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At least 757 records · Page 42Linked to original sources
USGS2010

Modeling the relations between flow regime components, species traits, and spawning success of fishes in warmwater streams

Modifications to stream hydrologic regimes can have a profound influence on the dynamics of their fish populations. Using hierarchical linear models, we examined the relations between flow regime and young-of-year fish density using fish sampling and discharge data from three different warmwater streams in Illinois, Alabama, and Georgia. We used an information theoretic approach to evaluate the relative support for models describing hypothesized influences of five flow regime components representing: short-term high and low flows; short-term flow stability; and long-term mean flows and flow stability on fish reproductive success during fish spawning and rearing periods. We also evaluated the influence of ten fish species traits on fish reproductive success. Species traits included spawning duration, reproductive strategy, egg incubation rate, swimming locomotion morphology, general habitat preference, and food habits. Model selection results indicated that young-of-year fish density was positively related to short-term high flows during the spawning period and negatively related to flow variability during the rearing period. However, the effect of the flow regime components varied substantially among species, but was related to species traits. The effect of short-term high flows on the reproductive success was lower for species that broadcast their eggs during spawning. Species with cruiser swimming locomotion morphologies (e.g., Micropterus) also were more vulnerable to variable flows during the rearing period. Our models provide insight into the conditions and timing of flows that influence the reproductive success of warmwater stream fishes and may guide decisions related to stream regulation and management. ?? 2010 US Government.

Environmental Management↗
USGS2017

Spatially explicit dynamic N-mixture models

Knowledge of demographic parameters such as survival, reproduction, emigration, and immigration is essential to understand metapopulation dynamics. Traditionally the estimation of these demographic parameters requires intensive data from marked animals. The development of dynamic N-mixture models makes it possible to estimate demographic parameters from count data of unmarked animals, but the original dynamic N-mixture model does not distinguish emigration and immigration from survival and reproduction, limiting its ability to explain important metapopulation processes such as movement among local populations. In this study we developed a spatially explicit dynamic N-mixture model that estimates survival, reproduction, emigration, local population size, and detection probability from count data under the assumption that movement only occurs among adjacent habitat patches. Simulation studies showed that the inference of our model depends on detection probability, local population size, and the implementation of robust sampling design. Our model provides reliable estimates of survival, reproduction, and emigration when detection probability is high, regardless of local population size or the type of sampling design. When detection probability is low, however, our model only provides reliable estimates of survival, reproduction, and emigration when local population size is moderate to high and robust sampling design is used. A sensitivity analysis showed that our model is robust against the violation of the assumption that movement only occurs among adjacent habitat patches, suggesting wide applications of this model. Our model can be used to improve our understanding of metapopulation dynamics based on count data that are relatively easy to collect in many systems.

Population Ecology↗
USGS2022

Establishment of invasive Black Carp (Mylopharyngodon piceus) in the Mississippi River basin: Identifying sources and year classes contributing to recruitment

Black Carp ( Mylopharyngodon piceus ) was imported to the USA to control aquaculture pond snails. This species has escaped captivity and occurs in parts of the Mississippi River, several tributaries, and floodplain lakes, which is concerning due to potential competition with native fishes and predation on native mussels, many of which are imperiled. However, Black Carp captures have primarily been incidental by commercial fishers, and evidence of reproduction in the wild is limited. The objectives of this study were to assess relative abundance of aquaculture-origin and wild Black Carp using ploidy and otolith stable isotope analysis, identify spatial extent of natural reproduction using otolith microchemistry, assess age distributions of wild and aquaculture-source Black Carp to infer years in which natural reproduction occurred and timing of aquaculture escapement or introductions, and estimate size and age at maturation to assess whether recruitment to adulthood has occurred. Results revealed that Black Carp are established in parts of the Mississippi River basin based on findings that: (1) non-captive Black Carp primarily consist of fertile, naturally-reproduced fish, (2) reproduction has occurred in several rivers, (3) multiple year classes of wild fish are present, and (4) wild fish have recruited to adulthood. Multiple introductions or escapements of aquaculture-source fish into the wild, including both fertile and functionally sterile individuals, were also inferred. Individual growth appears to be rapid, although considerable variation was observed among fish. Additional study is suggested to refine understanding of where and when Black Carp reproduction is occurring in the Mississippi River basin.

