Abstract
Increasing direct human pressures on the marine environment, coupled with climate-driven changes, is a concern to marine ecosystems globally. This requires the development and monitoring of ecosystem indicators for effective management and adaptation planning. Plankton lifeforms (broad functional groups) are sensitive indicators of marine environmental change and can provide a simplified view of plankton biodiversity, building an understanding of change in lower trophic levels. Here, we visualize regional-scale multi-decadal trends in six key plankton lifeforms as well as their correlative relationships with sea surface temperature (SST). For the first time, we collate trends across multiple disparate surveys, comparing the spatially and temporally extensive Continuous Plankton Recorder (CPR) survey (offshore) with multiple long-term fixed station-based time-series (inshore) from around the UK coastline. These analyses of plankton lifeforms showed profound long-term changes, which were coherent across large spatial scales. For example, 'diatom' and 'meroplankton' lifeforms showed strong alignment between surveys and coherent regional-scale trends, with the 1998-2017 decadal average abundance of meroplankton being 2.3 times that of 1958-1967 for CPR samples in the North Sea. This major, shelf-wide increase in meroplankton correlated with increasing SSTs, and contrasted with a general decrease in holoplankton (dominated by small copepods), indicating a changing balance of benthic and pelagic fauna. Likewise, inshore-offshore gradients in dinoflagellate trends, with contemporary increases inshore contrasting with multi-decadal decreases offshore (approx. 75% lower decadal mean abundance), urgently require the identification of causal mechanisms. Our lifeform approach allows the collation of many different data types and time-series across the NW European shelf, providing a crucial evidence base for informing ecosystem-based management, and the development of regional adaptation plans.
Highlights
Plankton provide primary and secondary productivity that fuel marine food webs
By understanding lifeform indicator dynamics over both large temporal and spatial scales, we provide a holistic overview of trends in the plankton assemblage
As a result of mapping trends, and correlating them with sea surface temperature (SST), we have identified significant changes in plankton lifeforms
Summary
Plankton provide primary and secondary productivity that fuel marine food webs. Plankton communities form a key part of marine natural capital, supporting globally important ecosystem services that include fish production and carbon sequestration (Beaugrand, Brander, Lindley, Souissi, & Reid, 2003; Canu et al, 2015). To maximize the utility of the plankton lifeform approach for informing the management of marine ecosystems, changes in the abundance of lifeforms need to be attributed to drivers of change These drivers may include ‘directly manageable’ anthropogenic pressures (such as eutrophication caused by nutrient loading) as well as larger-scale and longer-term changes in climate and oceanography (Bedford, Johns, Greenstreet, & McQuatters-Gollop, 2018). Comparison between surveys can highlight synergies between long- and short-term datasets, and increase the robustness of the attribution of drivers of change in shorter time-series This temporal comparison builds understanding as to whether the direction of shorter-term coastal trends are part of a longer-term, multi-decadal signal, or whether they are deviating from the long-term trend in abundance, reflecting the influence of local drivers. As plankton occupy the base of the food web, this information is critical for informing effective policy decisions and climate change adaptation measures into the future
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