• Penttila,D.and D.Doty.1990. Progress Report. Results of 1989 Eelgrass Shading Studies in Puget Sound. Washington Department of Fisheries, Marine Fish Habitat Investigations Division.
Return to : Study Objectives, Methods & Findings
CONCLUSIONS: The authors concluded that construction of partially shading types of structures, floating or on pilings, can be expected to largely eliminate the existing macroflora with little chance for replacement plant growth on new introduced solid structures. Algae species also appear to be impacted by shading structures. Other impacts they would expect over time include: altered sediment distribution and topography along piling lines, tidal drainage streams created by topographic changes, and substrates in the immediate vicinity of piling structures to be enriched with calcareous debris from barnacles and mollusks inhabiting the structures hard surfaces.
They suggest future studies of designs and orientations of fixed structures that might mitigate habitat damage. They recommend:
1) no fixed floating structures of any kind over herring spawning grounds vegetation,
2) fixed elevated structures over littoral zones should be designed to eliminate shade impacts,
3) elimination of net loss vegetation and structural shading, including moored vessel shadow, should be considered by WDF policy, mitigation techniques, and case-by-case design consideration,
4) seasonal fixed structure should not be permitted over littoral zone vegetation beds in excess of six continuous weeks, and
5) further field studies should be undertaken on dock designs that can reduce or eliminate shading.