Effects of mud fiddler crabs (Uca pugnax) on the recruitment of halophyte seedlings in salt marsh dieback areas of Cape Cod (Massachusetts, USA)

The effects of bioturbation by the mud fiddler crab (Uca pugnax) on salt marsh seedling recruitment were investigated experimentally in this study. Burrowing and foraging activity caused a large amount of soil disturbance, which in turn negatively impacted the establishment of seedlings. Either seeds did not germinate or seedlings were uprooted or buried. Although the majority of the published literature suggests a positive influence of Uca spp. on salt marsh plant growth, at high densities they have the potential to hinder the re-colonization of areas made bare by previous disturbance. This study illustrates the perhaps underappreciated role that bioturbators can have on vegetation patterns in salt marshes and other ecosystems.     

Overwintering habitat selection by the mummichog, Fundulus Heteroclitus, in a Cape Cod (USA) salt marsh

This study tracked the seasonal distribution and winter habitat selection of the mummichog, Fundulus heteroclitus (Linnaeus), in a Cape Cod, Massachusetts salt marsh. Fish (mean size = 43.1 mm total length, range = 10–93 mm) were collected with a 1 m² throw trap and by excavating sediments. In fall, F. heteroclitus began migrating upstream in creeks and eventually moved into upstream pools where they remained throughout winter. F. heteroclitus burrowed into the sediments of these pools at a density of 0.5 fish m^–2, but was not found burrowed in the sediments of downstream pools or any creeks. Sediments in upstream pools were composed of a higher proportion of fine-grained particles and organic content than other marsh pools and creeks, and winter temperatures in upstream pool sediments remained above 1 °C. Temperatures in the water column and sediments of downstream pools regularly dropped below –1.8 °C, exceeding the lethal limit for F. heteroclitus. These results support other recent work showing that F. heteroclitus migrates upstream in salt marshes in fall and overwinters in salt marsh pools. Moreover, this study demonstrates that F. heteroclitus does not utilize all available pools as overwintering habitat but apparently selects pools with sediments that offer a thermal refuge from lethal winter temperatures.     

Biochemical composition of ovary, embryo, and hepatopancreas in the grapsoid crabs Armases cinereum and Sesarma nr. reticulatum (Crustacea, Decapoda)

Biochemical composition of ovary, embryo, and hepatopancreas tissues in wild populations of Armases cinereum and Sesarma nr. reticulatum were monitored during the reproductive season. Total lipid, carbon, nitrogen, C:N ratio, and water concentration of the ovary, hepatopancreas and embryos were quantified over the course of ovarian maturation. Ovary nitrogen concentration decreased as ovaries matured. Ovary lipid and carbon concentration differed significantly over the course of ovarian maturation for both species, but there was no relationship between the concentration or total content of hepatopancreas lipid and the stage of ovarian development in females. Neither species showed a relationship between measures of hepatopancreas lipid and the gonadosomatic index. There was also no simultaneously measurable net decrease in mass of the females' hepatopancreas. Lipid demands of ovarian maturation thus appear to be met in large part by increased dietary intake rather than by substantial draw down of pre-existing lipid stores from the hepatopancreas. While these temperate grapsoid crabs live with putatively fluctuating quality and quantity of food resources, no evidence could be found to demonstrate depletion of lipid concentrations in the hepatopancreas concomitant with ovarian maturation.     

Ontogeny of osmoregulation and salinity tolerance in a mangrove crab, Sesarma curacaoense (Decapoda: Grapsidae)

The grapsid crab Sesarma curacaoense is believed to represent the closest saltwater relative to the ancestor which gave rise to an adaptive radiation of endemic freshwater and terrestrial species on the island of Jamaica. Living in mangrove swamps with variable salinity conditions and showing semiterrestrial behaviour, S. curacaoense exhibits ecological adaptations to non-marine conditions. In laboratory experiments, we studied the salinity tolerance during development from hatching to the end of the first juvenile stage. Successful development through metamorphosis occurred in the full salinity range tested (15-32 per thousand), although mortality was significantly enhanced and development delayed at 15 per thousand. In another series of experiments, we studied the ontogeny of the capability for osmoregulation, which is considered as the physiological basis of osmotic stress tolerance. Our results show that S. curacaoense is from hatching a fairly strong hyperosmoregulator in dilute media. This capability increased gradually from hatching throughout the larval and juvenile development. In seawater (32 per thousand) and at an enhanced salt concentration (44 per thousand), the zoeal stages remained hyperosmoconformers. The capability for hypoosmoregulation in concentrated media appeared first in the megalopa stage and increased thereafter. Adult crabs were observed to be strong hyper-hypo-osmoregulators in a salinity range from at least 1 per thousand to 44 per thousand. The unusually early appearance of strong regulatory capabilities, particularly in dilute media, is interpreted as a physiological preadaptation that should have facilitated the evolutionary process of adaptive radiation in non-marine environments on Jamaica.     

