Phytoplankton species and abundance in response to eutrophication in coastal marine mesocosms

In a mesocosm nutrient enrichment experiment the species (orcategories) and abundances of diatoms, dinoflagellates, flagellates,monads and ciliates were identified and counted over a 16-monthperiod. Diatoms and ciliates increased with increasing nutrienttreatment while monads and flagellates, <10 µm in size,did not. By contrast, in the field diatoms sometimes appearedto decrease while small phytoplankton µ10 µm appearedto increase under eutrophic conditions. In the experiment, insome instances, grazing controlled abundances to low levelsin nutrient-enriched treatments. Self-shading by phytoplanktonlimited upper levels of abundance when nutrients were excessive.While nuisance species were occasionally present in variousnutrient treatments, the intensity and frequency of their presencedid not tend to increase with nutrient treatment. Generallyspecies (or categories) did not appear to change with nutrienttreatment.