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At least 109 records · Page 6Linked to original sources
USGS2008

Assigning king eiders to wintering regions in the Bering Sea using stable isotopes of feathers and claws

Identification of wintering regions for birds sampled during the breeding season is crucial to understanding how events outside the breeding season may affect populations. We assigned king eiders captured on breeding grounds in northern Alaska to 3 broad geographic wintering regions in the Bering Sea using stable carbon and nitrogen isotopes obtained from head feathers. Using a discriminant function analysis of feathers obtained from birds tracked with satellite transmitters, we estimated that 88 % of feathers were assigned to the region in which they were grown. We then assigned 84 birds of unknown origin to wintering regions based on their head feather isotope ratios, and tested the utility of claws for geographic assignment. Based on the feather results, we estimated that similar proportions of birds in our study area use each of the 3 wintering regions in the Bering Sea. These results are in close agreement with estimates from satellite telemetry and show the usefulness of stable isotope signatures of feathers in assigning marine birds to geographic regions. The use of claws is currently limited by incomplete understanding of claw growth rates. Data presented here will allow managers of eiders, other marine birds, and marine mammals to assign animals to regions in the Bering Sea based on stable isotope signatures of body tissues. ?? Inter-Research 2008.

Marine Ecology Progress Series↗
USGS2009

Cascading effects of fishing on Galapagos rocky reef communities: reanalysis using corrected data

This article replaces Sonnenholzner et al. (2007; Mar Ecol Prog Ser 343:77–85 ), which was retracted on September 19, 2007, due to errors in entry of data on sea urchins. We sampled 10 highly fished and 10 (putatively) lightly fished shallow rocky reefs in the southeastern area of the Galapagos Marine Reserve, Ecuador. After the correction, these are the new results: there was a negative association between slate-pencil urchins Eucidaris galapagensis and non-coralline algae. In addition, pencil urchins were less abundant where there were many predators. An indirect positive association between predators and non-coralline algae occurred. Fishing appeared to affect this trophic cascade. The spiny lobster Panulirus penicillatus , the slipper lobster Scyllarides astori , and the Mexican hogfish Bodianus diplotaenia were significantly less abundant at highly fished sites. Urchin density was higher at highly fished sites. Non-coralline algae were nearly absent from highly fished sites, where a continuous carpet of the anemone Aiptasia sp. was recorded, and the algal assemblage was mainly structured by encrusting coralline and articulated calcareous algae.

Marine Ecology Progress Series↗
USGS2009

Regional estimates of reef carbonate dynamics and productivity Using Landsat 7 ETM+, and potential impacts from ocean acidification

Using imagery at 30 m spatial resolution from the most recent Landsat satellite, the Landsat 7 Enhanced Thematic Mapper Plus (ETM+), we scale up reef metabolic productivity and calcification from local habitat-scale (10 -1 to 10 0 km 2 ) measurements to regional scales (10 3 to 10 4 km 2 ). Distribution and spatial extent of the North Florida Reef Tract (NFRT) habitats come from supervised classification of the Landsat imagery within independent Landsat-derived Millennium Coral Reef Map geomorphologic classes. This system minimizes the depth range and variability of benthic habitat characteristics found in the area of supervised classification and limits misclassification. Classification of Landsat imagery into 5 biotopes (sand, dense live cover, sparse live cover, seagrass, and sparse seagrass) by geomorphologic class is >73% accurate at regional scales. Based on recently published habitat-scale in situ metabolic measurements, gross production (P = 3.01 ?? 10 9 kg C yr -1 ), excess production (E = -5.70 ?? 10 8 kg C yr -1 ), and calcification (G = -1.68 ?? 10 6 kg CaCO 3 yr -1 ) are estimated over 2711 km 2 of the NFRT. Simple models suggest sensitivity of these values to ocean acidification, which will increase local dissolution of carbonate sediments. Similar approaches could be applied over large areas with poorly constrained bathymetry or water column properties and minimal metabolic sampling. This tool has potential applications for modeling and monitoring large-scale environmental impacts on reef productivity, such as the influence of ocean acidification on coral reef environments. ?? Inter-Research 2009.

