Pacific Rocky Intertidal Monitoring: Trends and Synthesis

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Old 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).

The anemone plots at Old Stairs consist primarily of the colonial anemone, Anthopleura elegantissima rather than the solitary anemone Anthopleura sola (note that these were considered a single species prior to the past several years and they are not distinguished in our sampling methods).  These plots showed greater variability due to sand inundation from their inception in 1994 through 2002, and more gradual change thereafter with cover ultimately declining from 70% to around 40%.  Sand burial has not been a significant factor since 2002 though scour could still be influencing the plots.  As anemones have declined, invertebrate species (primarily Phragmatopoma and encrusting tunicates) and red algal species (namely Chondracanthus sp. and filamentous species) have taken their place, with each of these groups increasing to a mean cover of around 20%.  Each of these plots has a unique ecological story to tell.  One has a recurring colony of Phragmatopoma that grows for a period of time and then gets broken away, another has persistent colonies of both sponges and tunicates, along with recurring Egregia holdfasts which have periods of growth and senescence.  Two others have persistent patches or red algae and mussels respectively, and the final plot has remained nearly covered by colonial Anthopleura.

The barnacle plots at this site consist of a mixture of Chthamalus dalli/fissus (note that species were not distinguished until 2001) and Balanus glandula with the former being the dominant component of all plots.  Since their inception, barnacle cover has declined from nearly 100% in 1994 to less than 20% in 2010.  In fact, a single plot, which has remained at nearly 100% barnacle cover throughout the monitoring period, is responsible for most of that twenty percent.  The other four plots have become dominated by Endocladia, Mytilus, or a mixture of these two species along with bare rock.  In the past two seasons, small patches of Endocladia have been observed in that last barnacle dominated plot suggesting that it too may transition away from barnacle dominance. Motile invertebrate counts at this site began seasonally in the fall of 2000 and were changed to annual sampling in 2004.  Littorines were added to the protocol in the fall of 2001.  Within the barnacle plots, littorines and limpets are both highly abundant with the former varying in the neighborhood of 1000 individuals per plot and the latter steady at around 100 per plot.  Nucella spp. snails are also common with around ten individuals per plot in most seasons, though these were absent during three sampling events.

Shortly after site establishment, the mussel plots exhibited a precipitous decline in mean Mytilus cover from around 80% in spring 1995 to near 30% the following fall.  This decline was met by a corresponding increase in barnacle cover along with bare rock.  After that, mussels began a gradual recovery interrupted by brief declines of varying degrees. One of these subsequent declines occurred in 2004-2005 the other in 2009, and both were the result of breakouts in the mussel beds, presumably due to heavy winter storms.  Consistent recruitment of young mussels to this site has allowed these mussel beds to regenerate before other opportunistic species could become established in the plots. The data from the Motile invertebrate sampling show consistent low levels of chitons (Nuttalina spp.) and littorines in these mussel plots, along with higher and more variable numbers of whelks (Nucella spp.).  In addition, limpets have been quite abundant and highly variable in these plots since the spring of 2002.  

The Endocladia plots at this site are a mixture of turfweed, barnacles, mussels, and bare rock with no clear patterns developing throughout the monitoring period except that bare rock appears to be increasing of late.  Mean Endocladia cover has varied between about 10 and 50%, barnacles have varied more dramatically between 20 and 60%, and mussels have remained steadier at around 10 to 30%. The data from the Motile invertebrate sampling show consistent low levels of chitons (Nuttalina spp.) and whelks (Nucella spp.) in the Endocladia plots, along with higher and more variable numbers of limpets and littorines.

Rock ("Above Barnacles") plots were added to this site in the fall of 2008 to document any upward spread of intertidal species as a result of global climate change or other factors.  These plots are expected to remain dominated by bare substrates unless barnacles or other species begin to encroach upon them.  As of the spring of 2010, no barnacles had been recorded in the photoplot sampling, although a few small recruits had been observed within these plots. (Note - the decline of rock to zero in spring 2010 depicted in this figure is an error). The annual motile invertebrate counts began in these new rock plots in 2009.  So far, the only motile invertebrates present in these plots are littorines, whose numbers declined by about half between the first two sampling events. 

Seastar (Pisaster ochraceus) abundance within the original transect swaths began at around 30 total stars and remained below that level for the first 5 years of sampling. After 2000, the numbers of stars began to increase and become more variable, both through time, and seasonally (with higher numbers in the spring compared to fall).  In the spring of 2004, the push for methodological consistency among sites prompted the addition of a series of three large irregular plots to be sampled alongside the transects.  These data show a high number of stars during their first few seasons of sampling, and then declining numbers for the 1.5 years, followed by a gradual increase.  The size distribution figure shows that the population of seastars at Old Stairs is comprised of mostly larger individuals but with a fair amount of consistent recruitment (presence of stars less than 50mm). There are no clear pulses of recruitment that have moved through the population.  Seastars are often observed to be partially or completely buried in sand near the base of the reef structures at this site.  The degree to which recruitment, or migration from the subtidal maintains the seastar population at this site is not clear. The increase in seastar abundance in 2007 is associated with generally larger stars, suggesting an influx of stars from the subtidal.

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.

Anthopleura (Anemones)

Old Stairs barnacle trend plot

Chthamalus/Balanus (Acorn Barnacles) - percent cover

Old Stairs barnacle trend plot

Chthamalus/Balanus (Acorn Barnacles) - motile invertebrate counts

Old Stairs barnacle trend plot

Mytilus (California Mussel) - percent cover

Old Stairs Mytilus trend plot

Mytilus (California Mussel) - motile invertebrate counts

Old Stairs Mytilus trend plot

Endocladia (Turfweed) - percent cover

Old Stairs Endocladia trend plot

Endocladia (Turfweed) - motile invertebrate counts

Old Stairs Endocladia trend plot

Rock (Above Barnacles) - percent cover

Old Stairs rock trend plot

Rock (Above Barnacles) - motile invertebrate counts

Old Stairs rock 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

Old Stairs Pisaster trend plot

Pisaster (Ochre Star) - sizes in Transects

Old Stairs Pisaster size plot

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Interactive Map

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