Sea surface phytoplankton community response to nutrient and light changes

Abstract

The sea surface microlayer (SML) is the boundary layer between the ocean and the atmosphere and plays a unique role in marine biogeochemistry. Phytoplankton communities in this uppermost surface layer are exposed to extreme ultraviolet (UV) radiation and potentially high nutrient supplies. In order to understand the response of SML communities to such contrasting conditions, we conducted experiments at three different sites, the North Sea (open ocean) and two sites, outer and middle fjord, in the Sognefjord, Norway, with differing physical and chemical parameters. We manipulated light, nitrogen (N) and phosphorus (P) supply to natural communities collected from the SML and compared their response to that of the underlying water (ULW) communities at 1-m depth. Phytoplankton communities in both SML and ULW responded significantly to N addition, suggesting the upper 1-m surface phytoplankton communities were N-limited. While phytoplankton growth rates were higher with high N and high light supply, biomass yield was higher under low light conditions and with a combined N and P supply. Furthermore, biomass yield was generally higher in the ULW communities compared to SML communities. Nutrient and light effects on phytoplankton growth rates, particulate organic carbon (POC) and stoichiometry varied with geographical location. Phytoplankton growth rates in both SML and ULW at the open ocean station, the site with highest salinity, did not respond to light changes, whereas the communities in the middle fjord, characterized by high turbidity and low salinity, did experience light limitation. This work on the upper surface phytoplankton communities provides new insights into possible effects of coastal darkening and increases understanding of oceanic biogeochemical cycling.

Eco-Biology of Photosynthetic Picoeukaryotes in a Monsoon Influenced Tropical Bay: A Flow Cytometric and Chemotaxonomic Approach

“…In our study, the PPEUK biomass dominance by the Picocryptophytes during the MON could be explained by their ability to sustain adverse and light-limited environments as they possess physiological adaptations such as the green lightharvesting phycobiliproteins and photoacclimation [50], as corroborated by the negative and positive correlation with the SD depth and the total chl-a, respectively. A higher biomass yield and a lower growth rate under the low light condition for phytoplankton have been shown with N and P additions [51]. In our study, the positive correlation of its abundance with NH during the PrM could suggest its capability to utilize all kinds of inorganic nutrients.…”

The Role of Extracellular Carbonic Anhydrase in Biogeochemical Cycling: Recent Advances and Climate Change Responses

“…Besides, earlier studies [ 93 , 94 ] have described that the SML is dominated by diatom, cryptophytes, and dinoflagellates species. Indeed, various species of dinoflagellates and diatom are reported to express eCA [ 18 , 76 , 95 ].…”

“…Because of the unique location of the SML between the ocean and atmosphere, the communities in this layer are likely to be the first to be exposed to climate-related changes. For instance, previous studies have shown that light limitation affects growth rates and biomass in SML communities [ 95 ], and high nutrient loads changed the density and composition of SML communities [ 113 ]. Incomplete understanding of the C i acquisition strategy in the SML community’s response to future climate change leads to difficultly in predicting the global chemical enhancement of CO 2 and biogeochemical cycling by eCA.…”

Optical properties of dissolved organic matter along a salinity gradient from a boreal river estuary to open coastal waters.

“…Yet, for Norwegian coastal waters, peak spring phytoplankton bloom has been delayed by 22 days over the past century, which was attributed to coastal darkening (Opdal et al, 2019;Opdal et al, 2023). Mustaffa et al (2020) studied the relationship between light intensity and phytoplankton growth rates in the Sognefjord at the Norwegian west coast, impacted by freshwater inputs from several rivers. They found that increased light intensity led to higher phytoplankton growth rates in the central and outer fjord, but with no effect on phytoplankton in the open ocean, where the impact of terrestrial DOM is marginal.…”