Landscape aspects of oyster reefs: Effects of fragmentation on habitat utilization

Abstract

The functional value of oyster reefs is recognized in many estuarine systems, with increasing interest in oyster reef restoration for ecological function rather than for oyster fishery production. Reefs provide structure and refuge for juvenile fish and crustaceans, and may be loci for predator foraging. However, reef morphology influences the relative value of refuge and forage functions, and reef utilization by benthic, epibenthic, and nektonic organisms. Reef fragmentation increases the edge to interior ratio, and may enhance use by organisms that favor edge regions, or decrease use by species requiring more interior habitat. The influence of fragmentation was examined using created intertidal oyster reefs and natural reef patches in southeastern North Carolina. Experimental treatments included created reefs (uniform circular reefs, small fragmented reefs, and large fragmented reefs) reference natural reefs, and open mudflat areas. Naturally occurring uniform and fragmented patch reefs in two nearby tidal creeks were also sampled. Following construction of created reefs, all treatments were sampled quarterly over two years, targeting infauna, epifauna, and nekton. Effects of fragmentation on infauna were variable, with a combination of positive and negative species-specific responses. For the vast majority of epi-benthic macrofauna collected from excavations and Breder traps, no effect of small-scale fragmentation on utilization was observed. Preferential use of large fragmented reefs over small fragmented reefs was observed for two species, Lagodon rhomboides and Panopeus herbstii, suggesting that the small fragmented reefs may have been below the patch size threshold at which edge effects become beneficial. Our results suggest that, at least at the scale investigated here, multiple small reefs may provide similar habitat benefits to a single, larger oyster reef.