Intertidal Creeks Research Articles

Coastal residents, stingray style: Selecting the best intertidal creeks for seasonal living

ABSTRACTGraphing and calculating percentages are integral skills in a STEM curriculum. Teaching students how to create graphs allows them to identify numerical trends and to express results in a clear and concise manner. In this activity, students will remain engaged in the lesson by moving around the room and then work together to generate their own data. Students will act like stingrays and determine the costs and benefits of selecting different habitats. The skills honed in the activity will enable students to compare actual stingray data with in-class data and to express the results graphically. This activity aligns with Ocean Literacy Principles, Common Core Standards, and National Science Education Standards. The Next Generation Science Standard of including the analysis and interpretation of data to provide evidence for the effects of resource availability on organisms in an ecosystem is also incorporated.

Nekton Use of Flooded Salt Marsh and an Assessment of Intertidal Creek Pools as Low-Tide Refuges

Patterns of nekton occurrence on the salt marsh surface at high tide and in an adjacent intertidal creek pool at low tide were used to investigate movements of nekton in an intertidal basin. Paired collections were made in North Inlet estuary, SC on 67 dates over 9 years. Comparisons of high- and low-tide total abundance indicated that what remained in the creek pool at low tide was representative of the nekton on the flooded marsh. Of the 64 taxa collected, the same 8 species ranked in the top 10 in both the high- and low-tide collections. Abundances of most resident species were positively correlated with the area of marsh flooded, but mummichog (Fundulus heteroclitus), the most abundant resident, was not. Abundances of young-of-the-year transient species were not related to the extent of tidal flooding. Some transient species used the flooded marsh but did not occupy the pool at low tide, and others found in the pool did not use the marsh. Differences in abundance, biomass, and length between the marsh and pool collections indicated differences in the tendency of species and life stages to retreat downstream of the pool to the subtidal channel. Proportionately more of the nekton that were present on the flooded marsh left the intertidal basin when large changes in temperature and salinity occurred between high and low tides. More transients left the basin following higher tides, but more residents did not. The results demonstrate a wide range of taxonomic and ontogenetic patterns among nekton using intertidal salt marsh basins and the underappreciated importance of intertidal creek pools as alternative low-tide refuges.

Processing and performance of topobathymetric lidar data for geomorphometric and morphological classification in a high-energy tidal environment

Abstract. The transition zone between land and water is difficult to map with conventional geophysical systems due to shallow water depth and often challenging environmental conditions. The emerging technology of airborne topobathymetric light detection and ranging (lidar) is capable of providing both topographic and bathymetric elevation information, using only a single green laser, resulting in a seamless coverage of the land–water transition zone. However, there is no transparent and reproducible method for processing green topobathymetric lidar data into a digital elevation model (DEM). The general processing steps involve data filtering, water surface detection and refraction correction. Specifically, the procedure of water surface detection and modelling, solely using green laser lidar data, has not previously been described in detail for tidal environments. The aim of this study was to fill this gap of knowledge by developing a step-by-step procedure for making a digital water surface model (DWSM) using the green laser lidar data. The detailed description of the processing procedure augments its reliability, makes it user-friendly and repeatable. A DEM was obtained from the processed topobathymetric lidar data collected in spring 2014 from the Knudedyb tidal inlet system in the Danish Wadden Sea. The vertical accuracy of the lidar data is determined to ±8 cm at a 95 % confidence level, and the horizontal accuracy is determined as the mean error to ±10 cm. The lidar technique is found capable of detecting features with a size of less than 1 m2. The derived high-resolution DEM was applied for detection and classification of geomorphometric and morphological features within the natural environment of the study area. Initially, the bathymetric position index (BPI) and the slope of the DEM were used to make a continuous classification of the geomorphometry. Subsequently, stage (or elevation in relation to tidal range) and a combination of statistical neighbourhood analyses (moving average and standard deviation) with varying window sizes, combined with the DEM slope, were used to classify the study area into six specific types of morphological features (i.e. subtidal channel, intertidal flat, intertidal creek, linear bar, swash bar and beach dune). The developed classification method is adapted and applied to a specific case, but it can also be implemented in other cases and environments.

