Pacific Rocky Intertidal Monitoring: Trends and Synthesis

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Crystal Cove 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).

From 1996-2006, overall barnacle cover at Crystal Cove was generally high (50 to 80% cover) although abundance of barnacles fluctuated among sampling periods.  For most plots, the majority of the area not covered by barnacles was simply bare (recorded as bare rock) aside from the occasional and short-lived appearance of small patches of algae such as the ephemeral sea lettuce Ulva and the red turf Caulacanthus.  Mussels (Mytilus spp.) did recruit occasionally into barnacle plots, but their numbers were generally low with the exception of a single plot in which mussel cover began to increase steadily in 2001.  Average cover of mussels reached a peak of 16% in spring 2007; this was driven mostly by high mussel abundance in a single plot.  In 2006, barnacle cover dropped sharply across all plots, resulting in an increase in recorded coverage of bare rock.  Since this drop, barnacle cover has begun to slowly increase again.  Barnacle plots have consistently contained extremely high numbers of limpets and periwinkles (Littorina spp.).  Genreally, higher numbers of Littorina are recorded in fall than in spring sampling periods.

From 1996 to 2006, mussel cover in Crystal Cove mussel plots remained relatively high (above 60%) with the notable exception of a large drop in cover associated with the 1997-1998 El Niño.   Several different species moved in to fill the space opened up by this decline in mussel cover, including the annelid Phragmatopoma, the ephemeral alga Ulva, and articulated coralline algae; yet cover of these species declined over the next two years as mussels recovered to original cover levels.  Following this recovery, mussel cover remained relatively high until 2007 when a moderate decline was observed following a storm with extraordinarily large waves. The effect of the storm was variable in space: some plots lost only a small amount of mussel cover but one plot was completely denuded of all mussels.  Bare space created by the storm was filled quickly by a variety of algae including articulated corallines and non-calcified red algae.  Since 2007 overall mussel cover has remained below 60% while cover in individual plots has been dynamic.   In the plot most heavily affected by the storm, mussel cover has remained low in subsequent years of monitoring; and in other plots, minor disturbances have caused smaller occasional reductions in mussel cover.   Mobile animals in mussel plots consisted primarily of limpets in the genus Lottia, whose numbers were highly variable over time. 

Rockweeds show variation in cover within years with a pattern of higher cover in fall than in spring.  Across years, there appeared to be a slight and slow decline in rockweed cover from 2004 – 2010. Space created by the reduction in Silvetia cover was filled by a variety of species including mussels and the red turf alga Caulacanthus, though in general these other species did not persist long in Silvetia plots.  Several types of mobile invertebrates, including hermit crabs and turban snails, were regularly found in low abundance in the rockweed plots.  Limpets (Lottia spp) were the most abundant group of mobile animals in these plots; although numbers varied greatly over time, limpet counts were typically at least five times higher than counts of any other taxon. 

Surfgrass (Phyllospadix) cover varied within years (with higher cover in fall than in spring) and among years.  Despite these temporal fluctuations, surfgrass cover remained generally high at this site (typically above 50% cover).   While the feather boa kelp Egregia was the only other species with a notable contribution to cover in surfgrass habitat, several species of red algae (e.g. Pterocladiella and Plocamium) have been consistently present in this zone in low abundance.  This habitat is also heavily influenced by sand movement:  sand cover typically fluctuated between 3 and 22 %. 

Sea star (Pisaster) counts at this site varied greatly over the sampling period, with peaks in numbers in 1999 and 2008. 

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

Crystal Cove barnacle trend plot

Chthamalus/Balanus (Acorn Barnacles) - motile invertebrate counts

Crystal Cove barnacle trend plot

Mytilus (California Mussel) - percent cover

Crystal Cove Mytilus trend plot

Mytilus (California Mussel) - motile invertebrate counts

Crystal Cove Mytilus trend plot

Silvetia (Golden Rockweed) - percent cover

Crystal Cove Silvetia trend plot

Silvetia (Golden Rockweed) - motile invertebrate counts

Crystal Cove Silvetia trend plot

Transects

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)

Crystal Cove 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 ochraceus (Ochre Star)

Crystal Cove Pisaster trend plot

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Interactive Map

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