Pacific Rocky Intertidal Monitoring: Trends and Synthesis
Shaws 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).
Barnacle cover at Shaws Cove remained high from initiation of the monitoring in 1996 through 1999. Subsequently there appears to have been a steady but minor decline in cover from 1999-2007 with concurrent increases in the cover of bare rock. From 2007-2010, cover consisted of approximately half bare rock and half barnacles. After barnacles, non-coralline crusts were the next most abundant spaceholders observed in this zone. However, the abundance of non-coralline crusts was low (less than 2% cover most years) with a maximum of close to 7% cover in fall 2009. In fall of 1998, the red alga Endocladia encroached into barnacle plots with an average cover of ~2.5%. After fall 1998, cover of Endocladia was highly variable but never exceeded 1% of the plot. On rare occasions, recruitment of Hesperophycus was observed but individuals typically died off before the next sampling period. Motile invertebrate surveys in barnacle plots recorded high numbers of Littorina spp. and variable numbers of small limpets. Both motile invertebrates exhibited minor seasonal patterns with higher counts typical in the fall sampling period.
As in other sites in this region, mussel cover at Shaws Cove remained relatively static from Fall 1996 through Fall 1997, but cover declined during the 1997-1998 El Niño. During this period of lowered mussel cover, a moderate amount of bare rock cover was recorded. Other spaceholders included barnacles, crustose corallines, articulated corallines, and non coralline crusts. Interestingly, crusts and articulated corallines alternated in terms of the group which was more abundant in mussel plots from spring 1998 to spring 2000. From 1998 to 2006, mussel cover steadily increased. The largest increase in cover was observed in fall 2003 (increase of 20% cover) as gaps within the mussel plots were filled with adult mussels (recruitment did not appear to play a role). In spring 2007, a storm accompanied by large waves resulted in a moderate decrease in overall mussel cover. This storm caused a ~35% loss in cover but the patchy nature of the disturbance resulted in 2 plots being almost completely denuded of mussels while two plots remained undisturbed. In disturbed plots, there was an increase in cover of the ephemeral alga Ulva in fall 2007 followed by a steady increase of barnacles which replaced Ulva in 2008 and 2009. Since the loss of mussels in 2007, mussel cover has changed little in subsequent years. Motile invertebrate counts were dominated by limpets, showing a seasonal pattern of higher counts in the fall sampling period.
Rockweeds at Shaws Cove exhibited typical variations in cover within a year and across years with a pattern of higher cover in the fall than in the spring sampling periods. From 2004 through Spring 2010, there was a minor but steady decline in rockweed cover. By fall 2008, rockweeds had disappeared entirely from one plot. During this decline, bare rock cover increased in the plots. Some space created by the reduction in Silvetia cover was occupied by barnacles; low cover of crustose algae, Caulacanthus, articulated corallines, and mussels was also observed. In Fall 2010, Silvetia abundance increased in plots, returning average rockweed abundance to 2006 levels. Motile invertebrate counts were dominated by Littorina spp. and limpets with Littorina spp. numbers increasing in fall of 2005.
Abundance of the red alga Endocladia (turfweed) has varied greatly (from 7 to 52% cover) at Shaws Cove since initiation of monitoring in 1996. The period with the highest cover occurred between spring 2001 and spring 2003 with cover values between 40 and 50%. Large losses (~20%) in cover occurred in fall 2000, fall 2003, and fall 2007. Bleaching seems to have caused the largest loss of cover in 2003 (~25%); in spring 2003 observers noted damaged thalli, and large portions of the turfweed were gone by the next sampling period. In fall 2007, cover reached a low of 7% and has only increased moderately since then. In addition to Endocladia, bare rock and barnacles contributed to overall cover in these plots. Like Endocladia, recorded cover of bare rock and barnacles was highly variable over the years. Barnacle cover, on average, hovered around 30% with peaks in fall 1997 and spring 2006 at ~60% cover. Rockweed cover in Endocladia plots was relatively low from 1996 to spring 2003 but increased from fall 2003 to fall 2006, reaching a peak of 20% in fall 2004. Most of this change was driven by a dramatic increase in cover in two plots (which were located adjacent to the rockweed bed). Motile invertebrate counts were dominated by Littorina spp. and limpets with numbers remaining static over the years.
Sea Star (Pisaster) counts are taken over the entire site at Shaws Cove. Sea star numbers varied greatly over the sampling period with peaks in 2004, 2006, and 2009.
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
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 ochraceus (Ochre Star) - counts