Monterey Bay Aquarium Nearshore Surface Seawater Bacteria Monitoring
- Roger Phillips
Monterey Bay Aquarium
- Sarah Mansergh
Monterey Bay Aquarium
The Monterey Bay Aquarium has been monitoring various aspects of near shore seawater quality in the Monterey Bay since 1984. Densities of indicator bacteria have been monitored in the raw (unfiltered) seawater intakes since 1996 and from near shore surface waters since 2000. Indicator bacteria groups are used to assess water quality in a variety of applications including recreational water usage and ocean water discharges.
Weekly samples were analyzed for the presence and most probable number of total coliforms, Escherichia coli (a subset of the fecal coliforms) and Enterococci using an enzyme substrate method developed by IDEXX Laboratories (Westbrook, MN). Raw seawater samples were tested on a weekly basis from January 1996 through December 2001. Near shore surface samples have been tested on a weekly basis since October 2000 and the results are used to help inform divers about contamination in local waters.
Summary to DateThe intake lines for the raw seawater samples are located about 1000 feet offshore at a depth of about 50 feet. This unique location is out of the influence of runoff and surface contaminants and that is reflected in the results. From 1996 through 2001 indicator bacteria concentrations in the raw seawater (RSW) samples rarely exceeded a most probable number per 100mL sample (MPN) of 100 for total coliforms or E. coli and only once exceeded an MPN of 50 for the Enterococci.
The recreational limits set by the California Department of Health Services for a single sample are an MPN of 10,000 for total coliforms (unless the ratio of fecal coliforms to total coliforms exceeds 0.1, then the limit is 1,000), 400 for fecal coliforms and 104 for Enterococci. Due to the low densities of indicator bacteria in the RSW samples the weekly monitoring of RSW for these bacteria was discontinued at the end of 2001. Spot samples are still taken following sewage spills and during times of high surf. The values have remained low. The near shore surface samples show greater variability in the levels of indicator bacteria. Low densities of bacteria occur through every season and high densities of indicator bacteria can not be correlated to sewage spills or rain events.
The most likely cause for high levels seems to be the resident populations of cormorants, seals and sea otters that frequent the waters in front of the aquarium. These results raise a question about the applicability of using these indicator bacteria for human health and safety programs when there is a known localized population of non-human sources for these bacteria groups. Extensive studies have not been conducted to correlate non-human sources of contamination with human health problems. The original studies performed by the EPA were conducted in areas known to have high levels of human contamination. In fact the agent for the gastrointestinal illness that the indicator levels of bacteria are based upon was thought to be viral and the “ultimate source is human fecal wastes” (1).
(1) U.S. Environmental Protection Agency. 1986. Ambient water quality criteria for bacteria-1986. EPA-440/5-84-002. U.S. Environmental Protection Agency, Cincinnati
- Total coliform
- E. coli
Study MethodsThe raw seawater intake is submerged at a depth of approximately 50 feet and located about 1000 ft offshore from the Monterey Bay Aquarium at 37.62ºN 121.90ºW. The water is gravity fed to a pump house and then pumped through raw seawater lines throughout the aquarium. Raw seawater samples were collected in 250mL sterile sample bottles from a direct tap in the raw seawater line in the basement. Data is available from January 10th, 1996 through December 10th, 2001. The near shore surface samples were obtained using a handheld water sampler containing a 60mL sterile sample bottle. The sampler was lowered into the water just off the aquarium’s back deck at 36.37ºN 121.90ºW. Data for the near shore surface samples is available from October 11th, 2000 through last Monday. The graphs presented here contain data through 2004. For more recent data please contact Sarah Mansergh or Roger Phillips.
Enzyme substrate methods developed by IDEXX Laboratories (Westbrook, MN) were used to enumerate the three groups of indicator bacteria. Colilert-18 reagent was used to enumerate total coliforms and E. coli and the Enterolert reagent was used for enterococci. Seawater samples were diluted with sterilized laboratory grade water to either a 1:10 or 1:20 concentration before adding the reagent. The processed sample was poured into a Quanti-tray (IDEXX Labs) containing either 51 wells or 49 large wells and 48 small wells and run through a Quanti-Tray heat sealer which individually sealed each well. The Colilert-18 samples were incubated at 35ºC for 18 hours and the Enterolert samples were incubated at 41ºC for 24 hours. Positive wells for total coliforms turn yellow and the positive wells for both E. coli and enterococci fluoresce blue under UV (365 nm) light. Based on statistical tables provided by IDEXX, the MPN for each group was calculated, with possible values ranging up to 48,384 for a 1:20 dilution in the 49x48 well trays.
Figures and Images
Colilert-18/Enterolert system including Quanti-tray sealer, rubber inserts, Quanti-tray 2000 (49x48 well tray) with yellow positive wells indicating total coliforms, 51 well Quanti-tray fluorescing under UV (365nm) light indicating enterococci, dilution bottle, Colilert-18 and Enterolert reagent snap packs, UV light and MPN tables.
- Monterey Bay Aquarium Near Shore Surface Indicator Bacteria October 2000-December 2002
- Monterey Bay Aquarium Near Shore Surface Indicator Bacteria January 2003-December 2004
- Monterey Bay Aquarium RSW Indicator Bacteria January 1996-December 1998
- Monterey Bay Aquarium RSW Indicator Bacteria January 1999-December 2001