Plankton on the move

The distribution of organisms globally is governed by the range of environmental conditions each organism can tolerate. For example, temperature is a key variable structuring the distribution of life on earth. Whereas some organisms have wide temperature tolerance, so can be found across a variety of latitudes all with differing temperatures, many organisms have narrow temperature tolerances, and so the range of areas they can live are more restricted. In the oceans, global climate change means that these boundaries between different temperatures are becoming ever more obscured. Areas of warming that were historically too cold for survival may now be habitable for species needing warmer water, but species with narrow temperature tolerances may be forced out as it becomes too warm for their survival. These ‘range shifts’ lead to a global reshuffling of the distribution and abundance of biodiversity, which has profound implications for environmental policy and conservation management.  For example, range shifts mean that our concepts of native vs not-native species are being tested i.e., which species are ‘meant’ to be in a certain area because they occur there naturally, and which ones aren’t., This distinction is important for detecting and managing any negative impacts of ‘newly occurring species as a result of climate change. Similarly, range shifts affect fisheries policy. As fish move into different areas, they will become potentially exploitable by commercial fisheries. This means that fisheries managers will need to assess whether any newly occurring species can be fished sustainably and set appropriate management measures. Understanding range shifts is also key for building resilience to climate change through effective policy, for example placing protected areas in areas that are relatively sheltered from the effects of climate change.

Plankton are a key example of range shifting taxa in the oceans. Due to the sensitivity of plankton to changes in their environment, the distribution of different plankton species is tightly coupled with environmental conditions. In the North Sea for example, there has been northward movement of key ‘isotherms’ (lines on a map connecting points of the same temperature), as the water warms due to climate change (Beaugrand et al. 2009). With these isotherm movements there has been an increase in warmer-water affiliated copepod species as they expand their range into warming waters, and a decrease in colder-water species, as their range moves northwards chasing colder refuge. Phytoplankton have also shown range shifts, but the extent to which phytoplankton track the moving isotherms differs between groups of species, contributing to community reshuffling (Chivers et al. 2017). There have been also been parallel shifts in the abundance and distribution of species higher up the food web including in commercial fish. As such range shifts in plankton are important indicators that climate change is impacting food-webs and ecosystem functioning.

Calanus helgolandicus, a warmer-water copepod, is replacing C. finmarchicus, a colder-water copepod, as the North Sea warms.

In July 2019 we presented trends in plankton distributions found from the Continuous Plankton Recorder survey at ‘Species on the Move’, a conference series on range shift science, this year held in South Africa. A particular focus of the conference series is on the implications of range shifts for policy and management. We illustrated how the monitoring of plankton indicators is key for meeting regional and global biodiversity targets. We also highlighted however, that distributional shifts are not often explicitly managed under many policy frameworks, and that the relevance of range shifts is not always clear to policy makers for their day-to-day decision making. It is therefore vital that scientists frame evidence on species range shifts in a policy-relevant way to ensure effective communication, ultimately facilitating the adaptive management of marine ecosystems under a changing climate.

Jake, Plankton and Policy

Read more:

Bedford, J., Johns, D., Greenstreet, S., & McQuatters-Gollop, A. (2018). Plankton as prevailing conditions: a surveillance role for plankton indicators within the Marine Strategy Framework Directive. Marine Policy. 89:109-115.

Plankton on the move: implications for global biodiversity goals

References:

Beaugrand G, Luczak C, Edwards M (2009) Rapid biogeographical plankton shifts in the North Atlantic Ocean. Global Change Biology 15:1790-1803

Chivers WJ, Walne AW, Hays GC (2017) Mismatch between marine plankton range movements and the velocity of climate change. Nature Communications 8:14434

About Abigail McQuatters-Gollop

Marine biologist, guitarist, cat lover, red wine drinker. I like plankton.
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