High Intertidal Zone Research Articles

Long-term declines in an intertidal foundation species parallel shifts in community composition.

The earth is in the midst of a biodiversity crisis, and projections indicate continuing and accelerating rates of global changes. Future alterations in communities and ecosystems may be precipitated by changes in the abundance of strongly interacting species, whose disappearance can lead to profound changes in abundance of other species, including an increase in extinction rate for some. Nearshore coastal communities are often dependent on the habitat and food resources provided by foundational plant (e.g., kelp) and animal (e.g., shellfish) species. We quantified changes in the abundance of the blue mussel (Mytilus edulis), a foundation species known to influence diversity and productivity of intertidal habitats, over the past 40years in the Gulf of Maine, USA, one of the fastest warming regions in the global ocean. Using consistent survey methods, we compared contemporary population sizes to historical data from sites spanning >400km. The results of these comparisons showed that blue mussels have declined in the Gulf of Maine by >60% (range: 29-100%) at the site level since the earliest benchmarks in the 1970s. At the same time as mussels declined, community composition shifted: at the four sites with historical community data, the sessile community became increasingly algal dominated. Contemporary (2013-2014) surveys across 20 sites showed that sessile species richness was positively correlated to mussel abundance in mid to high intertidal zones. These results suggest that declines in a critical foundation species may have already impacted the intertidal community. To inform future conservation efforts, we provide a database of historical and contemporary baselines of mussel population abundance and dynamics in the Gulf of Maine. Our results underscore the importance of anticipating not only changes in diversity but also changes in the abundance and identity of component species, as strong interactors like foundation species have the potential to drive cascading community shifts.

Geomorphology and preservation potential of coastal and submerged aeolianite: Examples from KwaZulu-Natal, South Africa

The distribution and geomorphology of aeolianite outcrop on the coast of KwaZulu-Natal, South Africa are described in the context of its preservation potential in the geological record. Aeolianite on the contemporary coast comprises discontinuous, widely spaced, outcrops less than 100m in longshore extent and typically 50–60m wide that reflects the combined action of subaerial weathering and physical abrasion in the coastal zone since the mid-Holocene (approximately 7000yrs). The dominant morphological component is an intertidal erosional platform that slopes gently landward. It is fronted by a notch in the mid intertidal zone (0m MSL) and contains active erosional potholes on its seaward margin. The platform surface is encrusted by a variety of marine organisms. Landward of and contiguous with the intertidal surface are small elevated outcrops of aeolianite in the supratidal zone. These comprise a 3m-high seaward scarp with a basal notch in the high intertidal zone +1m MSL. Gullies in the scarp trap coarse clasts of eroded aeolianite as well as bedrock. The upper surface of the supratidal aeolianite is planar with large potholes within which accumulations of coarse clasts and oyster shells have been cemented. The upper surface is interpreted as a remnant of an intertidal platform formed at a higher mid-Holocene sea level. The supratidal outcrop is subject to weathering and disintegration. Major joints divide the outcrop into cuboid blocks with axes of 3–4m. Eroded blocks on the seaward face that exceed 1m diameter, remain in-situ and become locked in place by repeated shaking. Smaller blocks that collapse from the seaward face accumulate in small gullies or are dispersed. The facet most likely to be preserved in the geological record is the planar intertidal platform. The morphology of aeolianite on the contemporary coast is markedly different from submerged aeolianite ridges on the adjacent shelf which are of higher relief, wider and more laterally extensive. Preservation potential of aeolianite under subaerial conditions is low and the widespread high-relief aeolianite on the shelf is attributed to rapid inundation or burial during transgression.

