Pacific Rocky Intertidal Monitoring: Trends and Synthesis
Dana Point 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).
Barnacle cover at Dana Point showed frequent small increases and decreases since initiation of sampling in 1996, with a trend of declining cover over time. On a few occasions, small amounts of algae (including the rockweed Silvetia, the ephemeral sea lettuce Ulva, the brown blade Endarachne and the red turf Caulacanthus) recruited into barnacle plots, but these algae did not persist. Instead, rock in barnacle plots that was not occupied by barnacles generally remained bare. Snails in the genus Littorina were consistently found in very high abundance in barnacle plots. Limpets (genus Lottia) were also consistently present but at much lower densities than Littorina.
Mussel cover at Dana Point showed fewer fluctuations than barnacle cover from 1996 to 2006, though mussel cover did decrease during the 1997-1998 El Niño. After recovering following the El Niño, mussel cover dropped again in spring 2007 following a storm with extraordinarily large waves. As at other sites in the region (e.g. Crystal Cove) the effects of the storm were variable in space, with some plots losing more of their mussel cover than other plots. In general, following a drop in mussel cover, space on the rock not covered by mussels remained bare with occasional recruitment of barnacles (acorn barnacles and Tetraclita). Low and fluctuating cover of the red turf alga Caulacanthus has been observed on top of mussels in several plots since the early 2000s. After the 2007 storm, plots that lost large numbers of mussels have been slow to recover, and mussel abundance has remained relatively low. Several groups of molluscs are consistently found in low abundance in mussel plots (e.g. the chiton Nuttallina, the turban snail Tegula funebralis, and the periwinkle genus Littorina) but only limpets (genus Lottia) were found in very high abundance.
Rockweed cover at this site fluctuated within years (often with higher cover during fall sampling periods than spring sampling periods). Small amounts of sand were occasionally observed in a few of the rockweed plots during fall sampling, but overall sand influence appeared to be low. Across years, rockweed cover remained relatively high (above 60% of plot area, on average) from 1996 to 2010. When the cover of Silvetia dipped, the cover of bare rock typically increased: aside from the red turf alga Caulacanthus (which appeared at low levels in a few plots) and crustose algae, few other space-holding species were observed in rockweed plots. Limpets (Lottia sp) were very abundant in Silvetia plots, although limpet abundances fluctuated greatly over time (from a high average of 100 individuals per plot to a low average of approximately 20 individuals per plot). The turban snail Tegula funebralis was also regularly found in rockweed plots, though numbers of the snail were typically lower than the number of limpets.
Sea star (Pisaster) counts showed peaks in abundance in 2003 and 2008, but compared to other sites in Orange County (Crystal Cove, Shaws Cove, and Treasure Island) sea star counts at Dana Point were low throughout the monitoring period.
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
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 ochraceus (Ochre Star) - counts