Low Intertidal Areas Research Articles

Refined hydro-environmental modelling for tidal energy generation: West Somerset Lagoon case study

An accurate assessment of the hydro-environmental impacts of tidal range energy schemes, where the performance of the scheme has an impact on the marine environment and ecology, is crucial in optimising the design and development of such schemes. A proposal for a new coastally-attached impoundment, namely West Somerset Lagoon, has been investigated in this research and the numerical model TELEMAC-2D has been refined to model theimpacts of this scheme on the Bristol Channel and Severn Estuary. Domain decomposition was applied and full momentum conservation between the subdomains was included in the model by implementing momentum source terms at the turbine locations. The results have confirmed the importance of including full momentum conservation in modelling the effects of turbo-machinery in tidal lagoons. It was found that the operation of the scheme decreased the high water level slightly in the Bristol Channel and Severn Estuary, while there was a decrease in the low intertidal areas. The maximum velocity and bed shear stress were predicted to increase in the inner Bristol Channel, while they decreased noticeably across most of the interior of the lagoon, away from the turbine wakes. Furthermore, the operation of the lagoon significantly improved the water renewal in the region.

A Comparison of the Juvenile Dungeness Crab Metacarcinus magister Habitat Provided by Contemporary Oyster Aquaculture Versus Historical Native Oysters in a U.S. West Coast Estuary

Oysters and seagrasses provide structurally complex estuarine habitat for fish and invertebrate species. On the U.S. West Coast, complex oyster habitat was historically provided by the native Olympia oyster Ostrea lurida but is now provided by the commercially cultured oyster Crassostrea gigas. Ostrea lurida is found in subtidal and low intertidal areas, whereas C. gigas is predominantly cultured at higher intertidal elevations, resulting in a potential shift in available habitat for other fish and invertebrates that use this intertidal habitat. This change in the available habitat and its use was examined for the juvenile Dungeness crab Metacarcinus magister, and results showed the following: (1) comparable crab densities in remnant and restored populations of O. lurida and cultured C. gigas in two estuaries, (2) generally higher crab densities in both of these shell habitats than those observed in eelgrass Zostera marina or open mud habitat, (3) contemporary juvenile crab density in intertidal areas of Willapa Bay was most influenced by distance from the estuary mouth (declining with increasing distance) but also declined with increasing tidal elevation, and (4) when extrapolated to the estuarine ecosystem scale using areal estimates of habitat coverage, historical habitat provided by O. lurida potentially produced three times more juvenile crabs than those currently produced in cultured C. gigas. Nonetheless, both intertidal oyster habitats contribute more to juvenile crab production than eelgrass or open unstructured mud, and the ecosystem services associated with the placement of native and commercial oyster beds should be considered when defining goals for and permitting both aquaculture and native oyster restoration in Willapa Bay and other U.S. West Coast estuaries. Managers should consider this shifting temporal baseline in intertidal habitat provision, but also conducting similar evaluations at this broader estuary scale when evaluating habitat value for other resources that use these habitats differently.

Restoration potential of Asian oysters on heavily developed coastlines

Reef‐building oysters historically provided the main structural and ecological component of temperate and subtropical coastal waters globally. While the loss of oyster reefs is documented in most regions globally, assessments of the status of Asian oyster reefs are limited. The feasibility of restoration within the regional biological and societal contexts needs to be assessed before implementation. Here, we quantified the current distribution of natural oyster reefs (Crassostrea spp.) in the shallow coastal waters of Hong Kong, assessed the biological feasibility of reestablishing reefs using natural recruitment, and examined their current and potential water filtration capacity as a key ecosystem service provided by restoration. We found natural low‐relief oyster beds in the low intertidal coastal areas at a subset of the locations surveyed. These areas are, however, degraded and have sparse densities of oysters generally <2 years old. Recruitment was high in some areas (>500,000 indiv./m2) and while survival to maturity varied across sites there was adequate larval supply and survival for restoration. Filtration rates for a 1‐year‐old recruit (90 mm length, approximately 30 L/hour per individual) at summer temperatures (30°C) meant that even the small remnant populations are able to provide some filtration services (up to 31.7 ML/hour). High natural recruitment means that oyster reef restoration can be achieved with the addition of hard substrate for recruitment, increased protection of restoration sites, and would not only increase the ecological value of reefs regionally but also serve as a model for future restoration in Asia.

