The Population Ecology and Nutrient Transport of Gulf Menhaden in Fourleague Bay, Louisiana (Mortality, Growth, Feeding, Production, Migration).

An ecological study of the young-of-the-year of three year-classes of gulf menhaden (Brevoortia patronus) was conducted from July 1981 to December 1983 in Fourleague Bay, Louisiana. This study documented gulf menhaden population ecology and the importance of gulf menhaden in the nutrient and energy balance of estuaries. Young-of-the-year gulf menhaden immigrated in winter and moved to tidal creeks and ponds, where they remained until midsummer. They then moved into open bays, where they remained until the fall. This migration pattern coincides with sequentially available, but spatially separate, productivity peaks in marsh and open bays. In the fall, they emigrated to offshore coastal areas. Emigration is size-related, with larger individuals moving out first. The instantaneous growth coefficient (G), determined from otolith and length-frequency studies, ranged from 0.00454 to 0.00517 % day(\u27-1). Mortality rate was between 0.008 and 0.018 % day(\u27-1). In 1983, when river discharge was high and winter temperatures and salinities were low, fish grew more slowly and the mortality rate was higher. Major body composition changes from larvae to subadult included an increase in lipid content and energy content, and a decrease in nitrogen content. Young-of-the-year gulf menhaden did not exhibit the condition factor pattern typical of adult clupeids. Lipid condition (KF) peaked in midsummer, then declined, and increased again in the fall. The decline of KF in the fall may be because gulf menhaden with higher lipid contents migrated out of the estuary first. Gulf menhaden may export significant quantities of energy and nutrients from estuaries to the offshore ecosystem. The amount varies with growth and mortality rates and the abundance of fish. Typical values are 9.9 g biomass, 261.5 kJ, 5.6 g C, 1.0 g N, and 0.3 g P, m(\u27-2) marsh yr(\u27-1). These exports indicate that fish transport may be an important component of the nutrient budget of estuaries

Mummichog Fundulus heteroclitus responses to long-term, whole-ecosystem nutrient enrichment

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 492 (2013): 211-222, doi:10.3354/meps10495.The effects of eutrophication on coastal plants and sessile animals are becoming well known, but responses of mobile species are less well studied. Here, we link variation in abundance, biomass, body size, growth rate, and resource utilization in mummichogs (Fundulus heteroclitus) > 40 mm in length to experimental nutrient enrichment in Plum Island Sound, Massachusetts, USA. To mimic cultural eutrophication, dissolved fertilizer was released into replicate saltmarsh creeks on each rising tide throughout entire growing seasons. In the summer of the 6th year of enrichment, we released coded-wire tagged mummichogs into nutrient-enriched (n = 3733 fish) and reference (n = 3894 fish) creeks and recaptured them over the next two months. We found increased abundance (by 37%), biomass (58%), body size (8%), and herbivory (115%, measured as photosynthetic gut pigment content) in nutrient-enriched creeks, although body condition was unaffected. However, individual growth rates were 43% lower in nutrient-enriched creeks. Nutrient enrichment stimulated primary production causing a bottom-up enrichment of the food web, which fostered increased biomass and body size. However, the reduction in growth rate indicates an adverse consequence of long-term nutrient enrichment. This negative effect occurred in the absence of increased hypoxia in these highly tidally (4-m amplitude) flushed study creeks. The mummichog is an important predator/grazer in salt marshes, and nutrient-induced alterations in biomass or resource utilization will directly or indirectly affect lower trophic levels, including benthic algae, thereby impacting the 63 ecosystem-wide response to eutrophication.This material is based upon the work supported by the National Science Foundation under Grant Nos. 0816963, 0923689 and 0423565

Stage-discharge relationship in tidal channels

Author Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography: Methods 15 (2017): 394–407, doi:10.1002/lom3.10168.Long-term records of the flow of water through tidal channels are essential to constrain the budgets of sediments and biogeochemical compounds in salt marshes. Statistical models which relate discharge to water level allow the estimation of such records from more easily obtained records of water stage in the channel. Here we compare four different types of stage-discharge models, each of which captures different characteristics of the stage-discharge relationship. We estimate and validate each of these models on a two-month long time series of stage and discharge obtained with an Acoustic Doppler Current Profiler in a salt marsh channel. We find that the best performance is obtained by models that account for the nonlinear and time-varying nature of the stage-discharge relationship. Good performance can also be obtained from a simplified version of these models, which captures nonlinearity and nonstationarity without the complexity of the fully nonlinear or time-varying models.This research was supported by the National Science Foundation (awards OCE1354251, OCE1354494, and OCE1238212).2018-04-2

