Phytoplankton responses to changing temperature and nutrient availability are consistent across the tropical and subtropical Atlantic

Abstract

Temperature and nutrient supply interactively control phytoplankton growth and productivity, yet the role of these drivers together still has not been determined experimentally over large spatial scales in the oligotrophic ocean. We conducted four microcosm experiments in the tropical and subtropical Atlantic (29°N-27°S) in which surface plankton assemblages were exposed to all combinations of three temperatures (in situ, 3 °C warming and 3 °C cooling) and two nutrient treatments (unamended and enrichment with nitrogen and phosphorus). We found that chlorophyll a concentration and the biomass of picophytoplankton consistently increase in response to nutrient addition, whereas changes in temperature have a smaller and more variable effect. Nutrient enrichment leads to increased picoeukaryote abundance, depressed Prochlorococcus abundance, and increased contribution of small nanophytoplankton to total biomass. Warming and nutrient addition synergistically stimulate light-harvesting capacity, and accordingly the largest biomass response is observed in the warmed, nutrient-enriched treatment at the warmest and least oligotrophic location (12.7°N). While moderate nutrient increases have a much larger impact than varying temperature upon the growth and community structure of tropical phytoplankton, ocean warming may increase their ability to exploit events of enhanced nutrient availability.

Gymnodinium catenatum paralytic shellfish toxin production and photobiological responses under marine heat waves

“…Upon exposure to an environmental stressor -e.g., nutrient limitation -phytoplankton species appear to change the number and size of the photosystems involved in photosynthesis, a typical compensatory feedback mechanism that allow cells to maintain the PSII quantum e ciency [20,24]. Additionally, [7] showed that Fv/Fm ratios along different latitudes (~ 30 ° N to ~ 30° S) do not present clear trends and are independent of nutrient limitation and temperature, suggesting that similar processes could possibly be occurring in the cultures used in the present study.…”

“…Usually, higher temperatures tend to increase metabolic rate [20], promoting cell division and leading to higher cell concentrations. However, there is growing evidence that such responses are very dependent on latitude and nutrient availability [7,20]. Previous literature on G. catenatum exposed to different temperatures in laboratory conditions indicated that the optimal temperature for this species was between 20 and 30°C [14,15], depending on the site of origin of the strains.…”

“…Alongside the increasing frequency and severity of MHWs, there is an increased potential for more frequent outbreaks of algal blooms. Indeed, temperature uctuations may be one of the main drivers in phytoplankton species composition and abundance [6,7].…”

Spatio-temporal assessment of the impacts of the trends in physical and biogeochemical parameters on the primary production of the Gulf of Guinea

“…This has led to an increased thermal gradient between the surface water and the layer below which is expected to cause a reduction of nutrients supplied to the surface layer where primary production is predominant [ 11 ]. Similarly, studies have found that increasing SST has been implicated in the observed decline of oceanic phytoplankton biomass and other biological effect on plankton metabolic rates [ 12 , 13 ]. This has consequently reduced the climate regulating role of the global ocean through CO 2 capture by photosynthetic phytoplankton [ 14 ].…”

Seasonal Indian Ocean primary productivity and key drivers

“…The rapid warming in the tropical Indian Ocean (0.15°C/dec) directly affects PP, and acidi cation is putting calcifying plankton and marine life under a great threat (Krishnan et al, 2020;Nagelkerken and Connell, 2015). Recent studies suggest that tropical and subtropical ocean warming highly reduces phytoplankton growth in nutrient-limited regions (Fernández-González et al, 2022;Gittings et al, 2018). The rising ocean temperature can affect the intracellular transport process, pathway, and enzymatic turnover rates, and play an essential role in regulating phytoplankton life cycle and physiology (Jabre et al, 2021).…”