Abstract
Coastal waters are expected to undergo severe warming in the coming decades. Very little is known about how diatoms, the dominant primary producers in these habitats, will cope with these changes. We investigated the thermal niche of Cylindrotheca closterium, a widespread benthic marine diatom, using 24 strains collected over a wide latitudinal gradient. A multi-marker phylogeny in combination with a species delimitation approach shows that C. closterium represents a (pseudo)cryptic species complex, and this is reflected in distinct growth response patterns in terms of optimum growth temperature, maximum growth rate, and thermal niche width. Strains from the same clade displayed a similar thermal response, suggesting niche conservation between closely related strains. Due to their lower maximum growth rate and smaller thermal niche width, we expect the polar species to be particularly sensitive to warming, and, in the absence of adaptation, to be replaced with species from lower latitudes.
Highlights
Coastal waters have warmed during the last decades, and are predicted to continue to warm until the end of this century and beyond, potentially by as much as 2 to 3◦C depending on the geographical region (Stocker et al, 2013; Schleussner et al, 2015)
We investigated the thermal niche of Cylindrotheca closterium, a widespread benthic marine diatom, using 24 strains collected over a wide latitudinal gradient
Coral reefs are known to be threatened by global warming (Hughes et al, 2017) since the coral-algal symbiosis is living at its upper thermal limit, and temperature anomalies of just 1–2◦C above mean local summer maxima are sufficient to cause massive coral bleaching leading to high mortality (Lesser, 2011)
Summary
Coastal waters have warmed during the last decades, and are predicted to continue to warm until the end of this century and beyond, potentially by as much as 2 to 3◦C depending on the geographical region (Stocker et al, 2013; Schleussner et al, 2015). Evidence is accumulating that rising temperature affects the performance of coastal species in many regions worldwide. In temperate regions, warming coastal waters affect temperature-sensitive species such as the brown alga Fucus vesiculosus in the Baltic and the North Sea (e.g., Graiff et al, 2015). To accurately predict the Thermal Differentiation in C. closterium effects of coastal warming, a better understanding of how temperature and temperature variations will affect coastal marine organisms is required
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