Sanctuary Integrated Monitoring Network
Monitoring Project

Ecological Effects of the Moss Landing Thermal Discharge

Principal Investigator(s)

  • John Oliver
    Moss Landing Marine Laboratories, California State University
  • Nick Welschmeyer
    Moss Landing Marine Laboratories, California State University
  • Jim Harvey
    Moss Landing Marine Laboratories, California State University


  • SIMoN
Start Date: December 15, 2002
End Date: February 28, 2006

The proposed study will provide the first quantitative evaluation of the ecosystem impacts of thermal discharge into Monterey Bay from Moss Landing power plant. We will sample benthic invertebrate communities living in the intertidal sand beach, in the extensive subtidal sand bottoms, and in isolated reefs. These bottom communities are the best long-term indicators of potential negative impacts to the nearshore ecosystem. We will sample planktonic communities and marine birds, which are the best short-term indicators. Bottom communities are much less mobile than the plankton and birds. All three communities will be sampled at the thermal plume and at control sites that are outside the plume.

While planktonic bacterial production is temperature dependent and may change at the discharge, we will also process phytoplankton samples for dynamic fluorescence response as a real-time indicator of physiological stress. The thermal plume is rapidly mixed by upwelling water from Monterey Canyon, strong long-shore currents, and especially the large tidal exchange of water from Elkhorn Slough, which produces a permanent turbid plume that covers the thermal plume and a much larger area of the nearshore. Therefore, sampling will also attempt to separate impacts from the thermal plume and slough plume.

The sampling design permits us to resample benthic communities that were sampled in the 1970s at the end of a cold, productive period in the California current system. We have been in a warm period since 1976-77, and are apparently in transition to the next cold regime. Recent sampling of the subtidal bottoms revealed dramatic declines in diversity, abundance, and biomass – presumably from the significant decrease in pelagic food for the sea floor. The proposed sampling will determine if this ecosystem degradation extends into the intertidal beach and shallow subtidal bottoms. It will also create a complete baseline on the structure of benthic communities from the intertidal beach to 30 m. This is the inner, wave-exposed shelf ecosystem, which is highly sensitive to a wide variety of natural and anthropogenic disturbances, and therefore a prime target for exploring future, long-term changes in ecosystem dynamics.

We will document the relationships between nearshore plankton and hydrology and the plankton and hydrology of Elkhorn Slough (other SIMoN sponsored work), while providing the first complete baseline on nearshore planktonic communities, which are likely to change as the extremely high rates of habitat erosion in Elkhorn Slough accelerate. We will also extend the first quantitative survey of nearshore marine birds from 2 to 5 years, again providing a solid baseline for assessing future ecosystem changes. A major study objective is to compile all historical community data on benthic invertebrates, plankton, marine birds, fishes, and related physical and chemical habitats conditions into the project database. Most of these historical data were collected by students and staff at MLML. This study will stimulate considerable additional research during and for many years after the funded project.

Summary to Date

This monitoring project was completed in February 2006. A draft final report was submitted in early March 2006. We expect the final version of the report will be available by June 2006.

Monitoring Trends

  • Huge numbers of By-the-Wind-Sailor jellies Velella velella washed up on the beach during both April and May 2003. In some places there were drifts 1 foot deep, with concentrations approaching 100 percent cover in the upper intertidal along the entire beach. Velella continue to come ashore in significant numbers even in late July–an unusual occurrence. While Velella have always been present in the Bay, and generally are stranded during the late spring, the numbers seen this year surpass any that the investigators remember.
  • Three species of amphipods have been found in the lowest intertidal zone: Americhelidium (formerly Synchelidium), Grandifoxus grandis, and Mandibulophoxus gilesi. This is encouraging, because although no quantitative samples have been taken from the beach since the 70s, periodic qualitative surveys have not found amphipods. One amphipod that was previously found on the beach in significant numbers, Eohaustorius washingtonianus, has not yet been found.
  • In conjunction with the collection of subtidal samples, qualitative surveys were made by divers using underwater scooters. During the June 2003 collection large numbers of juvenile cancer crabs (probably Cancer gracilis) were observed on the sandflats surrounding the canyon head. Densities were several dozen per square meter. Despite numerous dives in the area over many years, we had not previously observed this phenonem. When we went out again in July 2003, most of the small crabs were gone from the shallow sandflats, but large numbers were seen on the walls of the canyon out to about 50’. Apparently, the sandflats near the canyon head are acting as a nursery area for cancer crabs.
  • On all but one of the 19 cruises through May 2003, increased temperature, relative to surrounding bay water, was observed at the plume site. Surface seawater temperature averaged 3.4 degrees C higher at the discharge site than at locations 500 m from the site (range 0.03 to 7 degrees C). Bacterial samples were streaked onto marine agar plates and incubated to evaluate colony development. Most experiments showed an increase in bacterial colony counts at the discharge site relative to the bay water 500 m away (Figure 1). On average, bacterial colony counts were two-fold higher at the discharge site than at the 500 m station.

Study Parameters

  • Habitat association
  • Habitat
  • Diversity
  • Disturbance
  • Abundance
  • Distribution
  • Density
  • Size structure
  • Temperature

Figures and Images

Figure 1. Sampling station locations and depths.

Figure 2. Relative bacteria colony counts vs. distance from discharge site at several points in time.

Figure 3. Moss Landing Marine Lab graduate students processing beach core samples.


  • MLML (2006)
    Ecological Effects of the Moss Landing Powerplant Thermal Discharge.
    3.4 MB PDF