Vegetation Species and Bed Position May Drive Epifaunal but Not Nekton Habitat Use in Estuarine Submerged Vegetation in the Mobile-Tensaw River Delta, Alabama

Estuarine submerged aquatic vegetation (SAV) provides vital habitat for macroinvertebrate communities that support diverse food webs and subsequent ecosystem services. Invasive SAV, however, has the potential to alter estuarine food webs through competition with native SAV, resulting in different associated biological communities. In the Mobile-Tensaw Delta (Alabama, USA), the invasive Eurasian milfoil, Myriophyllum spicatum, is fast becoming the dominant SAV, out-competing native SAV such as wild celery, Vallisneria americana. This study investigated the above- and belowground macroinvertebrate assemblages associated with these SAV habitats. We found significantly different assemblages between the SAV, with V. americana supporting more even and diverse epifaunal assemblages, and M. spicatum supporting greater total abundances of macroinvertebrates. Gammarid amphipods were more than 11 times more abundant in M. spicatum, while Polychaete species were threefold more abundant in V. americana. Our results suggest that V. americana may support a more diverse and even community compared to M. spicatum. If so, the continued decline in coverage of native V. americana and invasion of M. spicatum across the Mobile-Tensaw Delta could have system-wide ecological consequences.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 492:9-20 (2013) - DOI: https://doi.org/10.3354/meps10486 Effects of reduced hydrological connectivity on the nursery use of shallow estuarine habitats within a river delta Lawrence P. Rozas1,*, Charles W. Martin2,3, John F. Valentine2 1NOAA/National Marine Fisheries Service/SEFSC, Estuarine Habitats and Coastal Fisheries Center, Lafayette, Louisiana 70506, USA 2Dauphin Island Sea Lab and Department of Marine Sciences, University of South Alabama, Dauphin Island, Alabama 36528, USA 3Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA *Email: lawrence.rozas@noaa.gov ABSTRACT: We examined the effects of a hydrologically restrictive transportation corridor on the nursery use of various habitats in the Mobile-Tensaw River delta (MTD). We compared nekton assemblage structure in fall 2009 and spring 2010 among 3 locations and 3 major habitat types (marsh, submerged aquatic vegetation [SAV] dominated by Vallisneria americana, and shallow non-vegetated bottom [SNB]) commonly found throughout the MTD using 1 m2 drop samplers. Sample locations (Tensaw River [TR], Chocolatta Bay [CB], and Below Causeway [BC]) were selected based on their degree of tidal connectivity with the wider estuary (BC > TR > CB). Nekton assemblages varied among locations and habitat types. Recruitment by the young of transient fishery species appeared to drive the nekton assemblage structure at the least hydrologically restricted locations (BC and TR) in the delta, whereas estuarine-resident species dominated the nekton assemblage at CB. Species richness was greater at BC than at CB. Within locations, mean densities of abundant species were concentrated in SAV and marsh. Delta locations directly connected to Mobile Bay, therefore, likely provide an important nursery for fishery species such as white shrimp, blue crab, gulf menhaden, and southern flounder. Additional studies will be needed, however, to determine whether these fishery species represent strong conduits for cross ecosystem transfer of energy and nutrients between the delta and northern Gulf of Mexico. KEY WORDS: Habitat comparison · Tidal freshwater wetlands · Oligohaline marsh · Vallisneria americana · Mobile-Tensaw River delta · Gulf of Mexico Full text in pdf format Supplementary material PreviousNextCite this article as: Rozas LP, Martin CW, Valentine JF (2013) Effects of reduced hydrological connectivity on the nursery use of shallow estuarine habitats within a river delta. Mar Ecol Prog Ser 492:9-20. https://doi.org/10.3354/meps10486 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 492. Online publication date: October 31, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Nekton (fishes and decapod crustaceans) use of brackish submerged aquatic vegetation (SAV) habitat has been largely overlooked in comparison to fresh and marine SAV habitats. This study was designed to examine nekton use of brackish marsh SAV habitat and non-vegetated bottom. Specifically, we examined the effects of habitat location (defined by SAV distance from marsh edge) and complexity (defined by SAV biomass) on nekton community density, biomass, and diversity in shallow water brackish marsh ponds, which contained monospecific beds of Ruppia maritima L. Three habitat types were investigated: (1) inner-pond SAV (SAV habitat > 1 m from marsh edge), (2) near marsh-edge SAV (SAV habitat < 1 m from marsh edge), and (3) non-vegetated bottom. We tested the null hypotheses that nekton density, biomass, and diversity were unrelated to habitat type or habitat characteristics. Ninety-six quantitative samples were taken with a 1 m 2 throw trap between September 2001 and July 2002. Using multivariate analysis of variance (MANOVA), a significant habitat type by season interaction was found (Wilks' λ = 0.32, F24, 259 = 4.21, p < 0.0001) for nekton density, biomass, and diversity. Simple linear regression showed a positive relationship between SAV and nekton biomass (p < 0.0001); however, distance of the vegetated habitat from the marsh edge did not significantly influence SAV or nekton biomass. SAV biomass, but not location, appears to be a dominant factor that influences nekton use within these small brackish marsh ponds. This study highlights some of the intricacies associated with the identification and use of broad scale habitat classification for management purposes. Although brackish marsh SAV habitat types support higher densities of nekton compared to non-vegetated habitat, variation within this gross classifica- tion indicates a wide range of habitat 'value' that needs to be considered for management purposes.

