Pacific Rocky Intertidal Monitoring: Trends and Synthesis
Point Fermin 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 Point Fermin consist exclusively of Chthamalus dalli/fissus (note that species were not distinguished until 2001). Cover of Chthamalus typically varied inversely with rock cover, with relatively little else occurring in these plots. When this site was established in fall 2009, mean barnacle cover started out around 60%, declined to around 40% by 2003, when it rose to nearly 80% by 2004, and then declined after 2006 to around 25% where it remained through 2010. Inversely, rock began around 40% declined to around 20% by 2004, and then increased to 75% after 2006. 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 were consistently in the neighborhood of 1000 individuals per plot. Limpets also started out common with around 50 individuals per plot on average, but then gradually declined and were very uncommon in the barnacle plots by 2010.
Mussels have declined substantially at the Point Fermin monitoring site. Mytilus cover in and around the mussel plots started close to 100% at site inception in 1999, but immediately began a steady decline leveling off at around 15% by 2003. The plots have remained largely unchanged since that time. Three plots became completely devoid of mussels (except for a few small isolated recruits), while one remained steady at around 70% cover and the last plot contains one small persistent patch of mussels. These plots are representative of the surrounding reefs as widespread mussel bed contractions have occurred at this site, as has been the case at many other sites in southern California. As the mussel bed contracted, bare rock and barnacles became more prevalent, as did the cover of species that do not appear in this graph (Tetraclita, Lottia gigantea, chitons (Nuttalina sp.), crustose algae, articulated coralline algae, and others). Caulacanthus also invaded the lower and wetter portions of these mussel plots as that introduced and invasive alga spread throughout this site several years ago. As indicated above, a small number of mussels have recruited into the plots since the decline, but these have never survived beyond a season or two. The data from the Motile invertebrate sampling show that limpets, chitons (Nuttalina sp.) and shore crabs (Pachygrapsus crassipes) were all common in the mussel plots prior to the decline, each with and abundance of around 10 individuals per plot. As mussels declined, limpet abundance increased dramatically to around 1000 individuals per plot and shore crabs began a slow, then more rapid decline to near zero in 2010, while chiton abundance held steady. The sampling of littorines began in 2006. Littorine abundance in these mussel plots has remained generally low with less than 10 individuals per plot on average.
Within the rockweed plots, Silvetia has been seasonally variable (lower in spring and higher in fall) with the mean cover remaining steady near 100% (fall highs) for the first 5 years of sampling. Starting in 2005, the cover started to decline gradually with fall highs dropping first to around 90% and then to 80% by 2009. Much of this decline is due to a single plot which had dropped to less than 50% cover by fall 2010 and has declined further to less than 20% in subsequent years. The other plots are still in the 70 to 90% cover range during their fall highs. As Silvetia has declined, bare rock has become more prevalent in these plots, as have crustose algae and the invasive species Caulacanthus, neither of which appear in this figure. Motile intertebrate counts within these plots show that Cyanoplax spp. chitons are common under the rockweed canopy. These chitons exhibit seasonal variation in synchrony with Silvetia, suggesting that these chitons move to other areas as the rockweed thins out in the plots. In recent years, these chitons showed a reduction in their seasonal increases, and later in their basal abundance to just a few chitons per plot. Hermit crabs (Pagarus spp.) exhibited a similar, but more dramatic, pattern with their numbers high and variable in the earlier years of sampling, but then dropping to zero by 2004. Meanwhile turban snails (Tegula funebralis) displayed an opposite trend with their numbers growing in recent years, and limpets have likewise become more abundant (and also more variable) in recent years.
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, although a few small recruits had been observed in cracks and fissures within these plots.
The mean cover of Surfgrass (Phyllospadix spp.) at Point Fermin has shown seasonal variation (lower in spring, higher in fall) with moderate fluctuations and an overall increase in cover from around 60% in the initial sampling to around 80% in latter years (fall highs). Algal species have also shown seasonal variation with Egregia cover generally following Phyllospadix cover (though with lower seasonal swings), and red algae and articulated corallines displaying the inverse pattern (cover increasing when Phyllospadix is lower).
Seastar (Pisaster ochraceus) plots were added to this site in the spring of 2003 and consist of three large irregular plots surrounding an area of medium relief rock which includes several cracks and ledges. Seastars were common at this site when these plots were initiated, but declined steadily over the next two years such that just a few stars have been counted and measured each season since 2005. These plots are representative of the site as a whole. In recent seasons, timed searches of the entire site turned up just a few additional seastars. The size frequency figure indicates that the large number of seastars found during the first sampling seasons, in part, may have been the result of a large recruitment pulse occurring sometime in the preceding years. Recruitment has been low since that point but has, along with potential migration in and out from the adjacent subtidal, helped to keep the numbers of seastars above zero at this site.
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
Rock (Above Barnacles)
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