Dixon Lane-Meadow Creek, CA, United States
Dixon Lane-Meadow Creek, CA, United States

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News Article | April 12, 2016
Site: motherboard.vice.com

A “crusade of crabs” isn’t technically the correct collective noun for the ocean-dwelling crustaceans (for the record, it’s “cast”), but I propose that it should be. At least with special regard to this mesmerizing footage of thousands of determined pelagic red crabs (Pleuroncodes planipes) swarming in unison across the seafloor. The miraculous feat of nature was captured on film by a team of biologists off Panama’s Pacific coast at the Hannibal Bank seamount. Jesús Pineda, a senior scientist at the Woods Hole Oceanographic Institution, was aboard the the manned submersible Deep Rover 2 at a depth of approximately 1,263 feet when he and his crew spotted the swarm. As the newly released video reveals, thousands of crabs were filmed moving in sync with one another, seemingly away from and toward nothing. “It was unusual. In the past, we’ve noticed aggregations of breeding crabs hanging around the ocean floor, or migrating onto land if they’re terrestrial. But these particular crabs weren’t responding to food, or migrating, or reproducing. This was something different,” Pineda told me about the event. The team of biologists, which included staff from Point Loma Nazarene University, San Francisco Estuary Institute, and the Smithsonian Tropical Research Institute, were researching the hotspots of diversity found on Panama’s nutrient-rich underwater seamounts. Less than one percent of these ecosystems have been studied, but they’re of special interest to biologists because their high levels of biomass present exciting opportunities for new discoveries and insights into how deep-water organisms thrive. Pineda removed a few specimens from the swarm, and using DNA sequencing he was able to determine the species as the red crab. Named for their striking color, these crustaceans are also sometimes called “tuna crabs” due to their tendency to feed on yellowfin tuna. As to why this underwater murmuration might’ve occurred, Pineda and his colleagues are still looking for a definitive answer. One potential theory has to do with the feeding behavior of this species of crab. Red crabs have been observed moving up and down in the “water column”—a term used to describe the various ecological features of different ocean strata—to find and eat prey. “People have described schools of crabs six miles long in the water column. Some of these crabs have been reported to migrate vertically, which means that during the day, they can be found on the bottom of the ocean in the sediment. But at night, they ascend in the water column to feed on copepods and plankton near the surface. One possibility about this swarm is that it’s a school of crabs that’s just sitting on the bottom during the day,” Pineda told me. This particular area off the Panama coast features especially "hypoxic" (low oxygen) water levels, according to a statement. Red crabs have been detected in hypoxic areas before, and it’s also possible the swarm was seeking refuge from predators in a habitat where few predatory species are able to survive. Scientists not affiliated with the expedition have theorized that El Niño conditions may have contributed to the phenomenon. Thousands of red crabs have washed up on beaches in San Diego in the past, and have been positively linked to increased ocean temperatures. But according to Pineda, this explanation doesn’t describe what he saw at the Hannibal Bank seamount. “Red crabs are very abundant in southern Baja California. People have noticed during El Niño years that ocean currents change and cause the mass transport of water [in a northerly direction],” he explained to me. "With that, larvae is also transferred, resulting in huge schools of crabs that suddenly show up in southern California. But I don’t see a mechanism for El Niño explaining what we observed. At the time of the cruise one year ago, a full El Niño had not been declared." Pineda said he and his colleagues hope to eventually discover what was driving the exodus of thousands of red crabs that day. The team has just published their findings from last year’s expedition in the journal PeerJ. Their plan is to return to the Hannibal Bank seamount and continue their research on the ecosystem’s astounding levels of biodiversity. And who knows—maybe they’ll get lucky enough to come across another crusade of crabs. Or maybe we’ll just all have to chalk this up as being another one of the ocean’s many great mysteries.

McKee L.J.,San Francisco Estuary Institute | Lewicki M.,Arcadis | Schoellhamer D.H.,U.S. Geological Survey | Ganju N.K.,U.S. Geological Survey
Marine Geology | Year: 2013

