Science Advisory Report  2011/058

Definitions of harmful alteration, disruption or destruction (HADD) of habitat provided by eelgrass (Zostera marina)

Summary

• Eelgrass (Zostera marina) meadows by their vertical form and spatial coverage are important nearshore habitat for fishes (juvenile and adult) and invertebrates.
• As stress increases, an eelgrass meadow can respond by becoming patchy, less dense and/or occupying less of the available area.
• The effects of five stressors on eelgrass function as fish habitat were considered: sedimentation, turbidity, nutrients, flow regime, physical damage or removal.
• Thresholds for stressors that change the eelgrass function as fish habitat from a no effect case to a HADD case are proposed based largely on scientific studies but including an important component of expert opinion.
• There are very few studies that measure the fish habitat features of eelgrass meadows and how these vary with meadow form and structure (patchiness, density of shoots, area of contiguous bed). Landscape features including connectivity and contiguity of habitat on a bay scale are an additional and higher level of consideration.
• The knowledge gaps and uncertainties make it difficult to assign stressor threshold values to the HADD categories. Only the destruction HADD threshold can be well defined.
• Stressors often occur simultaneously and the thresholds for individual stressors are likely to be lower when they occur in combination.

This Science Advisory Report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, regional advisory meeting of March 17-18, 2011 on definitions of harmful alteration, disruption or destruction (HADD) of habitat provided by eelgrass (Zostera marin). Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

Complete document (PDF, 194 KB)

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