MARINE ECOLOGY PROGRESS SERIES Vol. 294: 131–140, 2005 Published June 9 Mar Ecol Prog Ser Primary production potential of non-geniculate coralline algae at Cape Evans, Ross Sea, Antarctica Anne-Maree Schwarz1, 3,*, Ian Hawes1, 3, Neil Andrew2, 4, Steve Mercer 2, Vonda Cummings2, Simon Thrush1 1National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand 2National Institute of Water and Atmospheric Research, PO Box 14-901, Wellington, New Zealand 3Present address: The Worldfish Center, PO Box 77, Gizo, Solomon Islands 4Present address: The Worldfish Center, PO Box 500 GPO 10670, Penang, Malaysia ABSTRACT: The abundance and photosynthetic characteristics of non-geniculate coralline algae were determined at Cape Evans, McMurdo Sound (Ross Sea), Antarctica, during spring 2003. At the time, the site was covered by 2.5 m of sea-ice through which only 0.48% of incident irradiance was able to penetrate. Coralline algae covered 4 to 60% of the seafloor from water depths of 13 to 26 m. –2 Coralline algal crusts showed light-saturated rates of photosynthesis from 9.4 to 20 mmol O2 m thal- –1 –2 –1 lus d and dark respiration rates from 0.15 to 0.96 mmol O2 m thallus d . The average irradiance –2 –1 at which the onset of light saturated photosynthesis occurred (E k) was 3.2 µmol photons m s , mea- sured using oxygen micro-electrodes, and 2.9 µmol photons m–2 s–1, measured using pulse amplitude modulated (PAM) fluorometry techniques. Irradiance at depths of 15 to 20 m did not exceed 2 µmol photons m–2 s–1 during the study, but frequently exceeded the light compensation point for photo- –2 –1 synthesis (Ec), estimated as 0.10 µmol photons m s . The effective quantum yield (ΔF/Fm’) of Photo- system II, measured in situ over diel periods at depths of 16, 18 and 20 m, averaged 0.691 (SD = 0.003), 0.639 (SD = 0.005) and 0.632 (SD = 0.007), respectively. These values were indicative of mini- mal down-regulation of photosynthesis, and were consistent with the observation that irradiance never exceeded Ek. Laboratory investigations, showed that on transfer from ambient irradiance to 23.5 µmol photons m–2 s–1, a change of 2 orders of magnitude, the algae showed minimal photo- inhibition and a small, but statistically significant increase in Ek and maximum electron transport rate. Coralline algae at Cape Evans are able to persist with net carbon accrual under ice, while being able to tolerate periods of higher irradiance during ice-free conditions. This contrasts to Phyllophora antarctica which is dependent on ice-free periods to achieve net production. KEY WORDS: Photosynthesis · Oxygen electrodes · Macroalgae · Phyllophora antarctica · Photoacclimation · Mesophyllum engelhartii · Synarthrophyton patena Resale or republication not permitted without written consent of the publisher INTRODUCTION ated with a high photosynthetic efficiency and a high capacity to store photosynthate (Steneck 1986). Similar Non-geniculate or crustose, coralline algae occupy considerations are likely to apply to the ability of crus- habitats that cover a broad range of irradiance. Some tose corallines to dominate the flora of high-latitude species occur in the extreme high irradiance of shallow marine systems where sea-ice plays a major role in tropical reefs (Payri et al. 2001), while other species structuring the light climate. Non-geniculate coralline comprise the deepest known record for attached algae have been described as being widespread in the macroalgae, where they receive less than 0.0009% of Ross Sea (Zaneveld & Sanford 1980), and are the dom- surface irradiance (Littler et al. 1991). The ability of inant macroalgae at depths below those where it is coralline algae to grow in deep water has been associ- possible for branched and foliose forms to grow (Cor- *Email: [email protected] © Inter-Research 2005 · www.int-res.com 132 Mar Ecol Prog Ser 294: 131–140, 2005 maci et al. 1998). Conspicuous coralline crusts are available light than P. antarctica, achieved either found at Cape Evans (Miller & Pearse 1991) on Ross through better assimilation of low light or through an Island, Antarctica, and extend further south to Hut enhanced ability to take up and store carbon during Point (Dayton 1990). Although previously referred to the periodic intervals of high light. as Phymatolithon foecundum (Kjellman) Düwel et In this study, we quantify depth-dependent cover Wegeberg 1996 (Alongi et al. 2002), collections made and pigment concentrations at 2 depths for coralline during recent years in the Ross Sea suggest that the algae at Cape Evans. We present the results of oxygen taxonomy of coralline algae in the region is, as yet, exchange and pulse amplitude modulated (PAM) fluo- poorly defined. Samples collected from Cape Evans, rometry investigations of the photosynthetic character- the site for this study, have recently been identi- istics of under-ice material