Experimental work with cultures of the red tide dinoflagellate Lingulodinium polyedrum suggested mycosporine‐like amino acids (MAAs) are a component of the organic matter excreted by cells. MAAs in dissolved organic matter (DOM) also may have a large influence on absorption of ultraviolet (UV) light through the water column. To test these hypotheses in a natural setting, data were collected from March 1995 through April 1996 i...