Tidal and Diel Patterns in Abundance and Feeding of a Marine-Estuarine-Dependent Fish from Macrotidal Mangrove Creeks in the Tropical Eastern Pacific (Colombia)

Mangrove ecosystems are nursery habitats for several snapper species worldwide. Yet the short-term dynamics in nursery habitat use of Lutjanidae remain poorly understood, with knowledge biased toward clear water, nonestuarine mangroves. Here, we document the effects of tidal-diel cycles and salinity on patterns in abundance and feeding of the yellow snapper, Lutjanus argentiventris, using samples collected from intertidal creeks in a macrotidal estuarine mangrove during 2009–2010 from Colombia, in the Tropical Eastern Pacific (TEP) region. Abundance and biomass were significantly higher in medium salinity versus low salinity creeks. Contrasting tidal-diel patterns of abundance-densities versus catch mass-biomass were due to a size-based intraspecific variation in mangrove use: fish 20 cm entered at night during both spring and neap tides. L. argentiventris had a generalist diet (mainly fish and porcellanid crabs). Fish <10 cm displayed a narrower diet breadth than larger size classes, with decreasing importance of fish size during ontogeny. The highest stomach fullness index values (especially of individuals <20 cm) during neap tide-daytime inundations contradicted the common assumption that snappers are nocturnal feeders and highlight the role of tidal-diel cycles in determining fish feeding preferences in macrotidal mangrove systems. Comparisons with other studies showed that habitat use and feeding patterns of this and other Lutjanids vary significantly according to size, tidal-diel dynamics, and mangrove settings, e.g., marine microtidal versus estuarine macrotidal systems. Therefore, generalized conclusions derived from a single mangrove setting should be drawn with caution.

Complexity in salt marsh circulation for a semienclosed basin

AbstractThe fine details of overmarsh circulation remain largely unexplored and yet they are typically assumed to control many attributes of salt marsh material cycling, transport, and accretion. We characterized the spatial and temporal variability in overmarsh circulation at a 2 km2 Georgia, USA, salt marsh using field observations, dye tracer, and numerical simulations. The marsh bathymetry was created with a high‐precision Global Positioning System survey that details the geomorphic structure of intertidal creeks and salt marsh platform features greater than about 1 m in width. We assessed flow path dynamics at four spatial scales ranging from 1 m to 1000 m. Results show the development and decay of simultaneous flow divergence and convergence, concentrated flow and large‐scale rotational flow, and strong differences between flood and ebb pathways. This current complexity is set by submergence and emergence of subtle salt marsh platform geomorphic structure, and it highlights the role of topography in system‐wide flow processes.

Seasonal Fisheries Changes in Low-Rainfall Mangrove Ecosystems of Iran

To determine the role of mangroves for fisheries in the arid region of the Persian Gulf, we investigated fish community structure and trophic diversity in intertidal creeks with and without mangroves. Fish community abundances and biomass were compared across habitats and seasons. To identify variations in overall community trophic niches among habitats and seasons, we measured niches with size-corrected standard ellipse areas (SEAc) calculated from C and N stable isotope values. Although there was a slightly greater species richness occurred in mangrove creeks, we found a general similarity in the diversity patterns in creeks with and without mangroves. Also, there were no consistent differences in fish abundance or biomass for mangrove vs. non-mangrove fish collections. Community trophic diversity measured as SEAc also showed no significant difference between mangrove and non-mangrove sites. Instead, strong seasonal patterns were observed in the fish assemblages. Winter samples had consistently higher fish abundance and biomass than summer samples. Winter SEAc values were significantly higher, indicating that the fish community had a larger isotopic niche in winter than summer. Overall, we found that seasonality was much stronger than habitat in determining fish community structure and trophic diversity in the mangrove and non-mangrove ecosystems of Qeshm Island, Iran.

