Benthic microalgal biomass on ocean beaches: Effects of sediment grain size and beach renourishment

摘要

Benthic microalgal biomass was measured as sediment chlorophyll a at two open ocean beaches in southeastern North Carolina between December 2003 and December 2004, spanning beach renourishment projects in spring 2004 at both beaches. Sampling design included replicate sampling (n 6) at three elevations in the surf zone along paired transects at paired renourished and unnourished (control) sites at each beach 17 times during the study period. Grain-size analyses of beach sediments and measurements of water temperature were also conducted. Sediment grain size, expressed as mean grain size and percentage of total sediments <500 m diameter, significantly affected sediment chlorophyll a values. Renourishment drove a small and temporary but significant increase in sediment chlorophyll a at one beach, which was interpreted as an effect of source material but otherwise had no detectable negative effects. The grain-size effects reinforce the importance of efforts to match material used for renourishment with existing beach sediments because benthic microalgae likely form a significant portion of the base of the food chain in surf-zone communities.