Offshore Facilities Abandonment

SHORELINE INVENTORY OF INTERTIDAL RESOURCES OF SAN LUIS OBISPO AND NORTHERN SANTA BARBARA COUNTIES

Principal Investigator: Pete Raimondi (UCSC)

Summary of Research

The purpose of the Shoreline Inventory Project is to provide baseline information on the rocky intertidal plants and animals along the central and southern California coast. This information is invaluable for providing “baseline” information that can be used for assessing change in the event of an oil spill or other disturbance. In addition, the monitoring studies yield important data on population dynamics on a local and regional scale which can be utilized for more effective resource management as well as provide fundamental ecological knowledge about the dynamics of these systems.

The rocky intertidal surveys of five sites in Northern Santa Barbara County (NSB) represent a continuation of previous semi-annual monitoring conducted for the Minerals Management Service from 1992 to 2002. Five additional sites were established in 1995 for San Luis Obispo County (SLO). A sixth site at which only black abalone and owl limpets are monitored was recently added in SLO County.

The sampling protocol focuses on target species or assemblages. Permanent photoplots are established in assemblages such as barnacles, mussels, anemones, turfweed, and rockweed. Cover of the major taxa is determined by point-contact photographic analysis for all plots except barnacles, which are scored in the field to allow samplers to distinguish Chthamalus spp. from Balanus glandula. Counts of mobile invertebrates occurring within the barnacle, mussel, Endocladia, Mastocarpus, Silvetia, and Hesperophycus photoplots are also done in the field. Additional permanent plots are established for large motile species such as owl limpets, black abalone, and seastars. Line transects are used to estimate the cover of surfgrass. Photographic overviews and field notes are used to describe general conditions at the site and to document the distribution and abundance of organisms not found within the photoplots.

Over the past years, we have completed efforts to fully standardize our sampling methods with all groups in MARINE (Multi-Agency Rocky Intertidal Network). One of MARINE’s goals has been to develop a database for all of the intertidal groups to use for data entry. This goal is complete, and the newly constructed MARINE database is in use. Summarized results for selected species are available to the public at: www.marine.gov

Photoplot Species

In 2002-2003, we changed our protocol for sampling photoplot species. We switched from photographing the plots using a Nikonos with slide film and scoring percent cover of species within the plot by projecting the slide onto a grid in the lab to using a digital camera and scoring the images on a computer. To insure that we were getting images at the optimal resolution for our purposes, we needed to spend some time experimenting with different camera settings and examining the images in the lab. In addition, time was needed to switch over from scoring photoplot images using a slide projector and screen to scoring the digital images on a computer monitor. All of these changes in the protocol were accompanied by a change in the technician scoring the images, which required some training time. A full discussion of the trends for photoplot species was provided in the final report that we completed at the end of summer, 2003.

The one photoplot species that we do have data for is barnacles, since these were scored in the field in order to distinguish Chthamalus spp. from Balanus glandula. Total barnacle cover at two SLO sites (Pt. Sierra Nevada and Cayucos) increased slightly as compared to recent years. Plots at both of these sites contained no, or almost no B. glandula. Barnacle cover at one SLO site (Hazards) declined over the past year. Plots at this site contained about ½ B. glandula and ½ Chthamalus spp. and were exposed to frequent sand scour. Barnacle cover at the remaining sites stayed about the same as compared to recent years. The only site with consistently high cover was Shell Beach, where only Chthamalus spp. were present. Cover at two sites (Occulto and Stairs) remained extremely low. At Occulto the barnacle zone has shifted up in tidal height, and “barnacle” plots are now dominated by algae and mussels. Barnacles at Stairs have been steadily declining over time due to a lack of recruitment of new individuals into the site. At Government Pt., percent of total barnacle cover consisting of B. glandula increased from around 60% in F02 to nearly 95% in SP03. As with Occulto, the barnacle zone appears to have shifted upward in tidal height at this site.