Exposure to solar radiation drives organismal vulnerability to climate: Evidence from an intertidal limpet

Understanding the physiological abilities of organisms to cope with heat stress is critical for predictions of species’ distributions in response to climate change. We investigated physiological responses (respiration and heart beat rate) of the ectotherm limpet Patella vulgata to heat stress events during emersion and the role of seasonal and microclimatic acclimatization for individual thermal tolerance limits. Individuals were collected from 5 microhabitats characterized by different exposure to solar radiation in the high intertidal zone of a semi-exposed rocky shore in winter and summer of 2014. Upper thermal tolerance limits (heat coma temperatures – HCTs, and heart rate Arrhenius break temperatures - ABTs) were determined for individuals from each microhabitat in both seasons under laboratory conditions. While we found a clear seasonal acclimatization, i.e., higher HCTs and ABTs in summer than in winter, we did not find evidence for microhabitat-specific responses that would suggest microclimatic acclimatization. However, operative limpet temperatures derived from in-situ temperature measurements suggest that individuals from sun exposed microhabitats have a much narrower thermal safety margins than those from less exposed surfaces or within crevices. Microhabitat specific thermal safety margins caused by high thermal heterogeneity at small spatial scales and the lack of short term acclimatization will likely shape small scale distribution patterns of intertidal species in response to the predicted increase in the frequency and intensity of heat waves.

Identification of Phymatolithon lamii (Me. Lemoine) Y.M. Chamberlain 1991 following bleaching in the upper intertidal zone of the Minas Basin, Nova Scotia, Canada

Objective: To identify an unusual encrusting calcareous organism found growing on upper intertidal rocks along the coast of the Minas Basin, Nova Scotia, Canada, which was thought to potentially represent a new, perhaps invasive species to the area. Methods: Observations were made of the organism growing in situ and of intact and dissected specimens under microscopes in the laboratory. Taxonomic keys were used to determine probable identity of the organism as a tunicate, sponge, bryozoan, marine lichen, or coralline red alga. These keys were then further used to identify samples to species. Results: The organism was determined to be Phymatolithon lamii (Me. Lemoine) Y.M. Chamberlain 1991, an encrusting coralline red alga native to the study region. This species normally occurs in the subtidal zone, so its occurrence in the high intertidal zone was unusual and resulted in the alga becoming bleached and taking on an unusual appearance. Conclusions: The sample did not represent a new or invasive species to the study area. However, occurrence of this species on the high intertidal zone was novel and may have resulted from unusual climatic and/or oceanographic conditions in the study area in 2015 that allowed this alga to settle and grow in the intertidal zone for a time before death and bleaching occurred. Events such as this resulting from climate change may negatively impact recruitment to populations of coastal marine species and should be investigated further.

Seed dispersal capacity and post-dispersal fate of the invasive Spartina alterniflora in saltmarshes of the Yangtze Estuary

Spartina alterniflora is one of the most serious invasive species in the coastal saltmarshes of China. Seeds are generally considered to be the main method for this species to colonise new habitat, but little is known quantitatively about the seed dispersal capacity and post-dispersal fate (i.e., germination and survival time). We measured the duration of seed flotation, seed persistence and seed germination of S. alterniflora in three intertidal zones [low intertidal zone (LIT), middle intertidal zone (MIT) and high intertidal zone (HIT)] in the Yangtze Estuary on the eastern coast of China. The results showed that (1) the flotation time of S. alterniflora seeds ranged from 3 to 13 days, and the values were higher in HIT and MIT than in LIT; (2) the period of seed germination was from February to June, mainly in March and April, and seed source affected seed germination as the values for seeds from HIT and MIT were much higher than those from LIT, while burial sites had no effect on germination percentages, and (3) the seed persistence was less than a year regardless of seed source, which was characterised by a transient seed bank, with values being higher in HIT and MIT than in LIT. Our results suggested that low marsh plants were far less able to produce successful seeds, or conversely, that the mid-marsh location had plants with the greatest seed production and seed mass, and the high- and mid-marsh plants had good seed floatation ability, germination and survival. Thus, plants in the mid-and high-marsh may contribute disproportionally to an invasion.

Temporal and spatial variation in female mating preferences in a fiddler crab

Female mating preferences can vary temporally, with females choosing different males at different times; and spatially, with females in different populations preferring different males. This level of complexity is now well established, but we know of no evidence for a mosaic of female preferences within a single population. Here we show that, in the banana fiddler crab, Uca mjoebergi, female preferences vary both temporally and spatially. Females living in the high inter-tidal zone changed their mating preference for male size over the duration of the 9-day mating period every semi-lunar cycle: early mating females selected larger males with cooler burrows, slowing embryonic development; those mating later, selected smaller males with warmer burrows, accelerating development. Females living lower in the inter-tidal zone, however, did not show this temporal variation: they select the same sized males throughout the mating period. It is only in the high inter-tidal zone, at the start of the fortnightly mating period, that large size confers a mating advantage to males.

