Widgeon Grass Ruppia Maritima Research Articles

Dataset on the isotopic (ẟ13C, ẟ15N) and elemental (C, N) composition of estuarine primary producers in the subtropical Southwestern Atlantic coast

Benthic and pelagic primary producers had their isotopic (ẟ13C, ẟ15N) and elemental (C, N) composition monitored in the Patos Lagoons estuary, in southern Brazil. The present dataset comprises temporal data obtained through seasonal samplings of C3 (Scirpus spp.) and C4 (Spartina densiflora) salt marsh plants, ephemerous bloom-forming drift macroalgae (Ulvophyceae), the widgeon grass Ruppia maritima, particulate (POM) and sedimentary (SOM) organic matter in shallow waters (< 2m) of a subtropical estuary from austral summer 2010 to autumn 2016. POM and SOM were collected as proxies of phytoplankton and microphytobenthos, respectively. Salt marsh plants were randomly sampled (N = 126) at a regularly flooded low marsh area, whereas submerged drift macroalgae (N = 29) and Ruppia plants (N = 14) were collected in adjacent mudflats. POM was collected (N = 33) by filtering water samples using glass fiber filter. SOM was obtained (N = 35) by removing superficial sediment. In laboratory, samples were processed and further analyzed for total organic carbon (TOC), total nitrogen (TN) and carbon (13C/12C) and nitrogen (15N/14N) stable isotopes ratios. With a total of 237 samples analyzed, this dataset provides key information on the isotopic and elemental composition of distinct estuarine primary producers and sources of particulate organic matter (POM and SOM) and their temporal variability in a highly variable aquatic environment. Such knowledge may add to ecological studies investigating food webs, biogeochemical cycles and sources tracking in coastal systems.

Inland Coal Mine Settling Pond as a Habitat for the Brackish-Water Plant Ruppia maritima

The research conducted in settling ponds located in the coal basin in Upper Silesia (southern Poland), detected in one of them presence of the widgeon grass Ruppia maritima. Currently, it is the only inland site of this species in Poland. The widgeon grass creates underwater meadows in the shore zone of the settling pond and it grows in dense communities together with the common reed Phragmites australis in the coastal zone. Apart from these two plants, no other species were found. The morphological features of the vegetative and generative organs of the studied population of R. maritima is similar to those that have been reported from Europe. The bottom of the pond is atypical for R. maritima – it is covered by mine waste. The water of the settling pond has a high salinity and the water chemistry corresponds to the more natural environments that are inhabited by widgeon grass. This substitute habitat, which imitates the natural environment of R. maritima contributes to the good development of these species. However the studied settling pond offers unstable conditions due to the ongoing mining activity and requires permanent monitoring.

Broad-scale association between seagrass cover and juvenile blue crab density in Chesapeake Bay

Although numerous small-scale laboratory, mesocosm, and field experiments have demonstrated that abundance, survival, and growth of juvenile fish and invertebrates are higher in vegetated than in unvegetated habitats, the effect of habitat quality (i.e. habitat complexity) within vegetated habitats has not been documented at a broad spatial scale. We examined the relationship between percent cover in seagrass beds (eelgrass Zostera marina, widgeon grass Ruppia maritima, and associated macroalgae) and juvenile blue crab Callinectes sapidus density at a broad spatial scale. We quantified the functional relationship between juvenile density and percent cover of vegetation by sampling in Chesapeake Bay (USA) seagrass beds utilized by juve- nile blue crabs in the fall of 2007 and 2008, following peak postlarval blue crab recruitment. Based on Akaike's information criterion model comparisons, the most plausible model included both percent cover of vegetation and region of Chesapeake Bay. Juvenile crab density was a positive exponential function of percent cover of vegetation, and was augmented by 14 to 30%, depending on year, for every 10% increase in cover. Density was approximately 2 times higher on the western shore of Chesapeake Bay than on the eastern shore. Seagrass bed area, presence or absence of algae, and distance to the mouth of the bay did not significantly influence density. An expected threshold (i.e. sigmoid) response of juvenile density to percent cover of vegetation was not evident, probably because this study was undertaken when recruitment was low, so habitats may not have been at carrying capacity. This study is the first to document the functional relation- ship between habitat quality and juvenile density at a broad spatial scale for a marine fish or invertebrate, and suggests that the quality of seagrass habitat influences population dynamics.