Marine Ecology Progress Series↗
USGS1992

Puffins as samplers of juvenile pollock and other forage fish in the Gulf of Alaska

We sampled the nestling diets of tufted puffins (Fratercula cirrhata) and horned puffins (F. corniculata) in 3 years at colonies from the north-central Gulf of Alaska to the eastern Aleutian Islands, Alaska, USA. Overall, tufted puffins consumed (by weight) 41% sandlance (Ammodytes hexapterus), 22% capelin (Mallotus villosus), 19% walleye pollock (Theragra chalcogramma), 13% other fish, and 5% invertebrates, whereas horned puffins took 85% sandlance, 4% capelin, 2% pollock, 8% other fish, and <1 % invertebrates. All of the pollock consumed were young of the year, whereas 4 year-classes of capelin were present, from young of the year through spawning adults. Puffins took mostly first-year sandlance, but fish in their second year or older were also common at colonies near Kodiak, Alaska. The importance of juvenile pollock in the diet of tufted puffins varied geographically from little or no use in the north-central Gulf and Kodiak areas to moderate use (5 to 20%) in the Semidi and Shumagin Islands to heavy use (25 to 75%) in the Sandman Reefs and eastern Aleutians. An estimated 11 billion pollock were consumed by tufted puffins throughout the region in 1986. The proportion of pollock in puffin diets at the Semidi Islands was strongly correlated with independent estimates of cohort strength in 3 years. Puffins may thus provide a useful index of distribution and year class abundance of first-year pollock, a species that currently supports an important commercial fishery in the Gulf of Alaska.

Alaska↗
USGS2009

Timing of breeding and reproductive performance in murres and kittiwakes reflect mismatched seasonal prey dynamics

Seabirds are thought to time breeding to match the seasonal peak of food availability with peak chick energetic demands, but warming ocean temperatures have altered the timing of spring events, creating the potential for mismatches. The resilience of seabird populations to climate change depends on their ability to anticipate changes in the timing and magnitude of peak food availability and 'fine-tune' efforts to match ('Anticipation Hypothesis'). The degree that inter-annual variation in seabird timing of breeding and reproductive performance represents anticipated food availability versus energetic constraints ('Constraint Hypothesis') is poorly understood. We examined the relative merits of the Constraint and Anticipation Hypotheses by testing 2 predictions of the Constraint Hypothesis: (1) seabird timing of breeding is related to food availability prior to egg laying rather than the date of peak food availability, (2) initial reproductive output (e.g. laying success, clutch size) is related to pre-lay food availability rather than anticipated chick-rearing food availability. We analyzed breeding biology data of common murres Uria aalge and black-legged kittiwakes Rissa tridactyla and 2 proxies of the seasonal dynamics of their food availability (near-shore forage fish abundance and sea-surface temperature) at 2 colonies in Lower Cook Inlet, Alaska, USA, from 1996 to 1999. Our results support the Constraint Hypothesis: (1) for both species, egg laying was later in years with warmer sea-surface temperature and lower food availability prior to egg laying, but was not related to the date of peak food availability, (2) pre-egg laying food availability explained variation in kittiwake laying success and clutch size. Murre reproductive success was best explained by food availability during chick rearing. ?? 2009 Inter-Research.