Four new species of Pyropia (Bangiales, Rhodophyta) from the west coast of North America: the Pyropialanceolata species complex updated.

Recent molecular studies indicate that the Pyropia lanceolata species complex on the west coast of North America is more speciose than previously thought. Based on extensive rbcL gene sequencing of representative specimens we recognize seven species in the complex, three of which are newly described: Pyropia montereyensis sp. nov., Pyropia columbiensis sp. nov., and Pyropia protolanceolata sp. nov. The new species are all lanceolate, at least when young, and occur in the upper mid to high intertidal zone primarily in winter and early spring. Pyropia montereyensis and Pyropia columbiensis are sister taxa that are distributed south and north of Cape Mendocino, respectively, and both occur slightly lower on the shore than Pyropia lanceolata or Pyropia pseudolanceolata. Pyropia protolanceolata is known thus far only from Morro Rock and the Monterey Peninsula, California; it occurs basally to the other species in the complex in the molecular phylogeny. A fourth newly described species, Pyropia bajacaliforniensis sp. nov., is more closely related to Pyropia nereocystis than to species in this complex proper. It is a thin species with undulate margins known only from Moss Landing, Monterey Bay, California, and northern Baja California; it also occurs in the high intertidal in spring. Porphyra mumfordii, a high intertidal winter species that has frequently been confused with species in the Pyropia lanceolata complex, has now been confirmed to occur from Calvert Island, British Columbia, to Pescadero State Park, California.

Succession and seasonal dynamics of the epifauna community on offshore wind farm foundations and their role as stepping stones for non-indigenous species

In recent years, offshore wind energy in the shelf seas of the southern North Sea is experiencing a strong growth. Foundations are introduced in mainly sandy sediments, and the resulting artificial reef effect is considered one of the main impacts on the marine environment. We investigated the macrobenthic fouling community that developed on the concrete foundations of the first wind turbines built in Belgian marine waters. We observed a clear vertical zonation, with a distinction between a Telmatogeton japonicus dominated splash zone, a high intertidal zone characterised by Semibalanus balanoides, followed by a mussel belt in the low intertidal–shallow subtidal. In the deep subtidal, the species turnover was initially very high, but the community was soon dominated by few species (Jassa herdmani, Actiniaria spp. and Tubularia spp.), and only seasonal dynamics within this species assemblage were observed after 1–1½ years. Ten non-indigenous species (NIS) were found. In the intertidal, eight out of the seventeen typical intertidal species observed were NIS, while only two out of a species pool of 80 species were NIS in the deep subtidal. NIS were found to use the foundations to expand their range and strengthen their strategic position in the area.

Relationship between tissue phosphorus and seawater phosphate in the brown alga Hormosira banksii

We measured tissue phosphorus content of high and low intertidal Hormosira banksii to test the hypothesis that tissue phosphorus content would be greater in individuals from the low intertidal because of greater total uptake associated with longer immersion in seawater. Moreover, we predicted that tissue phosphorus would be greater at sites where the seawater contained higher phosphate concentrations. There was a positive, linear relationship between local seawater phosphate concentrations and tissue phosphorus content of H. banksii from high and low intertidal zones at six different sites in winter. However, there were no comparable relationships in summer, even though the range of seawater phosphate concentration was similar in both seasons. The phosphorus contents of low intertidal H. banksii were significantly greater than high intertidal H. banksii in winter, but not in summer. Reasons for these differences may be related to greater access to seawater phosphate in low intertidal algae (than those in the high intertidal) in winter, followed by greater utilisation of the internal phosphorus between winter and summer, due to faster growth rates in the low intertidal.