Movements and site fidelity of grass shrimp (Palaemonetes pugio and P. vulgaris) in salt marsh intertidal creeks

Grass shrimp are abundant residents of shallow-water habitats in US Atlantic and Gulf coast estuaries. Mark-recapture events determined the extent and direction of their movements in meso-tidal salt marsh creeks at North Inlet, South Carolina. Microwire-tagged Palaemonetes vulgaris demonstrated high fidelity for a dock in a subtidal channel. In the 48 days following release, 11 % of the 422 tagged shrimp were recaptured and 99 % of all recaptures were made there an average of 14 days post-release. Palaemonetes pugio, which favored the use of shallow intertidal areas, exhibited moderate fidelity for pools within creek beds with 53 % of the recaptured shrimp collected at the release site. Higher fidelity was observed for confluences of intertidal creeks and the subtidal channels. Of the 5565 shrimp released with coded microwire tags, 7.5 % were recaptured and 98 % of those recaptures were at release sites up to 53 days later. During another event, P. pugio released 235 m from their origin demonstrated relatively low fidelity for the new site and a lack of homing behavior. Of the 544 tagged shrimp, 3 % were recaptured; only 40 % of those recaptured were from the release site. Site fidelity is a mechanism by which previously discovered large and consistent differences in grass shrimp use of neighboring intertidal creek basins can be sustained over weeks, seasons, and years. Spatial variations and the tendency of these keystone organisms to resist relocation by tidal currents and occupy certain areas for extended periods should be considered in decisions about proposed alterations to creeks and shorelines.

Tidal, diel and lunar patterns in intertidal and subtidal mangrove creek fish assemblages from southwest Thailand

Knowledge about short-term assembly patterns and connectivity in estuarine mangrove ichthyofauna from the Indo-West Pacific region is scant. We assessed tidal and diel dynamics of intertidal and subtidal fish assemblages in the mangrove forest of Sikao Creek, southwest (Andaman coast) Thailand. Over three lunar cycles, two intertidal creeks were blocked at high water according to the interaction of tidal and diel cycles; the adjacent subtidal area was seined at low waters. A total of 18,033 individuals (93 species, 36 families) were caught. Catch mass and abundances were dominated by small-sized fishes (intertidal creeks: Apogon hyalosoma, Ambassis interrupta, Ambassis vachellii; subtidal area: A. vachellii, Neostethus lankesteri, Oryzias javanicus, Siganus javus). Of 45 intertidal species, 78 % were also caught in the subtidal, suggesting close connectivity between the two habitat types. Overall intertidal fish biomass (0.3 g m−2) and density (0.03 fish m−2) were relatively low. Specific combinations of tidal magnitude and diel cycle explained recurring changes in intertidal fish assemblage structures, clearly observed at the species level, in the number of species, diversity, evenness and biomass. This pattern was strongly driven by new moon-night abundance maxima of dominant A. vachellii, which also displayed fullest stomachs at this lunar-diel cycle interaction. We suggest that estuarine mangrove fish studies of the Andaman Sea region may suffer significant bias when the importance of tidal-lunar and diel cycle interactions are not considered because the role of Ambassidae will be strongly underestimated.

A Tripartite Interaction Between Spartina alterniflora, Fusarium palustre, and the Purple Marsh Crab (Sesarma reticulatum) Contributes to Sudden Vegetation Dieback of Salt Marshes in New England

