Photosynthetic light requirements and vertical distribution of macroalgae in newly ice-free areas in Potter Cove, South Shetland Islands, Antarctica

Abstract

In Potter Cove, Antarctica, newly ice-free areas appeared due to glacial retreat. Simultaneously, the inflow of sediment increased, reducing underwater photosynthetically active radiation (PAR, 400-700 nm). The aim of this study was to determine the photosynthetic characteristics of two macroalgal species colonizing three newly icefree areas, A1, A2 and A3, with increasing degree of glacial influence from A1 to A3. Turbidity, salinity and temperature were measured, and light attenuation coefficients (K d ) calculated and considered as a proxy for glacial sediment input. The lower depth distribution of the red alga Palmaria decipiens and the brown alga Himantothallus grandifolius was 10 m in A3, 20 m in A2 and 30 m in A1. Both species were then collected, at 5 and 10 m at all areas. Photosynthetic parameters and the daily metabolic carbon balance (CB) were determined. K d was significantly higher in A3 compared with A1 and A2. The CB of P. decipiens was significantly higher in A1 followed by A2 and A3, and significantly higher at shallower than at greater depth. For H. grandifolius CB was significantly lower in A3 and in A2 at deeper depths compared with the rest of areas and depths. The lower distribution limit of the algae was positively correlated to the light penetration. An increase in the sediment run-off due to global warming might lead to an elevation of the lower depth distribution limit but retreating glaciers can open new space for macroalgal colonization. These changes will probably affect macroalgal primary productivity in Potter Cove with consequences for the coastal ecosystem.

Oxidative balance in macroalgae from Antarctic waters. Possible role of Fe

“…In the present study, the lower irradiance PAR values assessed in Island D compared to Peñón de Pesca are consistent with previous findings that have shown that the inflow of sediment during the warmer months leads to marked seasonal variations in turbidity (Deregibus et al, 2016). Algal growth is constrained during 2 (two) or 3 (three) months a year until the sediment enters the water column (Wiencke and Amsler, 2012).…”

“…An increase in sediment input can also have positive effects in reducing exposure to excessive ultraviolet radiation (280-400 nm), and current circulation and wind cause resuspension processes (Schloss et al, 2012). Seaweeds in Potter Cove are not only shade-adapted but can also cope with high PAR intensities in summer as they are not photoinhibited even under very high irradiances (Deregibus et al, 2016;Wiencke and Amsler, 2012). Quartino et al (2013) reported the presence of both G. skottsbergii and H. grandifolius in areas with high sedimentation showing that survival and reproduction skills of these algae under such circumstances are successful.…”

“…Measurements were performed using an Odyssey Photosynthetic Irradiance Recording System (Data Flow Systems, Christchurch, New Zealand). Light meters were calibrated 7 (seven) days prior to deployment against a LI-COR LI 1400 datalogger equipped with a LI-COR 190 PAR sensor (Deregibus et al, 2016). After calibration, light loggers were positioned standing upright on tripods and secured by SCUBA divers.…”

“…Photosynthesis vs. irradiance curves were obtained and used to calculate photosynthetic parameters (P max , which is the maximum photosynthetic rate; the photosynthetic efficiency, which is the initial slope of the curve at low irradiance; the saturation point, which is the light saturation point of photosynthesis; the light compensation point, and the respiration, which is the dark respiration rate) as described by Deregibus et al (2016). The continuous PAR data (μmol photons m −2 s −1 ) were plotted against time of the day (every 15 min) at 5 m depth for Peñón de Pesca and Island D. Calculations of daily net carbon balance (mg C g FW − 1 d − 1 ) were performed by using the obtained photosynthetic parameters and incident irradiances as described by Deregibus et al (2016).…”

“…Meltwater increments from glaciers due to global warming have substantial effects on light penetration, salinity, temperature, nutrient conditions and metal inputs due to higher sediment run-off in coastal waters (Dierssen et al, 2002;Quartino et al, 2013;Sahade et al, 2015). In the King George Island region, Antarctica, high sedimentation reduces underwater photosynthetically active radiation (PAR, 400-700 nm) leading to a lower carbon balance by some macroalgal species (Deregibus et al, 2016). Furthermore, the sediment and rocks in this island are rich in iron (Fe), containing 5 to 7% Fe (Tatur et al, 1999), and thus sediment ablation enriches the seawater in Fe (Ahn et al, 1996;Dierssen et al, 2002).…”