UNPRECEDENTED BLOOM OF TOXIN-PRODUCING CYANOBACTERIA IN THE SOUTHERN BAY-DELTA ESTUARY HAS NEGATIVE IMPACT ON THE AQUATIC FOOD-WEB

Authors

Chelsea L. Spier, University of the Pacific
William T. Stringfellow, University of the PacificFollow
Jeremy S. Hanlon, University of the Pacific
Mark Brunell, University of the Pacific
Monica Estiandan, University of the Pacific
Teemu Koski, University of the Pacific
Juha Kääriä, University of the Pacific

Introduction/Abstract

California’s Sacramento-San Joaquin Delta is an expansive fresh-water tidal estuary that is part of the San Francisco Estuary, the largest estuary on the US Pacific coast. Recently, there has been a collapse in the pelagic fish community in the San Francisco Estuary, known as the pelagic organism decline (POD). Blooms of the cyanobacteria Microcystis, which often produce the cyanotoxin microcystin, were first documented in the Sacramento-San Joaquin Delta in 1999. Cyanotoxins have been suspected as one contributing factor to POD. It has been proposed that microcystin could be contributing to POD directly though poisoning of fish or indirectly by affecting zooplankton and other food sources. Copepods, especially E. affinis and P. forbesi are important food sources for larval POD species. Delta and longfin smelt, threatened species, feed on rotifers and other small organisms the first weeks after hatching.

Purpose

In this study, we documented the spatial and temporal extent of cyanobacteria blooms in the Southern Bay-Delta Estuary, an area further east and upstream in the San Francisco Estuary than previously studied. Copepod, rotifer and total zooplankton abundance was examined in comparison to the spatial distribution of microcystin. The environmental factors associated with cyanobacteria blooms were investigated.

Method

Monthly water quality measurements were taken in-situ in 2009, 2011 and 2012. Grab samples were analyzed for nutrients in accordance with Standard Methods. Microcystin was measured by enzyme-linked immune-assay (ELISA). Cyanobacteria and zooplankton were identified and enumerated by microscopy. Climate and flow data was acquired through the CIMIS and CDEC websites respectively.

Results

In July and August of 2012, microcystin toxin concentrations in the southern area of the Delta were measured above California EPA recreational advisory limits of 800 ng/L and World Health Organization drinking water limit of 1,000 ng/L, with a maximum observed concentration of 2,800 ng/L. These concentrations were significantly higher in 2012 than concentrations observed in prior years or reported in prior studies. The total zooplankton rotifer and cladoceran mass were significantly lower when microcystin was present and the effect was pronounced for all zooplankton, including copepods, at concentrations above 15 ng/L. High densities of zooplankton were never observed when high concentrations of toxin were measured.

Significance

The cause of the 2012 bloom could not be attributed to any specific environmental condition, but timing of spring flows, consecutive days of high temperatures, and high nutrient concentrations might be contributing factors. Continued study of Microcystis, microcystin, and zooplankton is needed to determine the causes of cyanobacteria blooms in the region and to further understand the effect of these blooms on the aquatic food-web.

Location

DeRosa University Center, Stockton campus, University of the Pacific

Format

Poster Presentation