Arkansas, Illinois, Kentucky, Louisiana, Missouri,↗
USGS2014

Uncertainty, robustness, and the value of information in managing an expanding Arctic goose population

We explored the application of dynamic-optimization methods to the problem of pink-footed goose (Anser brachyrhynchus) management in western Europe. We were especially concerned with the extent to which uncertainty in population dynamics influenced an optimal management strategy, the gain in management performance that could be expected if uncertainty could be eliminated or reduced, and whether an adaptive or robust management strategy might be most appropriate in the face of uncertainty. We combined three alternative survival models with three alternative reproductive models to form a set of nine annual-cycle models for pink-footed geese. These models represent a wide range of possibilities concerning the extent to which demographic rates are density dependent or independent, and the extent to which they are influenced by spring temperatures. We calculated state-dependent harvest strategies for these models using stochastic dynamic programming and an objective function that maximized sustainable harvest, subject to a constraint on desired population size. As expected, attaining the largest mean objective value (i.e., the relative measure of management performance) depended on the ability to match a model-dependent optimal strategy with its generating model of population dynamics. The nine models suggested widely varying objective values regardless of the harvest strategy, with the density-independent models generally producing higher objective values than models with density-dependent survival. In the face of uncertainty as to which of the nine models is most appropriate, the optimal strategy assuming that both survival and reproduction were a function of goose abundance and spring temperatures maximized the expected minimum objective value (i.e., maxi–min). In contrast, the optimal strategy assuming equal model weights minimized the expected maximum loss in objective value. The expected value of eliminating model uncertainty was an increase in objective value of only 3.0%. This value represents the difference between the best that could be expected if the most appropriate model were known and the best that could be expected in the face of model uncertainty. The value of eliminating uncertainty about the survival process was substantially higher than that associated with the reproductive process, which is consistent with evidence that variation in survival is more important than variation in reproduction in relatively long-lived avian species. Comparing the expected objective value if the most appropriate model were known with that of the maxi–min robust strategy, we found the value of eliminating uncertainty to be an expected increase of 6.2% in objective value. This result underscores the conservatism of the maxi–min rule and suggests that risk-neutral managers would prefer the optimal strategy that maximizes expected value, which is also the strategy that is expected to minimize the maximum loss (i.e., a strategy based on equal model weights). The low value of information calculated for pink-footed geese suggests that a robust strategy (i.e., one in which no learning is anticipated) could be as nearly effective as an adaptive one (i.e., a strategy in which the relative credibility of models is assessed through time). Of course, an alternative explanation for the low value of information is that the set of population models we considered was too narrow to represent key uncertainties in population dynamics. Yet we know that questions about the presence of density dependence must be central to the development of a sustainable harvest strategy. And while there are potentially many environmental covariates that could help explain variation in survival or reproduction, our admission of models in which vital rates are drawn randomly from reasonable distributions represents a worst-case scenario for management. We suspect that much of the value of the various harvest strategies we calculated is derived from the fact that they are state dependent, such that appropriate harvest rates depend on population abundance and weather conditions, as well as our focus on an infinite time horizon for sustainability.

Ecological Modelling↗
USGS2021

Seed production patterns of surviving Sierra Nevada conifers show minimal change following drought

