Pacific Rocky Intertidal Monitoring: Trends and Synthesis

pacificrockyintertidal.org home

Paradise 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).

The barnacle plots at Paradise Cove consist of a mixture of Chthamalus dalli/fissus (note that species were not distinguished until 2001) and Balanus glandula with the former being the overwhelming dominant component of all plots.  In general, barnacle cover has varied inversely with bare rock with a small net decline of around 10% since their inception in 1994.  In recent years these plots were invaded from below by Endocladia (mostly as epiphytes on barnacles), and this was suggestive of a possible ecological transition, but this Endocladia has all but disappeared in the past few seasons. 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 were highly abundant and varied gradually in the neighborhood of 1000 to 2000 individuals per plot on average.  Limpets were also common and varied gradually between 5 and 50 individuals per plot on average. Motile invertebrate data were not obtained for these plots in 2004.

The mussel plots at have been fairly stable throughout the years with mussel cover in the 80 to 90% range most of that time.  A gradual decline in 1998 and a more precipitous decline in 2005 were each followed by gradual recoveries.  Not evident in this trend graph are changes in bed depth that have occurred throughout the years.  For example, in 2006 a line of advancing seastars just below these photoplots caused the mussels to pile up atop one another, changing what had been a tight monolayer to a loose multilayered bed. The data from the Motile invertebrate sampling show consistent low levels of snails (Tegula funebralis), along with higher and more variable numbers of limpets.  Peaks in limpet abundance occurred in 2003 and 2008 with the latter far exceeding the former.

Patterns of cover in the Endocladia plots have been dynamic with Endocladia, barnacles, mussels and rock all becoming dominant at one time or another.  Endocladia started out with a mean cover of around 20% in 1994 and it is close to that same level at the present; However, in the intervening years, turfweed rose to nearly 60% cover shortly after plot inception and remained there for 8 years before a precipitous crash in 2004.   Barnacles had initially been at over 40% cover in 1994, but then declined to very low numbers by 1996 where they have largely remained ever since.  On the other hand, mussel cover was negligible for the first nine years of sampling, but then began increasing in 2003 and reached 60% cover by 2006.  Subsequently, the mean mussel cover dropped back to 30% in the fall of 2008 and has remained close to that point ever since.  And as mussels have declined, recordings of bare rock have become more common and are currently near the 60% level. The data from the Motile invertebrate sampling show wide swings in both limpets and littorines in the Paradise Cove Endocladia plots.  Limpets started out in the spring of 2000 with a mean abundance of 100 individuals per plot and dropped to half that amount on two different occasions, but were back around 140 per plot by 2010.  On the other hand, littorines started out at 140 limpets per plot in 2003 and were almost completely gone by 2010.  

The mean cover of Surfgrass (Phyllospadix spp.) has fluctuated widely throughout the years at this site with seasonal variation (lower in spring, higher in fall) along with intermittent periods of modest sand burial.  Throughout the years, the cover of Phyllospadix hovered around 60% plus or minus 10 percent with one significant population decline in 1997 and 1998.  This period was marked by an initial increase in sand through the first two seasons of the decline, and then a sharp increase in rock during the spring 1998 sampling.  This is suggestive of Phyllospadix loss due to sand burial and/or scour followed by sand removal and subsequent Phyllospadix recovery.  Red algae also showed seasonal increases that were the inverse of the seasonal Phyllospadix declines.

Seastar (Pisaster ochraceus) plots were added to this site in the spring of 2002 and consist of three large irregular plots surrounding an area of medium relief rock and shallow tidepools.  At the first sampling, the total number of seastars counted and measured was around 180.  That number increased to nearly 300 by the following fall, but began to decline thereafter and has been hovering around 100 seastars since 2005.  While smaller (<50mm radius) stars have been common at this site throughout the years, those encountered tend to be larger (>70mm).  General observations, along with the size distribution depicted in the trend graph, suggest that most seastars are moving in and out from the subtidal though some may be recruiting to the monitoring site as young stars.

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

Paradise Cove barnacle trend plot

Chthamalus/Balanus (Acorn Barnacles) - motile invertebrate counts

Paradise Cove barnacle trend plot

Mytilus (California Mussel) - percent cover

Paradise Cove Mytilus trend plot

Mytilus (California Mussel) - motile invertebrate counts

Paradise Cove Mytilus trend plot

Endocladia (Turfweed) - percent cover

Paradise Cove Endocladia trend plot

Endocladia (Turfweed) - motile invertebrate counts

Paradise Cove 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 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)

Paradise 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 (Ochre Star) - counts

Paradise Cove Pisaster trend plot

Pisaster (Ochre Star) - sizes

Paradise Cove Pisaster size plot

Sites home

Interactive Map

pacificrockyintertidal.org home

See Also