Acid (H₂S0₄) production, persistence, and functional importance of the annual, brown seaweed Desmarestia viridis in Newfoundland, Canada

Abstract

Current models of shallow rocky community organization and stability in the northwestern Atlantic (NWA) emphasize kelps and their vulnerability to grazers and other mortality agents. This paradigm may overshadow the possible contribution of other groups of less studied seaweeds with overlapping distribution to ecosystem resilience. The annual, brown seaweed Desmarestia viridis is one of only a few species of fleshy seaweeds commonly found in urchin barrens in the NW A. The exceptional ability of D. viridis sporophytes to produce and store sulfuric acid (H₂S0₄) in intracellular vacuoles makes the species a compelling model for studies of controls and importance of acid production in seaweeds at the individual, population, and community levels. This research used laboratory experiments and surveys of individuals and populations throughout an entire growth season (February to October 2011) at two subtidal sites on the southeastern tip of Newfoundland (Canada) to determine controls of acid production in, as well as the functional importance and persistence of, D. viridis sporophytes. Results showed that light, grazing, and epibionts have no perceptible effects on intracellular acidity, whereas temperature and wave action exert strong, synergistic effects. Mortality rates and sea temperature from March to late June were relatively low, whereas the onset of increasing mortality in mid-August coincided with marked increases in sea temperature. The quick development of "Desmarestia beds" in urchin barrens created biological structure for major recruitment pulses in characteristic invertebrate and fish assemblages. These findings provide novel insights into the ecological and evolutionary causes and consequences of acid production in Desmarestiales, while elevating the importance of D. viridis as a foundation species in urchin barrens in the NWA.