Quantifying suspended sediment loads is important for managing the world's estuaries in the context of navigation, pollutant transport, wetland restoration, and coastal erosion. To address these needs, a comprehensive analysis was completed on sediment supply to San Francisco Bay from fluvial sources. Suspended sediment, optical backscatter, velocity data near the head of the estuary, and discharge data obtained from the output of a water balance model were used to generate continuous suspended sediment concentration records and compute loads to the Bay from the large Central Valley watershed. Sediment loads from small tributary watersheds around the Bay were determined using 235 station-years of suspended sediment data from 38 watershed locations, regression analysis, and simple modeling. Over 16years, net annual suspended sediment load to the head of the estuary from its 154,000km2 Central Valley watershed varied from 0.13 to 2.58 (mean=0.89)millionmetrict of suspended sediment, or an average yield of 11metric t/km2/yr. Small tributaries, totaling 8145km2, in the nine-county Bay Area discharged between 0.081 and 4.27 (mean=1.39)millionmetrict with a mean yield of 212metrict/km2/yr. The results indicate that the hundreds of urbanized and tectonically active tributaries adjacent to the Bay, which together account for just 5% of the total watershed area draining to the Bay and provide just 7% of the annual average fluvial flow, supply 61% of the suspended sediment. The small tributary loads are more variable (53-fold between years compared to 21-fold for the inland Central Valley rivers) and dominated fluvial sediment supply to the Bay during 10 out of 16yr. If San Francisco Bay is typical of other estuaries in active tectonic or climatically variable coastal regimes, managers responsible for water quality, dredging and reusing sediment accumulating in shipping channels, or restoring wetlands in the world's estuaries may need to more carefully account for proximal small urbanized watersheds that may dominate sediment supply. © 2013 Elsevier B.V.

Klosterhaus S.L.,San Francisco Estuary Institute | Dreis E.,South Dakota School of Mines and Technology | Baker J.E.,University of Washington
Environmental Toxicology and Chemistry | Year: 2011

Polybrominated diphenyl ethers (PBDEs) are flame-retardant chemicals that have become ubiquitous environmental contaminants. Polybrominated diphenyl ether no-uptake rates from estuarine or marine sediments to deposit-feeding organisms have not yet been reported. In the present study, the marine polychaete worm Nereis virens was exposed to field-contaminated and spiked sediments containing the penta- and deca-BDE commercial mixtures in a 28-d experiment to characterize the relative bioavailability of PBDE congeners from estuarine sediments. A time series sampling regimen was conducted to estimate uptake rate constants. In both field-collected and laboratory-spiked sediment exposures, worms selectively accumulated congeners in the penta-BDE mixture over BDE 209 and other components of the deca-BDE mixture, supporting the prevalence of these congeners in higher trophic level species. Brominated diphenyl ether 209 was not bioavailable to N. virens from field sediment and was only minimally detected in worms exposed to spiked sediments in which bioavailability was maximized. Chemical hydrophobicity was not a good predictor of bioavailability for congeners in the penta-BDE mixture. Direct comparison of bioavailability from the spiked and field sediments for the predominant congeners in the penta-BDE mixture was confounded by the considerable difference in exposure concentration between treatments. Biota-sediment accumulation factors (BSAFs) for N. virens after 28 d of exposure to the field sediment were lower than the BSAFs for Nereis succinea collected from the field site, indicating that 28-d bioaccumulation tests using N. virens may underestimate the in situ concentration of PBDEs in deposit-feeding species. The bioavailability of PBDEs to N. virens indicates that these chemicals can be remobilized from estuarine sediments and transferred to aquatic food webs. © 2011 SETAC.

Yee D.,San Francisco Estuary Institute | McKee L.J.,San Francisco Estuary Institute | Oram J.J.,San Francisco Estuary Institute
Environmental Toxicology and Chemistry | Year: 2011

The San Francisco Bay (California, USA) is a water body listed as impaired because of Hg contamination in sport fish for human consumption, as well as possible effects on resident wildlife. A legacy of Hg mining in local watersheds and Hg used in Au mining in the Sierra Nevada (USA) has contributed to contamination seen in the bay, with additional more recent and ongoing inputs from various sources. Methylmercury is the species of Hg most directly responsible for contamination in biota, so better understanding of its sources, loads, and processes was sought to identify the best means to reduce impacts. A regional scale model of San Francisco Bay was developed to characterize major methylmercury inputs and processes. The model was used to evaluate the potential impact of uncertainties in estimates for methylmercury loading pathways and environmental processes, identify major data gaps, and explore management prospects for reducing methylmercury contamination. External loading pathways considered in the mass balance include methylmercury loads entering via atmospheric deposition to the bay surface, and discharges from the Sacramento/San Joaquin Delta, local watersheds, municipal wastewater, and fringing wetlands. Internal processes considered include exchange between bed and suspended sediments and the water column, in situ production and demethylation, biological uptake, and losses via hydrologic transport to the ocean through the Golden Gate. In situ sediment methylation and demethylation were dominant sources and losses determining ambient steady-state concentrations in the model, with changes in external loads and export causing smaller changes. Better information on methylation and demethylation is thus most critical to improving understanding of methylmercury balances and management. © 2010 SETAC.

