Intertidal Locations Research Articles

Location also matters: The oxidative response of the intertidal purple mussel Perumytilus purpuratus during tidal cycle

For sessile intertidal organisms, periods of low tide impose both cellular and physiological challenges that can determine bathymetric distribution. To understand how intertidal location influences the cellular response of the bivalve Perumytilus purpuratus during the tidal cycle (immersion-emersion-immersion), specimens from the upper intertidal (UI) and lower intertidal (LI) of bathymetric distribution were sampled every 2 h over a 10-h period during a summer tidal cycle. Parallelly, organisms from the UI and LI were reciprocally transplanted and sampled throughout the same tidal cycle. Levels of oxidative damage (lipid peroxidation and protein carbonyls) as well as total antioxidant capacity and total carotenoids were evaluated as cellular responses to variations in environmental conditions throughout the tidal cycle. The results indicate that both the location in the intertidal zone (UI/LI), the level of aerial exposure, and the interaction of both factors are determinants of oxidative levels and total antioxidant capacity of P. purpuratus. Although oxidative damage levels are triggered during the low tide period (aerial exposure), it is the UI specimens that induce higher levels of lipid peroxidation compared to those from the LI, which is consistent with the elevated levels of total antioxidant capacity. On the other hand, organisms from the LI transplanted to the UI increase the levels of lipid peroxidation but not the levels of protein carbonyls, a situation that is also reflected in higher levels of antioxidant response and total carotenoids than those from the UI transplanted to the LI. The bathymetric distribution of P. purpuratus in the intertidal zone implies differentiated responses between organisms of the lower and upper limits, influenced by their life history. A high phenotypic plasticity allows this mussel to adjust its metabolism to respond to abrupt changes in the surrounding environmental conditions.

Taxonomic and Morpho-Functional Photosynthetic Patterns of 18 Intertidal Macroalgal Species in the Guangdong–Hong Kong–Macao Greater Bay Area, China

Macroalgae provide food for microbial, meio- and macro-faunal communities in coastal ecosystems, thus mediating nutrient dynamics and functions in these ecosystems. Because of this vital role, it is important to clarify physiological information about macroalgae as it reflects their growth potential in the field. In this study, we examined the biomass, pigment content, and photosynthetic O2 evolution rate versus irradiance curves of 18 macroalgal species from the intertidal zone of the Guangdong–Hong Kong–Macao Greater Bay Area, China, and investigated their photosynthetic patterns in relation to phyla characteristics, morphology, and growth locations. The results showed that green algae had the highest maximum photosynthetic O2 evolution rate (Pmax), light utilization efficiency (α), and dark respiration (Rd) among the three macroalgal phyla; the sheet-like macroalgal species had the highest Pmax, α, and Rd among the four morphological categories. The macroalgal species in the upper intertidal zone showed higher Pmax and α and lower saturation irradiance (EK) and compensation irradiance (EC) than those species in the lower intertidal location. The PCA results showed that the biomass of sheet-like macroalgal species was positively correlated with factor PC1 (50.34%), and that of finely branched species was negatively correlated with factor PC2 (25.17%). In addition, our results indicate that the light absorption and utilization capabilities of macroalgae could determine whether they could dominate the intertidal zone and that their photosynthetic characteristics could be used as a potential indicator of their biomass distribution in the Greater Bay Area.

Macrozoobenthos as an indicator of habitat suitability for intertidal seagrass

Seagrass meadows form the foundation of many coastal ecosystems, but are rapidly declining on a global scale. To conserve and restore these key-ecosystems, improved understanding of drivers behind seagrass presence and recovery is needed. Many animals are known to both facilitate and inhibit seagrasses, but biotic factors are still rarely used as indicators of seagrass presence. Hence, we investigate if macrozoobenthos could be used as an indicator for intertidal seagrass (Zostera marina and Zostera noltii) habitat suitability in the international Wadden Sea. Additionally, we explore if macrozoobenthos can explain the differing seagrass recovery rates that have been observed between the Northern (Denmark and Schleswig Holstein) and Southern (Lower Saxony and Netherlands) regions of the Wadden Sea. To achieve this, we performed a Wadden Sea-wide survey at 36 intertidal locations, across three countries, and investigated the importance of 21 abiotic and biotic variables in explaining the presence and absence of intertidal seagrasses. Seagrass presence or absence could be reliably predicted (prediction error: 16.7%) with a multivariate logistic regression with only four variables; chlorophyll a, bivalve, ragworm and mudsnail biomass. We also found higher chlorophyll concentrations and ragworm biomass in the South compared to the Northern Wadden Sea, suggesting that eutrophication and associated community shifts might still inhibit seagrass recovery in the South. Our findings highlight the potential of using macrozoobenthos as indicators for seagrass habitat suitability. In areas, like the Dutch Wadden Sea, where macrozoobenthic surveys are common and where benthic data is readily available, our findings can be used to improve the understanding of seagrass recovery dynamics and the selection of suitable seagrass restoration sites.

