Maria Liliana Quartino

Light and temperature demands of marine benthic microalgae and seaweeds in polar regions

Polar algae have a striking ability to photosynthesize and grow under very low light and temperatures. In seaweeds, minimum light demands for photosynthetic saturation and compensation can be as low as 10 and 2 mu mol photons m(-2) s(-1), respectively. For benthic microalgae, these values can be even lower because of the limited irradiance reaching deep sea floors. The extreme shade adaptation of these organisms sets their distributional limits at depths close to 40 m and enables them to tolerate long periods of extended darkness. In addition to their capability for efficient photosynthesis at extremely low light levels, polar algae possess metabolic adaptations to persist at low temperatures, which permit them to complete their life cycles at year-round temperatures close to 0 degrees C. Seaweeds with the lowest temperature demands are the species endemic to the Antarctic while Arctic algae are comparatively less cold-adapted. These adaptive characteristics allow benthic marine algae to make high contributions to high latitude coastal primary productivity and energy fluxes, exceeding or equaling the production of primary producers in more temperate systems. The studies summarized here give important insights into the major physiological adaptations allowing marine benthic microalgae and seaweeds to colonize these extreme habitats.

Distribution of macroalgae and macroalgal communities in gradients of physical conditions in Potter Cove, King George Island, Antarctica

The vegetation of a small fjord and its adjacent open shore was documented by subaquatic video. The distribution of individual species of macroalgae and the composition of assemblages were compared with gradients of light availability, hydrography, slope inclination, substratum, and exposition to turbulence and ice. The sublittoral fringe is usually abraded by winterly ice floes and devoid of large, perennial algae. Below this zone, the upper sublittoral is dominated by Desmarestia menziesii on steep rock faces, where water movements become irregular, or by Ascoseira mirabilis and Palmaria decipiens on weakly inclined slopes with steady rolling water movements. In the central sublittoral above 15 m, where turbulence is still active, Desmarestia anceps is outcompeting all other species on solid substratum, However, the species is not able to persist on loose material under these conditions. Instead, Himantothallus grandifolius may occur. Deeper, where turbulence usually is negligible, Desmarestia anceps also covers loose material. The change of dominance to Himantothallus grandifolius in the deep sublittoral cannot completely be explained at present. Himantothallus grandifolius also prevails in a mixed assemblage under the influence of grounding icebergs. Most of the smaller algae are opportunists with different degrees of tolerance for turbulence, but some apparently need more stable microhabitats and thus are dependent from continuing suppression of competitive large phaeophytes.

On the competitive balance of macroalgae at Potter Cove (King George Island, South Shetlands)

The sublittoral zonation of macroalgae and abundant animals in Potter Cove, King George Island, is described in relation to substrate, exposure to turbulence and impact of grounding icebergs. Implications on the ecological niches of the most prominent phaeophytes are discussed. It is concluded that Desmarestia anceps and D. menziesii exclude Himantothallus grandifolius under favourable conditions. However, Himantothallus, by its potential to inhabit unstable substrates, may be better adapted to withstand the ice impact. The replacement of Desmarestia by Himantothallus at greater depth can be explained only partially at present.

Biodiversity, biogeography and zonation of marine benthic micro- and macroalgae in the Arctic and Antarctic

This paper reviews the composition, biogeography and zonation of benthic algae in Arctic and Antarctic polar regions. There is a marked contrast in the literature between the amount of information on microalgae vs. macroalgae. Perhaps not surprising in view of their size and conspicuous nature, the macroalgae are better known than the microalgae and they have been studied more intensively. Macroalgal biodiversity is greater in Antarctica than in the Arctic, as is the number of endemic species. Both these characteristics of the Antarctic marine macroalgal flora can be explained by the biogeographical histories of the regions. In contrast, endemism amongst Arctic and Antarctic benthic microalgae is generally considered to be low; however, there is very little evidence to support this and further molecular research is needed to document and clarify the biodiversity of marine benthic microalgae of both polar regions. The zonation or local distribution of polar macroalgae and microalgae is influenced by physiological, morphological, chemical and ecological characteristics that determine responses to a range of environmental factors, including the ability to resist and survive algal grazing. Typically, the lower depth distribution limit elevates with increasing latitude.