Davis E.F.,Duke University | Klosterhaus S.L.,San Francisco Estuary Institute | Stapleton H.M.,Duke University
Environment International | Year: 2012

As polybrominated diphenyl ethers (PBDEs) face increasing restrictions worldwide, several alternate flame retardants are expected to see increased use as replacement compounds in consumer products. Chemical analysis of biosolids collected from wastewater treatment plants (WWTPs) can help determine whether these flame retardants are migrating from the indoor environment to the outdoor environment, where little is known about their ultimate fate and effects. The objective of this study was to measure concentrations of a suite of flame retardants, and the antimicrobial compound triclosan, in opportunistic samples of municipal biosolids and the domestic sludge Standard Reference Material (SRM) 2781. Grab samples of biosolids were collected from two WWTPs in North Carolina and two in California. Biosolids samples were also obtained during three subsequent collection events at one of the North Carolina WWTPs to evaluate fluctuations in contaminant levels within a given facility over a period of three years. The biosolids and SRM 2781 were analyzed for PBDEs, hexabromobenzene (HBB), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB), di(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH), the chlorinated flame retardant Dechlorane Plus (syn- and anti-isomers), and the antimicrobial agent 5-chloro-2-(2,4-dichlorophenoxy)phenol (triclosan). PBDEs were detected in every sample analyzed, and σPBDE concentrations ranged from 1750 to 6358. ng/g dry weight. Additionally, the PBDE replacement chemicals TBB and TBPH were detected at concentrations ranging from 120 to 3749. ng/g dry weight and from 206 to 1631. ng/g dry weight, respectively. Triclosan concentrations ranged from 490 to 13,866. ng/g dry weight. The detection of these contaminants of emerging concern in biosolids suggests that these chemicals have the potential to migrate out of consumer products and enter the outdoor environment. © 2011 Elsevier Ltd.

Sedlak M.D.,San Francisco Estuary Institute | Greig D.J.,Marine Mammal Center
Journal of Environmental Monitoring | Year: 2012

Previous research has documented the bioaccumulation of perfluoroalkyl compounds (PFCs) in apex predators in remote locations but few studies have evaluated urban estuaries. To assess the importance of PFCs in San Francisco Bay, two apex predators in the San Francisco Bay, double-crested cormorants (Phalacrocorax auritus) and Pacific harbor seals (Phoca vitulina richardii), were sampled. Prey fish (Atherinops affinis and Menidia audens) were also evaluated to better understand potential sources of PFCs to the foodweb. Perfluorooctane sulfonate (PFOS) was the primary PFC detected in cormorant eggs, small fish and harbor seal serum. PFOS detected in San Francisco Bay seal serum was typically an order of magnitude higher than those at the reference site. PFOS concentrations were highest in seals and cormorant eggs from the highly urbanized southern portion of the Bay. PFOS in eggs from the southern part of the Bay remained relatively constant between 2006 and 2009 despite the phase-out of perfluorosulfonyl-based compounds nationally. In addition, these levels exceed the avian predicted no effects concentration of 1.0 μg mL -1. Concentrations of the remaining PFCs measured were substantially lower than those of PFOS. © 2012 The Royal Society of Chemistry.

Greenfield B.K.,San Francisco Estuary Institute | Jahn A.,1000 Riverside Drive
Environmental Pollution | Year: 2010

In the San Francisco Estuary, management actions including tidal marsh restoration could change fish mercury (Hg) concentrations. From 2005 to 2007, small forage fish were collected and analyzed to identify spatial and interannual variation in biotic methylmercury (MeHg) exposure. The average whole body total Hg concentration was 0.052 μg g-1 (wet-weight) for 457 composite samples representing 13 fish species. MeHg constituted 94% of total Hg. At a given length, Hg concentrations were higher in nearshore mudflat and wetland species (Clevelandia ios, Menidia audens, and Ilypnus gilberti), compared to species that move offshore (e.g., Atherinops affinis and Lepidogobius lepidus). Gut content analysis indicated similar diets between Atherinops affinis and Menidia audens, when sampled at the same locations. Hg concentrations were higher in sites closest to the Guadalupe River, which drains a watershed impacted by historic Hg mining. Results demonstrate that despite differences among years and fish species, nearshore forage fish exhibit consistent Hg spatial gradients. © 2010 Elsevier Ltd. All rights reserved.

