complexity can influence demographics and population dynamics of resident fishes, having implications for competitive interactions, growth and predation. Understanding the susceptibility of reef fishes to habitat change requires increased knowledge of species-specific habitat preferences and requirements. In addition to habitat change, rising temperatures will directly impact cellular physiology, which has the potential to flow on to higher-level processes including behavior. The direct impacts of temperature on individual fish may alter the time they spent foraging vs sheltering, as well as the strength of their association with a given habitat. Therefore, we examined how tropical reef fishes associate with habitats of differing type and complexities at a range of temperatures, to determine how water temperature impacted habitat preference. Preferences of juvenile butterflyfishes (Chaetodontidae) and damselfishes (Pomocentridae) were examined in fully orthogonal choice experiments across three temperature treatments and four habitat types to test the effects of temperature on selection of habitat.
At ambient summer ocean conditions (27ºC) we found species specific differences in habitat preferences, with the butterflyfishes showing high specialization to one type (complex coral) and the damselfishes exhibiting a generalist association with all habitat types (complex coral, non-complex coral, coral rubble and rocky boulder). Interestingly, we found that the less specialized species showed behavioral plasticity at lower temperatures (22ºC), associated with ambient winter conditions, and shifted from no preference to a selection of boulder habitat associated with a degraded reef. While more specialized species maintained their habitat preference of complex coral across all temperatures (ambient summer, 27ºC, ambient winter, 22ºC, and predicted ocean warming, 31 ºC), suggesting their success may be constrained by habitat loss associated with climate change. Our results provide the first indication of behavioral plasticity in relation to temperature and habitat selection in a coral reef fish. Previous studies classify species specialization in relation to current ocean temperature scenarios; however our results suggest further investigation outside species thermal optimums is needed to provide further knowledge of how coral reef fishes will respond to climate change.