Stable isotope monitoring of benthic–planktonic coupling using salt marsh fish

Author Posting. © Inter-Research, 2008. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 369 (2008): 193-204, doi:10.3354/meps07644.Salt marshes are important coastal ecosystems whose trophic function can be monitored with stable isotopes of abundant fish biosentinel species such as the mummichog Fundulus heteroclitus and the Atlantic silverside Menidia menidia. We compared movement patterns and feeding biology of these species in the summers of 1999 and 2000 in the Rowley River salt marsh estuary north of Boston, Massachusetts, USA. A 15N tracer addition experiment showed that fish of both species were more resident than transient, with mummichogs resident at scales of 1 km or less. Natural abundance stable isotope C, N, and S distributions showed that mummichogs feed more strongly in the benthic food web while silversides feed more in the planktonic food web, with % benthic feeding respectively averaging 58 ± 5 and 32 ± 3% (mean ± 95% confidence limit, CL). For both species, isotope results indicated considerable individual specialization in foraging behavior, likely related to use of channel habitat versus use of the marsh. Power analysis showed that measuring 3 composite samples each comprising 10 to 15 individual fish should provide relatively low errors of 0.5‰ (95% CL) or less around stable isotope averages. Use of such composite samples in monitoring programs will allow detection of significant temporal and spatial changes in benthic-planktonic coupling for salt marsh ecosystems, as recorded in average fish diets. Analyzing some individual fish also is recommended to obtain more detailed information on fish food sources, feeding specializations, and end-member isotope values used in estimating importance of benthic and planktonic food sources.This work was supported by Louisiana SeaGrant Projects R/CEH-13 and R-EFH-07, NOAA MULTISTRESS award 16OP2670, and NSF award DEB 9815598 and BES SGER award 0553138-001

Seasonal use of a New England estuary by foraging contingents of migratory striped bass

Author Posting. © American Fisheries Society, 2009. This article is posted here by permission of American Fisheries Society for personal use, not for redistribution. The definitive version was published in Transactions of the American Fisheries Society 139 (2010): 257-269, doi:10.1577/T08-222.1.Using acoustic telemetry on migratory striped bass Morone saxatilis in Plum Island Estuary (PIE), Massachusetts, we found that striped bass (335–634 mm total length) tagged in the spring and summer of 2005 (n = 14) and 2006 (n = 46) stayed in the estuary for an average of 66.0 d in 2005 and 72.2 d in 2006. Striped bass spent the most time in two specific reaches: middle Plum Island Sound and lower Rowley River. In both years, three different use-groups of striped bass were observed in PIE. Short-term visitors (n = 24) stayed in the estuary only briefly (range = 5–20 d). Two groups of seasonal residents stayed for more than 30 d, either in the Rowley River (n = 14) or in Plum Island Sound (n = 22). Within PIE, the two seasonal-resident use-groups may be foraging contingents that learn how to feed efficiently in specific parts of the estuary. These distinct within-estuary use patterns could have different implications for striped bass condition and prey impact

Discontinuities Concentrate Mobile Predators: Quantifying Organism-Environment Interactions at a Seascape Scale

Understanding environmental drivers of spatial patterns is an enduring ecological problem that is critical for effective biological conservation. Discontinuities (ecologically meaningful habitat breaks), both naturally occurring (e.g., river confluence, forest edge, drop-off) and anthropogenic (e.g., dams, roads), can influence the distribution of highly mobile organisms that have land- or seascape scale ranges. A geomorphic discontinuity framework, expanded to include ecological patterns, provides a way to incorporate important but irregularly distributed physical features into organism–environment relationships. Here, we test if migratory striped bass (Morone saxatilis) are consistently concentrated by spatial discontinuities and why. We quantified the distribution of 50 acoustically tagged striped bass at 40 sites within Plum Island Estuary, Massachusetts during four-monthly surveys relative to four physical discontinuities (sandbar, confluence, channel network, drop-off), one continuous physical feature (depth variation), and a geographic location variable (region). Despite moving throughout the estuary, striped bass were consistently clustered in the middle geographic region at sites with high sandbar area, close to channel networks, adjacent to complex confluences, with intermediate levels of bottom unevenness, and medium sized drop-offs. In addition, the highest striped bass concentrations occurred at sites with the greatest additive physical heterogeneity (i.e., where multiple discontinuities co-occurred). The need to incorporate irregularly distributed features in organism–environment relationships will increase as high-quality telemetry and GIS data accumulate for mobile organisms. The spatially explicit approach we used to address this challenge can aid both researchers who seek to understand the impact of predators on ecosystems and resource managers who require new approaches for biological conservation