This study, conducted in 1997, reports the first estimates of the impacts of the proliferation of an exotic submerged aquatic vegetation (SAV) species (Myriophyllum spicatum) on macroinvertebrate production via comparisons with two co-occurring native SAV species (Heteranthera dubia and Vallisneria americana) in the tide-influenced Mobile–Tensaw Delta (located in the north-central Gulf of Mexico, 30°40′ N, 87°55′ W). Production of macroinvertebrates was greatest on M. spicatum and H. dubia and least on V. americana. The key determinant of these differences was a greater abundance of amphipods (Gammarus mucronatus) found on the leaves of M. spicatum and H. dubia. Macroinvertebrate production on M. spicatum was three times greater (>1 kg m−2 year−1) than on either of the native SAV species. No-choice palatability tests showed that these differences could not be attributed to differences in invertebrate grazing on these plants. Instead, it is probable that the high production within the structurally complex M. spicatum and H. dubia was the result of reduced predator foraging efficiency. If true, then the presence of this exotic species probably renders this elevated production inaccessible to most high-order predators.

Surveys conducted in the Mobile-Tensaw Delta, located in the Northern Gulf of Mexico, have documented a 96% decline in waterfowl populations from over 100,000 birds in 1939 to around 4,000 birds in 1999. Coincident with this decline has been the introduction and spread of nonnative Eurasian watermilfoil (Myriophyllum spicatum). Six surveys have documented the replacement of native wild celery (Vallisneria americana), the perceived preferred food for waterfowl, by M. spicatum as the dominant species of submerged aquatic vegetation (SAV) in this setting. Simple comparisons of SAV coverage and waterfowl surveys indicate that declines in waterfowl populations are not strongly related to invasion of M. spicatum. Stable isotope analysis of three species of waterfowl (Anas strepera, Anas fulvigula, and Aix sponsa) and their food sources show these waterfowl feed on both wild celery and milfoil. Isotopic signatures of animals living on these SAV were also in waterfowl tissues. Based on these two lines of evidence, it is unlikely that the invasion of milfoil, by itself, is responsible for waterfowl declines in this delta.

