Fate and processing of macroalgal wrack subsidies in beaches of Deception Island, Antarctic Peninsula

Drift macroalgae detached from rocky substrate frequently strands on the shore line, driving a number of ecological processes, such as degradation, consumption, habitat supply and biogeochemical processing. The algal subsidies received by beaches of Foster Bay, in Deception Island, were evaluated in terms of the spatio-temporal dynamics of wrack deposits. Predominance in the strands of a single red blade species, Palmaria decipiens, points toward an equivalent abundance in the subtidal macroalgal beds, accompanied by Desmarestia menziesii and Desmarestia antarctica, among others. Biomass measurements and wrack grooming along the intertidal range over time indicate that an instantaneous stock of 39.9 MT of algal debris strands on the shore line of Foster Bay, with more than 50% of these materials being renewed at each tidal cycle. Estimates of macrophyte production fluxing to the bay ecosystems suggest that only a small fraction (2.8%) of the detached material within the bay accumulates as wrack along the intertidal zone. Variability in the amount of algae along the shore is significantly affected by wind direction or coastal orientation, with larger strandings when sea-land winds prevail. The degradative process of algal wrack was analyzed through a litter bag experiment where pre-weighted fragments of P. decipiens and D. menziesii were sequentially removed from the drift line along 14 days. Degradation of wrack biomass occurs within the first days of decaying, loosing up to 41.3% of its initial weight (D. menziesii), with remarkable variability among the two species tested. Higher feeding rates of amphipods were obtained with P. decipiens compared to that on D. menziesii, which can be mediated by its low content in deterrents and its blade shape, as well as being the most abundant species in the Deception Island and in many coastal areas of the Antarctic Peninsula. Globally, the consumer species assayed could process through consumption 0.73% day− 1 of the instantaneous stock of algal deposits along the shore of Foster Bay. This study attempts to identify different linked processes poorly understood in the ecology of Antarctic shores, as the stranding, degradation and consumption of large amount of macroalgal subsidies from highly productive submerged rocky substrates toward low productive intertidal sedimentary shores.