Cape Arago Long-Term trends | MARINe

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Cape Arago 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).

With the exception of the mussel plots, all photoplots at Cape Arago have had high cover of barnacles throughout much of the 15 year period they have been monitored.  This site is an important pinniped haul-out, and the number of seals and sea lions using the site, as well as the duration of time spent at the site by seals and sea lions, appears to be increasing. We have had to re-schedule monitoring of this site several times during the past few years due to presence of seals and sea lions on the reef. 

Barnacle plots at Cape Arago tended to be dominated by the acorn barnacle, Balanus glandula, but the little brown barnacle, Chthamalus dalli/fissus, was also consistently present, and occasionally in even higher abundance than Balanus. Fucus cover in rockweed plots plummeted from over 90% to nearly 0% between 2000-2001, and has never recovered. The decline of Fucus was almost certainly due to disturbance resulting from sea lions. Since 2001, these plots have been dominated by bare space and barnacles, a relatively short-lived group that can easily recruit to newly disturbed patches on a reef. Mussels have periodically recruited to the Fucus plots, and were particularly high in cover in 2006 and 2007, but they’ve since declined. In 2008 the spike in “Other Invertebrates” was driven by a recruitment event of Mytilus trossulus into the Fucus plots, although they did not persist into 2009. 

As with Fucus, Pelvetiopsis and Endocladia cover in their respective target plots was generally low after the initial survey in 2000, and tended to be dominated by barnacles. Limpets and littorines were the primary motile invertebrates found in all above plot types.

Mussel plots are located in a different section of reef from the other photo plots, and were the only photo plot type not heavily impacted by sea lions. Mean cover of Mytilus in these plots remained near 100% from 2000-2011, then experienced a slight dip in 2012 to just under 80%, which has lasted through 2014. This dip was entirely due to a substantial loss of mussels from plot 1, which dropped from 83% cover in 2011 to 14% in 2012. Limpets and Nucella were common across all years in mussel plots.

The Phyllospadix transects at Cape Arago are located in a low-lying, calm bay just upcoast from the main site. It is an area rich in low intertidal/subtidal algae, and is unlike our surfgrass transect locations at most other sites in that it is not dominated by Phyllospadix. This difference is reflected in the long-term trend graph—surfgrass is high in cover at times, but low intertidal algae, particularly the boa kelp, Egregia, are also key players in the community.

Ochre stars in the sea star plots were relatively common overall, but experienced a decline in numbers between 2008-2010 (Cape Arago could not be sampled in 2009 due to sea lions hauled out on the reef). We expect counts to be down further due to Sea Star Wasting Syndrome when we return in 2015. The katy chiton, Katharina tunicata, was extremely abundant in the sea star plots, particularly in 2014.

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 also include any 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. Due to time constraints, motile invertebrate counts have not been done at most sites since 2012. For motile invertebrate size trend graphs by site, please use the Interactive Map.

Chthamalus/Balanus (Acorn Barnacles) - percent cover

Cape Arago barnacle trend plot

Chthamalus/Balanus (Acorn Barnacles) - motile invertebrate counts

Cape Arago barnacle trend plot

Mytilus (California Mussel) - percent cover

Cape Arago Mytilus trend plot

Mytilus (California Mussel) - motile invertebrate counts

Cape Arago Mytilus trend plot

Fucus (Northern Rockweed) - percent cover

Cape Arago Fucus trend plot

Fucus (Northern Rockweed) - motile invertebrate counts

Cape Arago Fucus trend plot

Pelvetiopsis (Dwarf Rockweed) - percent cover

Cape Arago Pelvetiopsis trend plot

Pelvetiopsis (Dwarf Rockweed) - motile invertebrate counts

Cape Arago Pelvetiopsis trend plot

Endocladia (Turfweed) - percent cover

Cape Arago Endocladia trend plot

Endocladia (Turfweed) - motile invertebrate counts

Cape Arago Endocladia 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 also include any 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)

Cape Arago 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. At some sites, other sea star species and Katharina are counted in addition to Pisaster. The sum of all individuals across all plots is displayed. Note that data gaps are represented by breaks in long-term count trend lines, but are not shown in size plots.

Pisaster (Ochre Star) - counts

Cape Arago Pisaster trend plot

Pisaster (Ochre Star) - sizes

Cape Arago Pisaster size plot

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