Seasonal changes in sediment erodibility associated with biostabilization in a subarctic intertidal environment, St. Lawrence Estuary, Canada

The sediment dynamics and the long-term evolution of intertidal environments depend on the erosion threshold, which is often increased by microbial biofilms. Intertidal biostabilization has been well studied in temperate and subtropical environments, but little is known for subarctic conditions with strong seasonal changes in vegetation cover and sea ice presence in winter because of the difficulty in studying the sediments under ice cover. The present project investigated the role of biofilms and their seasonal as well as spatial variations for sediment biostabilization in a subarctic intertidal area near Rimouski (Quebec, Canada). Grain size distribution reflected a seaward increasing trend in sand content and mean grain size. The poor sorting of sediments results from the contribution of sediment transport by ice rafting in addition to the hydrodynamic transport processes in this subarctic intertidal area. A Cohesive Strength Meter (CSM) was used to measure the erosion threshold (τcrit) across the entire intertidal area. Chlorophyll a (Chl a) and extra polymeric substances (EPS) were measured in the top 3 mm. The high marsh had a far higher τcrit than the low marsh, but there was much less variation between low marsh, mudflat and sandflat. τcrit was significantly correlated with Chl a, elevation, and organic matter content. EPS was not a good indicator for τcrit, except for the low marsh/high marsh difference. The results showed a seasonal cycle in intertidal bed erodibility. Lower intertidal areas had highest τcrit in autumn during the storm season, followed by lowest τcrit in winter under sea-ice cover, and no major difference between summer and spring. This study highlights the characteristics of cold climate intertidal areas, where low temperatures in autumn and land-fast ice cover during winter severely affect biofilms and intertidal vegetation, and ultimately their capacity to shield sediments from erosion.

Assemblage structure, distribution and habitat type of the grapsoid crabs (Brachyura: Grapsoidea) of the coastal forested swamps of northern Borneo

Several intertidal and supratidal systems were investigated in the Brunei Bay to assess the diversity and assemblage structure of grapsoid crabs (Brachyura: Grapsoidea) in different salinity and substrate conditions, type of vegetation, and distance from water bodies. The structure of the assemblages differed remarkably across and within sites, and several taxa were not previously recorded from this region. Diversity decreased towards more terrestrial conditions, with systems closer to the sea supporting more diversified assemblages. High and low intertidal areas also hosted different assemblages in terms of taxonomic composition. Most of these species can be considered habitat specialists, and only occurred in a small number of the investigated areas. A small number of habitat generalists were found in several areas, exhibiting eurytopic ecological traits. A time-based sampling method was used to estimate population densities. A few habitat specialists were recorded in high densities, suggesting adaptations to specific environmental conditions in which these species can bloom. These results highlight how the diversity of these assemblages needs to be considered in management plans, to prevent local extinctions and loss of diversity in the area.

Assessing the Eutrophic Susceptibility of New Zealand Estuaries

We developed a method to predict the susceptibility of New Zealand estuaries to eutrophication. This method predicts macroalgae and phytoplankton responses to potential nutrient concentrations and flushing times, obtained nationally from simple dilution models, a GIS land-use model and physical estuary properties. Macroalgal response was based on an empirically derived relationship between potential nitrogen concentrations and an established macroalgal index (EQR) and phytoplankton response using an analytical growth model. Intertidal area was used to determine which primary producer was likely to lead to eutrophic conditions within estuaries. We calculated the eutrophication susceptibility of 399 New Zealand estuaries and assigned them to susceptibility bands A (lowest expected impact) to D (highest expected impact). Twenty-seven percent of New Zealand estuaries have high or very high eutrophication susceptibilities (band C or D), mostly (63% of band C and D) due to macroalgae. The physical properties of estuaries strongly influence susceptibility to macroalgae or phytoplankton blooms, and estuaries with similar physical properties cluster spatially around New Zealand’s coasts. As a result, regional patterns in susceptibility are apparent due to a combination of estuary types and land use patterns. The few areas in New Zealand with consistently low estuary eutrophication susceptibilities are either undeveloped or have estuaries with short flushing times, low intertidal area and/or minimal tidal influx. Estuaries with conditions favourable for macroalgae are most at risk. Our approach provides estuary-integrated susceptibility scores likely to be of use as a regional or national screening tool to prioritise more in-depth estuary assessments, to evaluate likely responses to altered nutrient loading regimes and assist in developing management strategies for estuaries.

