Patterns of macroalgal abundance, nutrient availability, and sediment characteristics in 5 southern California estuaries

Worldwide, studies have found that increased nutrient enrichment has led to macroalgal blooms, which has also been true in southern California estuaries. The objective of this study was to compare spatial and temporal patterns of water column nitrogen concentrations, macroalgal abundance, as well as sediment characteristics in 5 estuaries in southern California. Total algal biomass ranged from <300 to >2000 g wet wt m-2, and was spatially and temporally variable within each estuary, with increases in summer and fall and at the heads for all but one estuary. Water column nutrient concentrations were higher in the wet season and were spatially variable within each estuary with maximum nitrate ~2000µM NO3. There was no relationship with water column nutrient concentration and algal biomass. This suggested that while nutrient availability is important, other factors, such as recruitment, water flow regimes, and sediment stability must be investigated to explain the variability of macroalgal accumulation. In one estuary I tested the hypothesis that recruitment of Enteromorpha intestinalis is neither density nor flow dependent. Results showed a spatial gradient for water flow with higher rates at the mouth of the estuary, and as expected, there was no relationship between recruitment and adult densities or water flow. We can infer from these results that in this system, recruitment of zoospores does not control spatial patterns of blooms. Further experiments investigating the relationship between water flow and algal removal may help to explain the variability of spatial patterns found in these systems.