| The role of habitat fragmentation per se, or the change of patch size, shape, perimeter: area ratio, and isolation without habitat loss, on ecological processes is incompletely understood in marine environments. Previous work has been limited to evaluating the effects of changes in patch characteristics on growth of bivalves, faunal abundances, and predation of tethered crabs. In the initial phase of this research, I measured abundances, secondary production, and the community composition of faunal seagrass communities from in situ sampling of different sized, naturally occurring seagrass patches and artificial seagrass units (ASUs) in two locations. To isolate the effects of patch dynamics on settlement, additional ASU experiments were conducted in an area where seagrasses were historically found but are now absent. I also measured predation on tethered pinfish (Lagodon rhomboides) on different sized ASUs. To determine if the response to fragmentation per se remained consistent with community composition, I conducted mesocosm experiments designed to measure the effects of predation and habitat selection using four distinct habitat types and many combinations of predator-prey guilds. Lastly, I examined growth and survival of the bivalve (Mercenaria mercenaria) in seagrass patches that varied in size and perimeter. For macrofaunal organisms and small fishes, neither organism abundance, secondary production, habitat selection nor predation responded consistently to patch size, shape, or isolation. For M. mercenaria, mortality responded negatively with patch size; however, growth (shell length) was positively related to patch size during the initial trial, but negatively related during the second trial. In conclusion, habitat fragmentation per se did not play a consistent role in structuring seagrass communities. Because habitat fragmentation per se rarely occurs without simultaneous habitat loss, the most important role of understanding habitat fragmentation per se may be as an early warning system signaling the break up and eventual decline of seagrass meadows. |