Vegetation patterns in a South American coastal wetland using high-resolution imagery

ABSTRACT The aim of this study was to identify and characterize the main plant communities in a temperate coastal wetland using high-resolution imagery. We produced a map of Samborombón Bay at 1:25,000 scale using a WorldView-2 image. An Object-based Image Analysis approach was chosen, and an unsupervised classification algorithm was applied. Overall classification accuracy was 81%, and the Kappa index was 78.1%. Six land cover types were mapped including four main natural monospecific plant communities. The lower intertidal area was dominated by mudflats without vegetation and stands of Bolboschoenus maritimus. The middle intertidal area was dominated by Sarcocornia ambigua, while, in the higher intertidal area, Sporobolus densiflorus and grasslands with Cortaderia selloana prevailed. We found four spatial patterns at a landscape scale, based on the presence and spatial distribution of the natural plant communities. This map represents a valuable tool for future studies on wetland environmental indicators.

Temporal changes in environmental conditions of a mid-latitude estuary (southern Chile) and its influences in the cellular response of the euryhaline anemone Anthopleura hermaphroditica

The cellular response of the estuarine anemone Anthopleura hermaphroditica was assessed during a tidal cycle (low tide at noon) and compared between organisms acclimated to summer and winter environmental conditions (UV-B and PAR levels, salinity and temperature), with the aim of understanding the strategies used by this dominant invertebrate in an estuary of southern Chile. Anemones were gathered every two hours from 8:00 to 20:00 h from the low intertidal area of the Quempillén estuary and immediately snap frozen to carry out biochemical analyses (oxidative damage, antioxidant capacity, photo-protective compounds). Additionally, levels of environmental radiation (UV-B and PAR), salinity and water temperature were recorded during the field survey. Our results indicate that during summer, lipid peroxidation and protein carbonyl levels in A. hermaphroditica were 3.72 and 16.51 folds higher than during winter, respectively. Maximum lipid peroxidation levels in A. hermaphroditica during summer occurred after UV-B radiation peaked (14:00 h) when water temperatures reached 31 °C. Carbonyl protein levels increased progressively reaching maximum levels at the end of the day. On the contrary, during winter when radiation levels are low and water temperature remained almost constant in the estuary throughout the day, significant variation in salinity levels occurred due to oxidative damage levels that increased significantly at the end of the day. Surprisingly, the mean antioxidant capacity level in A. hermaphroditica during winter was 1.7 folds higher than in summer, a situation that was positively correlated to total phenolic compounds content. Mycosporine 2-glycine (λmax: 331 nm) was the only mycosporine like amino acid (MAA) found in A. hermaphroditica, a photo-protective compound with constant levels throughout the year. Anthopleura hermaphroditica, is an estuarine anemone that are adapted to tolerate rapid fluctuations in the environmental parameters during tidal changes. Those fluctuations are highly affected by seasonal components that expose this invertebrate to different intensity and duration of stress factors between summer and winter. Thus, an efficient antioxidant strategy added to the use of secondary metabolites (phenolic compounds and MAA) may efficiently intercept and neutralize ROS in this animal that lacks of physical protection, allowing it to succeed in a very unstable environment characterized by strong fluctuations of salinity, temperature and environmental radiation through the year.

Taxonomy and distribution of benthic foraminifera in an intertidal zone of the Yellow Sea, PR China: Correlations with sediment temperature and salinity

Abstract Seasonal variations in foraminiferal populations from the intertidal environment of the Yellow Sea are not well known. This results in restricted understanding of environmental implications of foraminifera and their application in paleoenvironment reconstruction in this region. Community dynamics of both living and total (living plus dead) assemblages in a Qingdao intertidal flat were investigated from 2010 to 2012 during 17 months' sampling in two intertidal zones. Our study revealed a distinct seasonal variation in assemblages, which was more prominent in the low intertidal area. Foraminiferal abundance, species richness and Margalef index showed significant positive correlations to salinity, while species richness was negatively associated with temperature. A total of 52 species was identified and illustrated, including the dominant species: Ammonia beccarii , A. aomoriensis , A. aberdoveyensis , A. sobrina , Quinqueloculina seminula and Murrayinella globosa. Foraminiferal community parameters in the low intertidal area were higher than those in the high intertidal area, especially for the living assemblages, reflecting a seaward preference. Our study revealed that different tidal levels (low vs. high intertidal) had a more distinct influence in regulating foraminiferal assemblages than did seasonal influence.

