Abstract
Marine ecosystems are changing rapidly as the oceans warm and become more acidic. The physical factors and the changes to ocean chemistry that they drive can all be measured with great precision. Changes in the biological composition of communities in different ocean regions are far more challenging to measure because most biological monitoring methods focus on a limited taxonomic or size range. Environmental DNA (eDNA) analysis has the potential to solve this problem in biological oceanography, as it is capable of identifying a huge phylogenetic range of organisms to species level. Here we develop and apply a novel multi-gene molecular toolkit to eDNA isolated from bulk plankton samples collected over a five-year period from a single site. This temporal scale and level of detail is unprecedented in eDNA studies. We identified consistent seasonal assemblages of zooplankton species, which demonstrates the ability of our toolkit to audit community composition. We were also able to detect clear departures from the regular seasonal patterns that occurred during an extreme marine heatwave. The integration of eDNA analyses with existing biotic and abiotic surveys delivers a powerful new long-term approach to monitoring the health of our world’s oceans in the context of a rapidly changing climate.
Highlights
Changes in ocean temperatures, chemistry and currents are occurring faster than at any time in human history [1, 2]
We show that Environmental DNA (eDNA) metabarcoding is capable of responding to this challenge
Our study included two ‘marine heatwave’ periods and these data demonstrated that, using an effective eDNA metabarcoding toolkit, ecologically significant trends can be identified in response to a known environmental perturbation
Summary
Chemistry and currents are occurring faster than at any time in human history [1, 2] These changes will certainly impact the productivity in marine environments that is critical for social and economic wellbeing [3]. Zooplankton are the trophic link between phytoplankton and larger predators [8]. These highly diverse communities have been described as ‘beacons of change’ [9], as their community composition is known to respond to fluctuations in both abiotic and biotic factors [5, 9, 10]. Many species are fast growing and short-lived and so communities typically respond rapidly to changes in environmental conditions [5, 9,10,11]
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