Estuaries of the northern Gulf of Mexico contain an abundance of habitat-forming submerged aquatic vegetation (SAV) that provide refuge and protection for a variety of freshwater, estuarine, and marine organisms. However, many of these estuaries now contain numerous exotic species, the ultimate impacts of which are unclear. In the Mobile-Tensaw Delta, located in the upper portion of Mobile Bay, Alabama (USA), Eurasian milfoil (Myriophyllum spicatum, hereafter referred to as Myriophyllum) is now the most dominant submerged macrophyte. Myriophyllum is a structurally-complex macrophyte with the potential to dramatically alter estuarine food webs through reduced encounter rates between predators and their prey and other mechanisms. Previously, we surveyed faunal communities using throw traps, trawls, cores, and suction sampling to compare milfoil assemblages with other native macrophytes to explore the interactive role of hydrology, diel periodicity, and macrophyte presence in influencing community structure. Here, we use this previously collected data to generate a preliminary food web analyses to determine if milfoil, due to its high complexity, creates a "trophic dead end" and limits higher trophic level production. We found the number of nodes, links, linkage density, and connectance to all be greater in milfoil than Vallisneria americana (hereafter referred to as Vallisneria), indicating that a diverse, productive, and highly connected food web exists in this invasive habitat.

Estuaries of the northern Gulf of Mexico contain an abundance of habitat-forming submerged aquatic vegetation (SAV) that provide refuge and protection for a variety of freshwater, estuarine, and marine organisms. However, many of these estuaries now contain numerous exotic species, the ultimate impacts of which are unclear. In the Mobile-Tensaw Delta, located in the upper portion of Mobile Bay, Alabama (USA), Eurasian milfoil (Myriophyllum spicatum, hereafter referred to as Myriophyllum) is now the most dominant submerged macrophyte. Myriophyllum is a structurally-complex macrophyte with the potential to dramatically alter estuarine food webs through reduced encounter rates between predators and their prey and other mechanisms. Previously, we surveyed faunal communities using throw traps, trawls, cores, and suction sampling to compare milfoil assemblages with other native macrophytes to explore the interactive role of hydrology, diel periodicity, and macrophyte presence in influencing community structure. Here, we use this previously collected data to generate a preliminary food web analyses to determine if milfoil, due to its high complexity, creates a "trophic dead end" and limits higher trophic level production. We found the number of nodes, links, linkage density, and connectance to all be greater in milfoil than Vallisneria americana (hereafter referred to as Vallisneria), indicating that a diverse, productive, and highly connected food web exists in this invasive habitat.

Submerged aquatic vegetation (SAV) provides critical habitat for estuarine nekton in the Gulf of Mexico, but habitat quality of SAV beds may change when nonnative species, such as Eurasian watermilfoil (Myriophyllum spicatum), become established. We compared the habitat value of Myriophyllum with another common native SAV (Ruppia maritima) by using field collections to document shifts in nekton community structure and a field experiment to compare growth rates of commercially important juvenile white shrimp (Litopenaeus setiferus). Similar communities were collected from both SAV species, though nekton abundance scaled with SAV biomass. The habitat quality provided by Myriophyllum for white shrimp appeared to meet or exceed that of Ruppia, with densities and growth rates of shrimp in Myriophyllum (2.2 ± 0.47 m−2, 1.0 ± 0.07 mm TL day−1, 25.7 ± 2.98 mg day−1) higher than in Ruppia (1.0 ± 0.36 m−2, 0.6 ± 0.09 mm TL day−1, 11.6 ± 2.04 mg day−1). Though differences were detected between SAV species, other factors, such as hypoxia and interspecific competition, likely contributed to the differences we documented between these habitat types in shrimp densities and growth. Our study provides an example of a nonnative habitat-forming species providing a viable alternative to native habitat. This result contradicts the paradigm of negative effects associated with nonnative species following their introduction into an ecosystem.

