DNA and microscopes reveal changing plankton off Plymouth
A peer-reviewed study combined decades of microscope observations with environmental DNA samples from the western English Channel. The methods tracked similar changes in common crustacean plankton, while DNA distinguished seabed animals’ larvae in greater detail. Their complementary views help describe a changing food web at a long-running station off Plymouth.
Science··Evening
Two views from one station
Long-term observations off Plymouth, a city in southwest England, reveal changes in plankton through two complementary methods. The peer-reviewed Communications Biology study combines microscope observations from 1988 to 2022 with environmental deoxyribonucleic acid, or eDNA, sampled from 2012 to 2022. At station L4 in the western English Channel, the comparison includes 415 concurrently collected samples. The longer microscope series spans 35 years; the DNA series covers eleven.[1]
Agreement and added detail
For widespread crustacean plankton and jelly-like predators, changes through time largely agreed between the two approaches. The approaches agreed less closely for larvae that drift temporarily before developing into seabed-dwelling adults. DNA nevertheless identified these groups more precisely. Genetic signals indicated an increasing relative contribution from larvae whose adults live in soft sediments. Microscope observations associated stratified water with a growing presence of animals that filter fine particles. Several copepod groups declined.[1]
Different samples of a changing sea
Nets collect organisms through the water column for microscope counts, whereas surface-water DNA samples measure relative genetic signals. A share of genetic sequences does not directly specify how many organisms are present or their biomass. The authors link the observed shifts to a possible changing food supply, including smaller phytoplankton and reduced nutrients. Their observational analyses did not identify temperature alone as a simple direct cause of larval increases. Currents can also transport larvae and DNA beyond the location of adult populations.[1]