Tripartite interactions are common and occur when one agent (an arthropod or pathogen) changes the host plant in a manner that alters the attack of the challenging agent. We examined herbivory from the purple marsh crab (Sesarma reticulatum) on Spartina alterniflora following exposure to drought or inoculation with Fusarium palustre in mecocosms in the greenhouse and in crab-infested creek banks along intertidal salt marshes. Initially, drought stress on S. alterniflora and disease from F. palustre were examined in the greenhouse. Then, a second challenger, the purple marsh crab, was introduced to determine how drought and disease from F. palustre affected the attraction and consumption of S. alterniflora. Plant height and shoot and root weights were reduced in plants subjected to severe drought treatment when compared with normally irrigated plants. When the drought treatment was combined with inoculation with F. palustre, plants were significantly more stunted and symptomatic, had less fresh weight, more diseased roots, and a greater number of Fusarium colonies growing from the roots (P < 0.001) than noninoculated plants. The effects were additive, and statistical interactions were not detected between drought and inoculation. Estimates of herbivory (number of grass blades cut or biomass consumption) by the purple marsh crab were significantly greater on drought-stressed, diseased plants than on healthy plants irrigated normally. Drought increased attraction to the purple marsh crab more than inoculation with F. palustre. However, when only mild drought conditions were imposed, plant consumption was greater on inoculated plants. Healthy, nonstressed transplants set into plots in crabinfested intertidal creek banks were grazed less each year than inoculated plants or plants that were exposed to drought. Several hypotheses relating to nutrition, chemotaxis, and visual attraction are presented to explain how stress from drought or disease might favor herbivory.

Microphytobenthos sustain fish food webs in intertidal arid habitats: A comparison between mangrove-lined and un-vegetated creeks in the Persian Gulf

The dietary importance of mangroves for fish production often seems to be minor. However, robust comparisons of fish food webs at mangrove vs. non-mangrove sites are largely lacking. We analyzed stable carbon (δ13C) and nitrogen (δ15N) isotope values of dominant fishes (in terms of abundance) and their potential food sources in summer and winter from arid mangrove-lined and un-vegetated intertidal creeks in Qeshm Island, Persian Gulf, Northern Indian Ocean (26.8°N, 55.75°E). Detritivores Liza klunzingeri (47%) and Anodontostoma chacunda (34%) dominated the abundance at the un-vegetated site; at the mangrove site L. klunzingeri (41%) also dominated, while the zooplanktivores Leiognathus daura (18%), Thryssa vitrirostris (8%) and macrobenthivores Pentaprion longimanus (10%), Acanthopagrus latus (4%) also contributed. There was high dietary reliance by fish on food items associated with non-mangrove sources as indicated by 2 source mixing models. Mangrove-derived organic matter contributed a maximum of 36% to the fish tissue whereas organic matter produced by microphytobenthos and plankton played a major role in the diet of the most abundant fish species with contributions of 64–100%. Two trophic pathways, a pelagic pathway and a benthic pathway, were present in the fish food webs at both sites. The pelagic and benthic food sources of the un-vegetated site were 13C-enriched, consistent with stronger contributions of abundant benthic cyanobacteria found within that food web. Spatial δ13C variation of microphytobenthos and plankton was also reflected in the δ13C values of the feeding guilds and some fish species, suggesting that fish were relatively resident at each site. The isotope values of most food sources and fish did not differ significantly between seasons. Overall, regardless of habitat type and season, microphytobenthos and plankton largely sustained fishes in this region while mangroves, where present, were of minor importance. Our results suggest both mangrove and un-vegetated sites act as feeding grounds for fishes via pelagic and benthic food pathways in this arid region.

