Becky Hitchin explains how quickly a well-intentioned intervention can impact on coastal marine habitats
BECKYHITCHIN
Uninvited guests
Becky Hitchin explains how quickly a well-intentioned intervention can impact on coastal marine habitats
Anyone who has dived in one country over a long period will have seen many changes to the underwater world . These changes are an inevitable part of ongoing evolution , something that occurs naturally without any assistance from humankind . Temperatures cycle , landmasses move , new seas are formed and evolve . But above and beyond these natural rhythms is anthropogenically-induced climate change , and this accentuates change and evolution of marine communities . Also humanbased is the introduction of non-native species and invasive species – non-native species that are thought to actively harm the ecosystems they are introduced into . This is the story of one of those species , the carpet sea squirt , Didemnum vexillum . Otherwise known as sea snot , sea vomit or pancake batter squirt , all fairly accurate descriptions of what it looks like . It took up several years of my life when I was working in Kent when the first intertidal invasion of the UK happened . Now , Didemnum vexillum , or D . vex , has an interesting history . It is thought to have originated in Japan , something that was only recently verified through DNA , and over the last 20 years or so , has invaded waters in Europe , North America and New Zealand . D . vex can grow on pretty much anything , including cobbles , boulders , and artificial structures such as boats , dock pilings , and aquaculture equipment . It grows over and kills everything in its way , whether that is mussels , oysters , hermit crab shells and even seaweeds . So how did it get over here ? Maybe not as easily as you ’ d expect . This is a tale not only of D . vex but another invasive species too . In 1969 , the French and Portuguese oyster stocks were largely killed off by a viral disease . To replace the stock , large quantities of Pacific oyster spat ( Magellona gigas ) were imported from Japan . Once oyster larvae permanently attach to a surface , they are known as spat . In the early 1970s , spat was also introduced into the Pacific regions of the USA and Canada from Japan . Soon after each introduction , reports were made of a brown colonial squirt invading the oyster beds . In 2008 , the same brown squirt was found in Holyhead Marina , North Wales , likely introduced on the hull of a vessel from Ireland or the Netherlands . Over the winter of 2009 , an eradication attempt was made by wrapping up all
“ Also known as sea snot , sea vomit or pancake batter squirt ” the marina chains and pontoon structures . Calcium hypochlorite , a bleaching agent , was added to bags to accelerate the process . Unfortunately , though it was thought that the D . vex was eradicated , all the freshly treated surfaces of the marina were rapidly recolonised . Around 2008 , a transfer of spat was made from Brittany to an oyster farm in Kent . A year later , both the seafloor and local
The ‘ pancake batter ’ appearance of nonnative Didemnum vexillum on lost fishing gear intertidal regions were covered in a slimy , tan-coloured squirt , which was quickly identified as D . vex . This was the first invasion intertidally in the UK . In 2009 , D . vex was confirmed for the first time in Scotland and has since expanded to sea Loch MPAs , where it is being monitored carefully . A recent study looked at the genetics of D . vex from all the invasions across the UK . This found high genetic connectivity between marinas situated on opposite sides of the Irish Sea with busy boat traffic between them . Strangford Lough showed high genetic connectivity to an aquaculture site in Kent . It ’ s thought that movement of oysters between Kent and Strangford Lough for aquaculture may explain the similarity . The moral of this vomit-ridden story ? There is one ocean , connected across the world , and we all spend a lot of time on its ports and harbours , in it , and under it . Our actions on any shore , on any interaction underwater , can have consequences that might far outreach our days diving . �
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