Phytoplankton Trend Responce to Anthropogenic Influence. Nature. 2022-06-26. Jorma Jyrkkanen

and cmbustioon Future phytoplankton diversity in a changing climate. My Zoologist Friend in California says there has been a 40% decline in the oceans of phytpankton and starved baleen whales are washing up on shores.I have made a tentative link between this and combustion increase in decline of atmospheric oxygen Download PDF Article Open Access Published: 10 September 2021 Future phytoplankton diversity in a changing climate Stephanie A. Henson, B. B. Cael, Stephanie R. Allen & Stephanie Dutkiewicz Nature Communications volume 12, Article number: 5372 (2021) Cite this article 9038 Accesses 8 Citations 48 Altmetric Metrics details Abstract The future response of marine ecosystem diversity to continued anthropogenic forcing is poorly constrained. Phytoplankton are a diverse set of organisms that form the base of the marine ecosystem. Currently, ocean biogeochemistry and ecosystem models used for climate change projections typically include only 2−3 phytoplankton types and are, therefore, too simple to adequately assess the potential for changes in plankton community structure. Here, we analyse a complex ecosystem model with 35 phytoplankton types to evaluate the changes in phytoplankton community composition, turnover and size structure over the 21st century. We find that the rate of turnover in the phytoplankton community becomes faster during this century, that is, the community structure becomes increasingly unstable in response to climate change. Combined with alterations to phytoplankton diversity, our results imply a loss of ecological resilience with likely knock-on effects on the productivity and functioning of the marine environment. Introduction The socio-economic services provided by marine ecosystems are critical to human wellbeing. For example, fisheries provide almost half of Earth’s population with at least 20% of their animal protein intake1. Marine ecosystems also regulate Earth’s climate by absorbing and sequestering atmospheric CO2. Therefore, maintaining biodiversity is critical to providing resilience against future climate change and extremes2. At a global scale, biodiversity loss is being driven by human activities3,4, although clear trends of biodiversity decline in local ecosystems have proven difficult to identify5,6,7. Rather, the dominant species appear to be rapidly turned over, resulting in widespread reorganisation of ecosystems. These changes are potentially even more pronounced in the oceans than in the terrestrial realm8. In addition to human pressures on habitat, anthropogenic climate change is likely to drive biodiversity loss and hence decrease ecosystem stability2,9, thus affecting both the functioning and structure of marine ecosystems10,11,12. Ocean warming and alterations to nutrient supply via changing circulation or stratification, combined with additional stressors such as ocean acidification and deoxygenation, are likely to force community reorganisation. Predicting future changes to marine ecosystems is challenging, partly due to the relative paucity of consistent, repeated sampling, the inherent variability over daily to interannual scales in community composition13,14, and the lack of knowledge of how future climate change and other anthropogenic stressors may combine to alter biodiversity15. However, with future oceans predicted to be ~ 2−4 °C warmer, more acidic, and reduced in oxygen concentration16, species must adapt, migrate to regions of analogous conditions, or face extinction17,18,19. The expected resulting changes to biodiversity are likely to affect fundamental ecosystem functioning and processes, such as biomass production and maintaining water quality20,21,22, as well as the entire marine ecosystem structure, with consequences for the ocean’s capacity for food production and climate regulation23. As the base of the marine food web, phytoplankton play a fundamental role in setting the productivity of the entire marine ecosystem. Specific phytoplankton groups also play key roles in the biogeochemical functioning of the ocean; for example, by fixing atmospheric nitrogen (diazotrophs) or silica cycling (diatoms). Additionally, the size structure of the community affects trophic interactions, food web productivity, and carbon sequestration potential24,25,26. Here, we explore how phytoplankton diversity responds to a high emissions climate change scenario, similar to RCP8.527,28, using a marine ecosystem model with 35 phytoplankton types and 16 zooplankton size classes29,30,31, which are able to reorganise in response to changing oceanic conditions (see “Methods”). This model thus provides a more mechanistic representation of phytoplankton community structure than correlative or niche modelling approaches32,33,34, and greater realism than Earth System Models (ESMs) used for IPCC projections35,36.

Niche models and correlative approaches, by necessity, assume that the contemporary relationships between environmental conditions and phytoplankton abundance or diversity will remain the same in the future. These approaches do not have a mechanistic basis, and so changes in phytoplankton diversity driven by factors other than those included in the analysis (such as temperature, latitude, etc.), or conditions outside the bounds of variability in the contemporary ocean, cannot be reliably deduced. ESMs typically employ a very simplified ecosystem model, usually incorporating only 2 or 3 phytoplankton types. These models thus capture only a very limited diversity of phytoplankton communities. ESM results have focused on the response of phytoplankton to changing nutrient supply via changing stratification and circulation, which favours small species with high nutrient affinity37,38. However, in reality, phytoplankton respond to other factors which may result in changes to their relative competitiveness, or ultimately niche loss. Here, we use a complex ecosystem model with multiple functional groups of phytoplankton and several size classes of both phytoplankton and zooplankton types. Diversity in the model is set by several different mechanisms: the ratio of the supply rate of different limiting nutrients, the supply rate of limiting nutrients, grazing pressure, and transport/mixing39. Previous analysis of the modelled diversity has demonstrated that the combination of limiting nutrient supply and grazing controls the number of size classes that co-exist, and the ratio of supply rates of limiting resources contributes to setting the number of co-existing functional groups39. Transport and mixing tend to increase local diversity31. Although this model incorporates considerably more complexity than climate models, nevertheless it can only capture a fraction of the huge diversity of phytoplankton in the real ocean. Specifically, we capture diversity within biogeochemical functional groups (for example, diatoms, diazotrophs, etc.) and size classes (Extended Data Fig. 1). However, we do not capture the diversity that arises due to other traits, such as thermal norms, morphology, or colony formation39. Thus, in this study, the terms ‘richness’ and ‘diversity’ reflect functional richness and diversity, and should be understood in the context of these two important trait axes within the many different axes that set biodiversity in the real ocean. In this study, we quantify the response of marine phytoplankton diversity to climate change, focusing on future projections of community composition and turnover. We apply a high emissions climate scenario to a complex marine ecosystem model to explore the global and regional changes in phytoplankton community composition.