Pacific Rocky Intertidal Monitoring: Trends and Synthesis home

Hazards 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).

The barnacle plots at Hazards are located in an area heavily influenced by sand, and declines were often associated with scouring events. This was particularly true in spring 2003, when the opportunistic red alga, Porphyra, colonized large patches of bare space recently cleared by sand scour. A mixture of Chthamalus and Balanus was present in these plots. Littorines were typically present in very high numbers, often upwards of 1000 individuals per plot, while limpets tended to be an order of magnitude less common.

Initial mussel cover was somewhat low at Hazards (approximately 45%) because plots were established fairly high in the mussel zone to make sampling easier when large swells were present at the site.  Denser mussel beds were present at Hazards, but were located on exposed outer reefs.  An added benefit to placing the mussel plots higher in the intertidal is that Pollicipes cover was fairly high in the plots (almost 20%), so goose barnacles could be monitored along with the mussels. Both Mytilus and Pollicipes cover have been relatively stable at Hazards. Limpets were the most abundant motile invertebrate in the mussel plots and varied seasonally, with higher counts in fall than in spring. Tegula funebralis and Nucella spp. (mostly N. emarginata/ostrina) were also common.

Silvetia has declined gradually, but substantially over time at Hazards. As Silvetia cover has decreased, limpet cover has increased, likely due to the additional “open” space (crustose algae covered rock) available for grazing. The turban snail, Tegula funebralis is also common in the Silvetia plots at Hazards.

Endocladia declined during the first few years that it was monitored at Hazards, but has hovered around 10-20% cover since this initial decline. As with many other sites, turfweed cover fluctuated seasonally, with higher cover in spring than in fall. The open space resulting from the reduced cover of Endocladia has been colonized by barnacles, which have gradually increased in cover over time. Littorines are the most abundant motile invertebrate present in the Endocladia plots. Tegula funebralis and limpets are also common.

Mean cover of Mazzaella remained relatively constant over time at Hazards. Unlike Pt. Sierra Nevada, the only other site where Mazzaella is targeted, there was no apparent seasonal variation in cover. “Other Red Algae” consisted mainly of Chondracanthus canaliculatus.

Phyllospadix cover at Hazards remained high over time, although it should be noted that averages are not always based on all three transects. Transects at this site were established in the very low intertidal, and thus cannot always be sampled. In SP02 and FA04 transects were not accessible for sampling. In FA02, SP03, SP09, and FA09 only the highest transect could be sampled. In FA05, SP06, FA07, FA08, and SP10 only two transects were accessible.

Pisaster ochraceus were abundant but variable in the plots where they are monitored at Hazards. Numbers increased substantially in 2006/2007, and size data suggest that this increase may have been due to a large recruitment event just before this period as large numbers of juveniles were recorded.

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

Hazards barnacle trend plot

Chthamalus/Balanus (Acorn Barnacles) - motile invertebrate counts

Hazards barnacle trend plot

Mytilus (California Mussel) - percent cover

Hazards Mytilus trend plot

Mytilus (California Mussel) - motile invertebrate counts

Hazards Mytilus trend plot

Silvetia (Golden Rockweed) - percent cover

Hazards Silvetia trend plot

Silvetia (Golden Rockweed) - motile invertebrate counts

Hazards Silvetia trend plot

Endocladia (Turfweed) - percent cover

Hazards Endocladia trend plot

Endocladia (Turfweed) - motile invertebrate counts

Hazards Endocladia trend plot

Mazzaella (Iridescent Weed)

Hazards Mazzaella trend plot


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)

Hazards 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

Hazards Pisaster trend plot

Pisaster (Ochre Star) - sizes

Hazards Pisaster size plot

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