Black abalone (Haliotis cracherodii) shoreline inventory
- Pete Raimondi
University of California, Santa Cruz
- Mark Carr
University of California, Santa Cruz
Populations of black abalone Haliotis cracherodii have been steadily declining in the southern portion of the species' range due to a fatal disease called withering syndrome (WS). Withering syndrome is caused by a bacterium Candidatus Xenohaliotis californiensis, which attacks the lining of the digestive track and results in reduced body mass, weakness, and the eventual withering of the abalone's foot until it can no longer cling to the substratum. Declines have been so severe throughout southern California that the species is now a candidate for protection under the USA Endangered Species Act.
Researchers from the University of California at Santa Cruz (UCSC), working with MARINe (Multi-Agency Rocky Intertidal Network, www.marine.gov) and PISCO (Partnership for the Interdisciplinary Study of Coastal Oceans) have documented the northward progression of WS along the California coast. Recently, concern about the northward progression of WS into some of the final remaining large populations of black abalone prompted the Monterey Bay National Marine Sanctuary to provide funding to monitor additional sites within the sanctuary's boundaries. Since 2000, PISCO has continuously added sites to increase the spatial resolution and scale of the monitoring program. In January, 2004, 7 additional sites were established within the MBNMS, which have been incorporated into the larger monitoring program lead by PISCO. Overall, PISCO-UCSC monitors 20 sites within the MBNMS, 17 of which are monitored for black abalone. At a larger scale, of the more than 80 general monitoring sites along the West Coast (between Oregon and Baja California), black abalone are monitored at 55 sites. In 2007-08, 11 additional sites will be established within the MBNMS as part of the Marine Life Protection Act (MLPA) Initiative, and black abalone will be monitored at 5 of these sites.
Our monitoring has led us to several intriguing observations regarding California black abalone populations. First, it seems that the northward progression of WS is more rapid during El Niño events. The WS-causing bacterium may divide and spread more rapidly during these warm water periods. Second, we see little or no recruitment of black abalone into sites that have been devastated by WS, even when healthy populations are present 10's of kilometers to the north, suggesting that recruitment is very localized. Finally, we have observed changes in habitat that occur after the abalone have disappeared from an area, indicating that they play a key role in structuring their surrounding habitat. In particular, "good" abalone habitat (crustose coralline algae and bare rock) is replaced by habitat with higher cover of invertebrates and algae. This reduction in favorable habitat (i.e. crustose coralline algae and bare rock) when combined with limited recruitment severely hinders the recovery of black abalone in areas impacted by WS.
Related to the black abalone portion of our long-term monitoring program, the following questions are being addressed:
1) What population- and community-level consequences result from the loss of black abalone?
2) How does the community structure and function change when black abalone become locally extinct?
3) What is the spatial pattern of "withering syndrome"?
The central California sites, overseen by PISCO-UCSC, are the only sites listed in the MBNMS SIMoN database.
Summary to DateThe fatal condition termed "withering syndrome" (WS) has caused drastic declines in black abalone populations since the mid-1980's. It was first seen in the Channel Islands in 1986 and by 1992 the disease was observed near Point Conception on the mainland. The disease has since made its way as far north as Cayucos. Evidence of WS (significant declines in population, and the presence of sick individuals and fresh shells) has also been seen at the following sites farther north: Rancho Marino Reserve, San Simeon, Piedras Blancas, Pt Sierra Nevada, Carmel Point (2 withered individuals and lots of fresh shells) and Franklin Point (1 withered individual). However, the black abalone populations at the other MBNMS sites appear to be healthy and stable.
We continue to see recruitment of juvenile abalone at many of our sites in the MBNMS. Previously we thought that the disease spread during warm water events (the last great onslaught was during the 1998 El Nino), and that the Big Sur coast may escape infection due to cold water upwelling. However, we noted declines at our southern MBNMS sites in the fall of 2003. Whether this represents the beginning of a renewed spread of population crashes due to WS remains to be seen, however, the declines clearly point to the need for ongoing monitoring in the MBNMS because it is the only remaining area of healthy black abalone populations. The population and community consequences of the loss of this important species can not be assessed without a spatially expansive long-term monitoring program.
