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). Due to funding constraints, semi-annual sampling of plots/transects was reduced to annual sampling beginning in 2016. In addition, counts of motile invertebrates within plots at most sites ended in 2014.

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. Barnacles had been steadily recovering, and were nearly at initial levels, until they experienced a substantial drop again in Fall 2013 due to a possible scouring event. Barnacle cover has since recovered, and is once again near 90%. 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 was common within mussel plots between 2007-2014, but has since declined. 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, and sea star wasting syndrome (SSWS) resulted in the near-disappearance of stars at Shell Beach in spring 2014. Evidence of SSWS was first detected during our site visit in November 2013 and by spring 2014, no sea stars were observed in our plots, however, 3 Pisaster were found during a site-wide search. While a handful of small stars (<40mm) were observed between 2013-2016, only large individuals have been observed in recent years, indicating a lack of recruitment. As discussed above, the mussel bed at Shell Beach is small and not very dense; thus, the low number of sea stars at this site is likely due to a combination of sea star wasting and low food availability.