collected in spring 2003, fied as either Mesophyllum engelhartii (Foslie) and of experiments designed to assess their potential Adey or Synarthrophyton patena (Hook.f. et Harv.) to respond to higher irradiance likely to be associated Townsend (A. Harvey pers. comm.). M. engelhartii and with summer ice-free conditions. S. patena possess morphologically similar tetrasporan- gial conceptacles (Woelkerling 1996) and can only be separated by observing spermatangial filament bran- MATERIALS AND METHODS ching in the male conceptacles (unbranched in M. engelhartii, but both branched and unbranched in Site description. This study was carried out at Cape S. patena). To date, distinguishing between these 2 Evans, Ross Island, Antarctica, between 29 October species in samples from Cape Evans has not been and 4 November 2003. Collections were made by possible as male conceptacles were not available in SCUBA divers operating through an ice hole. The hole the samples. was located at 77° 38.085’ S,166° 24.843’ E over a water Polar macroalgae in general (Kirst & Wiencke 1995), depth of 20 m, enabling SCUBA access to a depth including coralline algae in the high Arctic (Roberts et range from 13 to 26 m. A hut erected over the hole pro- al. 2002), are well adapted to low light conditions. Nev- tected plant material that was collected from under the ertheless some polar macroalgae have also been ice from temperature and light shock upon arrival at shown to be capable of withstanding excessive light the surface. (Hanelt et al. 1997). An ability to acclimate to different Irradiance. Surface and under-ice photosyntheti- light conditions is illustrated by some Antarctic taxa, cally available radiation (PAR) was measured using including the foliose red algae Palmaria decipiens, by LiCor quantum sensors (Li190SA for surface and seasonal differences in photosynthetic performance Li192SB for underwater irradiance). Irradiance mea- that have been interpreted as enabling the algae to use sured by both sensors was logged at 5 min intervals short periods of relatively high irradiance soon after using a Li-1000 data logger for 7 d. The under-ice sen- sea ice break-up (Kirst & Wiencke 1995). While sor was attached to the underside of the ice using an photoacclimation may include changes in the size of ice screw at a distance of 20 m from the dive hole. This photosynthetic units, pigment composition, enzyme distance was found to be adequate to avoid the effect activity and/or the characteristics of P-I relationships of light focusing through the hole. The percent trans- (Kirst & Wiencke 1995), the physiological adaptations mission through the ice was calculated for the logging that enable coralline algae to persist at great depths period. On 2 occasions, divers made in situ measure- and high latitudes in the Antarctic, both of which ments of irradiance using an Li192SB underwater sen- impose strict limitations of the availability of light, sor attached to a Li145 meter in a waterproof housing. remain poorly understood. Measurements were made at 4 depth intervals be- At Cape Evans, the branched red alga Phyllophora tween 0 and 20 m below the ice, enabling the attenua- antarctica and coralline algae have overlapping depth tion coefficient for downwelling irradiance (Kd) to be distributions, with P. antarctica attached to rocks, estimated from the slope of the log-transformed PAR occurring predominantly between 10 and 18 m, while values with depth (Kirk 1994). coralline algae extend from 10 to >30 m (maximum Distribution and percent cover. A 50 m transect line diving depth) (Miller & Pearse 1991, Schwarz et al. was laid on the seafloor between water depths of 13 2003). Previously, we have shown that irradiance con- and 26 m. The seafloor along the transect was videoed sistently exceeds compensation levels for photosynthe- using a diver-held digital video camera at a fixed sis of P. antarctica, thereby enabling net carbon accu- height of 70 cm above the bottom. The gradient of the mulation only during the ice-free period (ca. 2 mo in transect was used to identify distances corresponding 2000–2001) (Schwarz et al. 2003). Given that corallines to 1 m depth increments, and at each of these a still are found at much greater depths, we hypothesised image was captured from the video record using a that they would have a more efficient utilisation of Sony digital cassette recorder. The percent cover of Schwarz et al.: Primary production potential of coralline algae 133 coralline algae was estimated within an area of 0.5 × (Schreiber et al. 1986) and so does not necessarily 0.5 m in each captured frame, overlain by a grid equiv- mimic a traditional light curve; rather, it provides a alent to 636 squares, each 1 × 1 cm. The number of grid snapshot of the current status of light adaptation to the intercepts that coincided with coralline algae and/or ambient light conditions.