Reproduction is a key component of ecological resilience in forest ecosystems, so understanding how seed production is influenced by extreme drought is key to understanding forest recovery trajectories. If trees respond to mortality-inducing drought by preferentially allocating resources for reproduction, the recovery of the stand to pre-drought conditions may be enhanced accordingly. We used a 20-year annual seed capture data set to investigate whether seed production by three tree genera commonly found in the Sierra Nevada ( Abies , Pinus , and Calocedrus ) was correlated with variation in local weather, which included an extreme drought spanning multiple years. We tested whether average seed production differed during the drought years, and whether annual seed counts could be explained by three weather variables: spring temperature, annual precipitation, and summer climatic water deficit (CWD). We fit models testing for four separate effects: (1) a priming year model (weather 1 year prior to reproductive bud initiation), (2) a bud initiation model (weather in the year of reproductive bud initiation), (3) a pollination year model (weather in the year of pollination), and (4) maturation year model (weather in the year of seed maturation). For genera with two-year reproductive cycles, the pollination and maturation models were combined. We found support for the summer CWD Abies maturation year model, which suggested higher seed outputs immediately following dry summer conditions. The spring temperature pollination year model was selected for Pinus , which suggested that seed output is higher following warm spring weather during pollination. The annual precipitation priming year model was selected for Calocedrus , which showed a negative association between seed production and wetter conditions two years prior to seed production. More parent tree basal area resulted in higher seed output for all genera, though the confidence intervals overlapped 0 for Calocedrus . Permutation tests sugested there was no systematic difference in mean seed production during the drought after accounting for live tree basal area, regardless of genus. These results highlight the variability in response across genera, and suggest that the influence of seed production on forest recovery following drought-related mortality may depend on affected species and the timing of the mortality event within the masting cycle. A greater understanding of species-level masting to drought stress is needed to more precisely predict community-level recovery following drought.

California↗
USGS2013

Sampling efficiency of the Moore egg collector

Quantitative studies focusing on the collection of semibuoyant fish eggs, which are associated with a pelagic broadcast-spawning reproductive strategy, are often conducted to evaluate reproductive success. Many of the fishes in this reproductive guild have suffered significant reductions in range and abundance. However, the efficiency of the sampling gear used to evaluate reproduction is often unknown and renders interpretation of the data from these studies difficult. Our objective was to assess the efficiency of a modified Moore egg collector (MEC) using field and laboratory trials. Gear efficiency was assessed by releasing a known quantity of gellan beads with a specific gravity similar to that of eggs from representatives of this reproductive guild (e.g., the Arkansas River Shiner Notropis girardi) into an outdoor flume and recording recaptures. We also used field trials to determine how discharge and release location influenced gear efficiency given current methodological approaches. The flume trials indicated that gear efficiency ranged between 0.0% and 9.5% (n = 57) in a simple 1.83-m-wide channel and was positively related to discharge. Efficiency in the field trials was lower, ranging between 0.0% and 3.6%, and was negatively related to bead release distance from the MEC and discharge. The flume trials indicated that the gellan beads were not distributed uniformly across the channel, although aggregation was reduced at higher discharges. This clustering of passively drifting particles should be considered when selecting placement sites for an MEC; further, the use of multiple devices may be warranted in channels with multiple areas of concentrated flow.

North American Journal of Fisheries Management↗
USGS2020

Regional ocean models indicate changing limits to biological invasions in the Bering Sea

Minimal vessel traffic and cold water temperatures are believed to limit non-indigenous species (NIS) in high-latitude ecosystems. We evaluated whether suitable conditions exist in the Bering Sea for the introduction, survival, and reproduction of NIS. We compiled temperature and salinity thresholds of known NIS and compared these to ocean conditions projected during two study periods: current (2003-2012) and mid-century (2030-2039). We also explored patterns of vessel traffic and connectivity for U.S. Bering Sea ports. We found the southeastern Bering Sea had suitable conditions for the year-round survival of 80% of NIS assessed (n=42). However, only 52% of NIS had conditions suitable for reproduction or development (n=25). Conditions north of 58° N that include sub-zero winter water temperatures were unsuitable for the survival and reproduction of most NIS. While mid-century models predicted a northward expansion of suitable conditions, conditions for reproduction remained marginal. Within the highly suitable southeastern Bering Sea is the port of Dutch Harbor, which received the most vessel arrivals and ballast water discharge in the U.S. Bering Sea. Our findings illustrate the potential vulnerability of a commercially important subarctic ecosystem and highlight the need to consider NIS reproductive and developmental life phases when evaluating limits to their establishment.

