Effects of dopamine, a compound released by the green-tide macroalga Ulvaria obscura (Chlorophyta), on marine algae and invertebrate larvae and juveniles

Abstract

:Dopamine is produced by Ulvaria obscura, a bloom-forming green alga that occurs from the mid intertidal to the shallow subtidal zones of North Pacific and North Atlantic shores. Its concentrations in the alga are approximately 0.5–1% of the alga's fresh mass. When experimentally desiccated and rehydrated at ecologically realistic densities, Ulvaria releases dopamine, resulting in seawater dopamine concentrations that can exceed 500 μM. Thus, dopamine could be responsible for previous reports of bioactivity by Ulvaria exudates. We tested this hypothesis by measuring the effects of dopamine in seawater on co-occurring macroalgae and crab larvae and juveniles. We ran assays that examined the effects of a range of dopamine concentrations on the growth of the green alga Ulva lactuca, on the germination of zygotes of the brown alga Fucus distichus, and on the survival, time to metamorphosis and time to first molt of crab (Metacarcinus magister and Cancer oregonensis) larvae and juveniles. Dopamine began to inhibit Fucus germination at concentrations above 5 μM, Ulva growth at concentrations above 50 μM, and the survival of Metacarcinus zoeae at concentrations above 168 μM. It did not affect the survival of Cancer megalopae or juveniles or the time to metamorphosis of megalopae. It had no effect on the time to first molt of Cancer juveniles, except at the highest concentration tested (738 μM), where it delayed molting by an average of a day and a half. These toxic effects could have been due to the dopamine or to its oxidation products. We concluded that the large-scale release of dopamine by U. obscura following stressful environmental conditions could significantly affect co-occurring species in intertidal pools as well as intertidal and shallow subtidal marine communities where the alga can form large blooms.