27 research outputs found
Tidal Flushing Restores the Physiological Condition of Fish Residing in Degraded Salt Marshes
Roads, bridges, and dikes constructed across salt marshes can restrict tidal flow, degrade habitat quality for nekton, and facilitate invasion by non-native plants including Phragmites australis. Introduced P. australis contributes to marsh accretion and eliminates marsh surface pools thereby adversely affecting fish by reducing access to intertidal habitats essential for feeding, reproduction, and refuge. Our study assessed the condition of resident fish populations (Fundulus heteroclitus) at four tidally restricted and four tidally restored marshes in New England invaded by P. australis relative to adjacent reference salt marshes. We used physiological and morphological indicators of fish condition, including proximate body composition (% lipid, % lean dry, % water), recent daily growth rate, age class distributions, parasite prevalence, female gravidity status, length-weight regressions, and a common morphological indicator (Fulton’s K) to assess impacts to fish health. We detected a significant increase in the quantity of parasites infecting fish in tidally restricted marshes but not in those where tidal flow was restored to reduce P. australis cover. Using fish length as a covariate, we found that unparasitized, non-gravid F. heteroclitus in tidally restricted marshes had significantly reduced lipid reserves and increased lean dry (structural) mass relative to fish residing in reference marshes. Fish in tidally restored marshes were equivalent across all metrics relative to those in reference marshes indicating that habitat quality was restored via increased tidal flushing. Reference marshes adjacent to tidally restored sites contained the highest abundance of young fish (ages 0–1) while tidally restricted marshes contained the lowest. Results indicate that F. heteroclitus residing in physically and hydrologically altered marshes are at a disadvantage relative to fish in reference marshes but the effects can be reversed through ecological restoration
Ecology of Phragmites australis and responses to tidal restoration
Tidal Marsh Restoration provides the scientific foundation and practical guidance necessary for coastal zone stewards to initiate salt marsh tidal restoration programs. The book compiles, synthesizes, and interprets the current state of knowledge on the science and practice of salt marsh restoration, bringing together leaders across a range of disciplines in the sciences (hydrology, soils, vegetation, zoology), engineering (hydraulics, modeling), and public policy, with coastal managers who offer an abundance of practical insight and guidance on the development of programs.
The book is an essential work for managers, planners, regulators, environmental and engineering consultants, and others engaged in planning, designing, and implementing projects or programs aimed at restoring tidal flow to tide-restricted or diked salt marshes.https://scholarworks.wm.edu/asbookchapters/1065/thumbnail.jp
Recommended from our members
Flow Management for Hydropower Extirpates Aquatic Insects, Undermining River Food Webs
Dams impound the majority of rivers and provide important societal benefits, especially daily water releases that enable on-peak hydroelectricity generation. Such “hydropeaking” is common worldwide, but its downstream impacts remain unclear. We evaluated the response of aquatic insects, a cornerstone of river food webs, to hydropeaking using a life history–hydrodynamic model. Our model predicts that aquatic-insect abundance will depend on a basic life-history trait—adult egg-laying behavior—such that open-water layers will be unaffected by hydropeaking, whereas ecologically important and widespread river-edge layers, such as mayflies, will be extirpated. These predictions are supported by a more-than-2500-sample, citizen-science data set of aquatic insects from the Colorado River in the Grand Canyon and by a survey of insect diversity and hydropeaking intensity across dammed rivers of the Western United States. Our study reveals a hydropeaking-related life history bottleneck that precludes viable populations of many aquatic insects from inhabiting regulated rivers.Keywords: citizen science, biodiversity, biological traits, river ecology, damsKeywords: citizen science, biodiversity, biological traits, river ecology, dam
Detection of decreased quantities of actively spawning female Fundulus heteroclitus in tidally restricted marshes relative to restored and reference sites
