Pacific Rocky Intertidal Monitoring: Trends and Synthesis

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Shell Beach Long-Term trends

See below for trend graphs

In order to standardize species resolution across all MARINe groups, and over time, some species (typically rare) were lumped for graphical presentation of Long-Term monitoring data. See lumped categories for definitions (some variation occurs between methods and over time).

Barnacle plots at Shell Beach consist almost exclusively of Chthamalus dalli/fissus, although Balanus glandula are recorded on rare occasion (note that species were not distinguished until 2001). Barnacle cover was consistently high at this site until 2008, when a sharp drop occurred. As of summer 2010, barnacles had not recovered to initial levels. Littorines were the most abundant motile invertebrate in these plots, followed by limpets. Tegula funebralis was commonly found in low numbers.

Mussel cover at Shell Beach was initially high, but then declined during the 1997/98 El Niño event. Mussels experienced a brief recovery in 2003/2004, but then rapidly declined to low levels in subsequent years.  Shell Beach is a highly accessible site and thus decline may be due, in part, to trampling and collection for food or bait. The mussel bed at Shell Beach is extremely small, and would be highly impacted by even a small level of collecting. Endocladia has slowly colonized the open space within the mussel plots, which could potentially enhance any future settlement of mussels, as this turf alga can act as an ideal recruitment environment for mussels. Fluctuations in the broad group “other invertebrates” largely consisted of periodic mass settlement events of the tube worm Phragmatopoma, followed by gradual die-offs. Limpets, and the turban snail Tegula funebralis, were quite common in mussel plots at Shell Beach.

Endocladia dominates the mid-intertidal at Shell Beach. This is evident in the trend plots for Silvetia, where rockweed cover steadily declined over time, and was replaced largely by turf weed. Endocladia was also the most abundant species in Mastocarpus plots. Plots established to target Endocladia are located in the upper-mid intertidal zone, where the turf weed appeared to be near its upper limit, sharing dominance with barnacles. Littorines, limpets, and Tegula funebralis were variable but generally abundant in both Silvetia and Endocladia plots (motile invertebrates are not counted in Mastocarpus plots). Cyanoplax hartwegii was present in Silvetia plots initially when the shelter-providing rockweed was more common, but became much rarer after cover declined to near zero.

Phyllospadix cover remained relatively high over time at Shell Beach, and exhibited the strong seasonal variation seen at many other sites, with higher cover in fall than in spring. “Other Red Algae” consisted mainly of Chondracanthus canaliculatus and Gastroclonium subarticulatum.

Counts of the seastar, Pisaster ochraceus, were variable over time, but in general not very high when compared to other sites. As discussed above, the mussel bed at Shell Beach is small and not very dense; thus the low number of seastars at this site is likely a result of low food availability. Pisaster size tended to be skewed toward the larger end of the scale, with juveniles rarely present.

Photo Plots

Long-Term methods Photo Plot thumbnail

Below are the trends observed for each Photo Plot target species at this site. Long-Term percent cover trend graphs show all species that reached a minimum of 25% cover during any single point in time within a given target species assemblage. Breaks in trend lines represent missed sampling events. For additional species observed that did not meet this 25% threshold, please use the Interactive Map.

For motile invertebrate Species Counts, a mean across all plots was calculated, and only those species with a value of at least 5 individuals for at least one sample are shown. For motile invertebrate size trend graphs by site, please use the Interactive Map.

Chthamalus/Balanus (Acorn Barnacles) - percent cover

Shell Beach barnacle trend plot

Chthamalus/Balanus (Acorn Barnacles) - motile invertebrate counts

Shell Beach barnacle trend plot

Mytilus (California Mussel) - percent cover

Shell Beach Mytilus trend plot

Mytilus (California Mussel) - motile invertebrate counts

Shell Beach Mytilus trend plot

Silvetia (Golden Rockweed) - percent cover

Shell Beach Silvetia trend plot

Silvetia (Golden Rockweed) - motile invertebrate counts

Shell Beach Silvetia trend plot

Endocladia (Turfweed) - percent cover

Shell Beach Endocladia trend plot

Endocladia (Turfweed) - motile invertebrate counts

Shell Beach Endocladia trend plot

Mastocarpus (Turkish Washcloth) - percent cover

Shell Beach Mastocarpus trend plot

Mastocarpus (Turkish Washcloth) - motile invertebrate counts

Shell Beach Mastocarpus trend plot

Transects

Long-Term methods Transects thumbnail

Below are the trends observed for each Transect target species at this site. Long-Term trend graphs show all species that reached a minimum of 25% cover during any single point in time within a given target species assemblage. Breaks in trend lines represent missed sampling events.

Phyllospadix (Surfgrass)

Shell Beach surfgrass trend plot

Species Counts and Sizes

Long-Term methods Counts thumbnail

Species Counts and Sizes (where recorded) for Pisaster are shown below for this site. The sum of all individuals across all plots is displayed.

Pisaster (Ochre Star) - counts

Shell Beach Pisaster trend plot

Pisaster (Ochre Star) - sizes

Shell Beach Pisaster size plot

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Interactive Map

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