The effect of off-bottom versus on-bottom oyster culture on total and pathogenic Vibrio spp. abundances in oyster tissue, water and sediment samples

Varying culture methods are commonly used for eastern oyster, Crassostrea virginica, aquaculture in the Northeast United States. Vibrio vulnificus and V. parahaemolyticus, two human pathogenic bacteria species, accumulate in this edible, filter feeding shellfish. This study examined the use of two methods in an intertidal area (oysters cultured in trays and in bags on sediment) and two methods in a subtidal area (oysters cultured in trays and loose on the sediment) in Massachusetts over the growing season in 2015. Abundance of total V. vulnificus along with total and pathogenic (tdh+/trh+) V. parahaemolyticus were determined in oysters, sediment and water using real-time PCR. Temperature, salinity, turbidity and chlorophyll were continually measured every 15 min at each location.There were significantly higher abundances of total and pathogenic V. parahaemolyticus in on-bottom cultured oysters, while significantly higher abundances of V. vulnificus were identified in oysters from off-bottom culture in a subtidal location in Duxbury Bay, MA. In an intertidal location, Wellfleet Bay, MA, significantly higher abundances of total and tdh+V. parahaemolyticus were found in off-bottom oysters, but significantly higher abundances of V. vulnificus and trh+V. parahaemolyticus were found in on-bottom oysters.Spearman's correlation indicated that temperature is positively associated with concentrations of Vibrio spp. in oysters, water and sediment, but positive correlations between salinity and Vibrio spp. was also observed. Conversely, turbidity had a negative effect on Vibrio spp. concentrations in all sample types. There was no observed relationship inferred between chlorophyll and Vibrio spp. abundances in oysters, water or sediment.

Mangrove forests under climate change in a 2°C world

AbstractThe world's nations are committed to keeping global temperature rises to less than 2°C to avoid the worst impacts of climate change. Such a target is crucial for mangrove forests, because they are located primarily in tropical and subtropical regions that are expected to see large changes in climatic conditions; their intertidal location and sensitivity to changes in environmental conditions means that mangroves are expected to be on the front line of climate change impacts. We conceptualize what a 2°C world might look like for mangroves, and in particular the potential negative and positive responses of the mangrove ecosystem to anticipated changes in future atmospheric CO2 concentrations, temperature, sea level, cyclone activity, storminess and changes in the frequency, and magnitude of climatic oscillations. We also assess the spatial distribution of such stressors, their relative contributions to mangrove ecosystem dynamics, and discuss the challenges in attributing mangrove ecosystem dynamics to climate change versus other global change stressors. Such knowledge can help future‐proof conservation and restoration activities, improve the Intergovernmental Panel on Climate Change's confidence level ascribed to climate change impacts on mangrove forests, and highlight the key temperature thresholds beyond which the future of the world's mangroves is less certain.This article is categorized under: Climate, Ecology, and Conservation > Modeling Species and Community Interactions Climate, Ecology, and Conservation > Observed Ecological Changes

Microbial communities in sandy beaches from the three domains of life differ by microhabitat and intertidal location.

