Opisthobranchs as bio-indicator species

February 8, 2006
From: Kira Alleyne

How is it that opisthobranchs are a bio-indicator species? I am currently doing research on the opisthobranchs of Barbados since the last study was in 1974 and am finding difficulty locating any. I have only been able at the moment (after sampling two locations) to find three specimens; Discodoris evelinae, Elysia crispata and Dendrodoris krebsii. I still have six more locations to sample.

Kira Alleyne


Alleyne, K., 2006 (Feb 8) Opisthobranchs as bio-indicator species. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/15732

Dear Kira,
I'm not quite sure what question you want answered. Firstly, what research are you doing? Are you just having a look for opisthobranchs or are you interested in some aspect of the biology or ecology of one or more species? Hopefully the era where people 'do a locality' and write a paper on what they found, is almost over, as without  a broader understanding of the biology and variability of individual species, such papers often cause their own problems for future workers.

If you are asking about bio-indicator species as a comment on lack of abundance - For example 'Why would you use an uncommon animal as an indicator species?" Then you may have a point. But your question raises other areas of discussion as well.

Since miners took canaries down coal mines in the 19th century to indicate when poisonous gases were about - [when the canary fell off its perch and died the miners ran] -  we have been looking for other animals to give us early warnings about impending disasters. Bio-indicators - as they are known - became a popular tool for researchers justifying the usefulness of their research when applying for grant funds. In desperation - I guess - they think politicians and bureacrats would think it valuable to have bio-indicators for pollution, global warming etc etc. While I sympathise with the problems of grant applicants, I can't say there are many true examples of what could be called a 'bio-indicator'. I certainly don't know of any opisthobranch that is truthfully a bio-indicator - though I am open to suggestions.

Now to your problem of a shortage of opisthobranchs in the Barbados. Opisthobranchs, especially in the tropics, are notoriously unreliable. While in cool temperate waters you can usually find a group of 'old faithfuls', in warmer waters this is not necessarily so. Many species have planktotrophic larvae, so their presence as benthic adults at any one place is dependent on the vagaries of the currents and the health of microscopic planktonic larvae. Their presence also depends on similar uncertainties in the life cycle of their food organism, be it plant, sponge, ascidian, hydroid etc etc which may also be dependent on a planktonic larval stage. When you think about it, it is amazing that sometimes everything clicks, the food organism passes through its larval stages and settles and grows to a suitable size to enable its prey nudibranch larvae to find it, to settle, to grow to maturity and then find a mate to start the cycle over again.

If you search for caribbean in the Forum you will find quite a diversity of species are found in the region. Unfortunately, apart from a few, we know very little about their abundance and natural history. I am afraid most studies of the fauna have been done during short stays by  visiting scientists during university holidays. Not to say that such studies aren't valuable, but you take a risk in hoping to find an abundance of animals at a particular time. Also to progress past the 'what I collected on my holidays research' we need some permanent residents to study populations in depth.
Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Feb 8). Comment on Opisthobranchs as bio-indicator species by Kira Alleyne. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/15732

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