RESPONSES BY MACROBENTHIC ASSEMBLAGES TO EXTENSIVE BEACH RESTORATION AT PERDIDO KEY, FLORIDA, USA

In this study, we examine complex responses by macrobenthic assemblage s to extensive beach restoration affecting 7 bm of open shoreline at P erdido Key, Florida. Beach restoration consisted of two phases, bead! nourishment and profile nourishment, each phase lasting roughly one ye ar. We examined macrobenthic responses using an optimal impact study d esign incorporating ten macrobenthic surveys completed over a three-ye ar period. This study is important because of its geographical region, its relatively large spatial scale, its long duration, and its consid eration of both nearshore assemblages from high energy sandy beaches a nd diverse assemblages from stable offshore habitats. The physical env ironment was altered by beach restoration through changes in depth pro files and sediment composition as well as through sediment dynamics. V arious macrobenthic responses attributable to beach restoration includ ed: decreased species richness and total density, enhanced fluctuation s in those indices, variation in abundances of key indicator tars, and shifts in macrobenthic assemblage structure. One long-term impact of beach nourishment at nearshore stations included the development of ma crobenthic assemblages characteristic of steep depth profiles. Two lon g-term negative impacts of beach restoration at offshore stations incl uded one from beach nourishment and another from profile nourishment. After beach nourishment, the macrobenthic assemblage structure changed markedly across a considerable offshore area in concert with increase d silt/clay loading. Macrobenthic impacts from silt/clay loading were still evident at the end of the study, more than two years after beach nourishment. Macrobenthic populations fluctuated widely at the farthe st seaward stations from apparent sediment disturbance, both during an d after profile nourishment. These fluctuations involved total densiti es, species richness, and densities of key indicator taxa. Macrobenthi c fluctuations continued through the end of the study, although profil e nourishment was completed for more than one year prior to that time. Considerable macrobenthic recovery was apparent during the study, alt hough macrobenthic recovery remained indeterminate in some places. Lon gterm macrobenthic impacts at several offshore stations supported the hypothesis that diverse offshore assemblages may be less resilient tha n contiguous nearshore sandy-beach assemblages.