Marine Resource Issues
Sabellid Infestations of California's Aquaculture Facilities

From Kevin Ruck:

Perspective from South Africa

Dear all

Since the sabellid is native to South Africa, I suppose I can approach this topic without any bias.

I agree with Carrie that accurate information is important to clear up any misunderstandings. So I will share some observations that I have made in South Africa.

Firstly, I have studied the distribution of the sabellid around our coastline pretty intensively. Whether this information can be extrapolated to a californian situation is debatable, but I am sure some features will apply. My data show that the sabellid is present in quite a few gastropod species but only attains really high numbers in a few species (4-5). The other species do not have an inbuilt coevolved resistance, because when placed in aquariums with infested abalone most of them do acquire the infestation (although to a lesser extent). So my feeling is that the worm is limited to a large extent by physical factors such as intertidal height and wave action. It thrives in species that live gregariously (important for transmission) in sheltered areas. The mechanism of shell deposition may also be a limiting factor. Thus certain species are never at risk even though they inhabit the same geographical area as heavily infested species.

The dispersal phase is a crawling larva which can be waterborne when dislodged. In fact I have caught larvae at the outflow of abalone tanks. The mesh size which I used was 100um, 58um and 45um. The larvae got through 100um were caught by 58um and one or two ended up in 45um. I think it will be expensive to filter water effluent from a farm since a drum filter would be required for such volumes. A settlement reservoir would help to reduce load.

But since the populations appear to have established in the wild already, placing limitations on the farmers will only serve to delay the spread. My feeling is that it is already too late to shut the farm gate. In fact when the first few larvae were released it was already too late. Since the sabellids brood their young and the larvae crawl to the edge of the same and adjacent animals, the chances of juvenile survival are very high (K-selected).

Local species that exhibit high levels of infestation do not appear to be adversely affected. They are healthy, are growing and in fact only close examination will reveal that there is an infestation at all. Even then there are many individuals of susceptable species which show low levels of infestation and even zero infestation. Again this points to dispersal problems of the worm or perhaps a control agent.

So in conclusion MY OPINION is that there will only be a small range of gastropods that will be hard hit. Carrie has indicated that they are more vulnerable, possibly because of the lack of a history of co- evolving, but gastropods are pretty well adapted to repairing their shell against various invasives so hopefully they will cope with this unique method of shell invasion.

Regards
Kevin Ruck

Kevin Ruck
Department of Zoology,
University of Cape Town
Private Bag, Rondebosch
Cape Town, South Africa
Tel: 27-21-650 3632
Fax: 27-21-650 3301
email: KRUCK@botzoo.uct.ac.za
www:http://www.uct.ac.za/depts/zoology/abnet/index.html