Kenneth S. Norris Rancho Marino Reserve

27 Jul, 12 PM - 29 Jul, 05 AM

Black abalone Haliotis cracherodii, which was once the largest and arguably most important herbivore in intertidal systems along the California coastline. It is essential to note that the only populations of black abalone in the United States occur along the California coast and were only common from the Mexican border to about San Francisco. Most black abalone along the mainland coast up to Point Conception were lost via legal harvesting and poaching prior to 1980, however large populations still persisted on the Channel Islands and along the mainland between Point Conception and San Francisco. Since the mid-1980s black abalone have experienced mass mortalities due to infection by a pathogen that leads to a fatal wasting disease called ?withering syndrome?. In animals with this disease, the foot of the abalone shrinks until it can no longer adhere to the substratum. The first massive die-offs due to withering syndrome occurred on the Channel Islands in 1986, and by 1992 the disease was observed by our group near Point Conception on the mainland. We currently sample abalone populations (PISCO, MMS and Monterey Bay National Marine Sanctuary funding) at 23 sites from Point Conception to Bodega Bay, including 8 in the Monterey Bay National Marine Sanctuary (Figure 1). In 2001 we reported on the pattern of mass mortality of the black abalone along the west coast. The general pattern of mortality once die-offs start is that within a few months to a year the population will decrease >90%, but a few remnant individuals will remain healthy and persist. Since the early 1990?s the disease has migrated sequentially northwards along the coast of California. By 2001 the documented northward spread of population crashes due to withering syndrome extended to the southern boundary of the Monterey Bay National Marine Sanctuary (MBNMS). At that time and currently the only extant healthy populations of Black Abalone in the United States resided in a very small area entirely in the Sanctuary ? this is the area of ecological viability. The mortality was so extraordinary that the species has been listed as threatened and is a candidate for endangered status. Two other aspects of the population crashes are critical to understand. First when populations crash the adult densities always decrease to less than 1 adult per square meter. Our data conclusively show that this density of adults is not viable because recruitment of new individuals at this density is completely suppressed at this density. Second, quantitative surveys before and after mass mortalities revealed that abalone declines were followed by shifts in the composition of the intertidal species assemblage from one dominated by bare rock and crustose coralline algae (good quality abalone habitat) to one with increased cover of sessile invertebrates and sea urchins. Hence, all data collected to date suggest that: 1) Withering disease is a continuing, chronic and devastating disease for black abalone 2) Populations stricken by the disease do not naturally recover via the recruitment of new individuals 3) The structure of nearshore communities is fundamentally altered after the local extinction of black abalone 4) It is highly unlikely that these important species will recover without intervention Project Goals and objectives Our overall goal is to estimate the population size and amount of suitable habitat available for black abalone in their area of ecological viability (currently from Piedras Blancas to San Mateo County). Neither of these critical pieces of information is currently available. Methodology At our abalone sampling sites we will establish an along shore transect. We will establish sampling areas (10 meters wide) at 10, 100 and 1000 meters up and down coast. These areas will be in the tidal range of black abalone but will not be moved to match likely abalone habitat except that we will not place sampling areas on sandy locations (explained later). We will sample each area for black abalone, according to MARINe methods. We will also characterize the quality of each area with respect to appropriateness for abalone occupation. This characterization is based on over 15 years of field sampling of black abalone. The categories are: 1) Considerable habitat suitable for abalone occupation. 2) Moderate habitat suitable for abalone occupation. 3) Minimal or no habitat suitable for abalone occupation. Suitable habitats are cracks, crevices and overhangs that constitute the typical locations in which abalone are found. The overall goal of the habitat characterization is to determine the amount of suitable habitat for abalone that exists in the species range of ecological viability. Current coastal geology maps allow discrimination between sand and rock, but not among geomorphologies within rocky shores. Hence, there is no point in sampling sandy areas since we can account for sand using coastal maps, but we have to differentiate among rocky areas based on habitat suitability. The data collected will be used together with the overall estimate amount of habitat in each of the 4 suitability categories. For example, if 10 % of rocky habitat is in category 1 and there are 150 linear km of rocky habitat in the region of interest, then ~15 km of coastline has considerable habitat suitable of abalone occupation. 1) Populations will be estimated as the product of abundances from the sample areas (each 10 m wide) X linear extent (in tens of km) of rocky habitat in the region of interest. We will also be able to determine if suitable habitat is spatial clustered using the gradient of sample areas away from an area of known suitable habitat (our current sampling site ? which will be the center of the gradient).

Visit #13474 @Kenneth S. Norris Rancho Marino Reserve

Approved

Under Project # 8795 | Research

Abalone Habitat Characterization

research_assistant - University of California, Santa Cruz

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Group of 3 Research Assistant (non-student/faculty/postdoc) Jul 27 - 29, 2007 (3 days)

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