Pacific Rocky Intertidal Monitoring: Trends and Synthesis
Government Point 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).
Long-term monitoring at Government Pt. was not done in fall 1999, and then ended in 2006 due to site access restrictions. We hope to regain access in the near future, as the location of this site at the junction of two major biogeographic provinces ranks it among the most important in our program.
A mixture of Chthamalus fissus/dalli and Balanus glandula was present in the barnacle plots at Government Pt. These barnacles facilitate recruitment of the turfweed, Endocladia muricata, by reducing grazing pressure by limpets. We have observed this facilitation at Government Pt., where dips in barnacle cover are associated with increases in turfweed cover in the plots. Limpets and littorines were both abundant within these plots.
Cover of the gooseneck barnacle, Pollicipes, was quite constant over time at Government Pt. These long-lived barnacles are harvested for food in many areas accessible to the public, but are protected from collection pressure at Government Pt.
The California mussel (Mytilus californianus), forms a dense bed in the mid-low intertidal zones of Government Pt., which provides food and shelter for an incredible diversity of organisms. Large storm events can tear out patches of mussels, as is evidenced by the dip in mussel cover during the 1997/98 El Niño period. This storm-induced decline was followed by rapid recovery, and long-term cover of mussels at Government Pt. was quite stable through 2006. Limpets were the most common motile invertebrate found in the mussel plots, but a number of other species were also common, including the snails, Tegula funebralis, Nucella spp. and littorines, and the shore crab, Pachygrapsus crassipes.
A significant downward trend in the cover of Silvetia compressa at Government Pt. was evident through 2006, and it would be useful to know if this trend has continued in recent years. As with many other sites, Silvetia showed a seasonal pattern in cover, with lower values in spring vs. fall samples. Silvetia plots contained high numbers of Tegula funebralis and limpets. Littorines and Nucella spp. were also common.
Turfweed (Endocladia muricata) forms distinctive dark red bands in the high zone of rocky intertidal shores north of Pt. Conception/Government Pt. Turfweed abundance fades in warmer waters to the south, thus monitoring at Government Pt. is critical for detecting the potential effects of warming water trends that might be associated with climate change. Turfweed provides habitat for a host of tiny organisms, and facilitates the recruitment of rockweeds. Turfweed abundance at Government Pt. has been highly variable over time, with typically much higher cover in spring than in fall. Littorines and limpets were the most common motile invertebrates found in these high intertidal plots.
Surfgrass (Phyllospadix spp.) beds are highly productive ecosystems, providing structurally complex microhabitats for a rich variety of organisms. Surfgrass provides nursery habitat for various fishes and invertebrates, including the California spiny lobster. Surfgrass can be particularly sensitive to pollution and oil spills, and large patches can be removed by high wave energy events, such as those associated with El Niño periods. Indeed, the surfgrass cover at Government Pt. experienced substantial decline only once in the 15 years that we monitored it—during the 1997/98 El Niño event. As observed at most other sites, Phyllospadix cover fluctuated seasonally, with higher cover in fall than in spring.
The ochre star (Pisaster ochraceus) is much more common north of Pt. Conception/Government Pt. than it is south of this biogeographic barrier, making Government Pt. an important site for detecting any impacts to this species that might spread northward up the coast, such as disease, or declines due to warming ocean temperatures. Seastar numbers were variable at Government Pt., but appeared to be increasing over the last few years that this site was sampled. Seastar sizes spanned the entire range, with abundant large individuals and juveniles commonly found, indicating a healthy population with ample recruitment. Plot 1 at Government Pt. is quite low in tidal height and cannot be sampled when waves are large, as was the case in spring 1992 and spring 2001. No seastar plots could be sampled in spring 1993.
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
Chthamalus/Balanus (Acorn Barnacles) - motile invertebrate counts
Pollicipes (Goose Barnacle)
Mytilus (California Mussel) - percent cover
Mytilus (California Mussel - motile invertebrate counts)
Silvetia (Golden Rockweed) - percent cover
Silvetia (Golden Rockweed) - motile invertebrate counts
Endocladia (Turfweed) - percent cover
Endocladia (Turfweed) - motile invertebrate counts
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.
Species Counts and Sizes
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
Pisaster (Ochre Star) - sizes