Coastal & Estuarine Science News (CESN)
Coastal & Estuarine Science News (CESN) is an electronic publication providing brief summaries of select articles from the journal Estuaries & Coasts that emphasize management applications of scientific findings. It is a free electronic newsletter delivered to subscribers on a bimonthly basis.
November 2009
Contents
Columbia River Salmon Food Webs Entangled with Ecosystem Alterations, Says Study
Unintended Consequences of a Gulf Coast Lake Diversion: Plans for More Marsh Leads to More Nutrients
New Patterns of Primary Production?
Study Finds Likely Population-Level Contaminant Effects on a Common Fish in San Francisco Bay
Columbia River Salmon Food Webs Entangled with Ecosystem Alterations, Says Study
Embattled Pacific salmon in the Columbia River Estuary may have yet another threat to contend with: Massive ecosystem alterations seem to have affected not only habitat, but food webs in this large system. Some components of the food web may have declined in availability and quality, ultimately affecting the ability of the Columbia to support Chinook salmon.
One hundred and fifty years of diking, damming, and channelization have resulted in a significant loss (82%) of historical emergent marsh and a concurrent decline in benthic macroalgal production (15% since 1870). Organic matter that used to come from these sources has been curtailed, while riverine phytoplankton from upriver impoundments has increased. These changes appear to be reflected in the estuary’s food web. A study that used stable isotope ratios to evaluate the food web pathways that support Chinook in the Columbia indicates that riverine phytoplankton (and hatchery feed) were dietary sources in most of the salmon food webs sampled. However, riverine phytoplankton was represented in lower proportions in fish tissue than in the organic matter of the estuary, suggesting it is being selected against by salmon prey or that many salmon do not use habitats in which these food webs dominate. The opposite was true for benthic diatoms and vascular plant detritus derived from marsh and intertidal habitats, which was in higher proportion in the salmon than in the estuary. These results indicate that Chinook invertebrate prey and salmon themselves preferentially use marshes and marsh production, which have become more scarce.
The authors suggest that the more common phytoplankton-based food webs, which are ephemeral and temporally unstable, are less important for salmon, and the ability of the estuary to support salmon may ultimately be reduced. Their analysis suggests that reestablishment of linkages to marsh habitats should be a high priority for restoration of Columbia Chinook, five populations of which are listed as threatened or endangered under the Endangered Species Act.
Source: Maier, G. O., and C. A. Simenstad. 2009. The role of marsh-derived macrodetritus to the food webs of juvenile Chinook salmon in a large altered estuary. Estuaries and Coasts 32 (DOI 10.1007/s12237-009-9197-1).
Unintended Consequences of a Gulf Coast Lake Diversion: Plans for More Marsh Leads to More Nutrients
The Davis Pond Diversion is a structure that directs water from the Mississippi River into two lakes and from there into the Barataria Basin in order to reduce salinity and encourage marsh restoration. This approach, engineered to reverse a serious trend of wetland loss on the Louisiana coast, supplies a controlled flow of freshwater to the coast. Because most freshwater systems are considered to be phosphorus-limited, the high concentrations of nitrogen in the river water (80 times the ambient receiving waters) were not considered to be a problem. However, results of nutrient addition bioassays to determine the impact of N, P, and silica (Si) loading on the diversion lakes and a nearby control lake revealed that algal growth in the lakes is actually N-limited. Additions of P or Si alone caused limited or no phytoplankton growth in microcosms, but additions of N always did. Additions of N+P were sometimes more effective in promoting algal growth than additions of N alone.
The same study also found high abundances of cyanobacteria in these lakes, including taxa known to form toxic blooms. Taken together, these results suggest that the diversion, intended to restore ecosystem function by promoting marsh growth, might actually be promoting nuisance and toxic algal blooms and increasing lake eutrophication. These results are a stark reminder that ecosystems are best managed as a whole, and that caution is called for when implementing ecosystem recovery plans.
Source: Ren, L., N. N. Rabalais, R. E. Turner, W. Morrison, and W. Mendenhall. 2009. Nutrient limitation on phytoplankton growth in the upper Barataria Basin, Louisiana: microcosm bioassays. Estuaries and Coasts 32 (DOI 10.1007/s12237-009-9174-8).
New Patterns of Primary Production?