ICES Journal of Marine Science↗
USGS2005

Gender identification of shovelnose sturgeon using ultrasonic and endoscopic imagery and the application of the method to the pallid sturgeon

Monthly sampling of shovelnose sturgeon Scaphirhynchus platorynchus, a biological surrogate for the endangered pallid sturgeon Scaphirhynchus albus, was conducted to develop a multiseasonal profile of reproductive stages. Data collected included histological characteristics of gonads from wild caught fish and laboratory and field ultrasonic and endoscopic images. These data were used to compare effectiveness of ultrasonic and endoscopic techniques at identifying gender of adult shovelnose sturgeon at different reproductive stages. The least invasive method (i.e. ultrasound) was least effective while the most invasive (i.e. endoscope through an abdominal incision) was the most effective at identifying shovelnose sturgeon gender. In most cases, success rate for identifying males was greater than females, with success at identifying both genders greater in more advanced reproductive stages. Concomitantly, for most months average reproductive stage was more advanced for males than females. April and May were the months with the most advanced reproductive stage, and were the months when ultrasound was most effective. Methods were also applied in the Upper Missouri River to validate their use on pallid sturgeon Scaphirhynchus albus. Ultrasound was successful at identifying pallid sturgeon gender, however, endoscopic examination through the urogenital duct was only successful at identifying pallid sturgeon gender when the urogenital duct was not opaque. ?? 2005 The Fisheries Society of the British Isles.

Journal of Fish Biology↗
USGS2015

Masked expression of life-history traits in a highly variable environment

Differing life-history strategies may act as a constraint on reproductive expression that ultimately limits the ability of individual species to respond to changes in the magnitude or frequency of environmental variation, and potentially underlies the variation often inherent in phenotypic and evolved responses to anthropogenic change. Alternatively, if there are environmental cues that predict reproductive potential, differential expression of life-history strategies may represent differences in the adaptive capacity to optimize current reproductive value given variation in environmental conditions. We compared several aspects of walleye Sander vitreus spawning ecology at two reservoirs that differ in environmental variability (i.e., annual water-level fluctuation) to identify the capacity of phenotypic expression and the corresponding association with age. Despite significant differences in female body and liver masses between reservoirs that differ in environmental variability, we found no difference in reproductive investment measured by egg size and fecundity. Walleye in a highly variable environment appear to exhibit reproductive traits more typical of a short-lived life-history strategy, which may be resultant from the interaction of environmental and anthropogenic pressures. This finding emphasizes the need to identify the degree to which life-history expression represents physiological constraints versus ecological optimization, particularly as anthropogenic change continues to alter environmental conditions.

Great Plains Research↗
USGS2005

Impact of food supplementation and methionine on high densities of cotton rats: Support of the amino-acid-quality hypothesis?

Considerable research supports the tenet that quantity and quality of food limit vertebrate populations. We evaluated predictions that increased availabilities of food and the essential amino acid methionine were related to population limitation of the hispid cotton rat (Sigmodon hispidus). Effects of supplemental food and methionine on density, survival, and reproductive parameters of wild cotton rats were assessed in north-central Oklahoma in 1998-1999. Twelve enclosed groups of 16 adult cotton rats each (8 male, 8 female) were randomly assigned to either no supplementation (control), supplementation with a mixed ration that had methionine at slightly below maintenance levels (0.20%), or a methionine-enhanced mixed ration (1.20%). In general, densities of cotton rats were twice as high and were sustained longer with dietary supplementation, and methionine-supplemented populations maintained the highest densities. Treatment effects on survival depended on time of year, with higher survival in supplemented enclosures in October and November. Per capita recruitment was highest with methionine-enhanced food. Treatment effects on proportions of overall and female cotton rats in reproductive condition depended on sampling date, but males were most reproductively active with methionine supplementation. Methionine supplementation resulted in an earlier and longer reproductive season. Density-dependent and density-independent factors no doubt interplay to determine population dynamics of cotton rats, but our results suggest that methionine plays a role in the population dynamics of wild cotton rats, apparently by enhancing overall density, recruitment, and reproductive activity of males.

