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Kelp forests are important habitats in the strongly environmentally and seasonally variable Arctic. There is a critical lack of knowledge about how seasonal conditions and climate change scenarios influence survival and reproduction of kelp early life stages. To better understand the regulation of kelp life cycle processes in this harsh environment we focused on the physiological performance and reproductive success of early life stages in Alaria esculenta and Laminaria digitata from Kongsfjorden, Spitsbergen. Gametophyte growth and survival during Arctic winter and subsequent sporophyte recruitment under spring conditions were investigated. Winter conditions (2°C, complete darkness) halted gametophyte growth and prevented the onset of gametogenesis in both species. The gametophytes of L. digitata but not A. esculenta became fertile after returning to spring conditions, suggesting that sporogenesis, sexual reproduction and recruitment in A. esculenta must occur successively during summer/autumn while in L. digitata a new generation of sporophytes could develop from over-wintering gametophytes. The effects of simulated canopy shading (offering protection against extreme irradiance stress, particularly as sea ice retreats), present-day and projected Arctic summer seawater temperatures, and nutrient levels on gametophyte survival, fertility and sporophyte recruitment success were also investigated in both species. A. esculenta gametophytes had greater survival and reproductive success than L. digitata, except under very low light (simulating dense canopy). In contrast, shading was required for reproductive success in L. digitata gametophytes. Predicted summer temperatures of 9°C reduced sexual reproduction in both species. Interactions observed between these environmental drivers probably reflect species-specific seasonal patterns of survival and reproduction. These differences between kelp species in response to abiotic factors and light levels (simulated canopy shading) suggest that climate change could alter community structure in the Arctic through effects on sexual reproduction and sporophyte recruitment success. HIGHLIGHTS• Gametophytes were able to endure long periods of darkness.• Parental kelp canopy is key for gametophyte survival and recruitment.• Climate change may alter kelp recruitment patterns. [ABSTRACT FROM AUTHOR]

Kelps are globally important bioengineering species with high ecological and economic value, but are increasingly threatened by climate-driven geographic range shifts. The inheritance of economically important traits from parents to offspring is poorly understood in kelps but it is of utmost interest to seaweed farmers wishing to select strains with superior performance and resilience to environmental change. For two allopatric kelp species (N-Atlantic Laminaria digitata and S-Atlantic L. pallida), we compared the speed of gametogenesis and reproductive success in parental gametophytes, and produced intraspecific and reciprocal interspecific crosses of female × male gametophyte parents isolated from the two species. We then compared the upper thermal resilience of microscopic and macroscopic sibling sporophytes in an exposure experiment over two weeks. The upper thermal limit of the sporophytes resulting from intraspecific crosses of the two species deviated by 1°C. In contrast, sporophytes from both interspecific hybrid crosses had a 2–3°C higher upper thermal tolerance than single species sporophytes, indicating heterosis for thermal tolerance. This phenotypic response appears partially sex-dependent in our study, with female parents being more important in determining the thermal-response phenotype than male parents. The presence of male gametophytes generally enhanced female reproductive success. Both gametogenesis rate and reproductive success differed among the types of reciprocal crosses. Although the interspecific crosses were artificial in an ecological sense, they may provide a tool for understanding the molecular basis of heterosis and thermal tolerance in kelps (e.g. by investigating species-specific gene expression), or for aquaculture breeding programmes against a background of rapid environmental change. [ABSTRACT FROM AUTHOR]

This review about the genus Laminaria sensu lato summarizes the extensive literature that has been published since the overview of the genus given by Kain in 1979. The recent proposal to divide the genus into the two genera Laminaria and Saccharina is acknowledged, but the published data are discussed under a 'sensu lato' concept, introduced here. This includes all species which have been considered to be 'Laminaria' before the division of the genus. In detail, after an introduction the review covers recent insights into phylogeny and taxonomy, and discusses morphotypes, ecotypes, population genetics and demography. It describes growth and photosynthetic performance of sporophytes with special paragraphs on the regulation of sporogenesis, regulation by endogenous rhythms, nutrient metabolism, storage products, and salinity tolerance. The biology of microstages is discussed separately. The ecology of these kelps is described with a focus on stress defence against abiotic and biotic factors and the role of Laminaria as habitat, its trophic interactions and its competition is discussed. Finally, recent developments in aquaculture are summarized. In conclusion to each section, as a perspective and guide to future research, we draw attention to the remaining gaps in the knowledge about the genus and kelps in general. [ABSTRACT FROM AUTHOR]

The existence of cryptic diversity in the ‘Porphyra leucosticta' complex of the North Atlantic and Mediterranean was confirmed from a wide variety of recent and over 100-year-old herbarium specimens using plastid and nuclear molecular data in combination with karyological, morphological and ecological observations. The results revealed the presence of a new species, P. olivii sp. nov., within the P. leucosticta complex. Possible evidence for sexual reproduction was observed in a culture of P. olivii from the holotype site, Gulf of Thessaloniki in Greece, where n = 2 chromosomes in male gametes and neutral spores, and 2n = 4 in zygotospores. Archeospores and neutral spores also formed in culture providing evidence for possible asexual reproduction. The results also revealed the presence of P. rosengurttii, originally described from the north-western Atlantic, in both the north-eastern Atlantic and the Mediterranean, and enabled new morphological and ecological information to be obtained for this species. The rbcL sequences for P. olivii, including from an 1889 specimen of ‘Porphyra leucosticta’, differed by one transition between the north-western Atlantic and Mediterranean. The ITS1 of the holotype of P. olivii differed by a single bp transition from another specimen from the same location. The ITS1 of specimens from the northwestern Atlantic were identical but differed by 3-4 bp substitutions from the specimens from the Mediterranean. Partial rDNA SSU sequences were identical. In P. rosengurttii, rbcL sequences, including from specimens dated 1890 and 1906, differed by a single transition between both regions, the ITS1 had 92–100% similarity and partial rDNA SSU sequences were identical. Our study indicates that molecular, morphological and ecological evidence from a wide variety of samples (recent and old) and locations should be investigated before a new species is erected. The molecular comparison with old herbarium specimens also revealed that P. olivii and P. rosengurttii are not recent invaders to the Mediterranean but have been present for at least 100 years. [ABSTRACT FROM AUTHOR]