Hydrologic restriction of salt marshes and subsequent invasion by Phragmites australis could influence the reproductive success of Fundulus heteroclitus, a common salt marsh resident that forages and spawns on the marsh surface at flood tide. Previous research in our laboratory using data from 2010 to 2011 examined the proportion of actively spawning F. heteroclitus residing in altered New England salt marshes as part of a larger experiment to examine the physiological condition of fish in restricted and restored marshes relative to paired unrestricted (reference) sites. We detected a significant decrease in the proportion of actively spawning fish in restricted relative to paired unrestricted marshes, but no difference between restored and paired unrestricted marsh fish. In this manuscript, we conduct a re-analysis of a portion of that data (July 2011) to explore potential mechanisms behind previous results. Using forward stepwise selection and generalized linear mixed models, we determined that the reduction in actively spawning restricted marsh fish was due to a single predictor (lipid mass); there were no effects of water temperature, body size, parasite prevalence, parasite density, and growth rate on the response. Previous results indicate healthy restricted marsh fish already have reduced energy reserves. Since investment in oocytes is energetically costly (this analysis), the effect could manifest at the population level as a reduction in actively spawning fish. In addition, oocyte quality is reduced in restricted marshes (as measured by % lipid; 13.9 ± 1.6 % SD) relative to paired unrestricted marshes (15.9 ± 2.3 % SD). Although these data are preliminary and represent a single lunar cycle, additional studies are warranted to explore relationships between P. australis invasion, restoration, and effects on the fecundity of this ubiquitous salt marsh fish
The Effects of Plant Invasion and Ecosystem Restoration on Energy Flow through Salt Marsh Food Webs
We measured the effects of a plant invasion (Phragmites australis) on resident fish (Fundulus heteroclitus) in New England salt marshes by assessing diet quality at the food web base and by quantifying the importance of primary producers to secondary production using a recently developed Bayesian mixing model (Stable Isotope Analysis in R, SIAR ). Spartina alterniflora, the dominant native plant, exhibited significantly greater leaf toughness and higher C/N ratios relative to P. australis. Benthic microalgae and phytoplankton (as suspended particulate matter) exhibited the lowest C/N indicating higher diet quality. We conducted a sensitivity analysis in SIAR by modeling F. heteroclitus at three separate trophic levels (1.5, 2.0, and 2.5) using species-specific discrimination factors to determine basal resource contributions. Overall, the best-fitting models include those that assume F. heteroclitus resides approximately 2.0 trophic levels above primary producers. Using discrimination factors from a range of data sources reported in the literature, our analyses revealed that consumers rely less on benthic microalgae and phytoplankton in restricted marshes (7-23 % and 11-44 %, respectively) relative to reference marshes (5-34 % and 23-48 %, respectively), resulting in a shift in diet toward invasive plant consumption (0-27 %). This is likely due to increased P. australis cover and marsh surface shading leading to decreased microalgal biomass, combined with reduced flooding of the marsh surface that favors terrestrial invertebrate assemblages. Restoration decreased the quantity of P. australis in the food web (0-15 %) and increased the importance of microalgae (1-30 %), phytoplankton (19-48 %), and native plants (23-63 %), indicating a shift in ecological recovery toward reference conditions. © 2013 Coastal and Estuarine Research Federation
Fish length vs. wet weight for healthy fish.
<p>Data pooled across seasons, regions, and by gender. (A) Restored vs. reference fish. (B) Restricted vs. reference fish.</p
Mean proximate body composition of fish in study, 2010–2011 (standard deviations in parentheses; data by marsh type are pooled across regions, seasons, and sex; data by region, season, and sex are pooled across marsh types; reference marshes adjacent to the restored and restricted marshes are noted in parentheses).
<p>Mean proximate body composition of fish in study, 2010–2011 (standard deviations in parentheses; data by marsh type are pooled across regions, seasons, and sex; data by region, season, and sex are pooled across marsh types; reference marshes adjacent to the restored and restricted marshes are noted in parentheses).</p
Proportion of fish parasitized (circles; females and males) or gravid (triangles; females only) by marsh type.
<p>Data is presented as the mean proportion ± standard deviation.</p
Results of repeated measures ANOVA for the restricted vs. reference systems [Model terms: Marsh type (termed “Marsh”: comparison of restricted vs. reference); Time (comparison of the two marsh types within summer 2010, fall 2010, summer 2011, fall 2011); Region (comparison of the two marsh types within the Gulf of Maine vs. Long Island Sound)].
<p>Results of repeated measures ANOVA for the restricted vs. reference systems [Model terms: Marsh type (termed “Marsh”: comparison of restricted vs. reference); Time (comparison of the two marsh types within summer 2010, fall 2010, summer 2011, fall 2011); Region (comparison of the two marsh types within the Gulf of Maine vs. Long Island Sound)].</p
Mean water quality 2010–2011, by marsh type (standard deviations in parentheses; data pooled across regions and seasons).
<p>Mean water quality 2010–2011, by marsh type (standard deviations in parentheses; data pooled across regions and seasons).</p