Journal of Mammalogy↗
USGS1999

Long-term prairie falcon population changes in relation to prey abundance, weather, land uses, and habitat conditions

We studied a nesting population of Prairie Falcons ( Falco mexicanus ) in the Snake River Birds of Prey National Conservation Area (NCA) from 1974-1997 to identify factors that influence abundance and reproduction. Our sampling period included two major droughts and associated crashes in Townsend's ground squirrel ( Spermophilus townsendii ) populations. The number of Prairie Falcon pairs found on long-term survey segments declined significantly from 1976-1997. Early declines were most severe at the eastern end of the NCA, where fires and agriculture have changed native shrubsteppe habitat. More recent declines occurred in the portion of canyon near the Orchard Training Area (OTA), where the Idaho Army National Guard conducts artillery firing and tank maneuvers. Overall Prairie Falcon reproductive rates were tied closely to annual indexes of ground squirrel abundance, but precipitation before and during the breeding season was related inversely to some measures of reproduction. Most reproductive parameters showed no significant trends over time, but during the 1990s, nesting success and productivity were lower in the stretch of canyon near the OTA than in adjacent areas. Extensive shrub loss, by itself, did not explain the pattern of declines in abundance and reproduction that we observed. Recent military training activities likely have interacted with fire and livestock grazing to create less than favorable foraging opportunities for Prairie Falcons in a large part of the NCA. To maintain Prairie Falcon populations in the NCA, managers should suppress wildfires, restore native plant communities, and regulate potentially incompatible land uses.

The Condor↗
USGS1964

Management of predator populations with antifertility agents

The search for methods, other than lethal techniques, for controlling predatory animals causing economic losses to the livestock industry prompted investigation of antifertility agents to suppress reproduction. Diethylstilbestrol was selected for initial trials because of its demonstrated antifertility effect on rabbits, mink ( Mustela vison ), dogs, and cattle. In penned tests with stilbestrol, pregnancy was terminated in six coyotes ( C anis latrans ) fed a single 100-mg oral dose dissolved in tallow. A subsequent field trial was conducted in New Mexico on 20 townships, March 5-15, 1963. Five thousand (100 mg stilbestrol in ½ ounce of tallow) drop baits were placed wherever coyote sign was found. After a delay of 3 weeks to allow the drug to take effect, a collection of female tracts from the treated area and a reference area 25 miles away was made to measure and compare reproductive success. Of the 20 females in reproductive condition recovered from the treated area, only 4 had viable embryos, while reproduction was blocked in 16 specimens by failure of implantation or resorption of embryos. All of the 13 females in reproductive condition from the reference area would have produced pups as evidenced by viable embryos. Future tests are scheduled to determine effects on other species and to confirm results on coyotes under a variety of field conditions.

Journal of Wildlife Management↗
USGS2010

The pallid sturgeon: Scientific investigations help understand recovery needs

Understanding of the pallid sturgeon (Scaphirhynchus albus) has increased significantly since the species was listed as endangered over two decades ago. Since 2005, scientists at the U.S. Geological Survey (USGS) Columbia Environmental Research Center (CERC) have been engaged in an interdisciplinary research program in cooperation with the U.S. Army Corps of Engineers Missouri River Recovery Program, U.S. Fish and Wildlife Service, Nebraska Game and Parks Commission, and numerous other State and Federal cooperators to provide managers and policy makers with the knowledge needed to evaluate recovery options. During that time, the USGS has worked collaboratively with river scientists and managers to develop methods, baseline information, and research approaches that are critical contributions to recovery success. The pallid sturgeon is endangered throughout the Missouri River because of insufficient reproduction and survival of early life stages. Primary management actions on the Missouri River designed to increase reproductive success and survival have focused on flow regime, channel morphology, and propagation. The CERC research strategies have, therefore, been designed to examine the linkages among flow regime, re-engineered channel morphology, and reproductive success and survival. Specific research objectives include the following: (1) understanding reproductive physiology of pallid sturgeon and relations to environmental conditions; (2) determining movement, habitat use, and reproductive behavior of pallid sturgeon; and (3) quantifying availability and dynamics of aquatic habitats needed by pallid sturgeon for all life stages.

