The response of fish larvae to decadal changes in environmental forcing factors off the Oregon coast

We conducted a statistical analysis to characterize the influence of large-scale and local environmental factors on presence-absence, concentration, and assemblage structure of larval fish within the northern California Current (NCC) ecosystem, based on samples collected at two nearshore stations along the Newport Hydrographic line off the central Oregon coast. Data from 1996 to 2005 were compared with historical data from the 1970s and 1980s to evaluate pseudo-decadal, annual, and seasonal variability. Our results indicate that the most abundant taxa from 1996 to 2005 differ from those of earlier decades. Concentrations of the dominant taxa and total larvae were generally greater in the winter ⁄ spring than summer ⁄ fall season. Using generalized additive modeling, variations in presence-absence and concentration of taxa were compared to climate indices such as the Pacific Decadal Oscillation, Northern Oscillation Index, and the multivariate ENSO index and local environmental factors, such as upwelling, Ekman transport, and wind stress curl. Significant relationships were found for various combinations of environmental variables with lag periods ranging from 0 to 7 months. We found that the large-scale climate indices explained more of the variance in larval fish concentration and diversity than did the more local factors. Our results indicate that readily available oceanographic and climate indices can explain variations in the dominant ichthyoplankton taxa in the NCC. However, variation in response among taxa to the environmental metrics suggests additional unknown factors not included in the analysis likely contributed to the observed distribution patterns and larval fish community structure in the NCC

The Effects of Habitat Complexity and Predation on the Distributionof Grass Shrimp (Decapoda: Palaemonetes) in the Lower St. Johns River Basin, Florida

Few studies have evaluated the abundance and distribution of grass shrimp (Decapoda: Palaemonetes) in the oligohaline and tidal freshwater portions of an estuary. In order to address this knowledge gap, I examined the seasonal patterns of habitat use by grass shrimp along the estuarine gradient in the oligohaline and tidal freshwater portions of the Lower St. Johns River Basin, Florida. Four species of grass shrimp (P. intermedius, P. paludosus, P. pugio and P. vulgaris) were found in this portion of the estuary; their absolute and relative abundances varied considerably along the estuarine gradient. In addition, all four species of grass shrimp were consistently more abundant in tapegrass (Vallisneria americana) than in adjacent sand flats. To determine the possible mechanism responsible for this pattern of habitat use, I performed laboratory experiments on habitat use by grass shrimp under the risk of predation. In the absence of predatory largemouth bass (Micropterus salmoides), grass shrimp used the vegetated and unvegetated portions of the experimental tanks equally. However, with the addition of largemouth bass, grass shrimp significantly increased their use of the vegetated portion of the tank. Sub-optimal and/or fluctuating environmental conditions (e.g. salinity) are hypothesized to contribute to the variation observed in lifehistory characteristics, such as ovigerous female size, ovary size and clutch size. I examined the seasonal and spatial patterns of ovigerous grass shrimp abundance in the Lower St. Johns River Basin. Ovigerous females were detected during three of the four sampling periods, possibly indicating that grass shrimp in the St. Johns River are not continuous spawners. Abundances of ovigerous females were greatest at two oligohaline stations (Buckman and Moccasin Slough). However, lifehistory characteristics (female length and mass, mean number of ova, mean individual ova mass, total ovary mass) differed significantly between these two locations. Field and laboratory studies indicate that grass shrimp assemblage structure and reproduction are influenced by both abiotic and biotic factors in the Lower St. Johns River Basin

The impact of sediment resuspension on mercury and methylmercury fate, transport and bioaccumulation is shallow estuaries

The objective of this study was to investigate the effects of resuspension on the fate and bioaccumulation of mercury (THg) and methylmercury (MeHg) in shallow estuarine environments, using mesocosms. Two 4-week experiments were conducted in July (Experiment 1) and October (Experiment 2) of 2001 with Baltimore Harbor sediments. Hard clams, Mercenaria mercenaria, were introduced into sediments for Experiment 2. Tidal resuspension (4 h on and 2 h off cycles) was simulated, with 3 replicate tanks for each treatment—resuspension (R) and non-resuspension (NR). Sediment cores were collected during the experiments for THg, MeHg, organic content and AVS analyses, and for the determination of methylation/demethylation using Hg stable isotopes (199 Hg(II) and CH 3 199 Hg(II)). Zooplankton samples were collected once a week while clams were taken before and after Experiment 2 for THg and MeHg analyses. Our results suggest that the interplay between Hg methylation and MeHg degradation determines the overall MeHg pool in sediments. Sediment resuspension does not appear to directly impact the Hg transformations but can lead to changes in the association to Hg binding phases, influencing Hg methylation. The bioaccumulation results indicate that sediment resuspension can play an important role in transferring sediment MeHg into organisms.https://www.researchgate.net/profile/Et_Porter/publication/233075659_The_impact_of_sediment_resuspension_on_mercury_and_methylmercury_fate_transport_and_bioaccumulation_is_shallow_estuaries/links/546df4cc0cf2bc99c21504c4/The-impact-of-sediment-resuspension-on-mercury-and-methylmercury-fate-transport-and-bioaccumulation-is-shallow-estuaries.pd

The impact of resuspension on sediment mercury dynamics, and methylmercury production and fate: A mesocosm study

The objective of this study was to investigate the effects of resuspension on the fate and bioaccumulation of mercury (THg) and methylmercury (MeHg) in shallow estuarine environments, using mesocosms. Two 4-week experiments were conducted in July (Experiment 1) and October (Experiment 2) of 2001 with Baltimore Harbor sediments. Hard clams, Mercenaria mercenaria, were introduced into sediments for Experiment 2. Tidal resuspension (4 h on and 2 h off cycles) was simulated, with 3 replicate tanks for each treatment—resuspension (R) and non-resuspension (NR). Sediment cores were collected during the experiments for THg, MeHg, organic content andAVS analyses, and for the determination of methylation/demethylation using Hg stable isotopes (199Hg(II) and CH3 199Hg(II)). Zooplankton samples were collected once a week while clams were taken before and after Experiment 2 for THg and MeHg analyses. Our results suggest that the interplay between Hg methylation and MeHg degradation determines the overall MeHg pool in sediments. Sediment resuspension does not appear to directly impact the Hg transformations but can lead to changes in the association to Hg binding phases, influencing Hg methylation. The bioaccumulation results indicate that sediment resuspension can play an important role in transferring sediment MeHg into organisms