Marine Resource Issues
Sabellid Infestations of California's Aquaculture Facilities

From Carrie Culver:

General Information on Sabellid Worm

Sender: abnet@uct.ac.za
From: c_culver@lifesci.lscf.ucsb.edu (Carrie Culver)
To: norcadiver@sonic.net
Subject: [ABNET:372] General Info. on Sabellid Worm
X-Comment: Issues Relating to Abalone (Zoology)
Date: Fri, 12 Sep 1997 05:21:47 +0200

INTRODUCTION

We, Dr. Armand Kuris and Carrie Culver, have been working on the biology of the sabellid worm since 1994. We are sending out this email to supply general scientific information regarding the sabellid. This is necessary because some mis-information has been distributed and we know that accurate information is needed to evaluate the situation at hand. The areas we feel are most important include the role of water temperature, the issue of sabellid establishment in the wild and the potential impacts of the sabellid to our natives. We would be happy to provide information on other topics if brought to our attention. We also have several publications submitted and in press. They will be available within the next several months. Anyone interested in these publications is invited to email us for inclusion on our mailing list for distribution of these publications as they become available.

ROLE OF WATER TEMPERATURE

Some have claimed that most California waters are not suitable for the sabellid worm and/or that only southern California is at risk because ambient temperatures elsewhere are too low to permit the worms to reproduce. Unfortunately, this is decidedly not the case. The sabellid worm has been found in facilities ranging from Baja, California to Newport, Oregon. Infestations have spread within ALL of these facilities indicating that their ambient water temperatures are suitable for sabellid survival and reproduction. In fact, we have recorded new infestations in our laboratory studies at temperatures as low as 11.5 degrees centigrade (54 degrees Fahrenheit). However, water temperature does appear to be important in the RATE of infestation.

SABELLID ESTABLISHMENT IN CALIFORNIA WATERS

We have been conducting research in the intertidal region around one onshore facility to determine whether sabellids have become established in California. The following is a summary of the supporting evidence which indicates that there is an established population at Cayucos These results were provided to the Abalone Sabellid Worm Advisory Committee as they became available.

1. Our surveys below the aquaculture facility discharge targeted an intertidal snail species rarely found in the culture facility (Tegula funebralis). Up to 25% of the snails in these samples had sabellids.
2. To show conclusively that infestations were occurring in the wild, and were not the result of animals being infested within the facility and then discharged out with the facility water, a mark & recapture study (where uninfested sentinel snails are marked with paint and then released into an area around the facility discharge) was conducted. In this study 8% of the marked snails had new infestations after two weeks and by the end of the study, (2 months after release), 16% of the snails had new infestations. THUS, INFESTATIONS WERE CERTAINLY OCCURRING OUTSIDE OF THE FACILITY. These infestation rates on our sentinel snails indicate a very high rate of transmission in nature at this site because the sentinel snail species is very abundant; 100,000s live in the intertidal zone at this site.
3. A second mark and recapture study was then conducted. Prior to placing these marked snails in the environment, observable shell debris was removed from the sampling area and a screen installed at the facility to eliminate discharge of infested animals and debris into the environment. Results from this 2 1/2 month experiment were similar to the first, although prevalences were slightly lower (4% at the start; 8% at the last sampling). THESE FINDINGS SUPPORT THE CONCLUSION THAT A SABELLID POPULATION IS ESTABLISHED at this intertidal site; actively reproducing adults were found and sustained a substantial level of local recruitment.
4. Sabellid larvae are benthic (a bottom crawling form), however they can become free floating in the water column if dislodged with aeration or when tanks are flushed. Thus, although installation of screens eliminated release of the substantial numbers of adult sabellids that previously came from the discharge, it is unclear whether larval release in discharge water could sustain the thousands of infested snails in the habitat below.

To determine whether larval release could have been responsible for the new infestations found in our second mark & recapture experiment, we took water samples at the discharge site. A few larvae were found at the first sampling. On the other 3 sampling dates we did not detect any larvae in the discharge water. This strongly suggests that the very few larvae in the discharge water could contribute little if anything to the new infestations seen in our experiment. This supports our conclusion that this population is established and likely self-sustaining. Further, it shows that the screening of discharge water is an inexpensive and highly effective method of risk reduction. Further argument that the sabellid is not established at this site leads inexorably to the conclusion that screening of just debris is inadequate and that the facility continues to badly contaminate the environment. We emphatically believe that our experiments have demonstrated that this is not so.

IMPACTS TO GASTROPODS: CALIFORNIA VS. SOUTH AFRICA

The sabellid worm is native to South Africa and infests many different gastropods (snails and limpets). Interestingly, shell deposition of infested South African species does not appear to be as heavily impacted as our California species at similar worm intensities. Because the sabellid has been interacting with South African species for so long, it is likely the gastropods have acquired certain adaptations (coevolution) which minimize impacts to growth.

Unfortunately for our California natives, no similar sabellid species exists in our waters. Thus, as witnessed in the abalone aquaculture facilities, our natives become heavily impacted by the sabellid even at moderate levels of infestation. That an invasive species causes substantially greater impacts in non-native areas is all too common.

Although current infestation levels in the wild are low, and thus no observable impacts are occurring, one can not assume that the situation will remain as such. The ocean is a more dynamic habitat than an onshore tank. In onshore tanks, recruitment is closed; larvae are retained and abalone become quickly reinfested at high rates. In the wild, recruitment is relatively open; larvae are dispersed and thus it would likely take many years before infestations build up to highly damaging levels. Ocean habitats in South Africa contain high infestation levels. An increase in sabellid infestations over time could be anticipated in California. If this happens, native gastropods will be impacted. How many and how badly remains to be seen.

Carrie Culver
E-Mail c_culver@lifesci.lscf.ucsb.edu
Department of Biology
University of California
Santa Barbara, CA 93106