Marine Ecology Progress Series↗
USGS2009

Differential escape from parasites by two competing introduced crabs

Although introduced species often interact with one another in their novel communities, the role of parasites in these interactions remains less clear. We examined parasite richness and prevalence in 2 shorecrab species with different invasion histories and residency times in an introduced region where their distributions overlap broadly. On the northeastern coast of the USA, the Asian shorecrab Hemigrapsus sanguineus was discovered 20 yr ago, while the European green crab Carcinus maenas has been established for over 200 yr. We used literature and field surveys to evaluate parasitism in both crabs in their native and introduced ranges. We found only 1 parasite species infecting H. sanguineus on the US East Coast compared to 6 species in its native range, while C. maenas was host to 3 parasite species on the East Coast compared to 10 in its native range. The prevalence of parasite infection was also lower for both crabs in the introduced range compared to their native ranges; however, the difference was almost twice as much for H. sanguineus as for C. maenas. There are several explanations that could contribute to C. maenas' greater parasite diversity than that of H. sanguineus on the US East Coast, including differences in susceptibility, time since introduction, manner of introduction (vector), distance from native range, taxonomic isolation, and the potential for parasite identification bias. Our study underscores not just that non-native species lose parasites upon introduction, but that they may do so differentially, with ramifications for their direct interactions and with potential community-level influences.

Europe;Northeastern Coast Of United States↗
USGS1992

Threshold foraging behavior of baleen whales

We conducted hydroacoustic surveys for capelin Mallotus villosus in Witless Bay, Newfoundland, Canada, on 61 days during the summers of 1983 to 1985. On 32 of those days in whlch capelin surveys were conducted, we observed a total of 129 baleen whales - Including 93 humpback Megaptera novaeangliae , 31 minke Balaenoptera acutorostrata and 5 fin whales B. phvsalus . Although a few whales were observed when capelin schools were scarce, the majority (96%) of whales were observed when mean daily capelin densities exceeded 5 schools per linear km surveyed (range of means over 3 yr: 0.0 to 14.0 schools km -1 ). Plots of daily whale abundance (no. h -1 surveyed) vs daily capelin school density (mean no. schools km -1 surveyed) in each summer revealed that baleen whales have a threshold foraging response to capelin density. Thresholds were estimated using a simple itterative step-function model. Foraging thresholds of baleen whales (7.3, 5.0, and 5.8 schools km -1 ) varied between years in relation to the overall abundance of capelin schools in the study area during summer (means of 7.2, 3.3, and 5.3 schools km -1 , respectively).

Newfoundland↗
USGS2010

Feeding preferences of West Indian manatees in Florida, Belize, and Puerto Rico as indicated by stable isotope analysis

The endangered West Indian manatee Trichechus manatus has 2 recognized subspecies: the Florida T. m. latirostris and Antillean T. m. manatus manatee, both of which are found in freshwater, estuarine, and marine habitats. A better understanding of manatee feeding preferences and habitat use is essential to establish criteria on which conservation plans can be based. Skin from manatees in Florida, Belize, and Puerto Rico, as well as aquatic vegetation from their presumed diet, were analyzed for stable carbon and nitrogen isotope ratios. This is the first application of stable isotope analysis to Antillean manatees. Stable isotope ratios for aquatic vegetation differed by plant type (freshwater, estuarine, and marine), collection location, and in one instance, season. Carbon and nitrogen isotope ratios for manatee skin differed between collection location and in one instance, season, but did not differ between sex or age class. Signatures in the skin of manatees sampled in Belize and Puerto Rico indicated a diet composed primarily of seagrasses, whereas those of Florida manatees exhibited greater regional variation. Mixing model results indicated that manatees sampled from Crystal River and Homosassa Springs (Florida, USA) ate primarily freshwater vegetation, whereas manatees sampled from Big Bend Power Plant, Ten Thousand Islands, and Warm Mineral Springs (Florida) fed primarily on seagrasses. Possible diet–tissue discrimination values for 15 N were estimated to range from 1.0 to 1.5‰. Stable isotope analysis can be used to interpret manatee feeding behavior over a long period of time, specifically the use of freshwater vegetation versus seagrasses, and can aid in identifying critical habitats and improving conservation efforts.

