Sensitivity of Laminariales zoospores from Helgoland (North Sea) to ultraviolet and photosynthetically active radiation: implications for depth distribution and seasonal reproduction

Depth distribution of kelp species in Helgoland (North Sea) is characterized by occurrence of Laminaria digitata in the upper sublittoral, whereas L. saccharina and L. hyperborea dominate the mid and lower sublittoral region. Laminaria digitata is fertile in summer whereas both other species are fertile in autumn/winter. To determine the light sensitivity of the propagules, zoospores of L. digitata, L. saccharina and L. hyperborea were exposed in the laboratory to different exposure times of photosynthetically active radiation (PAR; 400-700 nm), PAR + UVA radiation (UVAR; 320-400 nm) and PAR + UVAR + UVB radiation (UVBR; 280-320 nm). Optimum quantum yield of PSII and DNA damage were measured after exposure. Subsequently, recovery of photosynthetic efficiency and DNA damage repair, as well as germination rate were measured after 2 and 3 d cultivation in dim white light. Photosynthetic efficiency of all species was photoinhibited already at 20 mu mol photons m(-2) s(-1) PAR, whereas UV radiation (UVR) had a significant additional effect on photoinhibition. Recovery of the PSII function was observed in all species but not in spores exposed to irradiation longer than 4 h of PAR + UVA + UVB and 8 h of PAR + UVA. The amount of UVB-induced DNA damage measured as cyclobutane-pyrimidine dimers (CPDs) increased with exposure time and highest damage was detected in the spores of lower subtidal L. hyperborea relative to the other two species. Significant removal of CPDs indicating repair of DNA damage was observed in all species after 2 d in low white light especially in the spores of upper subtidal L. digitata. Therefore, efficient DNA damage repair and recovery of PSII damage contributed to the germination success but not in spores exposed to 16 h of UVBR. UV absorption of zoospore suspension in L. digitata is based both on the absorption by the zoospores itself as well as by exudates in the medium. In contrast, the absorption of the zoospore suspension in L. saccharina and L. hyperborea is based predominantly on the absorption by the exudates in the medium. This study indicates that UVR sensitivity of zoospores is related to the seasonal zoospore production as well as the vertical distribution pattern of the large sporophytes

In vitro ruminal fermentation and methane production of different seaweed species

Seaweeds have potentials as alternative feed for ruminants, but there is a limited knowledge on their nutritive value. Seven seaweed species collected along the coast above the Arctic circle of Norway, both in spring and autumn, were assessed for nutrients and total polyphenols (TEP) content, gas production kinetics and in vitro rumen fermentation in batch cultures of ruminal microorganisms. The seaweeds were three red species (Mastocarpus stellatus, Palmaria palmata and Porphyra sp.), three brown species (Alaria esculenta, Laminaria digitata and Pelvetia canaliculata) and one green species (Acrosiphonia sp.). Additionally, the abundance and diversity of total bacteria, protozoa and archaea in the cultures with the three red seaweeds collected in spring were analyzed by quantitative PCR and PCR-DGGE, respectively. The crude protein (CP) content varied widely. Pelvetia had the greatest (P 0.05) among the other seaweeds in VFA production, but Porphyra sp. had the second highest methane production (P 0.05) by either seaweed species or the collection season. Higher final pH (P 0.05) in the abundance or the diversity of total bacteria, protozoa and archaea. In the PCR-DGGE analysis, samples were separated by the incubation run for all microbial populations analyzed, but not by seaweed species. The results indicate that seaweed species differ markedly in their in vitro rumen degradation, and that samples collected in autumn had lower rumen degradability than those collected in spring

The abiotic environment of polar marine benthic macro- and microalgae

Due to different oceanographic and geological characteristics, benthic algal communities of Antarctica and the Arctic differ strongly. Antarctica is characterized by high endemism, whereas in the Arctic only few endemic seaweeds occur. In contrast to the Antarctic region, where nutrient levels never limit algal growth, nutrient levels in the Arctic regions are depleted during the summer season. Both regions have a strong seasonally changing light regime, fortified by an ice covering throughout the winter months. After months of darkness algae are suddenly exposed to high light caused by the breaking up of sea ice. Simultaneously, harmful ultraviolet radiation (UVR) entersthe water column and can significantly affect algal growth and community structure. In the intertidal zone fluctuations of temperature and salinity can be very large. Ice scours can further influence growth and settlement of intertidal algae. The subtidal zone offers a more stable habitat than the intertidal,permitting the growth of larger perennial algae and microbial mats. Polar regions are the areas most affected by global climate change, i.e. glacier retreat, increasing temperature and sedimentation, with yet unknown consequences for the polar ecosystem