Warmer winters in coastal areas caused by global climate change have resulted in structural change in estuarine ecosystems. This change is particularly evident in areas where seasonal cold temperatures historically prevented the invasion of mangroves, but warmer winter temperatures are now enabling their proliferation. This transition results in a drastic change in structure, particularly in areas where black mangrove (Avicennia germinans) pneumatophores are replacing bare sand. We sought to determine how this change from open water to dense areas of mangrove pneumatophores influenced habitat selection by a native predator/prey species, the Atlantic blue crab (Callinectes sapidus). We created a mesocosm composed of 50% pneumatophores in sand and 50% bare sand. We then conducted 12 experimental rounds in which a blue crab was introduced into the mesocosm. We video recorded these introductions for the first ~18 minutes. We analyzed these videos to determine how much time the blue crab spent in each environment. We compared these times, across all 12 experimental rounds, using a paired two-sample Wilcoxon test, which allowed us to account for the non-normal distribution of our data.
Results/Conclusions
The amount of time spent in each structural environment of the mesocosm (bare sand or pneumatophores in sand) spanned the full range of possible values (0-1062 seconds) for both environments. We found no support for differential habitat selection between areas of bare sand and areas with pneumatophores (p = 0.84), where the average time spent in each environment varied by just two seconds. This apparent lack of habitat preference may have been associated with our use of adult blue crabs, which are less susceptible to predation than juveniles. Alternatively, our findings may indicate that blue crabs do not perceive fear in the absence of predators, which were not included in our study. Further research is needed to determine how structural change resulting from climate change will influence blue crab habitat selection in natural environments where predators are present. Additionally, future research should seek to determine if pneumatophores, at increasing densities, negatively influences blue crab use as a result of decreased ease of movement and potential increased energetic costs associated with foraging.