Intertidal rocky shore fauna and flora of Quintana Roo, Mexico.

<p>Las costas rocosas de origen calizo, son ecosistemas comúnes en el estado de Quintana Roo en México. En el verano del 2012, se realizó una investigación de campo de comunidades inter-mareales rocosas en 10 sitios del Estado, tanto en la Riviera Maya como en la Gran Costa Maya, con el objetivo de conocer si existe algún patrón en la abundancia y diversidad de los grupos que las componen. En cada sitio se realizaron tres transecciones perpendiculares a la costa con un número variable de muestras que dependió de la longitud de la playa, en cada nivel se obtuvo una muestra de 25 cm<sup>2</sup>, realizando un total de 593. Las pendientes de las playas fueron variables (0.4-1 m); sin embargo, como patrón recurrente, la parte sur de cada playa fue más extensa que la norte. La fauna estuvo representada por los siguientes grupos: equinodermos (15 especies-11 géneros), moluscos (84-50), anélidos (10-9), crustáceos (23-22), sipunculidos (1-1) peces (1-1), algas (53-34), estableciendo un total de 187 especies pertenecientes a 128 géneros. Los resultados muestran que los moluscos dominaron en todas las zonas intermareales. Otros grupos tuvieron preferencias hacia las zonas intermareales bajas. Los patrones geográficos regionales de la abundancia, riqueza de especies y biodiversidad, son poco claros para algunos grupos. El sitio con mayor riqueza y diversidad fue Osho Oasis en la Riviera Maya. El agrupamiento de los sitios a un nivel de similitud del 50 %, presentan uniones fuertes entre sitios de la Riviera Maya y de la Costa Maya indistintamente, con excepción de los equinodermos que identifican y separan a ese nivel de similitud ambas zonas. Utilizando un análisis monotético de contenido de información de orden 2, se obtuvieron las especies responsables de las mayores caídas de información de cada grupo, se tienen los siguientes resultados: Algas- <em>Padina santae-crucis</em>, Moluscos-<em>Tectarius antonii</em>, Crustáceos- <em>Maera inaequipes</em>, Equinodermos- <em>Tripneutes ventricosus</em> y Annelidos- <em>Pseudonereis variegata</em>, estas especies se consideran indicadoras de cambios en la estructura de las comunidades de cada grupo y podrían ser objeto de una investigación más profunda que sirva de apoyo y soporte a programas de manejo en esas áreas.</p>

Association of Juvenile Salmon and Estuarine Fish with Intertidal Seagrass and Oyster Aquaculture Habitats in a Northeast Pacific Estuary

AbstractStructured estuarine habitats, such as salt marshes, seagrass beds, and oyster reefs, are recognized as critical nurseries for juvenile fish and crustaceans. Estuarine habitat usage by fish, including juvenile Pacific salmon Oncorhynchus spp., was characterized by sampling with a modified tow net in Willapa Bay, Washington, where 20% of the intertidal area is utilized for shellfish aquaculture and thus is difficult to sample with conventional gear. Our goal was to compare fish use of relatively undisturbed habitats (open mudflat, seagrass, and channel habitats) with the use of nearby oyster culture habitat. Although many species showed significant temporal and spatial trends within the estuary, only Shiner Perch Cymatogaster aggregata exhibited a significant association with habitat. Juveniles of three salmonid species exhibited few associations with the low intertidal habitats over which they were captured or in the prey types they consumed there. Chinook Salmon O. tshawytscha, likely hatchery‐released ocean‐type fish, were the most common salmonid captured, and they utilized low intertidal areas throughout the summer as their mean size increased from 85 to 100 mm FL. Diets consumed by these larger juvenile Chinook Salmon were not associated with benthic habitat but instead consisted primarily of (1) insects from nearby marsh or terrestrial habitats and (2) planktonic prey, like decapod larvae and tunicate larvaceans. Juvenile Coho Salmon O. kisutch and Chum Salmon O. keta were captured earlier (April and May) and fed on a slightly different suite of prey taxa, which were also primarily pelagic rather than associated with the intertidal benthos. Our findings suggest that in this relatively shallow coastal estuary, the role of benthic habitat is not closely linked to its value as a source of food for large juvenile salmon out‐migrants utilizing the low intertidal areas where aquaculture occurs.

