I was diving on mud a few weeks ago (yes, I know its a bit odd....) in north Cardigan Bay in Wales to find lots and lots of these worms. Vis was a staggering 2m max and depth ~14m I think. It is a hesionid called Ophiodromus flexuosus but having never seen them before I was surprised to see so many - there must have been thousands in the area all crawling around on the surface of the mud with just a few burrowing into it. What I would like to know is why there were so many, could this be a breeding aggregation or something?
It is a handsome brute!
Alex
Handsome indeed! Downright stunning, and I'd love to see pics of the aggregation if you took some. I've read that these groups occur and have looked for more information but haven't found anything definite. Sex is one possible reason, an abundance of food is another, or an unusually successful settlement of larvae (coincident with good food supply & lack of predators). Some studies that shown that O. flexosus is far more tolerant of pollution & low oxygen levels that other species & will accumulate in large numbers in such areas.
Scott Geitler documented a similar mass occurence of another hesionid - possibly Ophiodromus - from Bali -
Would love to have taken pix of more of them but the vis. was absolutely awful, ~2m max and dull light too. There isn't much mud in the area we were diving and what we were on could really be termed muddy sand - lots of burrows so stable enough - and I'm pretty certain that oxygen levels were ok because hermit crabs and the odd fish were fine. Its also a low pollution area with little industry and just a small amount of agricultural run off if anything. Unusually sunny late spring may have had something to do with it but the sizes of the worms ranged from ~1cm up to at least 5~6cm so I'd guess there it was a variable age group.
So we're back to the basic answer of "don't know".
We know so little about what's in the sea.... It's a tragedy that we seem determined to kill off so much of it.