The microbial communities of sandy beaches are poorly described despite the biogeochemical importance and ubiquity of these ecosystems. Using metabarcoding of the 16S and 18S rRNA genes, we investigated the diversity, microhabitats (with or between sand grains) and intertidal distributions of microorganisms (including meiofauna) from pristine sandy beaches in British Columbia, Canada, and hypothesized that abiotic variations due to microhabitat or intertidal gradients influence the distribution of microorganisms on local scales. Bacterial, archaeal and protistan communities of the sand were clearly distinct from interstitial communities, and from planktonic communities of the overlying seawater, which correlated with differences in function and lifestyle (e.g., sulphur reduction and gliding motility). In contrast, meiofaunal communities could not be distinguished by sample type, suggesting that they are more frequently mobilized between these microhabitats. Across intertidal zones, high intertidal, mid intertidal and low intertidal/swash communities were distinct and correlated with moisture, organic carbon and phosphate content, implying that the distribution of microorganisms is influenced by intertidal abiotic gradients. However, few taxa at the genus or species level individually contributed to this zonation pattern; rather, a unique combination of multiple microbial taxa was probably responsible. Although significant differences in microbial community composition on sandy beaches can be attributed to microhabitat and intertidal gradients, further investigations are needed to assess community assembly processes, the consistency of these distributions, and the functions of the majority of the microorganisms observed in the sand and their effects on the biogeochemistry and ecology of sandy beaches.

Alongshore upwelling modulates the intensity of marine heatwaves in a temperate coastal sea

Analyses of long-term temperature records based on satellite data have revealed an increase in the frequency and intensity of marine heatwaves (MHWs) in the world oceans, a trend directly associated with global change according to climate model simulations. However, these analyses often target open ocean pelagic systems and rarely include local scale, field temperature records that are more adequate to assess the impact of MHWs close to the land-sea interface. Here, we compared the incidence and characteristics of open ocean MHWs detected by satellites with those observed in the field over two decades (1998–2019) at two temperate intertidal locations in the central Cantabrian Sea, southern Bay of Biscay. Satellite retrievals tended to smooth out cooling events associated with intermittent, alongshore upwelling, especially during summer. These biases propagated to the characterization of MHWs and resulted in an overestimation of their incidence and duration close to the coast. To reconcile satellite and field records, we developed a downscaling approach based on regression modeling that enabled the reconstruction of past temperatures and analyze MHW trends. Despite the cooling effect due to upwelling, the temperature reconstructions revealed a six-fold increase in the incidence of MHWs in the Cantabrian Sea over the last four decades. A comparison between static (no trend) vs. dynamic (featuring a linear warming trend) MHW detection thresholds allowed us to attribute over half of the increase in MHW incidence to the ocean warming trend. Our results highlight the importance of local processes to fully characterize the complexity and impacts of MHWs on marine coastal ecosystems and call for the conservation of climate refugia associated with coastal upwelling to counter the impacts of climate warming.

Ecological value of the earliest human manipulated coastal habitats: Preliminary insights into the nursery function of a pre-colonial stonewalled fish trap in South Africa

Pre-colonial stonewalled fish traps, an ancient engineering feat in the intertidal region, represent the earliest proof of human manipulation of the coastline in Southern Africa, specifically by the First Indigenous Peoples of South Africa. We investigated the ecologically functioning of a fish trap located on the southeast coast of South Africa from a larval fish and invertebrate perspective. This research was done in collaboration with the Khoi traditional custodians of the area of study. Samples were collected using a light trap on four separate spring tide occasions, deployed for 3 consecutive nights during 2 full moon trips and 2 new moon trips during the known peak larval settlement period (November 2020–February 2021). Although time-dependent, the importance of this novel microhabitat for the development of coastal fishes and invertebrates was highlighted. Even with the high intertidal location of the stonewalled fish trap sampled at Cape Recife, the presence of a pool of permanent non-stagnant water within the fish trap, even during low spring tide, could provide protection to larvae, in the form of more stable environmental conditions, as well as less exposure to marine predators and harsh physical environmental conditions. This research aims to raise awareness of the stonewalled fish traps located on the southeast of South Africa with a view towards developing a more inclusive management of these marine cultural heritage sites, specifically involving the First Indigenous Peoples of South Africa.

