Pacific Rocky Intertidal Monitoring: Trends and Synthesis
Stairs 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 Stairs consist solely of Chthamalus fissus/dalli (note that species were not distinguished until 2001). Barnacle cover remained fairly high until 1997/1998, when both a large El Niño event and an oil spill impacted the site, and may have affected barnacles (see discussion below and “Publications and Data Products” section). Barnacle cover continued to plummet until around 1999/2000, when levels in all plots were less than 10%. A slight recovery was seen in four plots beginning in 2004, but cover has remained low in the fifth plot. No other species was recorded at any significant level within these plots. Limpets and littorines were present in the barnacle plots at Stairs, but were not as abundant as at most other sites.
Mytilus californianus cover in mussel plots was quite high until 1997, when Stairs was hit hard by a series of large-wave events associated with the 1997/98 El Niño. Mussels were likely stressed by the warmer water, and were ripped out in two plots by large waves. Some recovery has occurred in these plots over time, but slow, steady decline in two other plots has resulted in a mean cover of around 40% since 1998. Species filling in the available space within mussel plots include: Mazzaella spp, articulated corallines, and non-coralline crusts (crustose forms of non-coralline red algae). Limpets were by far the most common motile invertebrate present in mussel plots at Stairs. Other species present included the snails, Tegula funebralis , Nucella spp. (mostly N. emarginata/ostrina) and littorines, and the chiton, Nuttallina spp.
Cover of the rockweed, Silvetia, within plots where it was targeted was initially high, and then declined somewhat in 1995. As with most other species at Stairs, Silvetia was severely impacted by the 1997/98 El Niño event, and cover declined and then stabilized (with seasonal variation) at around 25%. This decline was accompanied by a slight increase of Endocladia, but rock cover also increased, indicating that some open space was not colonized by other species. Non-coralline crusts increased in several plots, and another rockweed, Fucus, colonized one plot. Although Silvetia cover has declined in the plots, it is common at the site overall. In fact, Stairs is one of the only sites in the entire MARINe network where all four west-coast rockweed species are present (Pelvetiopsis, Hesperophycus, Silvetia, and Fucus). Limpets and the turban snail, Tegula funebralis, were the most common species found within Silvetia plots at Stairs. Littorines were also present.
Endocladia cover in the Endocladia plots remained relatively constant over time, with strong seasonal variation (higher in spring). This seasonal fluctuation is typical of Endocladia and was observed at other sites. Limpets and littorines were abundant in these high intertidal plots.
“Recovery” plots were established after the 1997/98 El Niño event, when huge sections of reef (up to 17m x 5m) were removed by extreme wave events, leaving several large, newly exposed areas of bare rock. These natural clearings provided us with a unique opportunity to document community succession in the mid-intertidal. Nearly all succession studies are done in artificially cleared patches, which are small relative to the reef size and often recover via encroachment by surrounding species. Because newly exposed sections of reef at Stairs were so large, they were likely to “recover” via colonization by propagules and thus had the potential to develop into communities quite different from surrounding, undisturbed areas. Eight recovery plots were originally set-up, but four have been lost over time due to subsequent large-wave events that have removed additional sections of reef. “Non-coralline crusts”, the crustose forms of red and brown algae, were among the earliest colonizers of these completely bare plots. In these plots, non-coralline crusts consisted primarily of Ralfsia spp., Petrospongium rugosum, and the crustose form of Mastocarpus (formerly called “Petrocelis”). Unexpectedly, the green alga, Cladophora, also colonized a few plots early on and then disappeared. Non-coralline crusts have persisted in all remaining recovery plots, and the rockweed, Silvetia has also moved in. A large amount of bare rock is still present, so it is likely that it will be several more years before these plots reach a “stable state”.
Surfgrass (Phyllospadix) was impacted more than any other species by the 1997/98 El Niño event, experiencing a nearly 80% loss between fall 1997 (pre-storm destruction) and spring 1998 (post-destruction). Surfgrass grows from rhizome-like holdfasts, and has difficultly re-establishing itself once these holdfasts have been removed. The large wave events associated with the El Niño storms ripped out nearly all rhizomes, and even removed large sections of rock within the transects where surfgrass is sampled. Thus, it is surprising and encouraging that surfgrass has been steadily recovering in the years following this destructive event. Only two transects were sampled in fall 1998.
Pisaster (ochre seastar) numbers have fluctuated substantially at Stairs, but the long-term trend shows little change overall. Pisaster sizes are fairly evenly distributed for most samples, with radius measurements generally concentrated between 30mm-130mm, indicating good recruitment and retention of adults.
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
Silvetia (Golden Rockweed) - percent cover
Silvetia (Golden Rockweed) - motile invertebrate counts
Endocladia (Turfweed) - percent cover
Endocladia (Turfweed) - motile invertebrate counts
Recovery - percent cover
Recovery - 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