Use of non-natal estuaries by migratory striped bass (Morone saxatilis) in summer

This paper is not subject to U.S. copyright. The definitive version was published in Fishery Bulletin 107 (2009): 329-338.For most migratory fish, little is known about the location and size of foraging areas or how long individuals remain in foraging areas, even though these attributes may affect their growth, survival, and impact on local prey. We tested whether striped bass (Morone saxatilis Walbaum), found in Massachusetts in summer, were migratory, how long they stayed in non-natal estuaries, whether observed spatial patterns differed from random model predictions, whether fish returned to the same area across multiple years, and whether fishing effort could explain recapture patterns. Anchor tags were attached to striped bass that were caught and released in Massachusetts in 1999 and 2000, and recaptured between 1999 and 2007. In fall, tagged striped bass were caught south of where they were released in summer, confirming that fish were coastal migrants. In the first summer, 77% and 100% of the recaptured fish in the Great Marsh and along the Massachusetts coast, respectively, were caught in the same place where they were released. About two thirds of all fish recaptured near where they were released were caught 2–7 years after tagging. Our study shows that smaller (400–500 mm total length) striped bass migrate hundreds of kilometers along the Atlantic Ocean coast, cease their mobile lifestyle in summer when they use a relatively localized area for foraging (<20 km2), and return to these same foraging areas in subsequent years.This project was administered through the Massachusetts Cooperative Fish and Wildlife Research Unit. The Massachusetts Cooperative Fish and Wildlife Research Unit is an association among the U.S. Geological Survey; University of Massachusetts Department of Natural Resources Conservation; Massachusetts Division of Marine Fisheries; Massachusetts Division of Fisheries and Wildlife, and the Wildlife Management Institute

Nutrient enrichment induces dormancy and decreases diversity of active bacteria in salt marsh sediments

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 7 (2016): 12881, doi:10.1038/ncomms12881.Microorganisms control key biogeochemical pathways, thus changes in microbial diversity, community structure and activity can affect ecosystem response to environmental drivers. Understanding factors that control the proportion of active microbes in the environment and how they vary when perturbed is critical to anticipating ecosystem response to global change. Increasing supplies of anthropogenic nitrogen to ecosystems globally makes it imperative that we understand how nutrient supply alters active microbial communities. Here we show that nitrogen additions to salt marshes cause a shift in the active microbial community despite no change in the total community. The active community shift causes the proportion of dormant microbial taxa to double, from 45 to 90%, and induces diversity loss in the active portion of the community. Our results suggest that perturbations to salt marshes can drastically alter active microbial communities, however these communities may remain resilient by protecting total diversity through increased dormancy

Discontinuities in soil strength contribute to destabilization of nutrient-enriched creeks

In a whole-ecosystem, nutrient addition experiment in the Plum Island Sound Estuary (Massachusetts), we tested the effects of nitrogen enrichment on the carbon and nitrogen contents, respiration, and strength of marsh soils. We measured soil shear strength within and across vegetation zones. We found significantly higher soil percent organic matter, carbon, and nitrogen in the long-term enriched marshes and higher soil respiration rates with longer duration of enrichment. The soil strength was similar in magnitude across depths and vegetation zones in the reference creeks, but showed signs of significant nutrient-mediated alteration in enriched creeks where shear strength at rooting depths of the low marsh-high marsh interface zone was significantly lower than at the sub-rooting depths or in the creek bank vegetation zone. To more closely examine the soil strength of the rooting (10-30 cm) and sub-rooting (40-60 cm) depths in the interface and creek bank vegetation zones, we calculated a vertical shear strength differential between these depths. We found significantly lower differentials in shear strength (rooting depth \u3c sub-rooting depths) in the enriched creeks and in the interface zones. The discontinuities in the vertical and horizontal shear strength across the enriched marshes may contribute to observed fracturing and slumping occurring in the marsh systems. Tide gauge data also showed a pattern of rapid sea level rise for the period of the study, and changes in plant distribution patterns were indicative of increased flooding. Longer exposure times to nutrient-enriched waters and increased hydraulic energy associated with sea level rise may exacerbate creek bank sloughing. Additional research is needed, however, to better understand the interactions of nutrient enrichment and sea level rise on soil shear strength and stability of tidal salt marshes