Effects of grass shrimp versus nutrient addition on epiphytic algae associated with the ephemeral widgeongrass Ruppia maritima

Grazers can reduce epiphytic algal loads on submerged aquatic vegetation (SAV) and indirectly alter biotic interactions among epiphytic algal groups. In the present study, we elucidate responses by 3 major epiphytic functional groups (diatoms, rhodophytes, and chlorophytes) to grass shrimp Palaemonetes spp. addition and nutrient addition during 3 growth stages of the ephemeral estuarine SAV, Ruppia maritima. Three field experiments conducted in the Grand Bay National Estuar- ine Research Reserve, Mississippi, USA, revealed that grass shrimp altered the community composition of epiphytic algae mainly in the mid- and late-growth stages by selectively grazing red algal epiphytes. Corresponding diatom and green algal responses likely reflect release from biotic interactions, or possibly secondary shrimp feeding preferences. Except for a modest but significant increase in red al- gae relative to shrimp addition, which did not reflect effects of grazing, epiphyte groups did not respond noticeably to shrimp addition in the early stage experiment. Grass shrimp addition appeared to be more important in shaping epiphytic algal composition than nutrient addition. Enclosure effects possibly in- fluenced algal growth and shrimp addition effects. Changes in the composition of the epiphyte commu- nity relative to nutrient addition were modest and variable. The lack of significant shrimp-nutrient in- teractions across all 3 experiments reflected primarily independent effects of both factors on epiphyte composition. Disproportionate effects of grass shrimp on the SAV epiphyte community, as expressed within the context of the inherently plastic and complex trophic role played by these facultative grazers, should help maintain the diversity and function of structured SAV habitats.

A dynamic simulation model of the widgeon grass Ruppiamaritima and its epiphytes in the estuary of the Patos Lagoon, RS, Brazil

The dynamics of the vegetated beds of the estuary of the Patos Lagoon was investigated using a simulation model for two important benthic primary producers (the widgeon grass Ruppia maritima and its epiphytes). The model, of deterministic characteristics, simulated two development cycles of the beds from summer 1992/1993 to 1993/1994. Model validation and calibration were accomplished by using R. maritima biomass collected in shallow bays of the Patos Lagoon estuary during the two simulated cycles. The model simulated the seasonal variations in the biomass of blades, stems, roots plus rhizomes, seeds and fruit of R. maritima, by using the experimental components method, and the epiphytes biomass, by using the compartmental system method, all expressed in g dry wt. (gDW) m −2. The model accurately reproduced the processes of building and decay of R. maritima biomass, representing the maximum values observed in the environment. Plant height and its phenological stage were two important attributes included in the model. They were important to control the processes of light attenuation, beginning of the epiphytes installation and the removal of the grass by hydrodynamic action. Bending of the grass and biomass removal were very important to the model results and they seemed to be the primary factors that control the plant decay in late summer. Ecological modeling has proved to be a powerful tool for the proposition of new control mechanisms for the dynamics of the vegetated beds of the estuary of the Patos Lagoon.

North and South Carolina Coasts

This coastal region of North and South Carolina is a gently sloping plain, containing large riverine estuaries, sounds, lagoons, and salt marshes. The most striking feature is the large, enclosed sound known as the Albemarle–Pamlico Estuarine System, covering approximately 7530 km 2. The coast also has numerous tidal creek estuaries ranging from 1 to 10 km in length. This coast has a rapidly growing population and greatly increasing point and non-point sources of pollution. Agriculture is important to the region, swine rearing notably increasing fourfold during the 1990s. Estuarine phytoplankton communities in North Carolina are well studied; the most important taxonomic groups are diatoms, dinoflagellates, cryptomonads and cyanobacteria. Several major poorly flushed estuaries are eutrophic due to nutrient inputs, and toxic dinoflagellates ( Pfiesteria spp) can reach high densities in nutrient-enriched areas. Fully marine waters are relatively oligotrophic. Southern species enter in subsurface intrusions, eddies, and occasional Gulf Stream rings, while cool water species enter with the flow of the Labrador Current to the Cape Hatteras region. The Carolinas have a low number of endemic macroalgae, but species diversity can be high in this transitional area, which represents the southernmost extension for some cold-adapted species and the northernmost extension of warm-adapted species. In North Carolina the dominant seagrass, Zostera marina, lies at its southernmost extension, while a second species, Halodule wrightii is at its northernmost extent. Widgeon-grass Ruppia maritima is common, growing in brackish water or low-salinity pools in salt marshes. Seagrass meadows are now much reduced, probably due to elevated nitrogen and increased sedimentation. In sounds, numerically dominant benthic taxa include bivalves, polychaetes and amphipods, many showing gradients in community type from mesohaline areas of the eastern shore to near marine salinities in western parts. The semi-enclosed sounds have extensive shellfisheries, especially of blue crab, northern quahogs, eastern oysters, and shrimp. Problems include contamination of some sediments with toxic substances, especially of metals and PCBs at sufficiently high levels to depress growth of some benthic macroinvertebrates. Numerous fish kills have been caused by toxic Pfiesteria outbreaks, and fish kills and habitat loss have been caused by episodic hypoxia and anoxia in rivers and estuaries. Oyster beds currently are in decline because of overharvesting, high siltation and suspended particulate loads, disease, hypoxia, and coastal development. Fisheries monitoring which began in the late 1970s shows greatest recorded landings in 1978–1982; since then, harvests have declined by about a half. Some management plans have been developed toward improving water quality and fisheries sustainability. Major challenges include; high coliform levels leading to closures of shellfish beds, a problem that has increased with urban development and increasing cover of watershed by impervious surfaces; high by-catch and heavy trawling activity; overfishing which has led to serious declines in many wild fish stocks; and eutrophication. Comprehensive plans limiting nutrient inputs are needed for all coastal rivers and estuaries, not only those that already exhibit problems. There is a critical need to improve management of non-point nutrient runoff through increased use of streamside vegetated buffers, preservation of remaining natural wetlands and construction of artificial wetlands. Improved treatment processes, based on strong incentive programmes, should also be mandated for present and future industrial-scale animal operations.

