Treasure Island 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). Due to funding constraints, semi-annual sampling of plots/transects was reduced to annual sampling beginning in 2016.

Cover of acorn barnacles in permanent plots at Treasure Island has been variable over time. Acorn barnacles covered more than 80% of the rock surface, on average, when plots were established in 1997. Cover remained generally high (> 60%) through 2001, but then fluctuated between ~40% and 80 % through 2013. During periods of low barnacle cover, there were concurrent increases in the cover of bare rock, and from 2009-2012, acorn barnacles and bare rock covered approximately equal area in these plots. After dipping to a (mean) low of ~16% in Spring 2015, cover steadily increased again to an average of ~40% cover in 2018. The ephemeral alga Ulva was present in low abundance in barnacle plots in most sampling seasons, with noticeable peaks in 2006 and 2007 driven by large but patchy recruitment of the alga (with high abundance in one or two plots and low abundance in others). Non-coralline crusts were also present in the plots in extremely low abundance, although the cover of bare rock in the plots was affected by peaks in cover of the crusts in spring 2003 (17%) and spring 2008 (9%). Periwinkles (genus Littorina) were consistently extremely abundant in barnacle plots while the abundance of limpets was highly variable across sampling periods.

Mussels covered, on average, ~70% of the surface of permanent plots at this site at initiation of the monitoring in 1996. Cover declined substantially over subsequent sampling periods, potentially as a consequence of El Niño conditions in 1997 and 1998.  Mussel cover remained low (below 40%, on average) for several years before it rebounded to a high of 80% cover (on average) in 2004. From 2004 to 2012 mussel cover remained generally high (mean cover > 50%). Notably, although a decrease in mussel cover following a severe storm in 2007 was evident in the permanent sampling plots at other Orange County sites (see Crystal Cove and Shaws Cove), permanent plots at Treasure Island only experienced a minor (~10 %) cover loss. Mussel loss was noted after the storm at this site in the lower intertidal zone (below the area of the fixed photoplots). Mussel cover declined again starting in Fall 2012 (reaching a mean of ~15% in Fall 2016) but subsequently increased slightly to a mean of ~30% cover in 2019. Overall in years of low mussel cover, most of the plot surface was bare rock, although barnacles (Chthamalus / Balanus and Tetraclita) and crustose algae (including both coralline and non-coralline species) were present. Limpet abundance was consistently high in mussel plots from 2003 – 2014 while the abundance of periwinkles (genus Littorina) and chitons (genus Nuttallina) were consistently present but less abundant. The predatory whelk Nucella was also present consistently in plots through 2012, although the abundance of Nucella encountered in mussel plots dropped sharply after 2012 in conjunction with the decline in mussel cover observed in 2013 and 2014.

Rockweed cover in permanent plots was highly variable at this site over both short (seasonal) and long temporal scales. From 1997 through 2004, mean cover of rockweeds fluctuated between a low of ~50% to a high of ~90%, with generally higher cover recorded during Fall sampling periods than during Spring sampling periods.  From 2006 – 2010, cover was generally lower (~40 to ~60% cover) with a consistent seasonal pattern. After a period of relative high cover (> 60% on average) from 2010 - 2014, cover declined drastically in 2015 to the lowest level recorded at this site (mean ~22%). Cover subsequently increased slowly, but remained low (mean < 40%) through 2019. During periods of low rockweed cover, surveys generally recorded increases in the cover of bare rock and acorn barnacles. Barnacle cover reached particularly high levels in 2006 (~40%) and 2019 (~22%) cover. Mussels were consistently present in small numbers in rockweed plots (< 9% cover on average). Articulated corallines, crustose corallines, non-coralline crusts, other red algae, and Ulva were also common in Silvetia plots but their cover was highly variable over time. The high intertidal rockweed Hesperophycus, not present in Silvetia plots from 1996 to 2002, recruited at low levels into the rockweed plots in 2003, reaching a peak of 8% cover in spring. However, this increase was short-lived, as it was followed by a die off in fall, and Hesperophycus cover has since remained low since that time. Abundance of periwinkles (genus Littorina) varied greatly over time in rockweed plots, dropping below 50 individuals / plot in 2007 and exceeding 400 individuals / plot (on average) in 2009. Chitons (Nuttallina and Cyanoplax) the predatory snail Nucella, and hermit crabs have been found in plots in consistently low numbers.

Rock plots were established at this site in Spring 2011 in areas above the barnacle zone. A heavy influx of sand covered one plot (100% cover of sand) on three occasions (Fall 2011, Fall 2012, and Fall 2018), resulting in an overall lower average cover of rock in the sampling plots on these three sampling dates. Cover of sessile macroorganisms in these plots has remained negligible, resulting in 100% cover of ‘bare rock’ in almost all plots in almost all sampling periods since the plots were established. Periwinkles (genus Littorina) were the only mobile invertebrate consistently encountered in rock plots. Between 200-500 individuals were encountered during surveys (on average) with the exception of the survey in Spring 2016, in which only ~100 individuals were counted.

Site-wide sea star (Pisaster) counts were low (fewer than ~50 individuals / survey) from 1996 to 2005. Counts were higher but variable from 2006 – 2013 (with counts exceeding 100 individuals on three occasions). As with other Orange County sites, a large increase in sea star abundance was observed in Fall 2013, and during this survey signs of sea star wasting syndrome were noted in a few individuals. In Spring 2014, no Pisaster were found at this location; Sea Star Wasting Syndrome is a likely factor in this decline. Since 2014, only seven Pisaster individuals have been encountered in surveys (1 each in Spring 2015, Spring 2018, and Fall 2018, and four in Fall 2019).  Sea star sizes were consistently measured starting in Spring 2012. From 2012 – 2013 the population included individuals in a range of size classes (from 50 mm to 200 mm) although most individuals fell in the 100 – 150 mm size classes.  Since 2013, no individuals larger than 150mm have been encountered during monitoring surveys.

Photo Plots

Below are the trends observed for each Photo Plot target species at this site. Long-Term percent cover trend graphs also include any 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. Due to time constraints, motile invertebrate counts have not been done at most sites since 2012. 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)

Rock (Above Barnacles) - motile invertebrate counts

Species Counts and Sizes

Species Counts and Sizes (where recorded) for Pisaster are shown below for this site. At some sites, other sea star species and Katharina are counted in addition to Pisaster. The sum of all individuals across all plots is displayed. Note that data gaps are represented by breaks in long-term count trend lines, but are not shown in size plots.

Pisaster ochraceus (Ochre Star)

Pisaster ochraceus (Ochre Star) - sizes