Lifeform indicators reveal large‐scale shifts in plankton across the North‐West European shelf

Abstract

Increasing direct human pressures on the marine environment, coupled with climatedriven 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 regionalscale 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. K E Y W O R D S climate change, food webs, functional groups, indicators, pelagic, time-series BEDFORD Et al. | 3483 | INTRODUC TI ONPlankton provide primary and secondary productivity that fuel marine food webs. Plankton communities therefore form a key part of marine natural capital, supporting globally important ecosystem services that

Increasing picocyanobacteria success in shelf waters contributes to long‐term food web degradation

“…Based on an extensive network of time series, Bedford et al. (2020) show that this long‐term copepod decline extends from inshore to offshore areas right across the NW European shelf. Our study spans an even larger area and by detailing the species composition and seasonal timing of the copepod decline, we shed light on the potential causes.…”

The Plankton Lifeform Extraction Tool: a digital tool to increase the discoverability and usability of plankton time-series data

“…Zooplankton taxa which spend their entire life cycle in the plankton Changes in relative abundance provide an indicator of change in pelagic-benthic food web structure (Bedford et al, 2020a;Kirby et al, 2008).…”

“…Interannual trends in lifeform abundance can be related to changes in pressures within the marine system (Bedford et al, 2020a;. Given the strong seasonal variability, summarizing plankton abundance to compare across years is non-trivial.…”

“…Globally, plankton communities are undergoing significant changes in distribution (Reid et al, 2016), community composition (Beaugrand et al, 2002), phenology (Edwards and , and productivity (Kulk et al, 2020). These changes vary in space and time, reflecting both direct and locally acute anthropogenic pressure on the marine environment, such as nutrient loading, and wider-scale climate-driven changes in ocean chemistry and temperature (Beaugrand et al, 2010;Bedford et al, 2020a).…”

“…Furthermore, European plankton surveys employ different sampling methods, enumerate specimens at a variety of taxonomic levels, and employ different counting regimes (Raybaud et al, 2011). These methodological differences and the lack of direct comparability between datasets has meant that the tools to use all available datasets together to produce a comprehensive assessment have only recently been developed (Bedford et al, 2020a;. While most datasets are regularly submitted to appropriate data repositories (e.g.…”