Marine Resource Issues
Sabellid Infestations of California's Aquaculture Facilities

From Andrew Cohen:

Response to South African Perspective

Sender: abnet@uct.ac.za
From: Andy Cohen
To: norcadiver@sonic.net
Subject: [ABNET:375]
Date: Sun, 14 Sep 1997 08:38:29 +0200

We thank Mr. Kevin Ruck for further information, in his posting of September 12, about the abalone sabellid worm in South Africa. However, we are moved to quickly comment on his statement:

"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)."

In fact, we note that there are numerous examples of nonindigenous species that have been introduced and established reproducing populations in the wild, and then later gone extinct (with examples including introductions in terrestrial, freshwater and marine environments, in many parts of the world, and involving many different taxa). Many biocontrol insects, for example, have been released into the wild, only to become temporarily established on a highly localized basis and then die out. There are undoubtedly a much larger number of cases of organisms that were accidentally introduced, became temporarily established, and then disappeared without ever being observed or reported.

In San Francisco Bay known examples of temporary establishment followed by extinction include an Atlantic sponge, an Atlantic polychaete (a sabellarid) and several species of hydroids -- and, we now suspect, an exotic species of a nebaliid crustacean (a marsupial brooder) that was very abundant only a few years ago at two sites on the east Bay shore, and a ctenostome bryozoan that was abundant at one site on the western shore. Several species of introduced freshwater fish in California have reproduced for a time and then died out. The oyster drill (snail) Urosalpinx cinerea -- a species with crawl-away young from egg capsules -- and a well-known oyster pest on the American Atlantic coast, was evidently established in several American Pacific coast bays in which it is now extinct. In the Pacific Northwest, the Korean shrimp Palaemon macrodactylus appears to establish temporary reproducing populations and then becomes snuffed out, only to be reintroduced by subsequent ballast water discharges.

Further, it is our clear impression from our own work and our review of the literature that temporary-establishment-then-extinction is a far more common phenomenon with highly localized introductions (observed at only one or two sites) than with more widespread invasions. Thus, we conclude that it may by no means be too late to shut the farm gate, and indeed, based on the long history of biological invasions in terrestrial and aquatic ecosystems, there is good reason to close it immediately. This is because we have no way of determining whether the single known wild California population of the African sabellid will (a) persist, continue to reproduce and spread; (b) die out on its own; or (c) die out if we give it a little help, such as by removing as many infested and potential hosts from the area as we can. If we leave the gate open -- if we allow continued releases of the sabellid worm into the environment -- the likelihood of its permanent, irreversible establishment in Pacific waters can only be increased.

Andy Cohen
San Francisco Estuary Institute
acohen@sfei.org

Jim Carlton
Williams Collge -- Mystic Seaport
jcarlton@williams.edu

Andrew N. Cohen
San Francisco Estuary Institute
180 Richmond Field Station
1325 South 46th Street
Richmond, CA 94804 USA

phone: (510) 231-9423
fax: (510) 231-9414
email: acohen@sfei.org