Grazing by the Antarctic fish Notothenia coriiceps evidence for selective feeding on macroalgae

In Potter Cove, King George Island, Antarctica, macroalgae provide a significant food resource for herbivores. The demersal fish Notothenia coriiceps feeds on macroalgae. Eighteen algal species were identified in stomach contents: two chlorophytes, ten rhodophytes and six phaeophytes. Among these the rhodophyte Palmaria decipiens, the phaeophyte Desmarestia menziesii and the chlorophyte Monostroma hariotii comprised the greatest proportions of algal biomass. A food selection study showed four algae to be preferred (P. decipiens, M. hariotii, D. menziesii, Iridaea cordata) and two species to be avoided (Desmarestia anceps and Himantothallus grandifolius) by N. coriiceps. The present investigation indicates that this fish feeds not only intentionally, but also selectively, on macroalgae. Preference for particular algal species is not related to associated epifaunal biomass or to associated amphipod biomass.

Evidence of macroalgal colonization on newly ice-free areas following glacial retreat in Potter Cove (South Shetland Islands), Antarctica

Climate warming has been related to glacial retreat along the Western Antarctic Peninsula. Over the last years, a visible melting of Fourcade Glacier (Potter Cove, South Shetland Islands) has exposed newly ice-free hard bottom areas available for benthic colonization. However, ice melting produces a reduction of light penetration due to an increase of sediment input and higher ice impact. Seventeen years ago, the coastal sites close to the glacier cliffs were devoid of macroalgae. Are the newly ice-free areas suitable for macroalgal colonization? To tackle this question, underwater video transects were performed at six newly ice-free areas with different degree of glacial influence. Macroalgae were found in all sites, even in close proximity to the retreating glacier. We can show that: 1. The complexity of the macroalgal community is positively correlated to the elapsed time from the ice retreat, 2. Algae development depends on the optical conditions and the sediment input in the water column; some species are limited by light availability, 3. Macroalgal colonization is negatively affected by the ice disturbance, 4. The colonization is determined by the size and type of substrate and by the slope of the bottom. As macroalgae are probably one of the main energy sources for the benthos, an expansion of the macroalgal distribution can be expected to affect the matter and energy fluxes in Potter Cove ecosystem.

Biological and environmental characterization of marine macroalgal assemblages in Potter Cove, South Shetland Islands, Antarctica

Abstract We describe the macroalgal assemblages in Potter Cove and their distribution by depth, substratum, irradiation, nutrients, salinity, water temperature and light period. We determined groups by using K-means, the Hellinger index and the maximum Calinski-Harabasz pseudo-F-statistic as stopping rule. Indicator species were assessed with the IndVal index. Relationships between groups and environmental factors were determined by correspondence analysis, and results were validated by a canonical correspondence analysis of species and environment. To compare the group biodiversities we used species richness and diversity indices and abundance biomass comparisons curves. Analysis with incidence data discriminated one shallow Iridaea assemblage and one deep Himantothallus assemblage. Analysis using biomass discriminated three facies, the first in the upper zone (Iridaea cordata, Monostroma hariotii, Adenocystis utricularis, Enteromorpha bulbosa), the second (Desmarestia menziesii, D. antarctica, Ascoseira mirabilis, Curdiea racovitzae, Gigartina skottsbergii, Kallymenia antarctica, Neuroglossum delesseriae, Phaeurus antarcticus, Gymnogongrus turquetii) at intermediate depth and the third (H. grandifolius, D. anceps, Georgiella confluens, Ballia callitricha, Plocamium cartilagineum), coincident with the deep qualitative assemblage, was found in a less disturbed environment. The difference in species composition between the groups was mainly related to depth as an environmental variable. The high specific diversity at intermediate depths can be explained by the presence of patches in different successional stages caused by iceberg scouring.

SENSITIVITY OF ANTARCTIC UROSPORA PENICILLIFORMIS (ULOTRICHALES, CHLOROPHYTA) TO ULTRAVIOLET RADIATION IS LIFE-STAGE DEPENDENT(1).