Heavy metals in the blueband hermit crab, Pagurus samuelis (Stimpson, 1857) (Decapoda: Anomura: Paguridae), from two Southern California habitats

Abstract Although heavy metal concentrations naturally vary in the environment, anthropogenic sources of heavy metals can mask and override such fluctuations. Indicator species can be used to determine environmental concentrations of certain metals and evaluate the impacts of metals from associated anthropogenic sources. We sought to determine if the hermit crab Pagurus samuelis (Stimpson, 1857) may play a role as an indicator species along the Southern California coast. Seawater and P. samuelis samples were collected from both Cabrillo Beach and White Point Beach rocky intertidal locations and analyzed for concentrations of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) using microwave plasma-atomic emission spectrometry (MP-AES). Lead concentrations were higher in seawater at Cabrillo Beach compared to White Point Beach, whereas Zn concentrations were higher at White Point Beach than at Cabrillo Beach. All other metals were not significantly different between these locations. Cd was higher in hermit crabs collected from Cabrillo Beach than those from White Point Beach, whereas Cr was higher in crabs collected from White Point Beach compared with those from Cabrillo Beach. In comparisons of seawater with samples of hermit crabs, seawater had higher concentrations of Zn and Cd, whereas hermit crabs had higher concentrations of Cu at both locations, and higher levels of Cr at White Point Beach. While this study does not provide conclusive evidence that P. samuelis is an indicator species, it does demonstrate differences in metal concentrations between tested locations and populations of P. samuelis. Although P. samuelis may not be negatively impacted by the heavy metal concentrations we found, the risks of potential bioaccumulation at higher trophic levels is of concern.

Investigating food limitations in wild fisheries: Estuarine fish form dynamic aggregations around a supplementary feeding station and increase localised secondary productivity

Whether wild fish populations are food limited in some inshore and estuarine marine ecosystems is an area of increasing research and focus. To investigate this phenomenon, the abundance and behaviours of fish in a temperate South Pacific estuary were observed in response to the provision of supplementary feed. Observations were conducted over 120-weeks, involving a 60-week period over which fish were actively fed followed by a 60 week without feeding. During active feeding, estuarine associated fish (primarily yellow-eyed mullet Aldrichetta forsteri) showed a highly predictable pattern of fish abundance, biomass and behavioural formation coinciding with the almost daily feeder operation. Tidal current velocities and turbidity appeared to have little influence on the attendance and formations of fish over this period, although season did influence some variables. Peaking at close to 9000 individual fish and 880 kg biomass, fish attendance during the operation of the feeding station was markedly higher than during the period when the feed station was no longer active. Whereby only 0–100 individuals were typically present, and fish no longer showed collective behavioural formations. A direct result of the large number of fish aggregating on this feeding station was an increase in the secondary productivity of the observable zone around the feeding station. Whereby secondary productivity increased by a factor of ∼30 above that observed when the feed station was not operating. Supplementary feeding effectively transformed the study site – a highly modified intertidal location – from an area of very low productivity to one comparable with highly productive temperate estuary environments described elsewhere. The behavioural drivers and ecological relevance of these observations are discussed.

Half-hourly changes in intertidal temperature at nine wave-exposed locations along the Atlantic Canadian coast: a 5.5-year study

Abstract. Intertidal habitats are unique because they spend alternating periods of submergence (at high tide) and emergence (at low tide) every day. Thus, intertidal temperature is mainly driven by sea surface temperature (SST) during high tides and by air temperature during low tides. Because of that, the switch from high to low tides and vice versa can determine rapid changes in intertidal thermal conditions. On cold-temperate shores, which are characterized by cold winters and warm summers, intertidal thermal conditions can also change considerably with seasons. Despite this uniqueness, knowledge on intertidal temperature dynamics is more limited than for open seas. This is especially true for wave-exposed intertidal habitats, which, in addition to the unique properties described above, are also characterized by wave splash being able to moderate intertidal thermal extremes during low tides. To address this knowledge gap, we measured temperature every half hour during a period of 5.5 years (2014–2019) at nine wave-exposed rocky intertidal locations spanning 415 km of the Atlantic coast of Nova Scotia, Canada. This data set is freely available from the figshare online repository (Scrosati and Ellrich, 2020a; https://doi.org/10.6084/m9.figshare.12462065.v1). We summarize the main properties of this data set by focusing on location-wise values of daily maximum and minimum temperature and daily SST, which we make freely available as a separate data set in figshare (Scrosati et al., 2020; https://doi.org/10.6084/m9.figshare.12453374.v1). Overall, this cold-temperate coast exhibited a wide annual SST range, from a lowest overall value of −1.8 ∘C in winter to a highest overall value of 22.8 ∘C in summer. In addition, the latitudinal SST trend along this coast experienced a reversal from winter (when SST increased southwards) to summer (when SST decreased southwards), seemingly driven by alongshore differences in summer coastal upwelling. Daily temperature maxima and minima were more extreme, as expected from their occurrence during low tides, ranging from a lowest overall value of −16.3 ∘C in winter to a highest overall value of 41.2 ∘C in summer. Daily maximum temperature in summer varied little along the coast, while daily minimum temperature in winter increased southwards. This data set is the first of its kind for the Atlantic Canadian coast and exemplifies in detail how intertidal temperature varies in wave-exposed environments on a cold-temperate coast.

