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Effects of bioturbation on seagrasses: Implications for management and restoration
Citation:
DEWITT, T. H. AND S. Wyllie-Echeverria. Effects of bioturbation on seagrasses: Implications for management and restoration. Presented at Coastal and Estuarine Research Federation 2009 Biennial Meeting, Portland, OR, November 01 - 05, 2009.
Impact/Purpose:
Marine and estuarine fauna can diminish or enhance seagrass condition simply as a result of their burrowing, excavating, re-working, and feeding activities (e.g., bioturbation).
Description:
Marine and estuarine fauna can diminish or enhance seagrass condition simply as a result of their burrowing, excavating, re-working, and feeding activities (e.g., bioturbation). We present the first comprehensive review of the effects of bioturbators on seagrasses and associated implications for seagrass management. Several recent studies present compelling evidence that it may profoundly affect the local distribution, abundance, and productivity of seagrasses. Burrowing shrimp, sting rays, crabs, polychaete worms, and echinoderms have been identified as perpetrating biotubators; we summarize taxa-specific effects on seagrasses. Mechanisms by which bioturbators directly harm seagrasses are burial of shoots and seeds, uprooting of shoots and patches, undermining of seagrass patches, damaging roots or rhizomes, and shading by deposition of resuspended sediments onto leaves. Indirect mechanisms include reduced light availability due to increased turbidity, burial by storm-transported sediments previously excavated by bioturbators, and increased susceptibility to erosion due to reduced cohesion of sediments. Uprooting of outplanted turions or seedlings by stingrays, crabs, or polychaetes can be a significant deterent to seagrass restoration. Conversely, moderate bioturbation could be beneficial to seagrasses. For example, biotubation can reduce [H2S] in sediment porewater thereby facilitating seagrass growth in organic matter-rich sediments. Thus, the presence of bioturbators may help explain seemingly anomalous situations wherein seagrasses persist under conditions of poor water or sediment quality. Determining bioturator-specific density-damage thresholds and developing economical methods for measuring bioturbator abudance are two key practical needs for seagrass management and restoration.