Biogeochemistry of dissolved organic matter in an anoxic intertidal creek bank

Seawater circulation in permeable coastal sediments is driven by tidal changes in hydraulic gradients. The resulting submarine groundwater discharge is a source of nutrients and dissolved organic matter (DOM) to the water column. Yet, little is known about the cycling of DOM within tidal sediments, because the molecular DOM characterization remains analytically challenging. One technique that can dissect the multitude of molecules in DOM is ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). To aim at a high resolution DOM analysis we study the seasonal turnover and marine and terrestrial sources of DOM in an intertidal creek bank of the southern North Sea down to 3m depth and link the biogeochemical processes to FT-ICR-MS data and the analyses of inorganic porewater chemistry, δ13C of solid-phase extracted dissolved organic carbon (SPE-DOC), dissolved black carbon (DBC) and dissolved carbohydrates (DCHO). Increasing concentrations of dissolved Fe, Mn, P, total alkalinity, dissolved nitrogen, DOC and a concomitant decrease of sulfate along the seawater circulation path from the upper tidal flat to the tidal flat margin indicate continuous microbial activity. The relative increase of Si concentrations, unsaturated aliphatics, peptide molecular formulae and isotopically more 13C-enriched SPE-DOC towards the tidal flat margin suggests that remineralization processes mobilize DOM from buried algal (diatoms) and microbial biomass. Porewater in sediments <100cm depth contains 13C-depleted SPE-DOC and highly unsaturated compounds which are probably derived from eroded peats, suggesting rapid removal of bioavailable marine DOM such as DCHO from the water column and selective enrichment of terrestrial DOM. DBC concentrations are highest in the discharging porewater close to the tidal creek suggesting that the intertidal flat is an important DBC source to the coastal ocean. Porewater DOM accumulating at the low water line is enriched in N and S. We hypothesize that this is partly due to DOM reacting with dissolved sulfide and ammonium which may increase the refractory character of the DOM, hence making it less bioavailable for in situ active microbes.

Variability of polychaete secondary production in intertidal creek networks along a stream-order gradient.

Dendritic tidal creek networks are important habitats for sustaining biodiversity and ecosystem functioning in salt marsh wetlands. To evaluate the importance of creek heterogeneity in supporting benthic secondary production, we assess the spatial distribution and secondary production of a representative polychaete species (Dentinephtys glabra) in creek networks along a stream-order gradient in a Yangtze River estuarine marsh. Density, biomass, and secondary production of polychaetes were found to be highest in intermediate order creeks. In high order (3rd and 4th) creeks, the density and biomass of D. glabra were higher in creek edge sites than in creek bottom sites, whereas the reverse was true for low order (1st and 2nd) creeks. Secondary production was highest in 2nd order creeks (559.7 mg AFDM m−2 year−1) and was ca. 2 folds higher than in 1st and 4th order creeks. Top fitting AIC models indicated that the secondary production of D. glabra was mainly associated with geomorphological characters including cross-sectional area and bank slope. This suggests that hydrodynamic forces are essential factors influencing secondary production of macrobenthos in salt marshes. This study emphasizes the importance of microhabitat variability when evaluating secondary production and ecosystem functions.

The impact of geomorphology of marsh creeks on fish assemblage in Changjiang River estuary

Tidal marshes are an important habitat and nursery area for fish. In the past few decades, rapid economic development in the coastal areas of China has led to the interruption and destruction of an increasing number of tidal marshes. The growing interest in tidal marsh restoration has increased the need to understand the relationship between geomorphological features and fish assemblages in the design of marsh restoration projects. We studied temporal variations in, and the effects of creek geomorphological features on, the estuarine tidal creek fish community. Using modified channel nets, we sampled fish monthly from March 2007 to February 2008 from seven tidal creeks along an intertidal channel system in Chongming Dongtan National Nature Reserve. Fourteen creek geomorphological variables were measured or derived to characterize intertidal creek geomorphological features. The Gobiidae, with 10 species, was the most speciesrich family. The most abundant fish species were Liza affinis, Chelon haematocheilus, and Lateolabrax maculatus. The fish community was dominated by juvenile marine transients, which comprised about 80% of the total catch. The highest abundance of fish occurred in June and July, and the highest biomass occurred in December. Canonical redundancy analyses demonstrated that depth, steepness, cross-sectional area, and volume significantly affected the fish species assemblage. L. affinis favored small creeks with high elevations. Synechogobius ommaturus, Acanthogobius luridus, and Carassius auratus preferred deep, steep creeks with a large cross-sectional area and volume. These findings indicate that the geomorphological features of tidal creeks should be considered in the conservation and sustainable management of fish species and in the restoration of salt marshes.