Intertidal community responses to field‐based experimental warming

As the climate warms, there is little doubt that ecosystems of the future will look different from those we see today. However, community responses to warming in the field are poorly understood. We examined the effects of field‐based warming on intertidal communities in the Salish Sea, which is a regional thermal ‘hot spot’ and therefore a model system for studying thermally stressed communities. We manipulated temperature at three tidal heights by deploying black‐ and white‐bordered settlement plates. Black plates increased in situ substratum temperature by an average of 2.6°C (maximum temperature, 40.9°C). Barnacles fared poorly on black plates in all zones. When overall thermal stress was highest (summer in the high intertidal zone) herbivores were absent. In lower tidal zones, herbivores were abundant on white plates but were scarce on black plates. The total percent cover of algae was unaffected by the temperature treatment, despite the fact that macroalgae were expected to be the least thermally tolerant functional group. However, we did find that ephemeral green algae exhibited a delay in phenology on black plates. We also found that species richness declined and invertebrate assemblage structure was altered due to warming. Results from this year long experiment suggest that communities in thermally stressful habitats respond to warming via the interplay between species‐specific thermal responses and secondary adaptive strategies such as behavioral microhabitat selection. Declines in diversity and changes in the invertebrate assemblage were due to the decline of local thermally‐stressed species and the lack of replacement by warm‐adapted species. Given the low variation in the species pool along the northeast Pacific coastline, the arrival of warm‐adapted species to the Salish Sea may not occur over relevant time scales, leaving local communities depauperate.

Isopods of the genus Ligia as potential biomonitors of trace metals from the gulf of California and pacific coast of the Baja California peninsula.

Supralittoral and high intertidal coastal zones are exposed to pollution from both marine and terrestrial sources and undergo higher deposition rates than the subtidal zone. It is therefore important to identify organisms for this section of the coastal area that can be tolerant to contaminants. The aim of this study was to determine if supralittoral isopods of the genus Ligia can be used as biomonitors, since they are abundant and widely distributed. For this purpose, concentrations of trace elements were determined in Ligia isopods in toto from 26 locations across the Gulf of California and Pacific coast of the Baja California peninsula, which were collected during the summers of 2009 and 2010. The concentrations of trace elements followed the order of; Zn≥Cu>As>Cd>Pb>Hg. Elevated concentrations of copper (up to 1010μg/g) were detected in Ligia from Santa Rosalía (SRo), a locality where industrial mining of copper has historically occurred. Industrial and municipal sewage discharges appear to have contributed to the high concentrations of zinc (326μg/g) and lead (144μg/g) found in organisms from Guaymas location. The high mercury concentration in organisms from Mazatlán (M) (2.01μg/g) was associated with a thermoelectric plant. Natural sources of metals were also detected; coastal upwelling appears to be associated with high cadmium concentrations in Ligia from Punta Baja (PB) (256μg/g) in the Pacific coast, whereas hydrothermal vents may have contributed to high concentrations of arsenic at Ensenada (E) (61μg/g). Our results suggest that Ligia isopods reflect the natural and anthropogenic inputs of trace metals in the environment and could potentially be used as biomonitor organisms of the intertidal rocky shores of the Gulf of California and Pacific coast.

Biomass dynamics of the two dominant SW Atlantic Spartina species and its implications on the saltmarsh organic matter accumulation/exportation

We present a comparative analysis of the biomass dynamics of the two dominant Spartina plant species in South West Atlantic saltmarshes: Spartina densiflora Brong. (high intertidal zone) and Spartina alterniflora Loesel. (mid-low intertidal zone). We assessed aboveground biomass, live: dead ratios, net production, mortality and turnover rates, and then used this information to understand if saltmarshes dominated by one or the other Spartina species have different ecosystemic roles in the recycling of organic matter. Through field sampling we found that S. densiflora had larger live, dead and total biomass than S. alterniflora. When comparing within each species, S. alterniflora had larger live than dead biomass for most of the year, while S. densiflora had more dead than live biomass. Through the Weigert and Evans (1964) net aerial primary production (NAPP) estimating method we found that S. densiflora had larger annual NAPP, annual mortality and live turnover rates than S. alterniflora. In both species the amount of NAPP was similar to the amount of annual mortality. These results suggest that S. densiflora aboveground biomass is a carbon accumulation zone, while S. alterniflora is a carbon recycling one.