Our knowledge of the seasonal cycle of marine primary productivity has expanded exponentially since the early observations of phytoplankton populations in the North Atlantic and North Sea led to the development of the spring bloom paradigm. Studies of iconic coastal areas such as Chesapeake Bay furthered knowledge about these phenomena along coasts and in estuaries. The proliferation of comprehensive monitoring programs world-wide allowed authors of a recent paper to systematically investigate a much wider range of primary producer patterns observed in estuarine and coastal waters.
This study examined chlorophyll a (Chl a) concentrations measured in rigorous monitoring programs at 84 estuarine and coastal sites in 18 countries. An earlier study of a similar data set by the same authors revealed an unexpectedly high diversity in the timing and amplitude of biomass fluctuations, both within and across ecosystems. The current study takes a next step in the analysis of these data by measuring and comparing phytoplankton variability at different timescales, namely, year-to-year variability, average seasonal variability, and the variability due to shorter-term “events.” The authors separated out the different timescales using a simple method, based on the observation that the standard deviation at each scale was approximately proportional to the Chl a concentration: Systems with the highest Chl a were also the most variable. Analysis of the variability contributions at each site revealed that some systems were dominated by a recurrent seasonal pattern and some by annual variability, but most variability was residual and often associated with exceptional events such as red tides. The authors suggest that a dominant seasonal variability is a latitude-dependent effect and generally occurs where the system is governed by a strong annual climate cycle; a dominant annual variability may be a response to disturbance from human activities and/or large-scale changes in climate; and a dominant residual, or event-scale, variability often occurs at sites highly enriched with nutrients.This hypothesis can serve as a conceptual framework for future studies of chlorophyll and primary productivity variation. The study also demonstrates that long-term observations of coastal and estuarine sites have finally become numerous enough to allow more complex and realistic generalizations about the range of patterns and processes. Finally, the data-analytical methods employed in this study are straightforward and could easily be applied to other time series.
Source: Cloern, J. E., and A. D. Jassby. 2009. Patterns and scales of phytoplankton variability in estuarine-coastal ecosystems. Estuaries and Coasts 32.
Note: this paper appears in a special issue of Estuaries and Coasts which includes numerous papers describing phytoplankton dynamics from long-term studies in such diverse areas as Brazil, Bengal, and Portugal.
Study Finds Likely Population-Level Contaminant Effects on a Common Fish in San Francisco Bay
Estuaries are the unfortunate recipients of myriad anthropogenic chemical contaminants, which can have numerous effects on individual organisms. While it is fairly straightforward to use laboratory experiments to measure the effects of contaminants on individual fish, how does that information translate to the population level? Do contaminant levels impact fish population dynamics? A link to population-level effects has been demonstrated for one common resident fish species, the longjaw mudsucker (Gillichthys mirabilis), in San Francisco Bay, which may mean that this fish could be used as a bioindicator of ecosystem quality in this region.
Population parameters (abundance, growth, mortality, recruitment, and others) for this species were measured over five years at sites in polluted San Francisco Bay and relatively unimpacted Tomales Bay, CA. Sediment contaminants, including trace metals and organic contaminants, were measured as well. Overall, life is tough for San Francisco Bay mudsuckers. Mudsucker populations at the more contaminated San Francisco Bay sites exhibited lower abundance, slower growth, and higher mortality rates than populations in Tomales Bay. The most contaminated sites contained the least and smallest fish, while the least contaminated sites had the highest abundance and largest fish. Population age structure in three of the five years at the San Francisco Bay sites was skewed toward younger fish, indicating a lack of adult survival. In the year with the most rainfall (2006), mudsuckers were completely absent from the most contaminated San Francisco Bay site, possibly because a large pulse of contaminants accompanied the abundant rain.
In this system, it is clear that better habitat, in terms of contaminant levels, supports healthier populations of this fish. Evidence that sublethal levels of contaminants can lead to population-level effects on resident fish is uncommon in the literature, a further noteworthy aspect of this study.
Source: McGourty, C. R., J. A. Hobbs, W. A. Bennett, P. G. Green, H. Hwang, N. Ikemiyagi, L. Lewis, and J. M. Cope. 2009. Likely population-level effects of contaminants on a resident estuarine fish species: Comparing Gillichthys mirabilis population static measurements and vital rates in San Francisco and Tomales Bays. Estuaries and Coasts 32 (DOI 10.1007/s12237-009-9177-5).
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