Coastal saltmarsh managed realignment drives rapid breach inlet and external creek evolution, Freiston Shore (UK)

The creation of saltmarsh through the managed realignment of sea defences, implemented in NW Europe as a sustainable coastal defence option, represents a substantial hydrodynamic perturbation to the local coastal system. The impact of a significantly increased tidal prism on hydromorphological features was investigated at Freiston Shore, Lincolnshire UK. Local tidal conditions and inadequate drainage at this realignment trial contributed to significant channel erosion due to the establishment of water surface slopes and pooling between the newly realigned site and the adjacent intertidal zone. Very high spatial resolution aerial photography and blimp photography were used to monitor inlet evolution from breaching in August 2002 to March 2008, showing a highly non-linear response with breach channels increasing in width by up to 960% within 2.5months. Airborne laser scanning/LiDAR and terrestrial laser scanning quantified breach channel volume increases, showing a similar pattern. Breach channel evolution did not follow established tidal prism–channel width/cross-sectional area relationships that are often used to guide realignment design. Pre- and post-breach rates of external creek morphology change between 1999 and 2006 were also quantified, with intertidal creeks attached to the breach channels increasing significantly after realignment in both width and depth. This study highlights the physical processes affected by managed realignment, and the importance of understanding the causes of complex water surface slopes at multiple scales.

Estimates of Annual Food Consumption/Biomass Ratio (Q/B) from the Fish Fauna of a Mangrove Estuary in North Brazil

To contribute to mass balanced trophic model parametrization, estimates of annual food consumption/biomass ratio (Q/B) were compiled for 37 selected fish species of the Curuçá Estuary in Northern Brazil using an empirical model. Samples were taken bimonthly between July 2003 and July 2004 in the main channel and intertidal creeks using an otter trawl and a fyke net, respectively.

Linking Hydrogeomorphology and Food Webs in Intertidal Creeks

Intertidal creeks are shallow, photic ecosystems that potentially serve as sources of prey for many predators within estuaries. In a previous study, the link between nekton community structure and hydrogeomorphological variables for eight intertidal creeks was assessed for North Inlet estu- ary, South Carolina. Herein, we advance their findings through ecological network analysis of foodweb structure within two creeks and infer nekton trophic relationships to geomorphology and potential influences of hydrological condition and change. A summer network of a shallow, wide creek demonstrated greater carbon recycling, trophic effi- ciency and flow through consumers than that of a deep, narrow creek representing the same period. We infer greater export of nekton carbon from the former creek. These results were supported by analyses of nekton effective trophic levels and guilds across the eight creeks. Shallow, wide intertidal creeks appear to provide both physical and foodweb attri- butes that promote good nekton habitat relative to deeper and narrower creeks. Human alterations to flow regimes and sea- level rise have the ability to affect geomorphology of indi- vidual creeks and the landscape as a whole. These changes in turn have the potential to alter food webs of intertidal creeks and their ability to serve as sources of food for the larger estuary.

Nutrient subsidies from nekton in salt marsh intertidal creeks

Motile organisms are thought to play a role in biogeochemical cycles in tidal systems, but few studies have addressed links between animal activities and dissolved nutrients. Our observations and experiments indicated that movements, feeding, and excretion by fishes and shrimps resulted in subsidies of and to intertidal salt marsh creeks. During low tide, isolated pools inhabited by nekton became biogeochemical hotspots with up to fivefold increases in water column nutrient concentrations. In field experiments, simultaneous measurements in artificial pools and an adjacent natural intertidal pool demonstrated that nekton were sources of during day and night, contributing 17–109% of the net increase in and 3–18% of the in the natural intertidal pool. Nekton residing in intertidal pools generated the equivalent of 5% of the total imported to the creek. At night, nekton in pools contributed the equivalent of 12% of the and 4% of the imported from the subtidal channel. As the tide flooded the intertidal creek, nutrient enriched pool water was pulsed up the creek and into the intertidal basin. Tidally controlled patterns of nekton movements and feeding result in retention and reintroduction of nutrients to the upper reaches of intertidal creek basins. Accordingly, nekton contribute to the recycling of nutrients through a positive feedback loop that may enhance primary production and invertebrate prey within salt marsh creek basins. We conclude that nekton can be important and underappreciated contributors of dissolved nutrients in tidal systems.

