Warmer winters resulting from anthropogenic climate change have enabled mangroves to extend their range northward throughout the northern hemisphere. These encroaching mangroves outcompete native species, including smooth cordgrass (Spartina alternifloa). This transition results in substantial structural change, which may influence how prey species perceive fear. We investigated the implications of vegetative structural change on the landscape of fear using a mesocosm. We divided the mesocosm into vegetative structural zones, including smooth cordgrass and black mangrove (Avicennia germinans) pneumatophores. We placed three pieces of dried shrimp in each vegetative structural zone. We then released five native baitfish, either pinfish (Lagodon rhomboides) or Atlantic croaker (Micropogonias undulatus) minnows, into the mesocosm. We recorded bait consumption in each vegetative structural zone 15, 30, and 60 seconds after fish were added. We repeated this six times for pinfish and four times for Atlantic croaker. We compared bait consumption between vegetative structural zones for each time step using a paired t-test in program R. We hypothesized that both baitfish would consume more bait in cordgrass than in pneumatophores as a result of lower perceived fear in denser vegetation.
Results/Conclusions
Average bait consumption by pinfish was greater at each time step (15, 30, and 60 seconds) in smooth cordgrass (n=0.83, n=2.17, and n=3, respectively) than in black mangrove pneumatophores (n=0.17, 1.17, and 1.83, respectively), but differences were not statistically significant (p=0.07, p=0.15, and p=0.11, respectively). Likewise, average bait consumption by Atlantic croaker was greater at each time step (15, 30, and 60 seconds) in smooth cordgrass (n=0.75, n=3, and n=4, respectively) than in black mangrove pneumatophores (n=0, n=1.25, and n=3, respectively), but differences were only statistically significant after 30 seconds (p=0.04), not after 15 (p=0.15) or 60 (p=0.09) seconds. Our findings moderately support our hypothesis that both baitfish would perceive less fear, and subsequently eat more bait, in denser cordgrass vegetation than in black mangrove pneumatophores. Climate change, therefore, may alter the landscape of fear in estuarine systems experiencing mangrove encroachment, subsequently influencing prey species distribution. However, additional research is needed to determine the applicability of these results to natural systems.