Dynamics of nonstructural carbohydrates in seagrass Thalassia hemprichii and its response to shading

A field survey was performed to examine nonstructural carbohydrate (NSC) dynamics in seagrass Thalassia hemprichii at the Xincun Bay in southern China. An indoor experiment to investigate the response of NSC in T. hemprichii to shade was conducted. Belowground tissue of T. hemprichii was the dominant site of NSC reserves, and soluble sugar was the primary storage compound. The starch content of belowground tissue was lower in high intertidal areas than in low intertidal areas, indicating that the longer air exposure in high intertidal areas resulted in less NSC synthesis and less accumulation of NSC in T. hemprichii. The lowest level of soluble sugar and its proportion to NSC in belowground tissue were observed near the cage culture area, where the nutrient concentration in water and sediment was the highest; while the highest level of that was observed near the coastal shrimp farm, Where salinity was the lowest. Soluble sugar in belowground tissue showed the following trend: summer > spring > winter > autumn. This corresponded to seasonal changes in the intensity of light. Leaf sugar accumulated during the autumn-winter period, providing a carbon and energy source for flower bud formation and seed germination. Short-term shading decreased NSC accumulation. Collectively, these results suggest that nutrient enrichment, freshwater discharge and exposure to air affect NSC dynamics in T. hemprichii. Light intensity, flower bud formation, and seed germination were all found to induce seasonal variations in NSC in T. hemprichii.

The Willapa Bay Oyster Reserves in Washington State: Fishery Collapse, Creating a Sustainable Replacement, and the Potential for Habitat Conservation and Restoration

Oysters have been an important resource in Washington state since the mid 1800s and are intimately associated with recent history of the Willapa Bay estuary, just as they have defined social culture around much larger U.S. east coast systems. The Willapa Bay oyster reserves were set aside in 1890 to preserve stocks of the native oyster Ostrea lurida in this estuary, but these stocks were overfished and replaced with the introduced Pacific oyster Crassostrea gigas during the late 1920s. Pacific oysters have spawned and set naturally in this estuary on a fairly regular basis since that time, and have formed the basis of a sustainable fishery established on state oyster reserves. The fishery is managed as an annual sale of oysters to private aquaculture interests. Oysters are harvested mostly by hand from intertidal tracts, usually moved to better growing areas closer to the estuary mouth, and shell is required to be returned to the reserves to perpetuate the fishery. Although oyster harvest for human consumption will remain an important social management goal, these bivalves have been shown to provide a suite of other ecosystem functions and services. A survey of the reserves suggests that they represent 11.2% of the intertidal habitat in Willapa Bay and cover substantial subtidal areas as well. A comparison with historical maps suggests that most of the low intertidal area in the reserves formerly populated by native oysters is now covered primarily with eelgrass (Zostera marina), which potentially serves as important habitat for numerous other organisms, including juvenile salmon, Dungeness crab, and migratory waterfowl like black Brant. Native oysters can still potentially be restored to some of these areas, but the value of both introduced oysters and eelgrass as habitat and ecosystem engineers also deserves attention, and the reserves provide an excellent place to elucidate the role of these additional conservation targets at the landscape scale.

Microbial carbon oxidation rates and pathways in sediments of two Tanzanian mangrove forests

Temporal and spatial variations in benthic metabolism and anaerobic carbon oxidation pathways were assessed in an anthropogenically impacted (Mtoni) and a pristine (Ras Dege) mangrove forest in Tanzania. The objectives were (1) to evaluate how benthic metabolism is affected by organic carbon availability; (2) to determine the validity of diffusive release of CO2 as a measure benthic carbon oxidation; and (3) to assess the partitioning of anaerobic carbon pathways and factors controlling the availability of electron acceptors (e.g. oxidized iron). Microbial carbon oxidation measured as diffusive exchange of O2 and CO2 (32–67 and 28–115 mmol m−2 day−1, respectively) showed no specific temporal patterns. Low intertidal sediments at Mtoni fed by labile algal carbon of anthropogenic origin had higher diffusive CO2 release than high intertidal sediments that primarily received less reactive mangrove detritus. Diffusive release of CO2 apparently underestimated total sediment carbon oxidation due to CO2 loss from deep sediments via emission through biogenic structures (i.e. crab burrows and pneumatophores) and porewater seepage into creeks. We propose that diffusive fluxes in the present mangrove sediments are roughly equivalent to depth-integrated reactions occurring in the upper 12 cm. Anaerobic carbon oxidation was dominated by FeR irrespective of anthropogenic influence in sediments where the oxidizing effects of biogenic structures increased the Fe(III) level. More than 80% of the anaerobic carbon oxidation in Mtoni and Ras Dege sediments was due to FeR when reactive Fe(III) exceeded 30 μmol cm−3. The anthropogenic influence at Mtoni was primarily noted as up to one order of magnitude higher denitrification than at Ras Dege, but this process always accounted for less than 1% of total carbon oxidation. It is noteworthy that organic and nutrient enrichment of anthropogenic origin in Mtoni has no measurable effect on microbial processes, other than carbon oxidation in the low intertidal area and denitrification throughout the forest, and indicates a strong resilience of mangrove environments towards disturbances.