Study on Community Structure of Commercial Sea Cucumber in Intertidal Zone, Southeast Moluccas, and Tual, Moluccas

HighlightEight species of sea cucumber was found in four intertidal location in Southeast Moluccas and Tual watersHolothuria atra had the highest densitySea cucumber biodiversity in Southeast Moluccas and Tual waters categorized as lowLocal culture can be used for sustainability of sea cucumber resources management AbstractA study on the community structure of sea cucumber in Southeast Moluccas and Tual needs to be done due to the important role of sea cucumber in both ecologically and economically sustainability. This study aimed to investigate the community structure of sea cucumber in this region as one of the supporting information for the utilization and management of the resources. A survey was conducted by sweeping the target area, by walking and also snorkeling. The location where each sea cucumber found was marked using a GPS, the specimen was weighed, and some were preserved for species analysis. Water quality was measured at each location, while the substrate and vegetation were recorded. This study revealed different composition of species in the investigated area. As many as 8 species of sea cucumber were found, in which four were of genus Holothuria, three were of genus Stichopus and the rest were of genus Bohadschia. Species H. atra has the highest density. In general, the diversity index was relatively low (< 2), the evenness index was 0-81 indicating that the community was depressed. Certain species dominated at most of the investigated sites (0.50-1), and a low margalef index is 0-1.7. To conclude, the community structure of sea cucumber in Tual and Southeast Moluccas was in a depressed condition.

Microplastics in Kuwait marine environment: Results of first survey

Microplastic pollution status in Kuwait coastal areas was assessed A total of 44 intertidal locations were sampled for beach sediment. Short trawls (40) were conducted. In addition, 87 fish and mussels gastrointestinal contents were examined. Microplastics were characterized by Raman spectroscopy. Contrary to the expectation very few microplastic particles were found. Only 37 MPs were detected in beach sediments at 15 locations. Seawater trawls indicated that MPs were low in the numbers. MPs were found in just two samples from Kuwait Bay and also in two samples from the southern areas. In biota, only 3 pieces of plastics were recovered from gastrointestinal tracks of hamour fish. The identified MPs were dominantly polypropylene, polyethylene and polystyrene. It appeared that the microplastic levels in sediment, water and biota were much lower compared to published values from adjoining areas, however, were comparable to the absolute numbers of particles from Qatar and Oman.

Particle characteristics of microplastics contaminating the mussel Mytilus edulis and their surrounding environments

We investigated the environmental partitioning and particle characteristics of macro-, meso- and microplastics and their uptake into the mussel, Mytilus edulis. Sediment samples, overlying seawater and mussels from 9 intertidal locations in the South West of England were analysed for abundance and type of microplastic. Micro- and mesoplastic-like particles were found in 88.5% of the 269 mussels sampled, ranging from 1.43 to 7.64 items per mussel. Of these plastic particles, 70.9% were identified as semi-synthetic (mainly modified-cellulose). Mussel microplastic abundance, but not polymer type, was correlated with that of their surrounding sediment, but not with sea-surface microplastic concentration or mussel size for our study sites. We found significant differences in the relative abundance of polymer types and particle sizes between seawater, sediment, and mussels, with mussels over-representing modified-cellulose fibre abundance but under-representing polyvinyl. Mussels contained significantly smaller plastic fragments than their surrounding sediment and shorter fibres than their overlying seawater.

