Interactions of daylength, temperature and nutrients affect thresholds for life stage transitions in the kelp Laminaria digitata (Phaeophyceae)

Abstract

Kelp beds worldwide are under pressure from ongoing climate and environmental change. Along European coastlines increases in seawater temperature and changes in nutrient conditions occur where upwelling events are disrupted and also along eutrophicated coasts. In addition, seaweed responses to change may interact with seasonal daylength cycles. We performed a factorial experiment to examine the combined effects of seawater temperatures, nutrient regimes and photoperiod (long and short days) in order to better understand how latitudinal or seasonal differences in daylengths affect the sensitivity of transient microscopic kelp stages of Laminaria digitata from the North Sea to warming and eutrophication. While the optimal temperature range for vegetative gametophyte growth was 10°C-18°C under long summer photoperiod conditions, gametogenesis was induced at lower temperatures between 5°C and 15°C, with maximum sporophyte development under long photoperiods and enriched nutrient regimes, which represent local late spring conditions. Although gametogenesis was fastest at 10°C-15°C, sporophyte recruitment was highest at 5°C. As these particular early life cycle processes in L. digitata have different temperature optima, this may drive the seasonal cycle of recruitment in the field. Increasing summer temperatures due to global warming will increase gametophyte size due to enhanced vegetative growth and inhibition of gametogenesis. This will probably lead to delayed but enhanced recruitment of new sporophytes under cooler autumn to spring conditions over a wide geographical scale, preventing the formation of juvenile sporophytes under stressful summer conditions and possibly changing annual recruitment patterns.

How light and biomass density influence the reproduction of delayed Saccharina latissima gametophytes (Phaeophyceae)

“…, Martins et al. ). Microscopic observations showed that the young sporophytes only developed on the bottom of the well plates, and all were counted per triplet of the experimental conditions.…”

“…), and nutrient availability (Harries , Martins et al. ). Light intensity has been described as a generic abiotic factor controlling gametogenesis, with broad light intensity gradients in which gametogenesis was successfully induced (Lüning , Lee and Brinkhuis ).…”

Climate Change Impacts on Seagrass Meadows and Macroalgal Forests: An Integrative Perspective on Acclimation and Adaptation Potential

“…For example, the growth rate of Laminaria digitata gametophytes was highest at 10-18 • C, while gametogenesis required lower temperatures (i.e., 10-15 • C), and fertilization and recruitment of sporophytes was optimal at only 5 • C (Martins et al, 2017).…”

“…However, ocean warming can negatively affect kelp's asexual (sporogenesis) and sexual (gametogenesis) reproduction (Viejo et al, 2011;Bartsch et al, 2013;Roleda, 2016;Martins et al, 2017). The impacts of climate change on the reproduction (both sporogenesis and gametogenesis) and embryogenesis among macroalgae with complex life cycles require further studies.…”

Temperature Modulates Sex-Biased Gene Expression in the Gametophytes of the Kelp Saccharina latissima

“…Reproduction in kelps is tightly connected to environmental cues. Gametophytes may enter gametogenesis under the specific combination of nutrients, light, and temperature or remain vegetative if conditions are not favorable (Martins et al, 2017;Bartsch, 2018). In the latter case, vegetative gametophytes are considered to be dormant and may act as a "seed bank" allowing for the recovery of the population after a disturbance, e.g., storms or heat-waves (Edwards, 2000;Barradas et al, 2011).…”