Topographic control on distribution of modern microbially induced sedimentary structures (MISS): A case study from Texas coast

Modern back-barrier tidal flats of Galveston Island, Follets Island, and Matagorda Peninsula of the Texas coast are dominated by mud- to fine sand-sized siliciclastic sediments and prolific microbial mats. These microbial mats modify sediment behavior and result in a variety of microbially induced sedimentary structures (MISS). Common structures include: knobby surfaces, reticulated surfaces, gas domes, mat-cracks, sieve-like surfaces, erosional pockets, wrinkles, and mat chips. In general, mat thicknesses increase from ∼ 1 mm in the upper supratidal to ∼ 3 cm (maximum) in the lower supratidal and then decrease to ∼ 2 mm in the lower intertidal areas. This same wedge-shaped pattern is displayed by detailed measurements of mat thicknesses from the rims into the deeper centers of depressions (pools) on the supratidal flats. Measurements of 175 mat-cracks show that height of the curled edges of the mat-crack polygons increases with increase in mat thickness. Similarly, measurements of 150 gas domes reveal that the size of the gas domes also increases with increasing thickness of the associated mats. Because mat thickness varies with elevation on the tidal flat, curl height of the mat-cracks and size of the gas domes are also related to elevation. Six zones were identified based on the occurrence of MISS within the supratidal (zone-I) to upper subtidal (zone-VI) areas. At the highest elevation, knobby surfaces characterize zone-I whereas zone-II is defined by reticulated surfaces. Along with reticulated surfaces, gas domes and mat-cracks characterize zone-III and zone-IV, respectively. Association of sieve-like surfaces with mat-cracks typifies zone-V whereas mat deformation structures and sieve-like surfaces define zone-VI. Boundaries between the MISS-zones in general are parallel and related to tidal zones. The distribution patterns of the MISS-zones are strongly controlled by local topography of the sediment surface because the degree of inundation is the primary controlling factor for the mat growth and resultant MISS. Therefore, distribution of the microbially induced sedimentary structures in siliciclastics, along with the dimension of the mat-cracks and gas domes, can be potentially helpful in interpretation of topography of paleodepositional surfaces.

Community-level analysis of anthropogenic impacts on rocky shore communities in Sri Lanka