Florida↗
USGS2010

Divergent movements of walrus and sea ice in the northern Bering Sea

The Pacific walrus Odobenus rosmarus divergens is a large Arctic pinniped of the Chukchi and Bering Seas. Reductions of sea ice projected to occur in the Arctic by mid-century raise concerns for conservation of the Pacific walrus. To understand the significance of sea ice loss to the viability of walruses, it would be useful to better understand the spatial associations between the movements of sea ice and walruses. We investigated whether local-scale (~1 to 100 km) walrus movements correspond to movements of sea ice in the Bering Sea in early spring, using locations from radio-tracked walruses and measures of ice floe movements from processed synthetic aperture radar satellite imagery. We used generalized linear mixed-effects models to analyze the angle between walrus and ice floe movement vectors and the distance between the final geographic position of walruses and their associated ice floes (displacement), as functions of observation duration, proportion of time the walrus was in water, and geographic region. Analyses were based on 121 walrus-ice vector pairs and observations lasting 12 to 36 h. Angles and displacements increased with observation duration, proportion of time the walrus spent in the water, and varied among regions (regional mean angles ranged from 40&#xb0; to 81&#xb0; and mean displacements ranged from 15 to 35 km). Our results indicated a lack of correspondence between walruses and their initially associated ice floes, suggesting that local areas of walrus activities were independent of the movement of ice floes.

Marine Ecology Progress Series↗
USGS2010

Using Gambusia affinis growth and condition to assess estuarine habitat quality: A comparison of indices

Numerous indices have been used to estimate fish growth and condition however, differences in sensitivity and reliability of the methods have hampered efforts to identify appropriate indicators for routine evaluation of habitat quality in the field. We compared common morphometric (length, weight, somatic growth, length-weight condition) and biochemical (RNA:DNA ratio, relative DNA content, energy density) growth indices on the same wild-caught mosquitofish Gambusia affinis to examine their usefulness as indicators of habitat quality. A laboratory experiment was used to quantify growth rates of wild-caught G. affinis under different feeding treatments. Field studies consisted of both a short-term enclosure experiment (10 d) and weekly (7 wk) fish collections to compare growth indices in managed inflow and reference marshes during a winter/spring freshwater pulse event in upper Breton Sound, Louisiana, USA. Marshes flooded by restored freshwater pulses were capable of producing optimum growth (0.001 g DW d-1 DW = dry weight) and energetically valuable habitat (>6000 cal g-1 DW) for trophic transport. Because of differences in timing of response, morphometric and biochemical indices were generally not directly correlated, but there was clear agreement in direction and magnitude of response. The most striking difference in timing was that biochemical indices (RNA:DNA) responded more slowly to treatments than did morphometric growth indices. While gross patterns are comparable between indicators, differences in sensitivity and response time between indicators suggest that choice of indicator needs to be accounted for in interpretation and analysis of effects. ?? Inter-Research 2010, www.int-res.com.

Marine Ecology Progress Series↗
USGS2011

Grazing impact of the invasive clam Corbula amurensis on the microplankton assemblage of the northern San Francisco Estuary

Grazing by the overbite clam Corbula amurensis (formerly known as Potamocorbula) may be the cause of substantial declines in phytoplankton biomass and zooplankton in the San Francisco Estuary (SFE) following its introduction in 1986. While grazing rates have been examined on bacteria, phytoplankton, and copepod nauplii, the consumption of protistan microzooplankton by C. amurensis has not previously been measured. In this study, laboratory feeding experiments revealed that C. amurensis cleared 0.5 l ind -1 h -1 of microzooplankton (ciliates) and 0.2 l ind -1 h -1 of chlorophyll (chl) a. Despite the higher clearance rate on microzooplankton, clams obtained more of their carbon from phytoplankton, which dominated the prey assemblage on most dates. When the measured clearance rates are extrapolated to field populations of clams, fractional loss rates (50 to 90% d -1 ) exceed the population growth capacity of microzooplankton. Although microzooplankton may not be a major component of the diet of these clams, C. amurensis may further alter food web dynamics through consumption of this important trophic intermediary, thus disrupting this link from bacteria and phytoplankton to higher trophic levels.