Differential gene expression in Pyropia columbina (Bangiales, Rhodophyta) under natural hydration and desiccation conditions

In rocky shores, desiccation is triggered by daily tide changes, and experimental evidence suggests that local distribution of algal species across the intertidal rocky zone is related to their capacity to tolerate desiccation. In this context, the permanence of Pyropia columbina in the high intertidal rocky zone is explained by its exceptional physiological tolerance to desiccation. This study explored the metabolic pathways involved in tolerance to desiccation in the Chilean P. columbina, by characterizing its transcriptome under contrasting conditions of hydration. We obtained 1,410 ESTs from two subtracted cDNA libraries in naturally hydrated and desiccated fronds. Results indicate that transcriptome from both libraries contain transcripts from diverse metabolic pathways related to tolerance. Among the transcripts differentially expressed, 15% appears involved in protein synthesis, processing and degradation, 14.4% are related to photosynthesis and chloroplast, 13.1% to respiration and mitochondrial function (NADH dehydrogenase and cytochrome c oxidase proteins), 10.6% to cell wall metabolism, and 7.5% are involved in antioxidant activity, chaperone and defense factors (catalase, thioredoxin, heat shock proteins, cytochrome P450). Both libraries highlight the presence of genes/proteins never described before in algae. This information provides the first molecular work regarding desiccation tolerance in P. columbina, and helps, to some extent, explaining the classical patterns of ecological distribution described for algae across the intertidal zone.

Ecosystem carbon stocks of mangrove forest in Yingluo Bay, Guangdong Province of South China

Mangrove ecosystems could play important ecological, social and economic roles in addressing the mitigation of climate change through reduced deforestation. The present study aimed to estimate ecosystem carbon stocks (carbon accumulated in both biomass and soil) across the tidal gradient of mangroves in Yingluo Bay, Guangdong Province of South China. The ecosystem carbon storage, as well as vegetation biomass and soil organic carbon (SOC) storage, increased along with the tidal gradient of mangrove forests from the low intertidal zone to the high intertidal zone. The ecosystem carbon storage of the Avicennia marina, Sonneratia apetala, Aegiceras corniculatum+Kandelia obovata, Rhizophora stylosa and Bruguiera gymnorrhiza stands were 212.88t/ha, 262.03t/ha, 323.57t/ha, 443.13t/ha and 376.80t/ha, respectively and their vegetation carbon pools accounted for 11.65%, 29.79%, 19.19%, 37.76% and 25.94% of ecosystem carbon storage, respectively. Compared to the mangrove ecosystem, there was a much lower ecosystem carbon stock (97.32t/ha) at the bare mud flat. The relatively high vegetation biomass, which coupled with carbon-rich soils, resulted in the presence of larger ecosystem carbon stocks compared to other subtropical forests in the same latitude zone. A significant positive correlation was found between vegetation biomass and soil organic carbon concentration of the upper 0–50cm layers. This may indicate that the increase of vegetation biomass will raise the mangrove-derived SOC in the soil (especially the 0–50cm soil layers). Reforestation by using mangrove forests is an important way to increase ecosystem carbon sequestration in coastal areas.

Distribution and abundance of Abarenicola affinis (Arenicolidae, Polychaeta) in tidal inlets of Otago, New Zealand

Lugworms are important members of the macrobenthos of sheltered intertidal sediments, and this study assessed the abundance and distribution of Abarenicola affinis in Otago, southern New Zealand. Using a faecal cast:lugworm ratio (1.00:1.09) revealed a patchy distribution across inlets, with an overall mean abundance of 11.1 individuals/m2 (range: 3.8 to 21.3 individuals/m2). Distribution patterns varied among inlets, with lugworms mostly confined to the high intertidal zone, but spread across all intertidal zones in one inlet. The lugworm habitat was characterised by muddy to medium sand (55–233 µm mean grain size) with low organic matter (< 2%) and chlorophyll a (1–12 µg/g dry sediment) contents. Depending on the inlet, lugworm abundance was related to sediment parameters, indicating that their distribution across Otago inlets is habitat dependent. The present findings also indicate that factors other than those measured contribute to A. affinis distribution and abundance patterns in this region.