Tidal Migrations of Intertidal Salt Marsh Creek Nekton Examined with Underwater Video

Nekton tidal migration patterns were examined in oligo-mesohaline intertidal salt marsh creeks using underwater video observations collected throughout multiple tidal cycles (i.e., fl ood-ebb) during summer 2005-2006. Underwater video observations indi- cated that species composition and abundances varied with tide stage. Three intertidal salt marsh species (Fundulus heteroclitus, Morone americana, Menidia menidia) were the most abundant species observed. In general, resident species were most abundant in early fl ood and late ebb tide stages, whereas transient species were most abundant around slack high tide. F. heteroclitus displayed a consistent symmetrical tidal migration pattern and primarily occurred in early fl ood and late ebb tide stages. M. americana occurred throughout fl ood and high tides, but were largely absent from intertidal creeks during ebb tide. M. menidia was observed during all tide stages, but displayed no distinct migration patterns. The results of this study highlight the advantages and disadvantages of using underwater video for exam- ining small-scale tidal migrations of nekton in intertidal salt marsh creeks.

Salt marsh sediment and metal fluxes in response to rainfall

Lay AbstractWe hypothesize that rainfall during low tide is an important process that affects the cycling of materials (nutrients and metals) in estuaries. We simulated a 45‐min rainfall event in a salt marsh to examine the effects of a low‐tide summer storm on the sediment surface. Surface runoff (sediment concentration (SC), discharge, and rainfall rate) at the downslope end of a 1‐ × 2‐m plot was collected and analyzed chemically in the laboratory. SC peaked at 6100 mg L–1 after 3 min and remained elevated for 15 min before declining. The metal content of the sediments varied considerably with time but was consistently higher than the average background content by a factor of 4–4000. Based on these experimental results, we estimated that 4.8–8.4 tonnes of sediment per square kilometer per minute can be entrained by rainfall during low tide, or up to 96–168 tonnes per year. We also estimated the annual loading of heavy metals that occurs in larger subtidal channels fed by intertidal creeks draining the salt marsh in response to rainfall. Our results demonstrate that rainfall‐entrained sediment during low tides is an important process affecting the cycling of materials in estuarine ecosystems.

Host Quality and Spatial Patterning in Infections of the Eastern Mudsnail (Ilyanassa obsoleta) by Two Trematodes (Himasthla quissetensis and Zoogonus rubellus)

Several studies have suggested that the fitness of a parasite can be directly impacted by the quality of its host. In such cases, selective pressures could act to funnel parasites towards the highest-quality hosts in a population. The results of this study demonstrate that snail host quality is strongly correlated with spatial patterning in trematode infections and that habitat type is the underlying driver for both of these variables. Two trematodes (Himasthla quissetensis and Zoogonus rubellus) with very different life cycles assume the same spatial infection pattern in populations of the first intermediate host (Ilyanassa obsoleta) in coastal marsh habitats. Infected snails are disproportionately recovered from intertidal panne habitats, which offer more hospitable environs for snails than do adjacent habitats (intertidal creeks, coastal flats, and subtidal creeks), in terms of protection from turbulence and wave action, as well as the availability of food stuffs. Snails in intertidal panne habitats are of higher quality when assessed in terms of average size-specific mass, growth rate, and fecundity. In mark-recapture experiments, snails frequently dispersed into intertidal pannes but were never observed leaving them. In addition, field experiments demonstrate that snails confined to intertidal panne habitats are disproportionately infected by both trematode species, relative to conspecifics confined to adjacent habitats. Laboratory experiments show that infected snails suffer significant energetic losses and consume more than uninfected conspecifics, suggesting that infected snails in intertidal pannes may survive better than in adjacent habitats. We speculate that 1 possible mechanism for the observed patterns is that the life cycles of both trematode species allows them to contact the highest-quality snails in this marsh ecosystem.