There ’ s a lot more to marine life classification than dividing it all into ‘ wrasse ’ or ‘ squidge ’. Becky Hitchin explains
BECKYHITCHIN
Diversity : The i-d parade
There ’ s a lot more to marine life classification than dividing it all into ‘ wrasse ’ or ‘ squidge ’. Becky Hitchin explains
As most people who read this know , identifying small critters under the water can be difficult . I say difficult , I mean frustrating , annoying , depressing – and occasionally jubilation when you actually get one right . And just when you think you ’ ve got to grips with one particular favourite plant or animal , you can guarantee it ’ ll turn up in a different colour , on a different food , and you have to rethink everything you know .
There ’ s an important thing to know every time you get frustrated . It ’ s not ( always ) you . Sometimes of course , it is you . There are many reasons why identification is difficult . These include divers ’ innate abilities to spot interesting creatures as bycatch in downloaded photographs of large bits of metal festooned in kelp , and simple inability ( normally in my case at least ) to focus on what you actually need in focus rather than the broken shell debris before or after the important never-seen-before nudibranch .
But , sometimes , the critters are simply out to get you . Or , to speak more scientifically , there are a number of ecological or morphological reasons why identification of underwater plants , animals and everything else can be challenging .
1 . Identification features can present seasonally . So , you have to dive at the right time to be able to see some of the features noted in identification guides . Sea cucumbers are particularly known for this . Populations of Neopentadactyla mixta , the gravel sea cucumber , have been seen to withdraw further into the sediment between 1 or 4 hours after sunrise and remain in the substratum for one or two hours , re-emerging over a period of up to four hours . In September / October the entire population withdraws into the substratum and re-emerges in March / April .
Similar things happen in Scotland with populations of Psolus phantapus , the red spotted sea cucumber . One day , a piece of a sea loch seabed in springtime will suddenly sprout these colourful sea cucumbers . They ’ ll be there for a month or two , then vanish . Bizarrely , 100 metres down or up the sea loch , there won ’ t be a single one all year . Many colonial sea squirts instead
24 regress during the autumn / winter , which makes them look like amorphous bobs of jelly instead of blobs of jelly with interesting features such as siphons . The majority of the identification features are lost when this happens , even when specimens are taken .
2 . There can be a wide range of morphologies per critter . Particularly if you ’ re a sponge . This isn ’ t just a problem for most divers and shore searchers , but professional monitoring programmes too . Let ’ s look at how some sponges are described . Using descriptions from habitas . com , Haliclona simulans is described as “ very polymorphic , it may grow as a thin sheet or cushion or as a branching-repent or branchingerect colony ”, Amphilectus fucorum , the shredded carrot sponge , as a “ bright orange sponge that is extremely polymorphic and fast growing , changing shape in just a few weeks . It may be encrusting as thin sheets or cushions , massive lobose , with or without tassels , or branched ”. This provides increased risk of misidentifying a taxon if someone expects an organism to have a particular morphology .
It ’ s not only morphologies , it ’ s colour too . Colour of sponges can vary according to light regime , for example Halichondria panicea , the breadcrumb sponge , on the shore can become green when inhabited by photosynthetic algae . Pachymatisma johnstonia , elephant hide sponge , can be white instead of darkish grey in cave environments ( don ’ t go into caves to check this out unless you ’ re qualified !).
3 . Do you get the feeling that the marine environment is out to get you yet ? There can be convergence in morphology . Similar environmental stresses can cause convergent adaptation of different species . Growth forms of two very different species can adapt to almost similar shapes under influence of similar hydrodynamic forces . There can also be cryptic species . Think nudibranchs and their ever-changing taxonomy , and the increasing number of species being split out from the good old standard species found in the original Picton nudibranch bible .
But let ’ s go back to sponges and an example from a well-known Seasearcher , Claire Goodwin , who was involved in separating out some cryptic species in one of my favourite sponges , Cliona celata , a common sponge around the UK . They found clear incidence of hidden species and turned the one species we know and love into four . Now not only are there two morphs , but species hiding in plain sight . New headaches . And the annoying thing about hidden species is
PHOTO : SIMON ROGERSON
A wall on ‘ The Borroo ’, Isle of Man . How many invertebrates can you count , including anemones , hydroids , sponges , corals and bryozoans ?