California↗
USGS2011

Marine and terrestrial factors affecting Adélie penguin Pygoscelis adeliae chick growth and recruitment off the western Antarctic Peninsula

An individual-based bioenergetics model that simulates the growth of an Ad&eacute;lie penguin Pygoscelis adeliae chick from hatching to fledging was used to assess marine and terrestrial factors that affect chick growth and fledging mass off the western Antarctic Peninsula. Simulations considered the effects on Ad&eacute;lie penguin fledging mass of (1) modification of chick diet through the addition of Antarctic silverfish Pleuragramma antarcticum to an all-Antarctic krill Euphausia superba diet, (2) reduction of provisioning rate which may occur as a result of an environmental stress such as reduced prey availability, and (3) increased thermoregulatory costs due to wetting of chicks which may result from increased precipitation or snow-melt in colonies. Addition of 17% Antarctic silverfish of Age-Class 3 yr (AC3) to a penguin chick diet composed of Antarctic krill increased chick fledging mass by 5%. Environmental stress that results in >4% reduction in provisioning rate or wetting of just 10% of the chick&rsquo;s surface area decreased fledging mass enough to reduce the chick&rsquo;s probability of successful recruitment. The negative effects of reduced provisioning and wetting on chick growth can be compensated for by inclusion of Antarctic silverfish of AC3 and older in the chick diet. Results provide insight into climate-driven processes that influence chick growth and highlight a need for field research designed to investigate factors that determine the availability of AC3 and older Antarctic silverfish to foraging Ad&eacute;lie penguins and the influence of snowfall on chick wetting, thermoregulation and adult provisioning rate.

Marine Ecology Progress Series↗
USGS1993

Organic carbon sources and sinks in San Francisco Bay: variability induced by river flow

Sources and sinks of organic carbon for San Francisco Bay (California, USA) were estimated for 1980. Sources for the southern reach were dominated by phytoplankton and benthic microalgal production. River loading of organic matter was an additional important factor in the northern reach. Tidal marsh export and point sources played a secondary role. Autochthonous production in San Francisco Bay appears to be less than the mean for temperate-zone estuaries, primarily because turbidity limits microalgal production and the development of seagrass beds. Exchange between the Bay and Pacific Ocean plays an unknown but potentially important role in the organic carbon balance. Interannual variability in the organic carbon supply was assessed for Suisun Bay, a northern reach subembayment that provides habitat for important fish species (delta smelt Hypomesus transpacificus and larval striped bass Morone saxatilus). The total supply fluctuated by an order of magnitude; depending on the year, either autochthonous sources (phytoplankton production) or allochthonous sources (riverine loading) could be dominant. The primary cause of the year-to-year change was variability of freshwater inflows from the Sacramento and San Joaquin rivers, and its magnitude was much larger than long-term changes arising from marsh destruction and point source decreases. Although interannual variability of the total organic carbon supply could not be assessed for the southern reach, year-to-year changes in phytoplankton production were much smaller than in Suisun Bay, reflecting a relative lack of river influence.

California↗
USGS2012

Long-term effects of the 'Exxon Valdez' oil spill: Sea otter foraging in the intertidal as a pathway of exposure to lingering oil

The protracted recovery of some bird and mammal populations in western Prince William Sound (WPWS), Alaska, and the persistence of spilled 'Exxon Valdez' oil in intertidal sediments, suggests a pathway of exposure to consumers that occupy nearshore habitats. To evaluate the hypothesis that sea otter ( Enhydra lutris ) foraging allows access to lingering oil, we contrast spatial relations between foraging behavior and documented oil distribution. We recovered archival time-depth recorders implanted in 19 sea otters in WPWS, where lingering oil and delayed ecosystem recovery are well documented. Sea otter foraging dives ranged from +2.7 to -92 m below sea level (MLLW), with intertidal accounting for 5 to 38% of all foraging. On average, female sea otters made 16050 intertidal dives per year and 18% of these dives were at depths above the +0.80 m tidal elevation. Males made 4100 intertidal dives per year and 26% of intertidal foraging took place at depths above the +0.80 m tidal elevation. Estimated annual oil encounter rates ranged from 2 to 24 times yr -1 for females, and 2 to 4 times yr -1 for males. Exposure rates increased in spring when intertidal foraging doubled and females were with small pups. In summer 2008, we found sea otter foraging pits on 13.5 of 24.8 km of intertidal shoreline surveyed. Most pits (82%) were within 0.5 m of the zero tidal elevation and 15% were above 0.5 m, the level above which most (65%) lingering oil remains. In August 2008, we detected oil above background concentrations in 18 of 41 (44%) pits excavated by sea otters on beaches with prior evidence of oiling, with total PAH concentrations up to 56000 ng g−1 dry weight. Our estimates of intertidal foraging, the widespread presence of foraging pits in the intertidal, and the presence of oil in and near sea otter foraging pits documents a pathway of exposure from lingering intertidal oil to sea otters foraging in WPWS.