Human activities threat seashore communities in many areas of the world and their impacts on coastal ecosystem are a matter of increasing concern. Present study describes the anthropogenic disturbances on the rocky shore community structure by comparing the benthic communities of disturbed and non-disturbed areas in Sri Lanka where rocky shores remain virtually untouched so far by experimental studies. Impacts of human disturbances; trampling, handling and exploitation on the community structure of rocky macro benthic assemblages were tested in high-, mid- and low-intertidal area by stratified sampling method at Rumassala marine sanctuary and adjacent two localities at either side of the marine sanctuary, Galle and Unawatuna. Univariate measures, log series model and multivariate techniques were used to discriminate the communities with respect to the disturbances. Proximity of study localities and indistinguishable physicochemical parameters of sea surface water (temperature, Salinity, conductivity, dissolved oxygen and pH) indicated that overall environment of the study area was relatively uniform and changes in community structure was due to human disturbances. Human disturbances documented as visitor censuses by transect walk method lead to categorize the Rumassala as non-disturbed, Unawatuna as disturbed with Galle being of moderately disturbance. Community abundance showed a decreasing trend along with increasing disturbances, albeit community biomass, due to opportunistic algae species, increased in parallel to disturbances. Computed Index of disturbance revealed that macrofauna was very sensitive to the disturbances and increased disturbances reduced their competitive pressure on macroalgae, leading to outstanding macroalgal growth. Macroalgal domination in disturbed communities contributed to lessen the heterotrophic dominance in Galle and Unawatuna. 96 macrobenthic taxa were encountered from the study and Species richness, Shannon and Fisher’s diversity index showed decreasing trend with increasing disturbances. Moreover, initial rising slope of species accumulation curves for three communities indicated that community evenness was low in disturbed communities. The community compositions from dominant conservative species to fast growing opportunistic species were well described by the log series model, showing left skewed distribution. The SIMPER analysis further confirmed that most biomass dominant species in stress status were the opportunistic species such as Valoniopsis pachynema, Gracilaria cassa and Padina boerggesenii. Providing strong support to the results highlighted from univariate measures and log series model, multivariate cluster analysis and nMDS plots completely separated three communities at ordinal scale. This separation was further confirmed by one-way ANOSIM test with significantly higher (2.9%) similarity of study sites within each community. Present study indicated that, allowing less time for recovery, human activities created press-type disturbance on macro-benthic assemblages, and subsequent changes in community structure could be attributed to less suitable substrata. Study proposed that ecological stress is the best measured by multiple methods, and results from different approaches provide the robustness necessary to judge the reliability of the conclusion. Present study strongly supports the growing concern that human activities impact on intertidal assemblages all over the world by changing community composition. Present finding is a contribution to the published literature that is scarcer from tropical rocky shores.

Community-level analysis of anthropogenic impacts on rocky shore communities in Sri Lanka

AbstractHuman activities threat seashore communities in many areas of the world and their impacts on coastal ecosystem are a matter of increasing concern. Present study describes the anthropogenic disturbances on the rocky shore community structure by comparing the benthic communities of disturbed and non-disturbed areas in Sri Lanka where rocky shores remain virtually untouched so far by experimental studies. Impacts of human disturbances; trampling, handling and exploitation on the community structure of rocky macro benthic assemblages were tested in high-, mid- and low-intertidal area by stratified sampling method at Rumassala marine sanctuary and adjacent two localities at either side of the marine sanctuary, Galle and Unawatuna. Univariate measures, log series model and multivariate techniques were used to discriminate the communities with respect to the disturbances. Proximity of study localities and indistinguishable physicochemical parameters of sea surface water (temperature, Salinity, conductivity, dissolved oxygen and pH) indicated that overall environment of the study area was relatively uniform and changes in community structure was due to human disturbances. Human disturbances documented as visitor censuses by transect walk method lead to categorize the Rumassala as non-disturbed, Unawatuna as disturbed with Galle being of moderately disturbance. Community abundance showed a decreasing trend along with increasing disturbances, albeit community biomass, due to opportunistic algae species, increased in parallel to disturbances. Computed Index of disturbance revealed that macrofauna was very sensitive to the disturbances and increased disturbances reduced their competitive pressure on macroalgae, leading to outstanding macroalgal growth. Macroalgal domination in disturbed communities contributed to lessen the heterotrophic dominance in Galle and Unawatuna. 96 macrobenthic taxa were encountered from the study and Species richness, Shannon and Fisher’s diversity index showed decreasing trend with increasing disturbances. Moreover, initial rising slope of species accumulation curves for three communities indicated that community evenness was low in disturbed communities. The community compositions from dominant conservative species to fast growing opportunistic species were well described by the log series model, showing left skewed distribution. The SIMPER analysis further confirmed that most biomass dominant species in stress status were the opportunistic species such as Valoniopsis pachynema, Gracilaria cassa and Padina boerggesenii. Providing strong support to the results highlighted from univariate measures and log series model, multivariate cluster analysis and nMDS plots completely separated three communities at ordinal scale. This separation was further confirmed by one-way ANOSIM test with significantly higher (2.9%) similarity of study sites within each community. Present study indicated that, allowing less time for recovery, human activities created press-type disturbance on macro-benthic assemblages, and subsequent changes in community structure could be attributed to less suitable substrata. Study proposed that ecological stress is the best measured by multiple methods, and results from different approaches provide the robustness necessary to judge the reliability of the conclusion. Present study strongly supports the growing concern that human activities impact on intertidal assemblages all over the world by changing community composition. Present finding is a contribution to the published literature that is scarcer from tropical rocky shores.