Water depth selection, daily feeding routines and diets of waterbirds in coastal lagoons in Ghana

Water depth requirements, diet, feeding styles and diurnal activity patterns are described for waterbirds using two brackish water lagoon systems in coastal Ghana, the Songor and Keta Lagoons. We project the habitat and activity data on a guild structure defined on the basis of individual feeding style and the sensory mechanism used to detect food. A total of 3199 flocks containing 118,648 individuals of 36 different waterbird species were examined during October‐November 1994. Feeding habitats varied from dry mudflats to wet mud and shallow water of not more than 20 cm. The depth of water selected by waterbirds for foraging (but not for roosting) was correlated with tarsus length. Foraging birds exhibited a wide range of feeding styles using visual and/or tactile means for detecting prey: pecking, probing, stabbing, sweeping and ploughing, sometimes feeding singly, communally or socially in loose or dense flocks. Prey items taken ranged from seeds of Widgeongrass Ruppia maritima to invertebrates (mainly polychaetes, molluscs and crabs) and fish, mainly juvenile Tilapia. The daytime was spent on two main activities, feeding and roosting, with a small fraction of the time (average of 10% for 25 species) spent on comfort activities. The waterbirds exhibited either a circadian (most waders, except Common Sandpipers Actitis hypoleucos and Turnstones Arenaria interpres) or a diurnal foraging activity pattern (herons and terns), with no purely nocturnal species. Some species fed throughout the day, others showed peak foraging at various times of the day. The proportion of time spent foraging was related to guild (highest in visual and tactile surfaceforaging waders) and was negatively correlated with the size of the species. We conclude that the observed patterns in the use of the 24‐h day by waterbirds for foraging are not species specific but vary depending on conditions on the feeding grounds. Nocturnal foraging is a normal and a regular strategy used by waterbirds to obtain enough food to fulfill their energetic requirements, so that irrespective of the sensory mechanism used to detect prey and the conditions prevailing on the feeding grounds, waterbirds forage day and night as dictated by their energetic needs. Water depth appears to be the key environmental factor controlling the availability of food for the waterbirds in the Ghanaian lagoons.

Refuges from predation and the persistence of estuarine clam populations

Densities of adult infaunal clams Macoma balthica and Mya arenaria in mesohaline sections of Pamlico Sound, North Carolina, USA, declined rapidly between April and June 1991 and 1992, except in places where there was abundant shell material on the sediment or large densities of the mactrid bivalve Rangia cuneata. Survivorship of M. balthica and M. arenaria was examined experimentally in 1 M2 plots containing different types of habitat: widgeon grass Ruppia maritima, live R. cuneata, 'artificial' R. cuneata, shell valves of R. cuneata and clean sediments to determine whether these structures provided a refuge from predation for the clams. M. balthica and M arenaria obtained a substantial refuge from predation by crabs when living in patches containing R. cuneata. Neither species obtained a refuge from predation when in beds of widgeon grass. There were 2 surprising results in these experiments. First, survivorship of the clams was significantly reduced in patches containing both seagrass and R. cuneata compared with patches of only R. cuneata. Second, survivorship was significantly less in patches of live R. cuneata than in patches of 'sham' (artificial) clams or equal numbers of shell valves. Two alternative, but not necessarily exclusive, explanations are offered for these results. (1) Subsurface rhizomes of widgeon grass may reduce the depth to which clams are able to burrow into the substratum leaving them more susceptible to predation by digging crabs. (2) Increased availability of alternative prey in patches of widgeon grass causes predators to spend more time foraging in these patches and, by chance alone, they capture more clams. Alternatively, predators spend more time in the patches with widgeon grass because they obtain a partial refuge from their own predators. The occurrence of a refuge from predation for M arenaria and M balthica living with R. cuneata is a striking example of an associational defense between potentially competing species. Associational defenses such as this may be a common structuring force in soft-sediment systems and future work may help in producing a more synthetic understanding of their importance in aquatic systems.