Cyanobacterial blooms and their associated toxins have become increasingly problematic globally (Chen et al. 1993, Domingos et al. 1999, Lehman et al. 2005, Guo 2007, Paerl & Huisman 2008). Microcystis aeruginosa in particular is considered a cyanobacterial harmful algal bloom (CyanoHAB) organism because it can impede recreational use of waterbodies, reduce aesthetics, lower dissolved oxygen concentration, and cause taste and odor problems in drinking water, as well as produce microcystins, powerful hepatotoxins associated with liver cancer and tumors in humans and wildlife (Carmichael 2001). Until recently, Microcystis (and associated Cyanobacterial Harmful Algal Bloom (CyanoHAB) genera) blooms and microcystin intoxication were considered a public health issue solely of freshwater ponds, lakes, reservoirs, public water supplies and rivers; this assumption is reflected in the vast body of scientific literature available on potential public health risks from microcystin exposure in freshwater habitat. By comparison, monitoring of the freshwater-marine interface for similar ecological or public health risks has remained a low priority until very recently, despite observation of outflows of Microcystis and microcystin-contaminated fresh water to the ocean (Lehman et al. 2005; Tonk et al. 2007). Given the severe and ubiquitous nature of this problem in freshwater habitats and potentially coastal marine systems, surveillance and monitoring is critical. Traditional monitoring programs for phycotoxins typically rely on discrete sampling (“grab” samples) from a particular site or sites, sometimes augmented with automated sampling systems. Such methods are inherently biased if the sampling does not capture the spatial and temporal variability of the system due to behavioral adaptations of the algae such as vertical migration, hydrologic or circulation effects, and ephemeral or episodic events. Furthermore, grab sampling may underestimate the presence of low levels of toxins if the sampling protocol does not include pre-concentration and/or if the toxin concentrations are below the analytical limit of detection.
In response to this challenge, Dr. Kudela and colleagues at UCSC have been investigating the use of a passive sampling method, Solid Phase Adsorption Toxin Tracking (SPATT), to monitor microcystin (and other toxin) levels in seawater. SPATT was first proposed for HAB monitoring by MacKenzie et al. (2004), who developed this passive sampling device by placing SPATT resin, which binds an array of lipophilic algal toxins, within a polyester mesh bag. Over the last several years UCSC researchers have been further developing and applying SPATT for HAB detection in both marine and freshwater environments. Their results indicate that the sensitivity of this system is extremely high, which greatly facilitates source-tracking efforts. The researchers routinely detect biotoxins using SPATT when simultaneous point-sampling of water fails to detect the same toxins in a given waterway (Lane et al., 2010; Kudela, 2012).
Kudela and colleagues have conducted limited SPATT and grab-sampling within the Bay Delta and surrounding environment. Those data demonstrate that microcystins are present at moderate to high concentrations in source waters of the Bay (particularly the Delta, but also the ponds in the South Bay region; Figure 1). They have also tested SPATT in “flow-through” mode aboard the R/V Polaris during USGS cruises (Figure 2). Of particular concern, they have identified microcystins throughout the Bay during autumn, suggesting that toxins (but not necessarily cells) are being physically transported throughout the ecosystem.
This project is also related to monitoring program development, focused on the detection of algal toxins produced by harmful algal blooms (HABs). There was broad agreement within the conceptual model technical team that increased frequency and magnitude of algal toxin monitoring measurements are one likely outcome of elevated nutrient loads to the Bay and Delta. The group further concurred that the development of sensitive tools for measuring phytotoxins should be a high priority for the Bay monitoring program.
Applicable RMP Management Question
- Is there a problem or are there signs of a problem? Are anthropogenic nutrients currently, or trending towards, adversely affecting beneficial uses of the Bay? Are trends spatially the same or different in San Francisco Bay?
- What are appropriate guidelines for assessing SF Bay’s health with respect to nutrients and eutrophication?
This project is divided into three subtasks. First, it is proposed to continue deployment of SPATT during USGS monthly cruises. As in past cruises, one SPATT will be deployed per basin in the surface-sampling flow-through system on the Polaris, totaling 5 SPATTs per cruise. In other watersheds, UCSC has successfully deployed SPATT from fixed platforms such as moorings (this has been done in the Delta, Alviso Slough and Pond A6, and throughout the Monterey Bay region). SPATT can easily be deployed up to 30 days, and require minimal handling for field personnel. SPATT can be stored indefinitely in the freezer (-80°C) and are routinely shipped through common carriers (including US Postal Service). In Task 1, SPATT will be deployed at both the Dumbarton Bridge and Benicia Bridge for periods of ~1 month, taking advantage of existing fixed monitoring programs. A similar effort in Pinto Lake, CA for a year was sufficient to develop statistical models relating toxin concentrations to environmental conditions (Kudela, 2012).
Next, controlled experiments will be conducted in the laboratory to better characterize partitioning of phytotoxins out of solution and into the SPATT during exposure in ship-board flow-through systems. Specifically, experiments will be carried out in simulated flow-through systems in which SPATT will be exposed to brackish water and seawater containing varying concentrations of a microcystin-RR. Microcystin-RR uptake will be quantified as a function of both dissolved concentration and exposure time. This “calibration” information will allow for more accurate back-calculations of average ambient concentrations in natural systems. In addition, a time-series of “bottle” experiments will be conducted during which SPATT will be exposed in containers holding seawater with known concentrations of microcystin-RR. SPATT will be removed at several time points and microcystin-RR uptake will be measured. This information will aid in characterizing the uptake kinetics of microcystin under conditions simulating longer term deployments at a single site.
Lastly,a technical memo will be prepared that interprets the results from 2013 field sampling and the controlled experiments. The results of the field and laboratory studies are expected to inform future monitoring approaches in the Bay, and ultimately provide information to support management decisions related to HABs and biotoxins. It is anticipated that results will also be published as a journal article, to be submitted in the first half of 2014.
This project will be performed by Raphe Kudela and staff of the Ocean Sciences Department at UC-Santa Cruz.