Tissue Nutrient Content in Ulva spp. (Chlorophyceae) as Bioindicator for Nutrient Loading Along the Coast of East Africa

Eutrophication is an increasingly occurring problem that causes degradation of coastal ecosystems worldwide. Traditional monitoring of dissolved nutrients in the water column can be complicated by short term fluctuations, especially when levels of nutrients are low and turnover rapid. A proposed alternative method is the use of macroalgal tissue nutrient concentrations for indication of ambient nutrient availability, as they integrate nutrients over time. This study evaluates the use of macroalgae within the genus Ulva (Chlorophyceae), regarding their ability to reflect nutrient gradients off the coast of East Africa (i.e. Kenya and Tanzania). Ulva was able to reflect nitrogen (N) gradients from all three outlet sources, with up to 90% higher tissue N levels in vicinity of major cities compared to adjacent areas. Together with results from nutrientuptake and fluctuation experiments, this study suggests that macroalgal tissue nutrient content has potential as a complement to regular water nutrient sampling.