Exudates of the green alga Ulvaria obscura (Kützing) affect larval development of the sand dollar Dendraster excentricus (Eschscholtz) and the Pacific oyster Crassostrea gigas (Thunberg)

Accumulations of green macroalgae (green tides) are becoming increasingly common in many coastal habitats and substances released by these blooms may impact other organisms. In the northeastern Pacific, a dominant contributor to green tides is  Ulvaria obscura , an alga that produces dopamine which affects a variety of physiological processes and can trigger metamorphosis in marine invertebrates. Eggs, embryos, and larvae of Pacific oysters ( Crassostrea gigas ) and sand dollars ( Dendraster excentricus ) were exposed to  U. obscura exudates and dopamine to determine how exposure affects fertilization, development, and morphology. Exposing eggs to these compounds had no significant effect on fertilization of  C. gigas  and limited impact on  D. excentricus,  relative to unexposed controls. Early embryos exposed to the compounds developed successfully, but the resulting  C. gigas  veligers had larger shells and the  D. excentricus  gastrulae had shorter archenterons. When exposed to dopamine,  C. gigas  veligers had smaller shells, while larval arms of  D. excentricus  were significantly shorter relative to unexposed controls. Results indicate that compounds released by  U. obscura  affect development differently between invertebrate species and among developmental stages. The stage-specific responses likely result from changes in structure and metabolic activity at different life history stages, as well as changes in the localization and function of dopamine and dopamine receptors that occur during larval development. The changes in larval morphology and function induced by compounds released by marine macroalgae could ultimately impact the ability of larvae to feed and survive.