Ecosystem carbon storage affected by intertidal locations and climatic factors in three estuarine mangrove forests of South China

Recent studies have highlighted that mangroves could serve as an important carbon reservoir, playing an important role in climate regulation. Nonetheless, there remain uncertainties about their carbon storage estimations due to mangrove carbon-cycle processes affected by the interactions among climatic factors, hydro-geomorphic settings, and mangrove species. This study aimed to quantify how ecosystem carbon storage (ECS) (i.e., vegetation biomass and soil organic carbon (SOC)) was affected by intertidal locations and climatic factors based on new and published data from different latitudinal zones. Landward mangrove communities accumulated significantly higher carbon in both vegetation and soil compared with seaward mangrove communities. Average ECS of Dongzhai Harbor, Yingluo Bay, and Dongjiang Estuary were 351.35 Mg ha−1, 306.93 Mg ha−1, and 162.04 Mg ha−1, respectively. ECS values were underestimated because SOC storage accounting for more than 60% of ECS was only estimated on the top 100-cm sediment in this study. Compared with upland forests, there was remarkably higher SOC storage in mangroves, especially in Dongzhai Harbor and Yingluo Bay. Regression analysis indicated that ECS nonlinearly decreased as latitude increased. ECS significantly enhanced as air temperature of the coldest month (Tmin) and mean annual precipitation (Pmean) increased on a global scale, suggesting that Tmin and Pmean were the major controls of ECS. Nevertheless, ECS of mangroves in China was significantly correlated with mean annual air temperature (Tmean) and Tmin at a filed scale, and was nonlinearly increased as Tmin and Tmean increased. Therefore, the influencing factor of ECS spatial patterns was partly affected by statistical scales.

Spatial and temporal variability of sandy intertidal macrobenthic communities and their relationship with environmental factors in a tropical island

Spatial and temporal variability of macrobenthic community in intertidal habitats is governed by various physicochemical factors. Finding the relationship between environmental parameters and the biotic element of an ecosystem have been the centre of ecological studies. This paper describes the influence of environmental parameters in structuring the benthic community at spatial and temporal scales. Samplings were carried out on seasonal basis for a period of two years (August 2013 to July 2015). Fauna was collected from three soft-bottom intertidal locations (CH, MP and CT) using 25 × 25 cm quadrat along the Port Blair coast, south Andaman, India. A total of 112 macrofaunal taxa belonging to 4 major and 2 minor phyla were recorded. Polychaeta was the most dominant taxa followed by Amphipoda. Statistical analyses revealed that macrobenthic faunal assemblages were significantly different at spatial scale but not on temporal pattern. The distribution of macrobenthic fauna at spatial scale was mainly influenced by sediment characteristics (organic matter and grain size). Amphipods dominated the locations where sediment having coarser grain size and low organic matter whereas polychaetes and molluscs were found abundant at the locations characterised with fine sediment and high organic matter. This study concludes that in the regions where temporal variability is not significant, the sediment characteristics, which together with beach morphodynamics play an important role in structuring the benthic community.

Luminescent defensive behaviors of polynoid polychaete worms to natural predators

The intertidal polynoid scale worm Harmothoe imbricata emits a bright green luminescence from its elytra when provoked. These worms are hypothesized to use both luminescence and autotomization (voluntary loss of body parts) as specialized defenses against predators. Previous studies had focused on the mechanisms of light production or used human manipulation to provoke luminescent displays, rather than using actual predators. Worms and local crustacean predators collected in Cumberland County, Maine at three intertidal locations between June 2011 and March 2013 were placed in a small chamber with a removable center divider and their interaction was recorded with infrared cameras, a night vision device with an infrared barrier filter, and photomultipliers. Three different luminescent responses were observed: attached scale flashing, autotomized glowing scales, and autotomized flashing/glowing posterior segments. In some cases, autotomized scales/segments acted as successful decoys, with the anterior portion of the worm crawling away while the attacker focused on the posterior glowing portion. Worms appeared to use different combinations of defensive behaviors in different scenarios, such as when attacked by different predators. Luminescent defensive displays were also more complex than predicted and suggest that the predator’s actions during and following an attack may inadvertently aid in the scale worm’s escape. The use of live predators was pivotal to describing the worm’s defense mechanism and providing insight into how luminescence may be used in nature.

