Responses by Macrobenthic Assemblages to Extensive Beach Restoration at Perdido Key, Florida, U.S.A.

C. F. Rakocinski, R. W. Heard, S. E. LeCroy, J. A. McLelland, T. Simons

Abstract


In this study, we examine complex responses by macrobenthic assemblages to extensive beach restoration affecting 7 km of open shoreline at Perdido Key. Florida. Beach restoration consisted of two phases, beach nourishment and profile nourishment, each phase lasting roughly one year. We examined macrobenthic responses using an optimal impact study design incorporating ten macrobenthic surveys completed over a three-year period. This study is important because of its geographical region, its relatively large spatial scale, its long duration, and its consideration of both nearshore assemblages from high energy sandy beaches and diverse assemblages from stable offshore habitats. The physical environment was altered by beach restoration through changes in depth profiles and sediment composition as well as through sediment dynamics. Various macrobenthic responses attributable to beach restoration included: decreased species richness and total density, enhanced fluctuations in those indices, variation in abundances of key indicator taxa, and shifts in macrobenthic assemblage structure. One long-term impact of beach nourishment at nearshore stations included the development of macrobenthic assemblages characteristic of steep depth profiles. Two long-term negative impacts of beach restoration at offshore stations included 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 increased 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 farthest seaward stations from apparent sediment disturbance, both during and after profile nourishment. These fluctuations involved total densities, species richness, and densities of key indicator taxa. Macrobenthic fluctuations continued through the end of the study, although profile nourishment was completed for more than one year prior to that time. Considerable macrobenthic recovery was apparent during the study, although macrobenthic recovery remained indeterminate in some places. Long-term macrobenthic impacts at several offshore stations supported the hypothesis that diverse offshore assemblages may be less resilient than contiguous nearshore sandy-beach assemblages.


Keywords


Barrier island; beach restoration; Gulf of Mexico; macrobenthic recovery; macroinvertebrates

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