Phytoplankton and zooplankton of the Westport River Estuary,Massachusetts (USA)

Zooplankton and phytoplankton samples were simultaneously collected at approximately biweekly intervals over most of an annual cycle in the Westport River Estuary, Massachusetts. Phytoplankton numbers were overwhelmingly dominated throughout the study by athecate nanoplankton <5 µm in diameter. The zooplankton was primarily composed of copepod nauplii. Periods of occurrence of other zooplankters such as adult copepods, marine cladocerans, meroplankters and ctenophores were similar to those recorded for adjacent estuaries. Our results emphasize the abundance of smaller plankters that have been historically undersampled.     

Branchial Na,K-ATPase and osmoregulation in the purple shore crab,Hemigrapsus nudus (Dana)

The purple shore crab, Hemigrapsus nudus, controls its hemolymph osmolality over a wide range of external salinities: it is a strong hyperosmoregulator in 25%, 50% and 75% sea water (SW) and is isosmotic in 100% SW. The role of branchial sodium + potassium-activated, magnesium-requiring adenosine triphosphatase (NA, K-ATPase) in osmoregulation was investigated by assaying enzyme-specific activity (SEA) in gills from crabs acclimated for 14 d in the four sea water media. Assay conditions were characterized for optimal ESA with crude homogenates of gills; ion and cofactor requirements were found to be similar to those of other crustacean Na, K-ATPases. Branchial ESA was highest in crabs acclimated for 2 weeks in 50% SW and was significantly correlated with the osmotic gradient across the body wall in 50%, 75% and 100% SW. Gills 6, 7 and 8 had the highest ESA in all media and possessed approximately 70% of the total branchial Na, K-ATPase activity, but all gills showed significant, approximately twofold increases of ESA in 50% SW compared with values in 100% SW. The time courses of increased branchial Na, K-ATPase ESA and decreased hemolymph osmotic pressure in crabs transferred from 100% SW to 50% SW are consistent with both increased in vivo activity of existing enzyme in the short term and a longer-term synthesis of new enzyme by the gills which is measured by our in vitro assay.     

Hatching of an estuarine crab, Sesarma haematocheir: from disappearance of the inner (E3) layer to rupture of the egg case

Hatching of decapod crustaceans is characterized by the sudden rupture of the egg case. This study focused on the following two issues regarding the hatching mechanism of the estuarine terrestrial crab Sesarma haematocheir: (1) dissolution of the egg case, and (2) the site where the egg case breaks. The egg case comprises three layers: the outer two (E1 and E2) layers and the inner (E3) thin layer (0.2 microm in thickness). The outer layers showed no morphological changes upon hatching, but the inner layer (E3) was markedly digested. The digestion of this layer would enable the embryo to absorb ambient water via reverse peristalsis of the intestine, resulting in an increase of the volume. The egg case always ruptured perpendicular to the longitudinal axis of the embryo. In addition, breakage of the egg case occurred at the dorsal thorax of the embryo. The three major organs positioned at this area were (1) a sharp projection (dorsal spine), (2) an assemblage of muscles, and (3) a pair of secretory glands, each of which was about 30 microm in diameter. The dorsal projection is soft before hatching, and it is clear that the egg case does not break with the posterior expansion of this projection. The rupture instead appears to be caused by the expansion of the muscles arranged perpendicular to the body axis. In addition, some (unknown) factor might weaken the egg case just before hatching. The secretory glands may be a kind of rosette gland, but the role that this gland plays at hatching is not known. As a duct comes out from the center and enters the dorsal projection, some active substance may be released at the tip of this projection. However, immunochemical studies are not consistent with this substance being an ovigerous hair stripping substance (OHSS).     