Surfgrass

Surfgrass cover (Phyllospadix spp.) remained high during 2002-2003 at all sites except Stairs (NSB), where plots were decimated by the 1997/98 El Niño storms, and Shell Beach (SLO), where cover has gradually declined. All sites except Cayucos (SLO) experienced slight seasonal fluctuations, with higher cover in the fall than the spring. Surfgrass transects at Cayucos are located within permanent pools, so it makes sense that there would be no seasonal differences in cover at this site. Only one surfgrass transect of three at Hazards (SLO) could be sampled during the past two sampling periods. The other two remained underwater at low tide.

Motile Invertebrates

Pisaster ochraceus are counted and measured in plots at each site, and also grouped into color categories. Seastar numbers have fluctuated at most sites over time, and counts for the F02/SP03 samples did not appear to be abnormally high or low at any site. Numbers were higher at Occulto during 2002-2003 as compared to previous years, but this was confounded by the fact that we had better than normal tides when we sampled Occulto in F02 and SP03, which made it possible to count seastars in areas that are often splashed by waves. P. ochraceus color ratios were approximately the same among sites, with about 25% orange and 75% falling under the “other” category (primarily purple, but also some “brown” individuals). The sites with the highest proportion of juvenile P. ochraceus. in the population were Boat House and Hazards, with approximately 40% of the populations consisting of individuals <40mm in radius.

Numbers of the owl limpet, Lottia gigantea, were stable at all sites except Stairs, where large swells hit the site in winter 2003 and removed portions of the reef where two of the five Lottia plots were present. Recruitment of Lottia into our plots was higher than average during the past year at Cayucos, Hazards and Government Pt. The fatal condition termed “withering syndrome” has caused drastic declines in black abalone (Haliotis cracherodii) populations as far north as Cayucos (SLO). Recovery of these decimated populations is unlikely as recruitment is thought to be very localized and the remaining individuals at these sites are probably too sparsely distributed to allow for successful spawning. Although evidence of withering syndrome was seen at Rancho Marino (the SLO site just north of Cayucos) in SP00, numbers have not declined as rapidly as expected. Abalone numbers at Piedras Blancas, just upcoast of Rancho Marino, were stable while those at the northernmost site (Pt. Sierra Nevada) continued to increase slightly. This increase was attributed to recruitment of black abalone into our plots during the period ranging from summer 2000-spring 2002.

In addition to monitoring seastars and owl limpets, we also count and measure the small motile invertebrates that occur within our photoplots. The protocol for monitoring these invertebrates has been modified somewhat over the past year to ensure that our methods are comparable to other monitoring groups (UCSB, UCLA, CSUF, and the Channel Islands National Park Service). Species targeted in these plots include Tegula funebralis, Acanthina spp., Nucella emarginata, N. canaliculata, Ocenebra circumtexta, Lepidochitona harwegii, Nuttalina spp., Mopalia spp., three species of Pagurus, Littorina spp., and various limpets. Limpet and littorines were the most abundant motile invertebrates found in the photoplots. Limpets were common in all plot types at nearly all sites, while littorines were most abundant in the higher barnacle and Endocladia photoplots. Tegula was also common and was found in all plot types, but was most common in the lower mussel and Silvetia plots. Nucella were most commonly found in mussel plots, their preferred prey in the central California region. Another whelk, Acanthina, was consistently found at only two SLO sites, Cayucos and Shell Beach. Acanthina, which feed on barnacles, were occasionally found in barnacle plots, but were most common in Silvetia and mussel plots. Lepidochitona was also most common under Silvetia, which is though to provide refuge from desiccation for the chiton, but like Nucella they could be found in other plot types in lesser abundance. Another chiton, Nuttalina, was found almost exclusively in mussel plots. Ocenebra was rare or absent from most sites except in the mussel plots at Shell Beach, and the Silvetia plots at Cayucos.