Cyanobacteria isolated from the high-intertidal zone: a model for studying the physiological prerequisites for survival in low Earth orbit

AbstractCyanobacteria are capable of surviving the adverse conditions of low Earth orbit (LEO). We have previously demonstrated thatGloeocapsastrain OU_20,Chroococcidiopsisand akinetes ofAnabaena cylindricawere able to survive 548 days of exposure to LEO. Motivated by an interest to understand how cyanobacteria can survive in LEO, we studied the strategies thatGloeocapsastrain OU_20 employs to survive in its natural environment, the upper region of the intertidal zone. Here, cyanobacteria are exposed to fluctuations in temperature, UV radiation, desiccation and salinity. We demonstrated that an increase in salinity from 6.5‰ (BG-11 medium) to 35.7‰ (similar to that of seawater), resulted in increased resistance to UV radiation (254 nm), vacuum (0.7×10−3±0.01 kPa) and cold temperatures (–20 °C). Concomitantly, biochemical analyses demonstrated that the amount of fatty acids and mycosporine-like amino acids (a UV absorbing pigment) were higher in the stressed cells. Morphological analysis demonstrated that the electron density and thickness of the mucilaginous sheath were also greater than in the control cells. Yet, the control and stressed cells both formed aggregates. As a result of studying the physiological adaptation ofGloeocapsastrain OU_20 in response to salinity, we postulate that survival in the high-intertidal zone and LEO involves a dense extracellular mucilaginous sheath and the formation of aggregates. We conclude that studying the physiological adaptation of cyanobacteria in the intertidal zone provides insight into understanding survival in LEO.

Bioengineer effects on understory species richness, diversity, and composition change along an environmental stress gradient: Experimental and mensurative evidence

Canopy-forming bioengineer species are commonly assumed to increase local species richness and diversity. We tested this notion by investigating the effects of fucoid seaweed canopies on understory communities along rocky intertidal elevation gradients in Atlantic Canada. Such gradients exhibit increasing thermal extremes and variation from low to high elevations, and are broadly used in stress gradient studies. A manipulative experiment created canopy and no-canopy treatments at the low, middle, and high intertidal zones, eliminating all species (except fucoid canopies) from replicate quadrats. After recolonization, overall richness and diversity (considering all primary producers and consumers) were higher under canopies than uncovered by canopies at the high and middle zones, but no effects occurred at the low zone. Similarly, species composition was affected by canopies at the high and middle zones, but not at the low zone. A mensurative study that surveyed the full range of canopy cover (0–100%) using nearly five times more quadrats from pristine areas yielded the same results: richness and diversity increased with canopy cover at the high and middle zones (approaching stabilization toward high cover values), but no effects occurred at the low zone. Lack of canopy effects at low elevations is related to mild habitat conditions, which canopies are unable to modify, while positive effects at higher elevations relate to the capacity of canopies to ameliorate harsh conditions. This is the first time that a combined experimental and mensurative approach shows that the same bioengineer species affect overall species richness, diversity, and composition differently along a stress gradient. Overall, protecting canopy-forming bioengineers to preserve local biodiversity should be most effective in stressful environments.

Distribution of mangrove vegetation along inundation, phosphorus, and salinity gradients on the Bragança Peninsula in Northern Brazil

The Braganca Peninsula, in northern Brazil is characterized by macrotides (4 m) and specific edaphic conditions, which determine the local mangrove forest’s development. This study, conducted during the dry season evaluated the spatial patterns of Rhizophora mangle and Avicennia germinans species across an inundation gradient. Along a transect of 700 m, measurements of structure forest, soil moisture, porewater salinity, extractable phosphorus (extr.-P) in sediments, and phosphorus in the leaves (leaf-P) were conducted. The A. germinans (100 %) occurred in high intertidal (HI) zone. A. germinans (59 %) and R. mangle (41 %) co-occurred in mid intertidal (MI) zone, while R. mangle (58 %) predominated in low intertidal (LI) zone, followed by A. germinans (37 %) and Laguncularia racemosa (5 %). Covariance analysis (ANCOVA) indicated that salinity and soil moisture means are significantly different between the mangrove forests, but do not correlate with inundation frequency (IF). The means of extr.-P were significantly different in mangrove forests and correlated with IF and leaf-P. The inundation frequency, the availability of P in the sediments, phosphorus in the leaves and interstitial salinity are all important factors contributing to the distribution of the mangrove tree species A. germinans and R. mangle on the Braganca Peninsula.

