Becky Hitchin turns her gaze to the unsung heroes of the marine world , inviting us all to a plankton party
BECKYHITCHIN
The drifters
Becky Hitchin turns her gaze to the unsung heroes of the marine world , inviting us all to a plankton party
This month , we ’ re going to look at something you ’ ll ( almost ) never see when diving , but is guaranteed to surround you every time you get in the water . We ’ re talking about plankton , in all its myriad forms . The plankton surrounding us when we dive is a wonderland of species that drift around in water currents , either floating passively in the water or actively swimming . Plankton are at the base of all the marine food chains around the UK , meaning they are critical in maintaining and supporting all the marine and freshwater food webs with all the species we love watching and photographing . Without plankton , entire food webs around the world would likely collapse .
Phytoplankton are plants , containing chlorophyll and needing sunlight and nutrients to grow . They photosynthesise and convert carbon dioxide to oxygen and amazingly are responsible for up to half of the oxygen we breathe . Zooplankton , on the other hand , are small – or very small – animals . Some of these animals spend their entire lives in the plankton , while others are only in the plankton as larvae . Zooplankton includes animals such as copepods , and the larval stages of so many things – including worms , molluscs , barnacles , crabs and lobsters and echinoderms .
The body forms they take in the plankton are marvellous and miraculous , including iridescent lights strobing along tentacles and pseudopodia , radial symmetry , bilateral symmetry , long trailing antennae , shapes you ’ ve not seen anywhere else in the marine world .
The phytoplankton are eaten by small zooplankton , which are in turn eaten by other zooplankton , small fish and crustaceans . These are then eaten by larger predators , and so on up the food web . There are also some large animals that directly eat plankton . Blue whales , for example , can eat up to 4.5 tons of krill every day .
However , as you are probably expecting , plankton has been affected by change in ocean temperature and ocean acidification . Abundance has been decreasing , something we know because we have a long record of plankton abundance thanks , not least , to regional-scale offshore plankton monitoring provided by the Continuous Plankton Recorder ( CPR ) survey run by the Plymouth Marine Laboratory , which has been using volunteer commercial and research vessels to collect a consistent plankton time-series since 1958 .
Recent monitoring analysis shows that plankton has undergone multi-decadal , whole-region-scale change over the North- West European shelf . CPR data revealed a big increase in the amount of larvae in the plankton , with the last decadal mean over twice as high than the beginning of the time-series in 1950s . Abundance of full-time plankton , on the other hand , is decreasing hugely , with the last decadal mean approximately half that of the beginning of the time-series . These changes are consistent throughout the North Sea and most of the Celtic Seas .
These changes can be seen to correlate with sea surface temperature , providing strong evidence that the increase in larvae in the plankton is driven by climatic and oceanographic change . Over smaller spatial scales , the increasing trends in amount and types of larval plankton is shown to be largely driven by an increase in echinoderm and decapod larvae . How interesting is that , when bivalve larvae are showing decreases over the same time periods .
So next time you go diving , remember all those millions and millions of tiny plants and animals invisibly swimming and floating around you . Providing our oxygen and keeping our planet in balance . �
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