Preference and survival shape habitat use along a fluctuating wetland landscape

Background/Question/Methods

Humans redistribute habitats through climate-driven changes in the ranges of habitat-forming species, such as plants and corals. The maintenance of inhabitant communities in shifting systems depends on individual species’ abilities to recognize habitat throughout these changes. The relative importance of initial settlement and subsequent interactions then affects the organization of communities and their component species as they interact with resource landscapes that are shifting with climate change. Globally, mangroves are shifting poleward – displacing temperate grass marshes – with unknown consequences for wetland inhabitants. Along one mangrove-marsh ecotone on Florida’s Atlantic coast, we investigate settlement patterns of crabs who use wetlands as nursery habitat. We evaluate whether they differentiate between mangroves and marshes, whether habitats differ in refuge quality (i.e. reduced mortality), and how habitat use shifts after settlement. We expected preferences for structurally complex habitat due to higher survival. We also expected any habitat associations to become stronger over time and/or development. In the lab, we conducted choice experiments and survival trials to determine preference for and survival in each vegetation type. To evaluate the relative importance of initial preference and subsequent dynamics during natural settlement processes, results were then compared to crab recruitment onto artificial habitat panels in the field.

Results/Conclusions

In the lab, settling crabs preferred mangrove vegetation, especially short, simple black mangrove pneumatophores (snorkel roots). Settlers did not respond to structural habitat cues alone (presented as constructed vegetation mimics), suggesting that non-structural cues influence habitat selection. Settling crabs also survived best in black mangrove pneumatophores, which were the only vegetation structure that reduced mortality in the presence of a foraging predator.  Significantly higher survival in the preferred habitat suggests that habitat is selected based on refuge quality. Thus, it appears that crabs are using non-structural cues to select habitat that provides the best refuge, which is a structural attribute.

New data from the field experiment will evaluate patterns of habitat use by a cohort of portunid swimming crabs to determine habitat associations in the field and how they change through time and development. Evaluating the consequences of human-driven ecological change requires an understanding of how well inhabitants track their habitats and whether shifting habitats replace one another functionally where they displace each other spatially. Considering the relative strengths of initial settlement and subsequent environmental filtering as complimentary community-structuring ecological processes will help us understand the implications of global habitat modification on emerging communities.