ABSTRACTAvian diet quality is typically measured using true metabolizable energy (TMEN), which is a measure of assimilable energy of food items accounting for innate endogenous losses. Originally developed for use in the poultry industry, TMEN methods have been adapted to determine the value of natural foods consumed by waterfowl to parameterize bioenergetics models for conservation planning. Because there is little knowledge of the variation in TMEN estimates among food items and waterfowl species, we investigated TMEN of 6 common species of submersed aquatic vegetation for mallards (Anas platyrhynchos; i.e., a diet generalist) and gadwall (Mareca strepera; i.e., a diet specialist) in the midwestern United States during autumn 2015–2017. We precision fed and collected excreta from ducks using standard bioassays to estimate TMEN. Mallards had slightly greater TMEN than gadwall, but there was considerable variation in TMEN among vegetation species, duck species, and individuals within each species. True metabolizable energy (±SE; kcal/g[dry]) for mallards was greatest for Canadian waterweed (Elodea canadensis; 1.66 ± 0.26), followed by coontail (Ceratophyllum demersum; 1.51 ± 0.28), southern naiad (Najas guadalupensis; 1.37 ± 0.39), sago pondweed (Stuckenia pectinata; 0.50 ± 0.22), wild celery (Vallisneria americana; 0.05 ± 0.42), and Eurasian watermilfoil (Myriophyllum spicatum; –0.13 ± 0.42). Mean TMEN for gadwall was greatest for Eurasian watermilfoil (0.77 ± 0.32), followed by Canadian waterweed (0.70 ± 0.31), coontail (0.55 ± 0.28), southern naiad (–0.61 ± 0.34), wild celery (–0.98 ± 0.39), and sago pondweed (–1.07 ± 0.33). Generally, TMEN for most vegetation species was less than agricultural grains, but it was similar to ranges reported for seeds of naturally occurring hydrophytic vegetation and aquatic macroinvertebrates. We recommend that conservation planners incorporate species‐specific TMEN estimates in bioenergetics models and that future researchers improve TMEN assays for wild waterfowl following our recommendations. © 2020 The Wildlife Society.

The Barataria Preserve unit of Jean Lafitte National Historical Park and Preserve is located in wetlands of the upper Barataria-Terrebonne estuary near New Orleans, LA and subject to perturbations that affect aquatic resources. A study of submersed aquatic vegetation (SAV) was conducted to determine community composition, distribution, and abundance. Seven native species—Cabomba caroliniana, Ceratophyllum demersum, Heteranthera dubia, Najas guadalupensis, Potamogeton pusillus, Vallisneria americana, and Zannichellia palustris—and three exotic species—Egeria densa, Hydrilla verticillata, and Myriophyllum spicatum—were present. The highly invasive, exotic, floating fern Salvinia molesta was also present. The Preserve is affected by a coastal restoration project designed to return Mississippi River flow to the upper Barataria Estuary. Preserve SAV did not conform to the general estuarine management paradigm of decline and loss with nutrient introductions. Instead, freshwater dominated the Preserve, and sufficient light was present to support robust SAV growth in ponds, canals, and Lake Cataouatche. Native and exotic species formed large surface mats that clogged waterways. Vallisneria americana may be decreasing due to the increase in nuisance SAV and floating plants.This study is the first of its kind for any wetland habitat in the states of the Northern Gulf Coast and therefore will be an important baseline to future studies both generally and specifically for the Preserve as Louisiana's coastal wetland waterways experience change brought on by the general coastal wetland loss from sea level rise and efforts to restore the wetlands.

Biological invasions are among the most pervasive yet least understood of the con sequences of the urbanization of estuarine ecosystems. In Mobile Bay, Alabama (USA), the construction of a transportation corridor, locally known as the Mobile Bay Causeway, has been hypothesized to have modified natural disturbance regimes to the point that numerous invasive species now persist in oligohaline reaches of this estuary. Here, we provide the results of field surveys and experiments designed to determine if the causeway facilitated the proliferation of the dominant invasive species, Eurasian milfoil Myriophyllum spicatum Linnaeus, 1753, throughout the Mobile-Tensaw Delta (MTD). Field surveys showed that the composition of submerged aquatic vegetation (SAV) varies greatly with location in the MTD; SAV south of the causeway is dominated by a single native species, wild celery Vallisneria americana Michaux, 1803, while milfoil and canopy-forming native species dominate areas north of the causeway. We found no evidence that the differences in species composition were related to differences in salinity, sediment grain size composition along the causeway, or competitive exclusion of the dominant native species by milfoil. We did, however, find a strong negative relationship between milfoil biomass and maximum wave force. These results suggest the causeway functions as a breakwater, reducing the penetration of large, wind-driven waves into oligohaline embayments north of the causeway. Counter to current thinking, these findings suggest that reductions in the intensity of physical disturbances will create opportunities for invasive milfoil to proliferate in the estuarine waters of the northern Gulf of Mexico.

