Seagrass patch size affects fish responses to edges

1. Patch area and proximity of patch edge can influence ecological processes across patchy landscapes and may interact with each other. Different patch sizes have different amounts of core habitat, potentially affecting animal abundances at the edge and middle of patches. In this study, we tested if edge effects varied with patch size.

2. Fish were sampled in 10 various-sized seagrass patches (114–5934 m²) using a small (0·5 m²) push net in three positions within each patch: the seagrass edge, 2 m into a patch and in the middle of a patch.

3. The two most common species showed an interaction between patch size and the edge–interior difference in abundance. In the smallest patches, pipefish (Stigmatopora nigra) were at similar densities at the edge and interior, but with increasing patch size, the density at the edge habitat increased. For gobies (Nesogobius maccullochi), the pattern was exactly the opposite.

4. This is the first example from a marine system of how patch size can influence the magnitude and pattern of edge effects.

5. Both patch area and edge effects need to be considered in the development of conservation and management strategies for seagrass habitats.