Pacific Rocky Intertidal Monitoring: Trends and Synthesis
White 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).
The barnacle plots at White Point consist of Chthamalus dalli/fissus (note that species were not distinguished until 2001) and Balanus glandula with separate plots (5 of each) designated at this site based on the each the early dominance of each genera. However, as at all the southern California MARINe sites, these genera are not distinguished in the sampling of either plot type and are at collectively reported as "barnacle" cover here. Within these ten barnacle plots, barnacle cover has declined gradually throughout the monitoring period with one episode of precipitous decline and recovery in the late 1990's. Recordings of bare rock shot up during that period and have remained high ever since. In addition, the cover of red algae have gradually increased throughout the years and have begun filling in the plots as barnacles declined. In the earlier years, a single red alga was responsible for this increase which has been loosely identified as a very low growing form of Mazzaella affinis characterized by very small bladelets thickly emerging from a crustose base. Initially, this M. affinis carpet spread into the a significant portion of a single plot with as second plot impacted to a lesser extent. But in recent years those patches have grown and all plots have been invaded to some extent. And in 2002, the newly introduced and invasive alga, Caulacanthus, began spreading into these plots, initially growing atop the M. affinis carpet and then spreading further into the plots. These plots seem to be experiencing a slow transition toward an algae dominated state. Motile invertebrate counts at this site began seasonally in the Spring of 2001 (with littorines added the following fall) and were changed to annual sampling in 2004. Both limpets and littorines have been abundant in the Chthamalus plots with up to 500 or more individuals per plot in some sampling events and high variation generally. Neither species has shown variability tied to species cover in the photoplot sampling.
Mussels cover in the mussel plots remained high and largely stable in most years until 2006 when it dropped steeply from the 80% or greater range down to around 50% in 2008. After that a moderate rebound occurred with mussel cover leveling out in the 60 to 70% range through 2010. Two plots were largely responsible for this decline having undergone partial to complete mussel breakouts, presumably as a result of strong winter storms. However, mussel bed contraction has also been a factor at this site, albeit less severe than at other sites in southern California. In general, the beds at this site are characterized by tightly packed monolayers of small to medium sized mussels commonly with interspersed bare patches. In some plots, and in portions of mussel beds across the site, mussels are covered by a layer of epiphytic Caulacanthus that is thick enough to obscure the mussels completely in places. Thus far, Caulacanthus has not been observed to cause mussel mortality, but the spread of this species could certainly be having an influence on mussel recruitment and bed replenishment locally within this site. The data from the Motile invertebrate sampling show that limpets are common in the mussel plots in the range of around 100 individuals per plot in most years. Nuttalina sp. chitons and littorines are also present in these plots in low numbers. The infrequency of snails in these plots is notable, though Nucella snails are occasionally found in low numbers.
Within the turfweed plots, Endocladia cover is seasonal (higher in spring, lower in fall) and has declined from the 70 to 80% range found in initial years of sampling to around 40 to 50% in most years since. Cover dropped to a particularly low level below 20% in the spring of 2007 but rebounded to near 60% by the last reported sampling in 2010. Barnacles and bare rock have generally, but imperfectly, trended inversely to Endocladia cover. And red algae cover, which in this case is almost entirely comprised of Caulacanthus cover, has been increasing in the turfweed plots since the early 2000's. This alga has invaded many of the available topographic lows within these plots while Endocladia has been more successful in retaining the higher ground. Motile intertebrate counts within the turfweed plots depict a high abundance and a high variability of both limpets and littorines. However, multiple data points for both taxa in 2006 indicate a data problem that requires resolution before these data can be reliably interpreted.
Seastar (Pisaster ochraceus) plots were added to this site in the fall of 2003 and consist of three large irregular plots surrounding an area of medium relief rock which includes several large cracks and ledges. The initial samples yielded just under 50 total individuals each. Then abundance increased considerably in 2006 and 2007 to a high of around 200 seastars followed by a drop to basal levels in 2009 and another increase to over 100 total stars thereafter. Recruitment is common at this site with seastars in the 50mm or less range found in most seasons. It appears that a large recruitment event was responsible for the 2006-2007 increase, and the size frequency distribution follows the growth of those seastars throughout subsequent seasons. However, stars in the larger size classes are generally rare at White Point which is likely the result of high, and largely unregulated, human visitation, species manipulation and harvesting 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
Endocladia (Turfweed) - percent cover
Endocladia (Turfweed) - 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 (Ochre Star) - counts
Pisaster (Ochre Star) - sizes