Effects of nutrient enrichment of the cyanobacterium Lyngbya sp. on growth, secondary metabolite concentration and feeding by the specialist grazer Stylocheilus striatus

Abstract

Harmful blooms of the benthic cyanobacteria Lyngbya spp. are increasing in coastal marine habitats. Nutrient enrichment has been implicated in bloom formation; however, the effects of nutrient enrichment on secondary metabolite concentrations and the resulting palatability of Lyngbya spp. are not known. Using nutrient bioassays, we examined the effects of nitrogen (N), phosphorus (P) and chelated iron (Fe) on growth and secondary metabolite concentration in Lyngbya sp. collected from reefs in Broward County, Florida. The consequences of these nutrient additions on feeding behavior of a major specialist opisthobranch grazer, Stylocheilus striatus, were examined. Chelated Fe additions (+FeEDTA) significantly increased Lyngbya sp. growth, while additions of N, P and chelated Fe combined (+All) resulted in significantly lower concentrations of microcolin A than in the control. Overall, there was a negative correlation between growth and total concentrations of microcolins A and B. When crude extracts from the control, +FeEDTA and +All treatments of the Lyngbya sp. bioassay were offered to S. striatus in artificial food, they consumed greater quantities of the control and +FeEDTA treatments than the +All. These results provide the first evidence that changes in nutrient availability can affect secondary metabolite concentrations in marine Lyngbya spp. and support previous studies that show that Fe can stimulate growth in benthic marine cyanobacteria. This study also demonstrates quantifiable changes in feeding behavior by a specialist grazer in response to changes in the nutrient conditions under which Lyngbya sp. grows and underscores the need to consider secondary metabolite concentrations, and their effect on grazers, when managing harmful algal blooms. © Inter-Research 2009.