Pacific Rocky Intertidal Monitoring: Trends and Synthesis

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Occulto 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).

Barnacles (a mixture of Chthamalus fissus/dalli and Balanus glandula) within plots at Occulto declined substantially during the first few years of monitoring, but recovered somewhat in more recent years. While bare space was still present in the plots, much of it has become occupied by mussels and several algal species, including Endocladia, Silvetia and Cladophora. Barnacles recruiting into this site tended to settle above the barnacle plots, in an area that is at a higher tidal elevation than barnacles were commonly found when monitoring began at Occulto thirteen years ago. Thus, although barnacles in the plots have declined substantially, they are still common at the site overall. Limpets and littorines were common in these high intertidal plots, and a few Nucella spp. were found amongst the mussels.

Mytilus cover within the mussel plots at Occulto remained high over time in all but one plot, where mussels were partially removed in winter of 1995, followed by recovery, and then completely torn out in winter 2005. Mussel cover has been slowly recovering in this plot, but other species have colonized the available bare space, including Mazzaella, Phragmatopoma, and articulated corallines. Limpets are the most abundant motile invertebrate counted in the mussel plots, but other species such as the whelk, Nucella spp. (mostly N. emarginata/ostrina), and the chiton, Nuttallina spp., were also commonly found.

Mytilus has steadily recruited into the Endocladia plots and is now a dominant part of what used to be a turf weed dominated community at Occulto. Presence of Mytilus does not necessarily exclude Endocladia, as the alga can grow on top of mussels. Indeed, Endocladia abundance at the site overall is described as “common to abundant”. Limpets and littorines were the most common motile invertebrate found in the Endocladia plots, with a few Nucella present within mussel patches.

Pisaster counts at Occulto were highly variable, largely because they are influenced by sampling conditions, as much of the plot consists of steep reef edges that can be difficult to sample when the swell is large. Seastar size spanned the entire range with both juvenile and large individuals commonly found.

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

Occulto barnacle trend plot

Chthamalus/Balanus (Acorn Barnacles) - motile invertebrate counts

Occulto barnacle trend plot

Mytilus (California Mussel) - percent cover

Occulto Mytilus trend plot

Mytilus (California Mussel) - motile invertebrate counts

Occulto Mytilus trend plot

Endocladia (Turfweed) - percent cover

Occulto Endocladia trend plot

Endocladia (Turfweed) - motile invertebrate counts

Occulto Endocladia 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

Occulto Pisaster trend plot

Pisaster (Ochre Star) - sizes

Occulto Pisaster size plot

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Interactive Map

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