An inland freshwater population of the salt marsh mosquito,Aedes detritus (Haliday)

An account is given of the biology and taxonomy of an inland freshwater population of Aedes detritus. Results of artificially mating adults from this population with those collected from saltwater coastal localities are given.     

Oligochaeta in Spartina stems: the microdistribution of Enchytraeidae and Tubificidae in a salt marsh,Sapelo Island,USA

The distribution and abundance of Enchytraeidae and Tubificidae in and around Spartina alterniflora plants in a tidal salt marsh on Sapelo Island, Georgia, USA were studied using two different sampling techniques: wet funnel extraction and stem dissection. At least 80% of all worms inhabited leaf sheaths at the bases of S. alterniflora plants, and densities were low in sediment, root and surface debris samples. Oligochaete densities were dependent on the position within the marsh, the height on stems and the stage of sheath decay. Six predominant species were identified and included Marionina appendiculata, Marionina spartinae, Marionina waltersi, Marionina paludis, and Monopylephorus parvus. Individual species were distributed differently on stems and enchytraeids were more common than tubificids on standing-dead and further up S. alterniflora stems. Estimates of oligochaete densities in salt marsh habitats are increased dramatically when the numbers of worms on stems are considered. Possible advantages of the stem microhabitat are discussed in relation to the biology and ecology of oligochaetes.     

Seasonal movement of the American horseshoe crab Limulus polyphemus in a semi-enclosed bay on Cape Cod,Massachusetts (USA) as determined by acoustic telemetry

<正> American horseshoe crabs Limulus polyphemus were tracked using acoustic telemetry and traditional tagging in asemi-enclosed bay on Cape Cod (Pleasant Bay),Massachusetts,USA,to determine seasonal movement patterns.Fifty-five activelyspawning females were fitted with transmitters in 2008 and 2009 and were tracked using acoustic telemetry from May 2008through July 2010.Fifteen crabs with transmitters also had archive depth-temperature tags attached.In addition,over 2000spawning crabs (males and females) were tagged with US Fish and Wildlife (USFWS) button tags over the same period.Ninety-one percent of the crabs with transmitters were detected during this study.In the spring,crabs were primarily located inthe northern section of the bay near spawning beaches,whereas in the fall crabs moved towards the deeper portions of the bay,and some may have overwintered in the bay.There was evidence that a majority (58%-71%) of the females with transmittersspawned in two sequential seasons.One archive tag was recovered resulting in a year-long continuous record of depth and temperaturedata that,when integrated with telemetry data,indicated that the crab overwintered in the bay.The live recapture rate ofcrabs with USFWS button tags was 11%,with all re-sighted crabs except one observed inside Pleasant Bay.Eighty-three percentof recaptures were found within 2.5km of the tagging location,and 51% were observed at the same beach where they were tagged.This study provides further evidence that horseshoe crabs in Pleasant Bay may be philopatric to this embayment     

Activity and growth efficiency of heterotrophic bacteria in a salt marsh (Ria de Aveiro, Portugal)

Bacterial utilization of monomers is recognized as an important step in the biogeochemical cycling of organic matter. In this study we have compared the heterotrophic activity of bacterial communities from different micro-habitats within a salt marsh environment (Ria de Aveiro, Portugal) in order to establish spatial patterns of bacterial abundance, monomer turnover rates (Tr) and bacterial growth efficiency (BGE). Differences in bacterial abundance and activity could be found between distinct plant rhizospheres. BGE tended to be lower at Halimione portulacoides banks, when compared to Sarcocornia perennis subsp. perennis banks which, on the contrary, showed the highest bacterial densities. Experiments of amendment of natural samples with organic and inorganic supplements indicated that salt marsh bacteria are not strongly regulated by salinity but the increased availability of labile organic matter causes a significant metabolic shift towards mineralization.     