A combined field and modeling study of groundwater flow in a tidal marsh

Abstract. Bald mud beaches were found among the mangrove marshes in Dongzhaigang National Nature Reserve, Hainan, China. To investigate the possible reasons for this phenomenon, the intertidal zones of a mangrove transect and a bald beach transect with similar topography and tidal actions were selected for comparison study. Along both transects, observed water table variations were significant in the high and low intertidal zones and negligible in the middle intertidal zones. Despite the same tidal actions and above-mentioned similarities, observed groundwater salinity was significantly smaller along the mangrove transect (average 23.0 ppt) than along the bald beach transect (average 28.5 ppt). These observations invite one hypothesis: the hydraulic structure of tidal marsh and freshwater availability may be the main hydrogeological factors critical to mangrove development. Two-dimensional numerical simulations corroborated the speculation and gave results in line with the observed water table. The two transects investigated were found to have a mud-sand two-layered structure: a surface zone of low-permeability mud and an underlying high-permeability zone that outcrops at the high and low tide lines. The freshwater recharge from inland is considerable along the mangrove transect but negligible along the bald beach transect. The high-permeability zone may provide opportunity for the plants in the mangrove marsh to uptake freshwater and oxygen through their roots extending downward into the high-permeability zone, which may help limit the buildup of salt in the root zone caused by evapotranspiration and enhance salt removal, which may further increase the production of marsh grasses and influence their spatial distribution. The bald beach is most probably due to the lack of enough freshwater for generating a brackish beach soil condition essential to mangrove growth. It is also indicated that seawater infiltrated the high-permeability zone through its outcrop near the high intertidal zone, and discharged from the tidal river bank in the vicinity of the low tide line. These processes thereby formed a tide-induced seawater-groundwater circulation, which likely provided considerable contribution to the total submarine groundwater discharge (SGD). Finally, implications and uncertainties behind this study were summarized for future examinations.

Halophilanema prolata n. gen., n. sp. (Nematoda: Allantonematidae), a parasite of the intertidal bug, Saldula laticollis (Reuter)(Hemiptera: Saldidae) on the Oregon coast

BackgroundIt is rare to find terrestrial nematode lineages parasitizing arthropods inhabiting the intertidal or littoral zone of the oceans. During an ecological study along the Oregon dunes, an allantonematid nematode (Tylenchomorpha: Allantonematidae) was discovered parasitizing the intertidal shore bug, Saldula laticollis (Reuter)(Hemiptera: Saldidae). This shore bug is adapted to an intertidal environment and can survive short periods of submergence during high tides. The present study describes the nematode parasite and discusses aspects of its development, ecology and evolution.MethodsAdults and last instar nymphs of S. laticollis (Hemiptera: Saldidae) were collected from the high intertidal zone among clumps of Juncus L. (Juncaceae) plants at Waldport, Oregon on October 3, 2011. The bugs were dissected in 1% saline solution and the nematodes killed in 1% Ringers solution and immediately fixed in 5% formalin (at 20°C). Third stage juveniles removed from infected hosts were maintained in 1% saline solution until they matured to the adult stage, molted and mated.ResultsHalophilanema prolata n. gen., n. sp. (Nematoda: Allantonematidae) is described from last instar nymphs and adults of the intertidal bug, Saldula laticollis on the Oregon coast. The new genus can be distinguished from other genera in the Allantonematidae by a stylet lacking basal knobs in both sexes, an excretory pore located behind the nerve ring, ribbed spicules, a gubernaculum, the absence of a bursa and the elongate-tubular shape of the ovoviviparous parasitic females. Studies of the organogenesis of Halophilanema showed development to third stage juveniles in the uterus of parasitic females. Maturation to the free-living adults and mating occurred in the environment. The incidence of infection of S. laticollis ranged from 0% to 85% depending on the microhabitat in the intertidal zone.ConclusionsBased on the habitat and morphological characters, it is proposed that Halophilanema adapted a parasitic existence fairly recently, evolutionarily speaking. It was probably a free-living intertidal or shore nematode that fed on microorganisms, especially fungi, in the intertidal habitat and became parasitic after saldids entered the environment. Halophilanema represents the first described nematode parasite of an intertidal insect.