Tara S. Schraga

Climate anomalies generate an exceptional dinoflagellate bloom in San Francisco Bay

] We describe a large dinoflagellate bloom,unprecedented in nearly three decades of observation, thatdeveloped in San Francisco Bay (SFB) during September2004. SFB is highly enriched in nutrients but has lowsummer-autumn algal biomass because wind stress andtidally induced bottom stress produce a well mixed andlight-limited pelagic habitat. The bloom coincided withcalm winds and record high air temperatures that stratifiedthe water column and suppressed mixing long enough formotile dinoflagellates to grow and accumulate in surfacewaters. This event-scale climate pattern, produced by anupper-atmosphere high-pressure anomaly off the U.S. westcoast, followed a summer of weak coastal upwelling andhigh dinoflagellate biomass in coastal waters that apparentlyseeded the SFB bloom. This event suggests that some redtides are responses to changes in local physical dynamicsthat are driven by large-scale atmospheric processes andoperate over both the event scale of biomass growth and theantecedent seasonal scale that shapes the bloom community.

Detritus Fuels Ecosystem Metabolism but not Metazoan Food Webs in San Francisco Estuary's Freshwater Delta

Detritus from terrestrial ecosystems is the major source of organic matter in many streams, rivers, and estuaries, yet the role of detritus in supporting pelagic food webs is debated. We examined the importance of detritus to secondary productivity in the Sacramento and San Joaquin River Delta (California, United States), a large complex of tidal freshwater habitats. The Delta ecosystem has low primary productivity but large detrital inputs, so we hypothesized that de tritus is the primary energy source fueling production in pelagic food webs. We assessed the sources, quantity, composition, and bioavailability of organic matter among a diversity of habitats (e.g., marsh sloughs, floodplains, tidal lakes, and deep river channels) over two years to test this hypothesis. Our results support the emerging principle that detritus dominates riverine and estuarine organic matter supply and supports the majority of ecosystem metabolism. Yet in contrast to prevailing ideas, we found that detritus was weakly coupled to the Deltas pelagic food web. Results from independent approaches showed that phytoplankton production was the dominant source of organic matter for the Deltas pelagic food web, even though primary production accounts for a small fraction of the Deltas organic matter supply. If these results are general, they suggest that the value of organic matter to higher trophic levels, including species targeted by programs of ecosystem restoration, is a function of phytoplankton production.

Ecological Values of Shallow-Water Habitats: Implications for the Restoration of Disturbed Ecosystems

A presumed value of shallow-habitat enhanced pelagic productivity derives from the principle that in nutrient-rich aquatic systems phytoplankton growth rate is controlled by light availability, which varies inversely with habitat depth. We measured a set of biological indicators across the gradient of habitat depth within the Sacramento–San Joaquin River Delta (California) to test the hypothesis that plankton biomass, production, and pelagic energy flow also vary systematically with habitat depth. Results showed that phytoplankton biomass and production were only weakly related to phytoplankton growth rates whereas other processes (transport, consumption) were important controls. Distribution of the invasive clam Corbicula fluminea was patchy, and heavily colonized habitats all supported low phytoplankton biomass and production and functioned as food sinks. Surplus primary production in shallow, uncolonized habitats provided potential subsidies to neighboring recipient habitats. Zooplankton in deeper habitats, where grazing exceeded phytoplankton production, were likely supported by significant fluxes of phytoplankton biomass from connected donor habitats. Our results provide three important lessons for ecosystem science: (a) in the absence of process measurements, derived indices provide valuable information to improve our mechanistic understanding of ecosystem function and to benefit adaptive management strategies; (b) the benefits of some ecosystem functions are displaced by water movements, so the value of individual habitat types can only be revealed through a regional perspective that includes connectedness among habitats; and (c) invasive species can act as overriding controls of habitat function, adding to the uncertainty of management outcomes.

Intradaily Variability of Water Quality in a Shallow Tidal Lagoon: Mechanisms and Implications

Although surface water quality and its underlying processes vary over time scales ranging from seconds to decades, they have historically been studied at the lower (weekly to interannual) frequencies. The aim of this study was to investigate intradaily variability of three water quality parameters in a small freshwater tidal lagoon (Mildred Island, California). High frequency time series of specific conductivity, water temperature, and chlorophylla at two locations within the habitat were analyzed in conjunction with supporting hydrodynamic, meteorological, biological, and spatial mapping data. All three constituents exhibited large amplitude intradaily (e.g., semidiurnal tidal and diurnal) oscillations, and periodicity varied across constituents, space, and time. Like other tidal embayments, this habitat is influenced by several processes with distinct periodicities including physical controls, such as tides, solar radiation, and wind, and biological controls, such as photosynthesis, growth, and grazing. A scaling approach was developed to estimate individual process contributions to the observed variability. Scaling results were generally consistent with observations and together with detailed examination of time series and time derivatives, revealed specific mechanisms underlying the observed periodicities, including interactions between the tidal variability, heating, wind, and biology. The implications for monitoring were illustrated through subsampling of the data set. This exercise demonstrated how quantities needed by scientists and managers (e.g., mean or extreme concentrations) may be misrepresented by low frequency data and how short-duration high frequency measurements can aid in the design and interpretation of temporally coarser sampling programs. The dispersive export of chlorophylla from the habitat exhibited a fortnightly variability corresponding to the modulation of semidiurnal tidal currents with the diurnal cycle of phytoplankton variability, demonstrating how high frequency interactions can govern long-term trends. Process identification, as through the scaling analysis here, can help us anticipate changes in system behavior and adapt our own interactions with the system.

