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Sancutary Program Accomplishments Intertidal Systems Open Ocean & Deep Water Systems Endangered & Threatened Species
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Twenty-five years ago domestic sewage was discharged onto the rocky intertidal on two sides of Monterey Bay. The Pacific Grove outfall at Point Pinos and the Santa Cruz County "Eastcliff" outfall at Soquel (Pleasure) Point both had been in operation for over twenty years. By the early 1970s they discharged daily 1.5 to 3 million gallons of primary treated sewage, respectively, over the wave-swept rocks. These sewage-impacted areas were characterized by classes taught at Stanford University's Hopkins Marine Station (the Point Pinos site) and UCSC (the Soquel site). The effect was similar at both: fishes, crustaceans, limpets, snails, sponges, ascidians, foliose red algae, and surfgrasses were conspicuously absent. In their place was a near-complete cover of diatoms and low-growing coralline algae, interspersed with clumps of sea lettuce, the red alga Prionitis lanceolata, deformed individuals of oar kelp, and large, solitary sea anemones.
Both outfalls were terminated in the mid-1970s when the sewage was redirected to longer outfalls discharging subtidally. Changes following termination were similar. Ephemeral green algae, especially sea lettuce, were conspicuous within months, to be replaced over the succeeding few years by a variety of foliose red algae and kelps, along with numerous invertebrates previously missing. Other species, such as sponges and ascidians, took much longer to become re-established. Particularly slow in becoming re-established were the visual dominants in these low intertidal areas, surfgrasses (Phyllospadix scouleri and P. torreyi); their come-back was accompanied by the slow decimation of the low-growing coralline algae, the visual dominant of the sewage-impacted areas. From a distance, the areas slowly changed from pink (coralline algae) to green (surfgrasses) as they recovered.
The abundance of surfgrass at Opal Cliffs remained high throughout the twenty-five years of sampling, with over half of the squares containing plants on most sampling dates. Considering the number and length of the surfgrass leaves (most over 30 cm long), this abundance means that there was nearly complete and uniform cover of surfgrass. In contrast, there was no surfgrass at all at the Soquel Point site when the sewage was being discharged. (See figure 1 below.) The first plants were noted in a few quadrats in 1980, four years after the discharge was stopped, but their abundance increased very slowly, mainly as the seedlings spread by clonal growth. The two sites were finally statistically indistinguishable with respect to surfgrass cover in 1997, twenty-one years after the outfall was abandoned, and a similar high abundance was found again in 1998.
Periodic examination of the abandoned outfall site at Point Pinos also revealed a slow recovery of the surfgrass beds, and they now appear nearly as fully recovered as at the Soquel Point site. The re-establishment of surfgrass was probably inhibited at both sites by the dense cover of low-growing coralline algae. At Soquel Point, where quantitative data are available, the abundance of coralline algae has slowly decreased from being present in all the 10 x 10 cm squares in 1976 and before to being present in slightly more than half in 1998, compared to fewer than 10 percent at the Opal Cliffs site. The two species apparently compete for space, and when well established, the coralline algae probably inhibit seedlings from getting established (the seedling may attach to the algal fronds, which then break off, carrying the seedlings with them). However, once securely attached on the underlying rock, the surfgrass rhizomes slowly grow outward, replacing the coralline algae and trapping sand, which further changes the habitat.
John Pearse, Eric Danner,
Lani Watson, and Chela Zabin
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Changes
following the termination of the discharge at
Soquel Point were documented by teams from UCSC,
following sampling done the previous three years.
Each spring the teams quantitatively sampled the
Soquel Point site. A comparative site 1 km to the
northeast at Opal Cliffs that showed little sign of
impact from the discharge was also sampled.
Quarter-meter-square quadrats were placed randomly
within permanent plots at each site and the
abundance of species recorded. Abundance of
surfgrass was estimated by counting the number of
10x10cm squares in the quarter-meter-square
quadrats that contained attached plants (total
number of squares in a quadrat=25).
Surfgrass
beds are rich, productive, and diverse systems. The
twisted rhizomes and long leaves provide shelter
and habitat for many animals, as does the thick
layer of sand trapped by the rhizomes.
Storm-detached leaves become litter that is
scattered across the ocean floor and down into
deeper water, providing resources for numerous
detritivores and their predators far beyond the
intertidal. It is reassuring that these surfgrass
beds, decimated by sewage discharge, have now -
after several decades - essentially recovered to
their former health.