Authors:
John S. Pearse, William T. Doyle, Vicki B. Pearse, Marcia M. Gowing, J. Timothy Pennington, Eric Danner, Ann Wasser
Surfgrass meadows are major habitats along the coast of the North Pacific Ocean, providing complex biotic communities and nurseries for fishes and crustaceans. They have been little studied in most areas, including central California. We present here the results of monitoring two 450m2 plots over a period of 42 years within the Monterey Bay National Marine Sanctuary by citizen scientists (trained students and naturalists). One, the Soquel Point plot, was near a small (~3 million gallons per day) domestic sewage outfall that was discontinued in 1976, and the other, the Opal Cliffs plot, was in a comparison site ~1 km away. Monitoring was done nearly annually between 1973 and 2003, then in 2006, 2012, 2014, and 2015. The abundance of common seaweeds and invertebrates was recorded each year from counts of individuals, or their presence in 25 10x10 cm squares, in randomly placed 50x50 cm quadrats (mean number of counts, 24.3; range 10-41).
Surfgrasses (Phyllospadix spp., mainly P. torreyi) were absent in the Soquel Point plot when the sewage was being discharged and were first seen in the plot in 1978, two years after the sewage discharge was terminated. Surfgrass abundance increased slowly and was comparable to that in the Opal Cliffs plot only in the late 1990s, over 20 years after the termination of the sewage discharge. In contrast, species in one genus of coralline algae (Corallina) were abundant when the sewage was being discharged and declined slowly for 30 years following discharge termination, never reaching levels comparable to those in the Opal Cliffs plot. Frilly red algae (Cryptopleura spp.) were nearly absent from the Soquel Point plot when the sewage was discharged and rose just before the discharge was terminated, reaching levels comparable to those of Corallina spp. Levels of Cryptopleura spp. and Corallina spp. slowly decreased in parallel while those of Phyllospadix spp. rose, suggesting both facilitation (Corallina spp. facilitating both Cryptopleura spp. and Phyllospadix spp.) and competition (Phyllospadix spp. eventually dominating).
The abundance of species of a second genus of coralline algae, Bossiella, was low in the Soquel Point plot when the sewage was discharged, increased just before termination of the discharge, and remained similar to or slightly higher than that at Opal Cliffs during the rest of the monitoring period. Abundances of sea lettuces (Ulva spp.), turban snails (Tegula spp.), and hermit crabs (Pagurus spp.), which were low when the sewage was discharged, also increased just before the discharge was terminated. The increase in the abundance of these taxa corresponded to a steady decrease in grease content in the sewage. Within a few years after the sewage discharge was terminated, the abundances of all these taxa stabilized; they remained low and similar to those in the Opal Cliffs plot for the remainder of the monitoring period.
In the Opal Cliffs plot, ~1 km downstream from the discharge, the sewage discharge apparently enhanced the abundance of coralline algae (both Corallina and Bossiella), frilly red algae, sea lettuces, and honeycomb tube worms. Abundance of all these taxa decreased after the discharge was terminated, indicating that they had benefited from the nutrients in the sewage.
Sunburst anemones (Anthopleura sola) were more abundant in the Soquel Point plot than the Opal Cliffs plot throughout most of the monitoring period. They were likely established in the Soquel Point plot when the sewage had denuded the area, exposing bare rock suitable for attachment, then were able to persist for decades following the termination of the sewage discharge and the re-establishment of the surfgrass meadow.
Overall taxon richness of both seaweeds and invertebrates was lowest in the Soquel Point plot and highest in the Opal Cliffs plot when the sewage was discharged, converged to moderate levels in both plots within a few years after the discharge was terminated, and then remained steady and indistinguishable throughout the rest of the monitoring period. This overall stability in taxon richness was similar to the abundances seen for most specific taxa monitored. The surfgrasses, Corallina spp., and frilly red algae in the Soquel Point plot took longer to stabilize, 20 to 30 years after the termination of the sewage discharge.
This long-term monitoring program demonstrates that citizen science programs using trained students and naturalists can provide robust information about the condition of intertidal communities within National Marine Sanctuaries. It found that surfgrass communities are remarkably resilient, even after chronic disturbance (in this case by domestic sewage) removes the foundation species (surfgrasses). Although recovery of the surfgrasses took decades, most taxa in the community returned to abundances similar to those recorded in the comparison plot within a few years, and the overall community structure displayed persistent stability. Similar resilience can be expected with other disturbances such as major storms, chemical spills, or ship groundings that could damage surfgrass meadows. The consequences of disruption from global warming are uncertain, and these data provide a baseline for future evaluation.
Key Words:
Monterey Bay National Marine Sanctuary, citizen science, LiMPETS, surfgrasses, Phyllospadix, coralline algae, Cryptopleura, domestic sewage impact and recovery, long-term monitoring