Submerged aquatic vegetation (SAV) provides many critical ecosystem services, yet we lack basic information on SAV assemblages, biomass and diversity across expansive coasts such as the northern Gulf of Mexico (nGoM). This research investigated SAV along the nGoM from 2013-2015 examining (1) inter-annual variation in SAV assemblages and biomass across salinity zones and gulf coast eco-regions (Texas Mid-Coast, Texas/LA Chenier Plain, Louisiana Delta, MS/AL), (2) intra-annual variation in SAV assemblages and biomass across salinity zones, (3) response of two species, Ruppia maritima and Myriophyllum spicatum, to salinity and light regimes, and (4) estimated organic carbon stock and storage of SAV habitat soils across salinity zones. Coast wide, there was no variation among years, but significant differences in biomass and diversity within zones and regions were observed. Specifically, fresh zones and the Louisiana delta region had higher species diversity and contained more biomass than other zones and regions. Intra-annually, there were significant differences in SAV biomass and assemblages by salinity zone and month. Fresh/ intermediate zones contained more species and biomass than brackish/saline zones, and biomass was higher in summer months than winter months. Competitive relationships between co-occurring species were examined using M. spicatum and R. maritima growth response, under different salinity and light regimes. M. spicatum growth decreased with increasing salinity, while R. maritima growth was not impacted. R. maritima was also not impacted by light, while M. spicatum growth increased in high light. We observed strong competitive interactions; both species decreased in mixture and under no conditions was production in mixtures greater than monocultures. We estimated organic carbon stocks (Corg) within Mississippi River Delta Plain (MRDP) SAV habitat, out to the Chandeleur Islands, and found that MRDP SAV Corg did not differ across salinity zones, but was greater than Chandeleur SAV Corg. MRDP SAV habitat (159,609 ha) contains greater than 3.2 * 107 Mg of Corg, representing an unaccounted for reservoir of “blue carbon,” particularly when extrapolated across the Gulf Coast. These new data provide a better understanding of factors controlling SAV spatial distribution, temporal variation and ecosystem services, which helps managers prepare for coastal changes.

Feeding preference and foraging impact of wintering coots on submerged aquatic vegetation

The Central Yangtze ecoregion in China includes a number of lakes, but these have been greatly affected by human activities over the past several decades, resulting in severe loss of biodiversity. In this paper, we document the present distribution of the major lakes and the changes in size that have taken place over the past 50 years, using remote sensing data and historical observations of land cover in the region. We also provide an overview of the changes in species richness, community composition, population size and age structure, and individual body size of aquatic plants, fishes, and waterfowl in these lakes. The overall species richness of aquatic plants found in eight major lakes has decreased substantially during the study period. Community composition has also been greatly altered, as have population size and age and individual body size in some species. These changes are largely attributed to the integrated effects of lake degradation, the construction of large hydroelectric dams, the establishment of nature reserves, and lake restoration practices.

Eastern oysters (Crassostrea virginica) in Gulf of Mexico estuaries create complex reefs and provide important habitat for fish and crustaceans. Oyster reefs have suffered historic losses due to overharvest, disease, and degraded water quality, and recent efforts have focused on restoring reefs to benefit nekton populations. Oyster shell is the preferred substrate for oyster reef restoration, but as a consequence of its limited supply, a variety of alternative substrates are being used. We used field experiments to quantify the effects of substrate type (concrete, porcelain, limestone, river rock, and oyster shell) on oyster recruitment, growth, and nekton habitat use in St. Charles Bay, TX. After 4 months, oyster spat recruitment density, nekton density and community structure were similar across substrate types—and analogous to those on natural reefs—but differed from samples collected on bare sediment. To determine refuge value of the alternative substrates, we tested mud crab (Panopeidae) prey mortality with and pinfish (Lagodon rhomboides) or blue crab (Callinectes sapidus) predators. Prey mortality was similar across substrate types for both predators, and was significantly lower than no substrate and bare sand controls. Alternative substrates can provide important structural materials to support the development of oyster populations and nekton assemblages, and may be used to promote sustainable management of oyster reef resources via restoration.