Fact Sheet↗
USGS2006

Near-Field Receiving Water Monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California: 2005

Trace elements in sediment and the clam Macoma petalum (formerly reported as Macoma balthica (Cohen and Carlton 1995)), clam reproductive activity and benthic, macroinvertebrate community structure are reported for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay. This report includes data collected for the period January to December 2005, and extends a critical long-term biogeochemical record dating back to 1974. These data serve as the basis for the City of Palo Alto’s Near-Field Receiving Water Monitoring Program, initiated in 1994. Metal concentrations in both sediments and clam tissue during 2005 were consistent with results observed since 1990. Copper and zinc concentrations in sediment and bivalve tissue displayed a continued decrease over the last decade. In 2005, Cu concentrations were at or below the effects range-low (ERL) concentration (34 µg/g) for the entire year, the first time this has been observed. Also, zinc concentrations never exceeded the ERL (150 µg/g). Yearly average concentrations of copper, zinc and silver in Macoma petalum for 2005 were some of the lowest recorded since monitoring for metals began in 1975. The concentrations of mercury and selenium in sediments, during April and January 2004, respectively, were the highest values observed for these elements during this study. Later in 2005, concentrations decreased to historic levels. The increase in mercury and selenium in 2004 was not a permanent trend and concentrations of these elements in sediments and clams at Palo Alto remain similar to concentrations observed elsewhere in the San Francisco Bay. Analyses of the benthic-community structure of a mudflat in South San Francisco Bay over a 31-year period show that changes in the community have occurred concurrent with with reduced concentrations of metals in the sediment and in the tissues of the biosentinal clam Macoma petalum from the same area. Analysis of the reproductive activity of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable with almost all animals initiating reproduction in the fall and spawning the following spring of most years. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that suggests a more stable community that is subjected to less stress. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals. Heteromastus filiformis , a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying their eggs on or in the sediment has shown a concurrent increase in dominance. These changes in species dominance reflect a change in the community from one dominated by surface dwelling, brooding species to one with species with varying life history characteristics. For the first time since its invasion in 1986, the non-indigenous filter-feeding bivalve Corbula ( Potamocorbula ) amurensis has shown up in small but persistent numbers in the benthic community.

California↗
USGS2007

Near-field receiving water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California--2006

Results reported herein include trace element concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica (Cohen and Carlton 1995)), clam reproductive activity, and benthic macroinvertebrate community structure for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay. This report includes data collected for the period January 2006 to December 2006, and extends a critical long-term biogeochemical record dating back to 1974. These data serve as the basis for the City of Palo Alto's Near-Field Receiving Water Monitoring Program, initiated in 1994. Metal concentrations in both sediments and clam tissue during 2006 were consistent with results observed since 1990. Most notably, copper and silver concentrations in sediment and clam tissue increased in the last year but the values remain well within range of past data. Other metals such as chromium, nickel, vanadium, and zinc remained relatively constant throughout the year except for maximum values generally occurring in winter months (January-March). Mercury levels in sediment and clam tissue were some of the lowest seen on record. Conversely, selenium concentrations reached a maximum level but soon returned to baseline levels. In all, metal concentrations in sediments and tissue remain within past findings. There are no obvious directional trends (increasing or decreasing). Analyses of the benthic-community structure of a mudflat in South San Francisco Bay over a 31-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam M. petalum from the same area. Analysis of the reproductive activity of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable, with almost all animals initiating reproduction in the fall and spawning the following spring of most years. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that suggests a more stable community that is subjected to less stress. In addition, two of the opportunistic species (Ampelisca abdita and Streblospio benedicti) that brood their young and live on the surface of the sediment in tubes, have shown a continual decline in dominance coincident with the decline in metals. Heteromastus filiformis, a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying their eggs on or in the sediment, has shown a concurrent increase in dominance. These changes in species dominance reflect a change in the community from one dominated by surface dwelling, brooding species to one with species with varying life history characteristics. For the first time since its invasion in 1986, the non-indigenous filter-feeding clam Corbula (Potamocorbula) amurensis has shown up in small, but persistent, numbers in the benthic community.