Embryonic and larval development of Ensis arcuatus (Jeffreys, 1865) (Bivalvia: Pharidae)

The razor clam Ensis arcuatus (Jeffreys, 1865) is distributed from Norway to Spain and along the British coast, where it lives buried in sand in low intertidal and subtidal areas. This work is the first study to research the embryology and larval development of this species of razor clam, using light and scanning electron microscopy. A new method, consisting of changing water levels using tide simulations with brief dry periods, was developed to induce spawning in this species. The blastula was the first motile stage and in the gastrula stage the vitelline coat was lost. The shell field appeared in the late gastrula. The trochophore developed by about 19 h post-fertilization (hpf) (19°C). At 30 hpf the D-shaped larva showed a developed digestive system consisting of a mouth, a foregut, a digestive gland followed by an intestine and an anus. Larvae spontaneously settled after 20 days at a length of 378 µm.

Ecological implications of intertidal mariculture: observed differences in bivalve community structure between farm and reference sites

Summary Despite recent growth in shellfish aquaculture in British Columbia, Canada, the impacts of common practices on non‐target species are poorly understood. Two practices employed on clam farms to increase production of the exotic clam Venerupis philippinarum include the addition of juvenile ‘seed’ clams to the sediment and covering seeded clam beds with protective netting, ostensibly to exclude large mobile epibenthic predators. We expected the effects of predator exclusion to be most evident among other bivalves, which made up more than 80% of the infaunal macrobenthos at all sites surveyed. A field study across three regions collected infaunal bivalve density and biomass data. We compared species richness, composition and abundances of communities between clam farms and reference sites, paired on the basis of physical characteristics such as sediment type, slope and aspect. Venerupis philippinarum was the only species found in higher abundance on farm sites in low intertidal areas (227 ± 241·6 clams m−2, P= 0·02; 872·9 ± 792·9 g m−2, P= 0·037). Farmed sites showed no difference in mid‐intertidal areas, nor in density of the other 25 bivalve species, although an increase would be expected if netting excluded important predators. Although statistically non‐significant, there were indications that biomass of species other than V. philippinarum may have been lower on farm sites. Bivalve species composition was not significantly different between farm and reference sites. Nevertheless, farm sites were more similar to each other as a group than reference sites, leading to a loss of regional distinctness that was evident among reference sites. Synthesis and applications. Our findings support the hypothesis that predation and competition play minor roles in structuring communities in soft‐bottomed environments. Given the potential for cumulative effects of seeding and netting at large scales, a precautionary approach is recommended in future development of intertidal clam aquaculture.

Experimental demonstration of plasticity in the heat shock response of the intertidal mussel Mytilus californianus

We report the results of a reciprocal transplant experiment that tested plasticity in the heat shock response (HSR) of an intertidal mussel, Mytilus californianus (Conrad), in its natural habi- tat. We predicted that mussels inhabiting the upper edge of their vertical distribution, the high inter- tidal mussel bed, would display physiological signatures of greater thermal stress, specifically higher levels of an inducible heat shock protein isoform, Hsp72, and a higher temperature at which de novo synthesis of Hsp72 begins (threshold induction temperature). However, due to limits in physiological plasticity, we also predicted that the HSR of mussels transplanted between high and low areas would resemble that of mussels from both their source and their transplant microhabitats. The transplant experiment was conducted on the central coast of Oregon; mussels were transplanted between and within the high and low intertidal areas of the mussel bed in May 2001 and collected for measure- ment in August 2001. In addition, mussels from the natural populations of these areas were collected for comparison with experimental groups in May and August 2001. Using dissected gill tissue from each group of mussels, threshold induction temperatures and cellular levels of isoforms of the 70 kDa Hsp gene family were measured using in vitro metabolic labeling and immunochemical detection, respectively. The results demonstrated that the HSR was highly plastic over small spatial scales in the rocky intertidal habitat, although the compensation of the transplanted mussels was not perfect in every group. For example, although the induction temperature range was similar among mussels either collected from, or transplanted to the high-bed, those transplanted to the low-bed from the high zone displayed a broader range of induction temperatures, indicating that some mussels retained elements in their HSR with greater resemblance to mussels from their source microhabitat than those in their new microhabitat. Levels of inducible Hsp72 were greater in mussels from the high-bed than the low-bed, indicating that organisms from closely spaced microhabitats experience different levels of protein damage from environmental stress.