Shore Walk 11 August 2010

August 18th, 2010
broad clawed porcelain crab
a broad clawed porcelain crab in the palm of a hand

Thanks to everyone who turned up to brave a rather windy Roa Island.  Unfortunately the wind made it difficult to see into pools and the sea at the shore line, and the sky was overcast meaning little light for photography.  However it didn’t rain (much) and I think everyone had an interesting time looking for critters with the tide out so far.   I was really happy to see the two species of porcelain crab – broad clawed Porcellana platycheles and long clawed Pisidia longicornis – as these have been recorded here before and I have been looking for them at Roa without success.  Unfortunately I left my survey sheets in the car at the car share point, but I think it was probably more enjoyable as an informal event anyway; if anyone has any lists/records of what they saw it would be really useful to have a copy to compare with past data. 

hermit crab
A hermit crab sizes up a potential new home. It has a firm grip on this new shell, but does it already have an occupant?

The oldest data we have for Roa Island is a survey by Clare & Jones from 1968 and exercises like this walk highlight the rapidly changing landscape of scientific knowledge and naming of species.  For instance, one find I have made preparing for the shore walk was the strawberry anenome Actinia fragacea; this species does not appear on the Clare & Jones survey, so is it a new species for this area?  The  answer is that we can’t tell – in 1968 the strawberry anenome was widely regarded as a colour form of the beadlet anenome Actinia equina, which does appear on the Clare & Jones list and so it could easily have been present.  Despite having some excellent baseline data we have to be very careful how we compare our findings today back to it.

A sponge is stranded on the shore at low tide

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