Drift macroalgal abundance in seagrass beds: Investigating large-scale associations with physical and biotic attributes

The relationship between a suite of physical and biological factors and drift macroalgal abundance was examined in 12 seagrass sites spanning a distance of over 50 km within Tampa Bay, Florida, USA. Field sampling was conducted in December 1991, and drift algal abundance was determined by recording algal percent cover from 25 quadrants at each site. Additionally, drift macroalgae were collected from gridded plots and dry weight biomass measured. Sediment characteristics and seagrass biomass, shoot density, blade length and percent cover at each site were also determined. Likewise, position of site within Tampa Bay was categorized by spatial coordinates. Step-wise regression indicated that percent silt-clay and percent seagrass cover combined to explain 57% of the variance of drift algal cover in seagrass beds, while percent silt-clay alone explained 35% of algal biomass variance. Neither drift macroalgal cover nor biomass demonstrated any significant relationship with shoot density or aboveground biomass. Over the large spatial scale of this study, our findings suggest a Link between hydrodynamic regime, as reflected by sediment characteristics, and drift macroalgal abundance in seagrass beds.