Recovery of black abalone populations to pre-withering syndrome levels is unlikely as recruitment is thought to be localized and the remaining individuals at these sites are probably too far apart to allow for successful spawning. This idea is substantiated by the lack of juvenile black abalone at all sites that have experienced WS-induced declines. Black abalone recruitment and survival may be further limited by habitat changes that occur after the animals disappear from an area. We have noticed that after WS decimates a local population, cracks that had been occupied by black abalone soon become filled with encrusting invertebrates. Additionally, seastars populations seem to increase. These opportunistic scavengers may be eating abalone weakened by WS. Urchin numbers also increase. These changes in habitat may affect recruitment and survival of black abalone, thereby hindering black abalone recovery.
This project is on-going. We continue to collect data bi-annually at all of our sites. The findings presented below are unpublished, preliminary results, and should not be cited, copied, or referenced without the permission of the principal investigators.
- While southern California black abalone populations have been decimated by withering syndrome, the black abalone populations within the MBNMS appear to be stable.
- The northward progression of the disease is more rapid during El Nino events.
- We see little or no recruitment of black abalone's into sites devastated by "withering syndrome" even when healthy populations are present 10's of kilometers to the North, suggesting that recruitment is localized.
- Changes in the habitat occur after abalone have disappeared from an area, indicating that they play a key role in structuring their surrounding habitat. The reduction in favorable habitat in combination with recruitment limitations may severely hinder the recovery of black abalone in areas impacted by "withering syndrome".
DiscussionIn January 2009, black abalone (Haliotis cracherodii) was listed by NOAA's Fisheries Service as an endangered species under the Endangered Species Act. The final ruling was published in the Federal Register, volume 74 no. 9., pages 1937-1946.
- Dispersal & Recruitment
- Habitat association
- Size structure
Study MethodsHabitat Studied: Mid to low zone of the rocky intertidal
Sites range from Point Conception to Half Moon Bay.
At each site, black abalone (Haliotis cracherodii) are counted and measured within 3 permanently marked plots. Every abalone is sampled for size (length) and health (is the foot plump and visible and is the animal strongly attached to the surface). Abalone shell lengths are measured with calipers or a ruler to the nearest 5 mm for small abalone (<40 mm) and to the nearest 10 mm for larger abalone (>40 mm). Each abalone is temporarily marked with a yellow lumber crayon to avoid duplication. Sometimes it is necessary to estimate shell lengths of abalone lodged deeply in cracks or otherwise inaccessible. In addition, any unusual conditions are recorded, such as disease, predation, or empty shells. No animals are collected or moved.
These data allow us to document both population declines (indicated by decreases across all abalone size classes) and recruitment events (indicated by increases in the number of abalone < 50 mm in length). Sampling occurs twice a year, conditions permitting.
For more information, visit: http://www.piscoweb.org or http://www.marine.gov or pacificrockyintertidal.org
Figures and Images
Figure 1. In healthy black abalone populations, abalones are often found stacked on one another. Photo: Christy Bell
Figure 2. A “withered” black abalone found at Point Sierra Nevada, California. Photo: Melissa Miner
Figure 3. Some of the fresh shells removed from plot 2 at the San Simeon site in December 2005. Photo: Christy Bell
Figure 4. Researchers from UCSC counting and measuring black abalone in a permanent plot. Photo: Dave Lohse
Figure 5. Abundance of black abalone in central California from 1992 to 2007 at sites 1-14. Seven of these sites were initiated through funding from Monterey Bay National Marine Sanctuary. Nota bene: these are combined totals for all plots at each site for each sample and were produced to show general patterns in population number over time. In several cases, a subset of plots were sampled, so dips in the count may simply be a result of a reduced number of plots being sampled, not an true decline in the population (real declines are evident over time). Additionally, some sites have had changes in plot number or size over time (e.g., due to substrate loss, etc), and trends should be interpreted only with this additional, site specific, information.
Figure 6. Abundance of black abalone in central California from 1992 to 2007 at sites 15-27. Seven of these sites were initiated through funding from Monterey Bay National Marine Sanctuary. Nota bene: these are combined totals for all plots at each site for each sample and were produced to show general patterns in population number over time. In several cases, a subset of plots were sampled, so dips in the count may simply be a result of a reduced number of plots being sampled, not an true decline in the population (real declines are evident over time). Additionally, some sites have had changes in plot number or size over time (e.g., due to substrate loss, etc), and trends should be interpreted only with this additional, site specific, information.