SPATIAL AND TEMPORAL VARIATION                                    IN RECRUITMENT TO ROCKY SHORES: RELATIONSHIP       TO RECOVERY RATES OF INTERTIDAL COMMUNITIES

Principal Investigators: Peter Raimondi and Richard Ambrose

Summary of Research

Our general objective is to understand the recruitment patterns of the dominant space-holding organisms in the rocky intertidal and to couple this understanding with information from our ongoing monitoring of adult dynamics.  This will help us determine whether patterns of recovery will occur over a broad spatial scale, be associated with geographic "neighborhoods," or be unpredictable in space.  Ultimately this approach will allow us to address our program goal: to be able to predict site specific recovery rates following an oil spill or other large scale disturbance. 

We used the following criteria to select sites for this study:

1. Proximity to existing monitoring plots. Only sites adjacent to MMS monitoring sites were considered as candidates for this recovery study. This will allow placing results in the context of historical species abundances.
2. High abundance of all four target species (Chthamalus fissus/dalli, Endocladia muricata, Silvetia compressa and Mytilus californianus.) This was determined qualitatively by assessing each potential site for the target species.
3. Geographic distribution of sites such that one site would fall in each of the three target biogeographic regions (North, near to and South of Point Conception).

Using these criteria, Point Sierra Nevada, Stairs and Point Fermin were selected as sites for this recovery study (see Figure 1.)

Figure 1. Map of sites where recovery plots were established. Note distribution of one site North, near to, and South of Point Conception.

Experimental layout and initial sampling of Recovery and Control plots.

At each site, 8 recovery plots and 3 control plots were established in the Chthamalus, Endocladia, Silvetia and Mytilus assemblages (see Figure 2).

Figure 2. Schematic drawing of Recovery (R) and Control (C) plots in each assemblage.

Plots ranged from 8 cm x 12 cm to 50 cm x 75 cm, with one plot of every size. Control plots were the size of the largest clearing size, 50 cm x 75 cm. This is also the same size as the MMS monitoring plots. The total area cleared in each assemblage was approximately 1 square meter. A total of 44 plots were established at each site (8 Recovery plots and 3 Control plots in 4 assemblages). Length to width ratio was held constant for each size (approximately 1:1.5). Prior to clearing, every recovery plot was photographed and sampled in two ways:

1. A Uniform Point-Contact method was employed for each plot. The number of points in each plot reflected the size of the plot to accurately capture the plot: 100 points for the 5 largest sizes, and 50, 40, and 30 points for the three smallest plots. PVC "quadrats" were strung with fishing line to allow for the greatest precision possible when sampling plots. Data were collected by using a CSM 150 bar code scanner attached to a HandSpring handheld. Species were identified to the smallest taxonomic level possible.
2. Mobile critters were counted in each plot. Limpets and littorines were generally sub-sampled. Species were identified to the smallest taxonomic level possible. Only investigators who were experienced mobile counters (from either Shoreline Inventory or SWAT team) collected the data.

Experimental disturbances

Experimental disturbances were established in Recovery plots of all sites in late November - December of 2003. All biota were removed using chisels, paint scrapers, wire brushes and ice picks. All sites were cleared within 3 weeks of each other. A propane torch was used to sterilize all plots to remove microscope propagules.

All plots were photographed after they were cleared. Mussels, Silvetia and mobile invertebrates from Pt. Sierra Nevada and Pt. Fermin were collected and frozen.

Recruitment collectors

Recruitment collectors were deployed at each site. Five safety-walk plates were put amongst the barnacle plots (see Figure 3), 5 barnacle mimics in the Endocladia plots (see Figure 4), 5 Endocladia mimics in the Silvetia plots (see Figure 5), and 4 tuffies in the mussel plots (see Figure 6). In the barnacle zone, a rock area (10 cm x 10 cm) adjacent to the collector was cleared, in the Endocladia zone, Endocladia was removed from barnacles adjacent to the barnacle mimics, and in the Silvetia zone, Silvetia was removed from the Endocladia adjacent to the Endocladia mimics. These plots were also 10 cm x 10 cm, the same size as the collectors. At Pt. Fermin, where there was no Endocladia in the Silvetia zone, the collectors were place adjacent to patches of Caulacanthus ustulatus, a turfy red alga in which juvenile Silvetia plants have been observed.

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Figure 5. Silvetia collector and Silvetia recruitment plot in Silvetia zone.

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Initial trends - Recovery plots

Recovery plots were sampled (Pt. Contacts, Mobiles and Photographs) in March 04 and again in June 04. Chthamalus recruits are present in all sizes of all Chthamalus plots at all three sites.  Endocladia has shown some vegetative reproduction (encroachment) at all three sites. Barnacles have also recruited into most Endocladia plots. Two Recovery plots at Stairs have shown Endocladia recruitment into the middle of the plot. As of the March sampling, there were no Silvetia or Fucoid recruits in any of the plots. However, in the June sampling, Fucoid recruits (<2 cm) were detected in some of the Recovery plots at all three sites. Some mussel plots have shown varying degrees of encroachment; no mussels have recruited into the plots.

Initial trends - Monthly recruitment:

Barnacle recruitment data is presented in Figure 7. Point Fermin and Point Sierra Nevada have showed higher mean monthly recruitment from January to May than Stairs .

Figure 7. Mean monthly barnacle recruitment (± SD) at Point Sierra Nevada, Stairs and Point Fermin from January 2004 to May 2004.

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