Patterns of abundance, distribution, and alary polymorphism among the salt marsh Delphacidae (Homoptera: Fulgoroidea) of Northwest Florida

Abstract. 1. The species of Delphacidae captured in nearly 16000 sweeps of salt marsh vegetation in Northwest Florida, U.S.A., are examined. Individuals belonging to fourteen species were captured during the 15-month study, a somewhat larger number than is found in most locations.
2. Abundances ranged from one to 1064 individuals per species. The abundances, habitat preferences, and patterns in wing-polymorphism among the species collected were similar to those reported previously from other locations, but important differences were found which reflect the vegetational composition typical of our study area.
3. Wing-morph ratio differences between delphacid populations may reflect strategies for dealing with differences in stability and distribution of their respective habitats. The ratio of macropter/brachypter individuals in various populations of delphacids investigated correlates with the probability that a dispersing individual will find a more suitable habitat patch. The phenomenon is illustrated with a comparison of wing-morph ratios in populations of Prokelisia marginata (Van Duzee) from locations which differ in the extent, distribution, and stability of their stands of Spartina alterniflora Loisl. (smooth cordgrass), the common host of P.marginata .
4. Macroptery is favoured in Atlantic Coast marshes, where habitat patches are differentially suitable, but extensive and predictable. The probability of finding a better patch by dispersing is therefore high.
5. Brachyptery predominates at Cedar Key, Florida, where habitat patches are extensive, stable, and equally suitable during most of the year; and at St Marks, Florida, where resource patches are small, infrequent, isolated, and regularly disturbed. Under these conditions, the probability of finding a better patch by dispersal is low.
6. The conditions at St Marks may have promoted a local host expansion by P.marginata at this location.     

Living foraminifera and total populations in salt marsh peat cores: Kelsey Marsh (Clinton, CT) and the Great Marshes (Barnstable, MA)

Common species of intertidal agglutinated benthic foraminifera in salt marshes in Massachusetts and Connecticut live predominantly at the marsh surface and in the topmost sediment (0–2.5 cm), but a considerable part of the fauna lives at depths of 2.5–15 cm. Few specimens are alive at depths of 15–25 cm, with rare individuals alive between 25–50 cm in the sediments. Specimens living between the sediment surface and 25 cm deep occur in all marsh settings, whereas specimens living deeper than 25 cm are restricted to cores from the lower and middle marsh, and have an irregular distribution-with-depth. Lower and middle marsh areas are bioturbated by metazoa, suggesting that living specimens reach these depths at least in part by bioturbation. High-marsh sediments in New England consist of very dense mats of Spartina patents or Distichlis spicata roots and are not bioturbated by metazoa. In this marsh region bioturbation by plant roots and vertical fluid motion may play a role in moving the foraminifera into the sediment. The depth-distribution of living specimens varies with species: living specimens of Trochammina inflata consistently occur at the deepest levels. This suggests that species have differential rates of survival in the sediment, possibly because of differential adaptation to severe dysoxia to anoxia, or because of differing food preferences. There is no simple correlation between depth-in-core and faunal diversity, absolute abundance, and species composition of the assemblages. It is therefore possible to derive a signal of faunal changes and thus the environmental changes that may have caused them from the complex faunal signal of fossil assemblages.     

Ecological attributes of a native and exotic emergent subtropical marsh community in lake okeechobee, Florida (USA)

Ecological attributes of native Eleocharis cellulosa and exotic-invasive Panicum repens communities were compared in the western littoral marsh of Lake Okeechobee, USA. Water quality, periphyton and macroinvertebrates were monitored for 2 years. Fish and zooplankton were monitored during the second year. Mean dissolved oxygen, pH and Secchi transparency were significantly higher in Eleocharis while total phosphorus was marginally higher in Panicum. Periphyton biomass was higher in Panicum but biovolumes were higher in Eleocharis. There were clear differences in the within-habitat periphyton assemblages, less difference in the among-habitat assemblages and moderate to clear differences in periphyton over time in both habitats. Both habitats were dominated by small omnivorous fish. Habitat and date were the most influential factors in differences among both macroinvertebrates and zooplankton, although these differences were marginal to moderate in both cases. Macroinvertebrate densities were higher in Eleocharis while zooplankton densities were higher in Panicum. These data suggest that contrary to the paradigm that Panicum is undesirable as habitat, sparse (<1,000 stems m^?2) Panicum in close proximity to Eleocharis may exhibit a similar suite of ecological attributes. Both habitats also appear to contain similar food webs to nearby Everglades marsh communities.     