The sensitivity of different life stages of the eulittoral green alga Urospora penicilliformis (Roth) Aresch. to ultraviolet radiation (UVR) was examined in the laboratory. Gametophytic filaments and propagules (zoospores and gametes) released from filaments were separately exposed to different fluence of radiation treatments consisting of PAR (P = 400–700 nm), PAR + ultraviolet A (UVA) (PA, UVA = 320–400 nm), and PAR + UVA + ultraviolet B (UVB) (PAB, UVB = 280–320 nm). Photophysiological indices (ETRmax, Ek, and α) derived from rapid light curves were measured in controls, while photosynthetic efficiency and amount of DNA lesions in terms of cyclobutane pyrimidine dimers (CPDs) were measured after exposure to radiation treatments and after recovery in low PAR; pigments of propagules were quantified after exposure treatment only. The photosynthetic conversion efficiency (α) and photosynthetic capacity (rETRmax) were higher in gametophytes compared with the propagules. The propagules were slightly more sensitive to UVB‐induced DNA damage; however, both life stages of the eulittoral inhabiting turf alga were not severely affected by the negative impacts of UVR. Exposure to a maximum of 8 h UVR caused mild effects on the photochemical efficiency of PSII and induced minimal DNA lesions in both the gametophytes and propagules. Pigment concentrations were not significantly different between PAR‐exposed and PAR + UVR–exposed propagules. Our data showed that U. penicilliformis from the Antarctic is rather insensitive to the applied UVR. This amphi‐equatorial species possesses different protective mechanisms that can cope with high UVR in cold‐temperate waters of both hemispheres and in polar regions under conditions of increasing UVR as a consequence of further reduction of stratospheric ozone.

Drivers of colonization and succession in polar benthic macro- and microalgal communities

Information on succession in marine benthic primary producers in polar regions is very scarce, particularly with regard to effects of abiotic and biotic drivers of community structure. Primary succession begins with rapid colonizers, such as diatoms and ephemeral macroalgae, whereas slow, highly seasonal recruitment and growth are characteristic of annual or perennial seaweed species. Colonization of intertidal and subtidal assemblages on polar rocky shores is severely affected by physical disturbance and by seasonal changes in abiotic conditions. Biotic factors, such as grazing, can strongly affect colonization patterns and also alter competitive interactions among benthic algae. Ambient UV radiation affects the diversity of macroalgal communities during early and later stages of succession. In contrast, microalgal assemblages have high tolerance to UV stress. Climate warming could alter algal latitudinal distribution and favor invasion of polar regions by cold-temperate species. Reduced sea ice cover and retreating glaciers could expand colonization areas but alter light, salinity, sedimentation and disturbance processes. Although the key role of macroalgae in coastal systems and, to a much reduced extent, the importance of microphytobenthos have been documented for polar regions, information on the successional process is incomplete and will benefit from further ecological studies.

The biology of an Antarctic rhodophyte, Palmaria decipiens: recent advances

Abstract Palmaria decipiens (Reinsch) R.W. Ricker (1987) represents one of the dominant rhodophyte species in Antarctic coastal ecosystems. Due to its high abundance in the intertidal and upper subtidal it plays a key role in ecosystem structure and function, providing habitat, food and shelter for a multitude of associated organisms. The physiology, reproductive strategy and life cycle of P. decipiens is considered as being well adapted to the Antarctic environment, which is characterized by permanent low water temperatures and a strong seasonality in light climate. With its obvious ecological significance and adaptive strategies P. decipiens was frequently studied as a typical representative of an endemic Antarctic macroalga. Here we provide an overview of the recent literature, summarizing the knowledge gained about the alga during the last 25 years. This review focuses on the species life cycle and physiological responses, such as temperature requirements, photosynthetic characteristics, pigment content and protective mechanisms with regard to enhanced ultraviolet radiation (UV-B radiation, 280–315 nm and UV-A radiation, 315–400 nm). The ecology of P. decipiens is reviewed focussing on grazing activity and abundance patterns. Since most studies on P. decipiens have been conducted at King George Island off the western Antarctic Peninsula this overview serves as a summary of baseline data from an ecosystem particularly prone to environmental change.