Microplastic-associated bacterial assemblages in the intertidal zone of the Yangtze Estuary

Plastic trash is common in oceans. Terrestrial and marine ecosystem interactions occur in the intertidal zone where accumulation of plastic frequently occurs. However, knowledge of the plastic-associated microbial community (the plastisphere) in the intertidal zone is scanty. We used high-throughput sequencing to profile the bacterial communities attached to microplastic samples from intertidal locations around the Yangtze estuary in China. The structure and composition of plastisphere communities varied significantly among the locations. We found the taxonomic composition on microplastic samples was related to their sedimentary and aquatic origins. Correlation network analysis was used to identify keystone bacterial genera (e.g. Rhodobacterales, Sphingomonadales and Rhizobiales), which represented important microbial associations within the plastisphere community. Other species (i.e. potential pathogens) were considered as hitchhikers in the plastic attached microbial communities. Metabolic pathway analysis suggested adaptations of these bacterial assemblages to the plastic surface-colonization lifestyle. These adaptations included reduced “cell motility” and greater “xenobiotics biodegradation and metabolism.” The findings illustrate the diverse microbial assemblages that occur on microplastic and increase our understanding of plastisphere ecology.

Shorebirds, Stakeholders, and Competing Claims to the Beach and Intertidal Habitat in Delaware Bay, New Jersey, USA

Birds have specific habitat needs as a function of their life cycle and reproductive stage. Migrant shorebirds that may fly from the Arctic to the southern tip of South America have foraging and habitat requirements at sites where they stop to refuel before continuing their migration north or south. Throughout the world, shorebirds mainly forage on mudflats at low tide. Red knots (Calidris canutus rufa) are threatened in the United States and elsewhere, and it is critical to determine factors that might contribute to their decline. This paper uses Delaware Bay as a case study to examine shorebird (and red knot) use of the intertidal habitat, and competing claims to habitats they require during their northward migration, as well as some of the key stakeholders that play a role in protecting red knots. Shorebirds are drawn to Delaware Bay to feed on the eggs of Horseshoe Crabs (Limulus polyphemus) that are concentrated at the high tide. But they also feed on the intertidal mudflat. We examined intertidal habitat use on 17 beaches in an extensive study in 2015, and 5 key beaches in 2016. Most of the beaches were longitudinal, but four were more complex, and were used extensively for resting as well as foraging; numbers there were higher than on the longitudinal beaches. On foraging beaches, some shorebirds were present on over 85% of the intertidal censuses, and red knots were present on over 48% of the intertidal censuses. Average numbers of red knots on the longitudinal beaches varied from 0 to 354 ± 116 when any shorebirds were present, but averaged up to 1184 ± 634 when knots were present in 2015. Some beaches in 2015 had no knots (a beach with long-term aquaculture). Tide, intertidal location, and beach (name) determined the number of knots (and all shorebirds). Numbers decreased with distance from the mean high tide line. The average number of knots present in the intertidal mudflats two hours before or after low tide when knots were present (e.g. no censuses with zeros) was 2040 (=maximum flock size, in 2015). Major threats to red knots are from recreationists, overfishing of horseshoe crabs (reduction in egg prey base), and use of the intertidal by aquaculture. We discuss the role of stakeholders in conservation and protection of red knots.

A 12-year record of intertidal barnacle recruitment in Atlantic Canada (2005-2016): relationships with sea surface temperature and phytoplankton abundance.

On the Gulf of St. Lawrence coast of Nova Scotia (Canada), recruitment of the barnacle Semibalanus balanoides occurs in May and June. Every year in June between 2005 and 2016, we recorded recruit density for this barnacle at the same wave-exposed rocky intertidal location on this coast. During these 12 years, mean recruit density was lowest in 2015 (198 recruits dm−2) and highest in 2007 (969 recruits dm−2). The highest recruit density observed in a single quadrat was 1,457 recruits dm−2 (in 2011) and the lowest was 34 recruits dm−2 (in 2015). Most barnacle recruits appear during May, which suggests that most pelagic larvae (which develop over 5–6 weeks before benthic settlement) are in the water column in April. An AICc-based model selection approach identified sea surface temperature (SST) in April and the abundance of phytoplankton (food for barnacle larvae, measured as chlorophyll-a concentration –Chl-a–) in April as good explanatory variables. Together, April SST and April Chl-a explained 51% of the observed interannual variation in recruit density, with an overall positive influence. April SST was positively related to March–April air temperature (AT). April Chl-a was negatively related to the April ratio between the number of days with onshore winds (which blow from phytoplankton-limited offshore waters) and the number of days with alongshore winds (phytoplankton is more abundant on coastal waters). Therefore, this study suggests that climatic processes affecting April SST and April Chl-a indirectly influence intertidal barnacle recruitment by influencing larval performance.