Pacific Rocky Intertidal Monitoring: Trends and Synthesis
Cayucos 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 Cayucos contained nearly pure stands of Chthamalus dalli/fissus, with very few Balanus glandula recorded (note that species were not distinguished until 2001). Cover of Chthamalus varied inversely with rock cover, with little else occurring in these plots. Littorines were common in the barnacle plots and limpets were also present in moderate numbers. The turban snail, Tegula funebralis, occurred consistently in the plots in low numbers.
Mussel plots at Cayucos consisted mainly of their targeted species, Mytilus californianus. When cover of Mytilus declined, rock cover increased, indicating that bare space was generally not colonized by other species. Mussel cover declined somewhat between 1999-2001, and then increased to over 90% cover in 2005-2006, followed by a more recent decline to near-original levels. Limpets were abundant in the mussel plots and exhibited strong seasonal variation, with much higher numbers in fall than in spring.
Decline of the upper-shore rockweed, Hesperophycus, was striking at Cayucos during the first few years it was monitored, where cover dropped from over 90% to less than 20%. Hesperophycus cover then stabilized at around 20-30% for nearly 13 years, but has recently increased slightly. Although some reduction in Hesperophycus abundance occurred site-wide, declines were more severe within permanent plots. Thus the plots did not necessarily reflect site-wide coverage of this rockweed. Limpets, littorines, and the turban snail, Tegula funebralis, were all common within Hesperophycus plots.
Silvetia cover was quite high during the first 5 years at Cayucos, but experienced a substantial decline in 2001, followed by more gradual decline until 2006, when cover appeared to stabilize. Endocladia and Hesperophycus have increased in these plots over time, filling in some of the space vacated by Silvetia. Silvetia cover was highly seasonal, with lower values in spring vs. fall samples. This pattern is present at many sites, and may be due to a combination of factors including seasonal growth cycles, physical removal by winter storms and desiccation from extreme low tides that occurred in the middle of the day in the spring (timing of low tide is cyclical, so low tides are not always mid-day in spring in this region). Tegula funebralis and limpets were abundant in Silvetia plots, and the chiton, Lepidochitona hartwegii, was consistently present. This chiton is frequently associated with Silvetia, which it uses for protection from desiccation.
Endocladia cover was relatively stable over time. A significant drop in 1998 was followed by a recovery to near-original levels. Limpets and littorines were common in the Endocladia plots, which had a large amount of bare space, where diatoms typically grow and provide food for these grazers.
Surfgrass cover at Cayucos was consistently high over time, with only slight dips during the 1997/98 El Niño event, and again in 2001. The lack of a seasonal pattern in surfgrass cover at Cayucos is likely due to the unique location of the transects at this site. Unlike other sites, where surfgrass transects were established in areas that drain during low tide, transects at Cayucos are located in large pools, which reduces the amount of stress experienced by the plants due to air exposure, and perhaps also abrasion.
Pisaster numbers have been variable, but increasing overall at Cayucos. We have seen increases only in the larger size classes, indicating that individuals are moving into the plots from outside, rather than recruiting to the plots.
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
Mytilus (California Mussel) - percent cover
Mytilus (California Mussel) - motile invertebrate counts
Hesperophycus (Olive Rockweed) - percent cover
Hesperophycus (Olive Rockweed) - 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