California↗
USGS2008

Near-field receiving water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California: 2007

Results reported herein include trace element concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica (Cohen and Carlton 1995)), clam reproductive activity, and benthic macroinvertebrate community structure for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay. This report includes data collected for the period January 2007 to December 2007, and extends a critical long-term biogeochemical record dating back to 1974. These data serve as the basis for the City of Palo Alto’s Near-Field Receiving Water Monitoring Program, initiated in 1994. Metal concentrations in both sediments and clam tissue during 2007 remained consistent with results observed since 1990. Most notably, copper and silver concentrations in sediment and clam tissue are elevated for the second consecutive year, but the values remain well within the range of past findings. Other metals such as chromium, nickel, vanadium, and zinc remained relatively constant throughout the year except for maximum values that generally occur in winter months (January-March). Mercury levels in sediment and clam tissue were some of the lowest seen on record. Last year’s elevated selenium levels appear to be transient, and selenium concentrations have returned to background levels. Overall, metal concentrations in sediments and tissue remain within past findings. Analyses of the benthic-community structure of a mudflat in South San Francisco Bay over a 31-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam, M. petalum , from the same area. Analysis of the reproductive activity of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable, with almost all animals initiating reproduction in the fall and spawning the following spring of most years. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that suggests a more stable community that is subjected to less stress. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes, have shown a continual decline in dominance coincident with the decline in metals. Heteromastus filiformis , a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying their eggs on or in the sediment, has shown a concurrent increase in dominance and is now showing signs of population stability. These changes in species dominance reflect a change in the community from one dominated by surface dwelling, brooding species to one with species with varying life history characteristics.

California↗
USGS2009

Near-field receiving water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California: 2008

Results reported herein include trace element concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica (Cohen and Carlton, 1995)), clam reproductive activity, and benthic macroinvertebrate community structure for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in South San Francisco Bay. This report includes data collected for the period January 2008 to December 2008 and extends a critical long-term biogeochemical record dating back to 1974. These data serve as the basis for the City of Palo Alto's Near-Field Receiving Water Monitoring Program, initiated in 1994. In 2008, metal concentrations in both sediments and clam tissue were among the lowest concentrations on record and consistent with results observed since 1991. Following significant reductions in the late 1980's, silver (Ag) and copper (Cu) concentrations appeared to have stabilized. Annual mean concentrations have fluctuated modestly (2–4 fold) in a nondirectional manner. Data for other metals, including chromium, mercury, nickel, selenium, vanadium, and zinc, have been collected since 1994. Over this period, concentrations of these elements, which more likely reflect regional inputs and systemwide processes, have remained relatively constant, aside from typical seasonal variation that is common to all elements. Within years, concentrations generally reach maximum in winter months (January–March) and decline to annual minima in spring through fall. Mercury (Hg) in sediments spiked to the highest observed level in January 2008. However, sedimentary concentrations for the rest of the year and concentrations of Hg in M. petalum for the entire year were consistent with data from previous years. Average selenium (Se) concentrations in sediment were the highest on record, but there is no evidence, yet, to suggest a temporal trend of increasing sedimentary Se. Selenium in M. petalum was not elevated relative to past years. Overall, Cu and Ag concentrations in sediments and soft tissues of the clam, M. petalum , remained representative of the concentrations observed since 1991 following significant reductions in the discharge of these elements from PARWQCP, suggesting that, similar to other elements of regulatory interest, regional scale factors now largely influence sedimentary and bioavailable concentrations of Cu and Ag. Analyses of the benthic-community structure of a mudflat in South San Francisco Bay over a 31-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam, M. petalum , from the same area. Analysis of the reproductive activity of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable, with almost all animals initiating reproduction in the fall and spawning the following spring of most years. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that suggests a more stable community that is subjected to less stress. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes, have shown a continual decline in dominance coincident with the decline in metals. Heteromastus filiformis , a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying their eggs on or in the sediment, has shown a concurrent increase in dominance and is now showing signs of population stability. An unidentified disturbance occurred on the mudflat in early 2008 that resulted in the loss of the benthic animals, except for those deep dwelling animals like Macoma petalum . Animals immediately returned to the mudflat, which is indicative that the disturbance was not due to a persistent toxin or due to anoxia. This event allows us to examine the response of the mudflat benthic community to a natural disturbance (possible causes include sediment accretion or freshwater inundation) and compare this recovery to the longer term recovery we observed in the 1970s.

