An Experimental Reef Program to Test Designs of an Artificial Reef for Kelp Mitigation

Abstract

An artificial reef is being planned to mitigate alleged losses of giant kelp and the invertebrate and fish communities associated with a kelp bed. The project's first step was to initiate comprehensive siting and design studies. A 25-yr time series of kelp surface canopy maps for a 100 km reach of coastline was entered into a GIS database and analyzed in conjunction with geotechnical and humanuse information to define ecologically favorable and acceptable sites in the general area. A site was chosen near an area that appeared most promising in the primary study area. This study's field work determined that the design of the mitigation reef will not be straightforward and that an experimental phase to test various designs needs to be performed. We recommend that a low relief (0,5-1.5 m) reef with relatively high exposure to sand scour and occasional, partial burial be constructed in order to promote the establishment of kelp. Scattered rock and broken concrete at three different density spreads (17, 34, and 67%) on the bottom will be tested. This study has revealed that existing artificial reefs have not typically sustained a persistent kelp bed. This fact, therefore, makes the Phase I experiment even more critical than originally thought.

Design considerations for an artificial reef to grow giant kelp (Macrocystis pyrifera) in Southern California

“…Treatments include 17%, 34%, and 67% coverage of both quarry rock and concrete and two additional sets of 34% quarry rock and concrete onto which small kelp sporophytes were transplanted. The modules were constructed offshore of San Clemente at the site selected for the full mitigation reef based on biological, physical and political criteria (Deysher et al, 1998). The modules were placed in the optimum depth range for kelp recruitment and growth of 12-14.5 m, at sites having a thin layer (30-50 cm) of sand overlaying hard substrate, because individual rocks and concrete pieces should not become buried owing to wave action.…”

“…Second was to create a set of design specifications. Siting studies have determined the region offshore of San Clemente, California, just north of SONGS, to be the optimum location (Deysher et al, 1998). Here, we present the results of surveys that led to the design specifications for a recently completed experimental reef consisting of 56 modules with eight different design configurations.…”