Alaska↗
USGS2012

Step-changes in the physical, chemical and biological characteristics of the Gulf of Maine, as documented by the GNATS time series

We identify step-changes in the physical, chemical and biological characteristics of the Gulf of Maine (GoM) using the Gulf of Maine North Atlantic Time Series (GNATS), a series of oceanographic measurements obtained between September 1998 and December 2010 along a transect in the GoM running from Portland, ME, to Yarmouth, NS. GNATS sampled a period of extremes in precipitation and river discharge (4 of the 8 wettest years of the last century occurred between 2005 and 2010). Coincident with increased precipitation, we observed the following shifts: (1) decreased salinity and density within the surface waters of the western GoM; (2) both reduced temperature and vertical temperature gradients in the upper 50 m; (3) increased colored dissolved organic matter (CDOM) concentrations and particle scattering in the western GoM; (4) increased concentrations of nitrate and phosphate across all but the eastern GoM; (5) increased silicate, particularly in the western GoM, with a sharp increase in the ratio of silicate to dissolved inorganic nitrogen; (6) sharply decreased carbon fixation by phytoplankton; (7) moderately decreased chlorophyll, particulate organic carbon (POC) and particulate inorganic carbon (PIC) in the central GoM and (8) decreased POC- and PIC-specific growth rates. Gulf-wide anomaly analyses suggest that (1) the surface density changes were predominantly driven by temperature, (2) dissolved nutrients, as well as POC/PON, varied in Redfield ratios and (3) anomalies for salinity, density, CDOM, particle backscattering and silicate were significantly correlated with river discharge. Precipitation and river discharge appear to be playing a critical role in controlling the long-term productivity of the Gulf of Maine by supplying CDOM and detrital material, which ultimately competes with phytoplankton for light absorption.

Maine↗
USGS2012

Variations of transcript profiles between sea otters Enhydra lutris from Prince William Sound, Alaska, and clinically normal reference otters

Development of blood leukocyte gene transcript profiles has the potential to expand condition assessments beyond those currently available to evaluate wildlife health, including sea otters Enhydra lutris , both individually and as populations. The 10 genes targeted in our study represent multiple physiological systems that play a role in immuno-modulation, inflammation, cell protection, tumor suppression, cellular stress-response, xenobiotic metabolizing enzymes, and antioxidant enzymes. These genes can be modified by biological, physical, or anthropogenic impacts and consequently provide information on the general type of stressors present in a given environment. We compared gene transcript profiles of sea otters sampled in 2008 among areas within Prince William Sound impacted to varying degrees by the 1989 ‘Exxon Valdez’ oil spill with those of captive and wild reference sea otters. Profiles of sea otters from Prince William Sound showed elevated transcription in genes associated with tumor formation, cell death, organic exposure, inflammation, and viral exposure when compared to the reference sea otter group, indicating possible recent and chronic exposure to organic contaminants. Sea otters from historically designated oiled areas within Prince William Sound 19 yr after the oil spill had higher transcription of genes associated with tumor formation, cell death, heat shock, and inflammation than those from areas designated as less impacted by the spill.

Alaska↗