California↗
USGS2010

Near-field receiving water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California; 2009

Results reported herein include trace element concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica (Cohen and Carlton, 1995)), clam reproductive activity, and benthic macroinvertebrate community structure for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in South San Francisco Bay. This report includes data collected for the period January 2009 to December 2009 and extends a critical long-term biogeochemical record dating back to 1974. These data serve as the basis for the City of Palo Alto’s Near-Field Receiving Water Monitoring Program, initiated in 1994. In 2009, metal concentrations in both sediments and clam tissue were among the lowest concentrations on record and consistent with results observed since 1991. Following significant reductions in the late 1980s, silver (Ag) and copper (Cu) concentrations appeared to have stabilized. Annual mean concentrations have fluctuated modestly (2–4 fold) in a nondirectional manner. Data for other metals, including chromium, mercury, nickel, selenium, vanadium, and zinc, have been collected since 1994. Over this period, concentrations of these elements, which more likely reflect regional inputs and systemwide processes, have remained relatively constant, aside from typical seasonal variation that is common to all elements. Within years, the winter months (January–March) generally exhibit maximum concentrations, with a decline to annual minima in spring through fall. Mercury (Hg) in sediments and M. petalum were comparable to concentrations observed in 2008 and were generally consistent with data from previous years. Selenium (Se) concentrations in sediment varied among years and showed no sustained temporal trend. In 2009, sedimentary Se concentrations declined from the record high concentrations observed in 2008 to concentrations that were among the lowest on record. Selenium in M. petalum was unchanged from 2008. Overall, Cu and Ag concentrations in sediments and soft tissues of the clam, M. petalum , remained representative of the concentrations observed since 1991 following significant reductions in the discharge of these elements from the PARWQCP. This suggests that, as with other elements of regulatory interest, regional-scale factors now largely influence sedimentary and bioavailable concentrations of Ag and Cu. Analyses of the benthic community structure of a mudflat in South San Francisco Bay over a 36-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam, M. petalum , from the same area. Analysis of the reproductive activity of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable, with almost all animals initiating reproduction in the fall and spawning the following spring of most years. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that suggests a more stable community that is subjected to fewer stressors. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals; both species had short-lived rebounds in abundance in 2008 and 2009. Heteromastus filiformis (a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying its eggs on or in the sediment) showed a concurrent increase in dominance, with the last several years prior to 2008 showing a stable population. An unidentified disturbance occurred on the mudflat in early 2008 that resulted in the loss of the benthic animals, except for those deep-dwelling animals like Macoma petalum . Animals immediately returned to the mudflat in 2008, which was the first indication that the disturbance was not due to a persistent toxin or to anoxia. The use of functional ecology was highlighted in the 2009 benthic community data, which show that the animals that have now returned to the mudflat are those that can respond successfully to a physical, nontoxic disturbance. Today we see plenty of animals that consume the sediment, have pelagic larvae that must survive landing on the sediment, and in some cases have eggs that must survive being laid in the sediment. We continue to observe the community’s response to the defaunation event, because it allows us to examine the response of the community to a natural disturbance (possible causes include sediment accretion or freshwater inundation) and compare this recovery to the longer-term recovery we observed in the 1970s, when the decline in sediment pollutants was the dominating factor.

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