Primary Production and Carrying Capacity of Former Salt Ponds After Reconnection to San Francisco Bay

Over 6,110 ha of the commercial production salt ponds surrounding South San Francisco Bay, CA, have been decommissioned and reconnected to the bay, most as part of the largest wetlands restoration program in the western United States. These open water ponds are critical habitat for millions of birds annually and restoration program managers must determine the appropriate balance between retention of ponds versus re-conversion to tidal salt marsh, knowing that both are essential ecosystems for endangered bird species. Our study describes the ecological value of the new open water pond ecosystems as feeding habitats for birds. We used the oxygen rate of change method to determine ecosystem metabolic parameters from high resolution time-series of dissolved oxygen concentration. Areal gross primary production (8.17 g O2 m−2 d−1) was roughly double the world’s most productive estuaries. High rates of phytoplankton photosynthesis were balanced by equally high rates of community respiration (8.25 g O2 m−2 d−1). Metabolic equilibrium was delicately poised: sharp irradiance and temperature shifts triggered short term photosynthesis reduction resulting in oxygen depletion. We converted net primary production (NPP) into potential carrying capacity of the forage biota that support targeted pond waterbirds. NPP was processed through both a pelagic food web, resulting in forage biota for piscivorous birds and a benthic food web, resulting in forage biota for shorebirds and diving benthivores. Both food webs included efficient algal-based and inefficient detrital trophic pathways. The result of all primary production being routed through simple food webs was high potential forage production and energy supply to waterbirds, equivalent to 11–163 million planktivorous fish or 19–78 billion small estuarine clams within the 330-ha pond between May and October. Food quantity does not necessarily equal quality and these systems have the potential to produce toxic or inedible algae. Our study provides the first measurement of primary production in the open water ponds of San Francisco Bay and presents a novel approach for transforming primary production into forage production as a metric of an ecosystem’s energetic carrying capacity.

Heat wave brings an unprecedented red tide to San Francisco Bay

An exceptional red tide in San Francisco Bay was observed on 8 September 2004. The red tide had chlorophyll concentrations approaching 200 mg/m3 (Figure 1) in red/purple surface streaks containing high abundances of the dinoflagellate Akashiwo sanguinea. Red tides and harmful algal blooms (HABs) are common features of coastal ecosystems, and their growing frequency is a suspected outcome of coastal eutrophication. However, the authors have never observed a dinoflagellate bloom of this scale during 28 years of sampling in the nutrient-rich San Francisco Bay. Phytoplankton biomass along this transect is typically <5mg Chla/m3, and has never exceeded 21 mg Chla/m3 during summer-autumn

Water quality measurements in San Francisco Bay by the U.S. Geological Survey, 1969–2015

The U.S. Geological Survey (USGS) maintains a place-based research program in San Francisco Bay (USA) that began in 1969 and continues, providing one of the longest records of water-quality measurements in a North American estuary. Constituents include salinity, temperature, light extinction coefficient, and concentrations of chlorophyll-a, dissolved oxygen, suspended particulate matter, nitrate, nitrite, ammonium, silicate, and phosphate. We describe the sampling program, analytical methods, structure of the data record, and how to access all measurements made from 1969 through 2015. We provide a summary of how these data have been used by USGS and other researchers to deepen understanding of how estuaries are structured and function differently from the river and ocean ecosystems they bridge.

Phytoplankton Species Composition, Abundance and Cell Size in San Francisco Bay: Microscopic Analyses of USGS Samples Collected 1992-2014

This Data Release makes available measurements of phytoplankton species composition, abundance and cell size made on samples collected in San Francisco Bay (CA) from April 1992 through March 2014. Phytoplankton samples were collected at 31 stations along a 145-km transect where the variability of salinity, temperature, turbidity and nutrient concentrations reflected a broad range of environmental factors that regulate phytoplankton growth and abundance (map of sampling locations is available on the project website at: https://sfbay.wr.usgs.gov/access/wqdata/overview/wherewhen/stnmap.html). Whole water samples were preserved with acid Lugol s solution, and 2 to 50 ml aliquots were settled in chambers for 6 to 24 hours (Utermohl 1958). Phytoplankton cells were then counted and identified using a phase-contrast inverted microscope at 125x magnification, all cells greater than 30 μm diameter were enumerated. Cells smaller than 30 μm were counted at 1250x magnification; following the APHA (1989) strip count method, at least 100 cells of the most numerous taxon were counted. Cell volumes were estimated from measured linear dimensions and geometric formulas that varied with cell shapes. Phytoplankton samples representing 923 distinct date, station and depths were included. The 16,442 entries in this dataset include 609 different taxa within 11 functional groups. Diatoms dominated the total biovolume contributed by each functional group (77%) followed by dinoflagellates (14%) and cryptophytes (4.5%). The top 5 species contributing to the summed biovolume in all samples were: Thalassiosira punctigera, Chaetoceros socialis, Ditylum brightwellii, Thalassiosira rotula and Noctiluca scintillans. By frequency of occurrence, the top 5 species were: Teleaulax amphioxeia, Nannochloropsis spp., Plagioselmis prolonga var. nordica, Skeletonema costatum and Thalassiosira eccentrica. APHA. (1989). Standard methods for the examination of water and wastewater, 17th edn. American Public Health Association, Washington, DC Utermohl H. (1958). Zur Vervollkommnung der quantitativen Phytoplankton-Methodik. Mitt Int Verh Theor Angew Limnol 9:1-38