Grenier J.L.,San Francisco Estuary Institute | Davis J.A.,San Francisco Estuary Institute
Reviews of Environmental Contamination and Toxicology | Year: 2010

Reengineering of the natural world is a hallmark of the human species. Along with this reengineering comes a need to sometimes reverse previous modifications. Management of wetlands in the USA is one example of this cycle of modification and restoration. Loss of wetlands across the USA during European colonization and industrialization has been followed decades and even centuries later by efforts to restore many of these habitats. Habitats can never be restored to their original, pristine form and function, and complete restoration is even more difficult in highly modified landscapes that have large human populations. In this chapter, we address water quality concerns that derive from chemical contamination that is related to the restoration of a large area of former tidal wetlands in the highly urbanized San Francisco Estuary in California, USA. Other water quality concerns are also briefly addressed. We begin by describing the San Francisco Estuary and cogent background associated with the South Bay Salt Pond Restoration Project. © 2010 Springer New York.

Greenfield B.K.,San Francisco Estuary Institute | Allen R.M.,San Francisco Estuary Institute
Chemosphere | Year: 2013

Industrialized waterways frequently contain nearshore hotspots of legacy polychlorinated biphenyl (PCB) contamination, with uncertain contribution to aquatic food web contamination. We evaluated the utility of estuarine forage fish as biosentinel indicators of local PCB contamination across multiple nearshore sites in San Francisco Bay. Topsmelt (Atherinops affinis) or Mississippi silverside (Menidia audens) contamination was compared between 12 targeted sites near historically polluted locations and 17 probabilistically chosen sites representative of ambient conditions. The average sum of 209 PCB congeners in fish from targeted stations (441±432ngg-1 wet weight, mean±SD) was significantly higher than probabilistic stations (138±94ngg-1). Concentrations in both species were comparable to those of high lipid sport fish in the Bay, strongly correlated with spatial patterns in sediment contamination, and above selected literature thresholds for potential hazard to fish and wildlife. The highest concentrations were from targeted Central Bay locations, including Hunter's Point Naval Shipyard (1347ngg-1; topsmelt) and Stege Marsh (1337ngg-1; silverside). Targeted sites exhibited increased abundance of lower chlorinated congeners, suggesting local source contributions, including Aroclor 1248. These findings indicate that current spatial patterns in PCB bioaccumulation correlate with historical sediment contamination due to industrial activity. They also demonstrate the utility of naturally occurring forage fish as biosentinels of localized PCB exposure. © 2012 Elsevier Ltd.

McKee L.J.,San Francisco Estuary Institute | Gilbreath A.N.,San Francisco Estuary Institute
Environmental Monitoring and Assessment | Year: 2015

Water-quality policy documents throughout the world often identify urban stormwater as a large and controllable impact to sensitive ecosystems, yet there is often limited data to characterize concentrations and loads especially for rare and more difficult to quantify pollutants. In response, concentrations of suspended sediments and silver, mercury and selenium including speciation, and other trace elements were measured in dry and wet weather stormwater flow from a 100 % urban watershed near San Francisco. Suspended sediment concentrations ranged between 1.4 and 2700 mg/L and varied with storm intensity. Turbidity was shown to correlate strongly with suspended sediments and most trace elements and was used as a surrogate with regression to estimate concentrations during unsampled periods and to compute loads. Mean suspended sediment yield was 31.5 t/km2/year. Total mercury ranged between 1.4 and 150 ng/L and was, on average, 92 % particulate, 0.9 % methylated, and 1.2 % acid labile. Total mercury yield averaged 5.7 μg/m2/year. Total selenium ranged between non-detect and 2.9 μg/L and, on average, the total load (0.027 μg/m2/year) was 61 % transported in dissolved phase. Selenate (Se(VI)) was the dominant species. Silver concentrations ranged between non-detect and 0.11 μg/L. Concentrations and loads of other trace elements were also highly variable and were generally similar to other urban systems with the exceptions of Ag and As (seldom reported) and Cr and Zn which exhibited concentrations and loads in the upper range of those reported elsewhere. Consistent with the semi-arid climatic setting, >95 % of suspended sediment, 94 % of total Hg, and 85–95 % of all other trace element loads were transported during storm flows with the exception of selenium which showed an inverse relationship between concentration and flow. Treatment of loads is made more challenging in arid climate settings due to low proportions of annual loads and greater dissolved phase during low flow conditions. This dataset fills an important local data gap for highly urban watersheds of San Francisco Bay. The field and interpretative methods, the uniqueness of the analyte list, and resulting information have general applicability for managing pollutant concentrations and loads in urban watersheds in other parts of the world and may have particularly useful application in more arid climates. © 2015, Springer International Publishing Switzerland.

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