Intertidal zonation of benthic macrofauna in a subtropical salt marsh and nearby unvegetated flat (SE, Brazil)

Intertidal zonation and seasonal variability of benthic macrofaunawere analysed along a Spartina alterniflora (Loisel) marshand nearby unvegetated flat in a subtropical bay. Fivereplicate samples were taken along six tidal levels from the uppermarsh, limited by mangroves, to the lower unvegetated flat.Sediment composition, live and dead above- and below-ground biomassof S. alterniflora and detritus biomass from the vegetatedand unvegetated areas were determined to evaluate whethervariations on plant structure and detritus along the 25 m transectaffect the dynamics of benthic invertebrates. Composition andabundance of invertebrates varied with the elevation and plantcover clearly plays a key role on the distribution patterns of themacrofauna. Below-ground and dead above-ground biomass presentedthe highest correlation with the densities of the invertebrates.Vertical distribution of benthic fauna, however, appears not to beaffected by bellow-ground fraction. Higher detritus biomass in theupper unvegetated flat coincided with higher densities ofdetritivorous or omnivorous species in this level. An eruptivealgal growth during summer affected positively most of the dominantspecies.     

Dynamics of Alexandrium fundyense blooms and shellfish toxicity in the Nauset Marsh System of Cape Cod (Massachusetts,USA)

Paralytic Shellfish Poisoning (PSP) toxins are annually recurrent along the Massachusetts coastline (USA), which includes many small embayments and salt ponds. Among these is the Nauset Marsh System (NMS), which has a long history of PSP toxicity. Little is known, however, about the bloom dynamics of the causative organism Alexandrium fundyense within that economically and socially important system. The overall goal of this work was to characterize the distribution and dynamics of A. fundyense blooms within the NMS and adjacent coastal waters by documenting the distribution and abundance of resting cysts and vegetative cells. Cysts were found predominantly in three drowned kettle holes or salt ponds at the distal ends of the NMS – Salt Pond, Mill Pond, and Town Cove. The central region of the NMS had a much lower concentration of cysts. Two types of A. fundyense blooms were observed. One originated entirely within the estuary, seeded by cysts in the three seedbeds. These blooms developed independently of each other and of the A. fundyense population observed in adjacent coastal waters outside the NMS. The temporal development of the blooms was different in the three salt ponds, with initiation differing by as much as 30 days. These differences do not appear to reflect the initial cyst abundances in these locations, and may simply result from higher cell retention and higher nutrient concentrations in Mill Pond, the first site to bloom. Germination of cysts accounted for a small percentage of the peak cell densities in the ponds, so population size was influenced more by the factors affecting growth than by cyst abundance. Subsurface cell aggregation (surface avoidance) limited advection of the vegetative A. fundyense cells out of the salt ponds through the shallow inlet channels. Thus, the upper reaches of the NMS are at the greatest risk for PSP since the highest cyst abundances and cell concentrations were found there. After these localized blooms in the salt ponds peaked and declined, a second, late season bloom occurred within the central portions of the NMS. The timing of this second bloom relative to those within the salt ponds and the coastal circulation patterns at that time strongly suggest that those cells originated from a regional A. fundyense bloom in the Gulf of Maine, delivered to the central marsh from coastal waters outside the NMS through Nauset Inlet. These results will guide policy decisions about water quality as well as shellfish monitoring and utilization within the NMS and highlight the potential for “surgical” closures of shellfish during PSP events, leaving some areas open for harvesting while others are closed.     

Temporal and spatial variation of arbuscular mycorrhizas in salt marsh plants of the Tagus estuary (Portugal)

The factors which may influence temporal and spatial variation in plant arbuscular mycorrhizal (AM) colonization and propagule occurrence were evaluated in a Portuguese salt marsh poor in plant diversity. Two distinct sites were studied: a more-flooded (low marsh) and a less-flooded zone (high marsh). AM root colonization, AM fungal spore number and inoculum potential, soil edaphic parameters and tidal flooding time periods were analysed. Levels of AM colonization were considerable in Aster tripolium and Inula crithmoides but very low in Puccinellia maritima and non-existent in Spartina maritima, Halimione portulacoides, Arthrocnemum fruticosum and Arthrocnemum perenne. Fungal diversity was very low, with Glomus geosporum dominant at both marsh zones. Colonization showed no spatial variation within marsh zones but temporal variation was observed in the high marsh, dependent on plant phenological phases. In the low marsh, no significantly seasonal variation was observed. Apparently, plant phenological events were diluted by stressful conditions (e.g. flooding, salinity). Spore density was significantly different between marsh zones and showed temporal variation in both zones. This study showed that distribution of mycorrhizas in salt marsh is more dependent on host plant species than on environmental stresses.