Inshore Sites Research Articles

Phytoplankton growth and grazing dynamics during anomalous heat wave and suppressed upwelling conditions in the southern California Current

We investigated phytoplankton dynamics in the southern California Current System (SCCS) in August 2014 during the early phase of the 2014-15 marine heat wave (MHW). Multi-day experiments were conducted at three inshore and two offshore sites, with daily depth profiles of dilution incubations on a drifting array to determine growth and grazing rates and shipboard assessments of nutrient effects. Picophytoplankton populations were analyzed by flow cytometry and eukaryotic phytoplankton by 18 S sequencing. Mixed-layer nutrients were low across the region, but inshore sites had substantial nitrate concentrations and prominent Chla maxima in the lower euphotic zone. Shoreward transport of warm-stratified waters from the offshore suppressed coastal upwelling and shifted picophytoplankton distributions toward increased onshore abundance of Prochlorococcus and decreased Synechococcus and picoeukaryotes. These trends were reinforced by higher-than-average growth of Prochlorococcus at inshore sites and higher grazing of Synechococcus and picoeukaryotes. Prasinophytes (Chlorophyceae) were notably important among eukaryotic taxa, and pennates replaced centric taxa as the dominant diatoms in inshore waters compared to normal upwelling. Despite substantial spatial variability in community composition, offshore and inshore experimental locations both showed growth-grazing balances, with microzooplankton consuming similar percentages (80%) of primary production. We thus confirm expectations that the 2014-15 MHW resulted in greater trophic flow through the microbial food web at the expense of reduced direct phytoplankton (Chla) consumption by mesozooplankton. However, impacts on mesozooplankton energy budgets were partially offset by increased trophic flow through protistan microzooplankton and higher phytoplankton C:Chla.

Determining growth rates of heterotrophic bacteria from 16S rRNA gene sequence-based analyses of dilution experiments

Vital rates, including growth responses to environmental variability, are poorly characterized for the diverse taxa of heterotrophic bacteria (HBact) in marine ecosystems. Here, we evaluated the potential for combining molecular analyses with dilution experiments to assess taxon-specific growth (cell division) and net growth rates of HBact in natural waters. Two-treatment dilution experiments were conducted with in situ incubations under 3 environmental conditions in the California Current Ecosystem, at offshore and inshore sites during a warm upwelling-suppressed year (2014) and for normal inshore upwelling, representing a 33-fold primary production range. Relative sequence reads from 16S rRNA metabarcoding were normalized to total HBact counts from flow cytometry for community abundance and rate calculations. Composition varied from dominance of Alphaproteobacteria (56%) in oligotrophic offshore (SAR11) and mesotrophic inshore waters (SAR11 and Rhodobacteria) to Bacteriodes/Flavobacteria dominance (64%) and mixed sub-taxon importance (Polaribacter, Rhodobacteria, Formosa) during upwelling. Net growth rates in bottles, validated by comparison to ambient community net growth following a satellite-tracked drifter, varied from near steady state for offshore and inshore conditions to dynamic community changes during upwelling. Mean growth rates doubled (0.33 to 0.62 d-1) over the productivity range, and taxon estimates varied from -0.17 d-1 (Formosa, offshore) to 1.53 d-1 (SAR11, upwelling). Increasing growth of Flavobacteria and Rhodobacteria paralleled their abundance and dominance increases with productivity. SAR11 growth remained higher than average with increasing production, despite declining abundances. We highlight possible PCR or 16S rRNA gene copy biases of growth rate estimates as research needs for further applications of this approach.

Divergent responses of the coral holobiont to deoxygenation and prior environmental stress

Ocean deoxygenation is intensifying globally due to human activities – and is emerging as a grave threat to coral reef ecosystems where it can cause coral bleaching and mass mortality. However, deoxygenation is one of many threats to coral reefs, making it essential to understand how prior environmental stress may influence responses to deoxygenation. To address this question, we examined responses of the coral holobiont (i.e., the coral host, Symbiodiniaceae, and the microbiome) to deoxygenation in corals with different environmental stress backgrounds. We outplanted Acropora cervicornis fragments of known genotypes from an in situ nursery to two sites in the Florida Keys spanning an inshore-offshore gradient. After four months, fragments from the outplanted corals were transferred to the laboratory, where we tested differences in survivorship, tissue loss, photosynthetic efficiency, Symbiodiniaceae cell density, and coral microbiome composition after persistent exposure to one of four oxygen treatments ranging from extreme deoxygenation (0.5 mg L-1) to normoxia (6 mg L-1). We found that, for the short duration of exposure tested in this study (four days), the entire coral holobiont was resistant to dissolved oxygen (DO) concentrations as low as 2.0 mg L-1, but that the responses of members of the holobiont decoupled at 0.5 mg L-1. In this most extreme treatment, the coral host showed decreased photosynthetic efficiency, tissue loss, and mortality, and lower Symbiodiniaceae densities in a bleaching response, but most microbial taxa remained stable. Although deoxygenation did not cause major community shifts in microbiome composition, the population abundance of some microbial taxa did respond. Site history influenced some responses of the coral host and endosymbiont, but not the coral microbiome, with corals from the more stressful inshore site showing greater susceptibility to subsequent deoxygenation. Our study reveals that coral holobiont members respond differently to deoxygenation, with greater sensitivity in the coral host and Symbiodiniaceae and greater resistance in the coral microbiome, and that prior stress exposure can decrease host tolerance to deoxygenation.

The Western Channel Observatory: a century of physical, chemical and biological data compiled from pelagic and benthic habitats in the western English Channel

Abstract. The Western Channel Observatory (WCO) comprises a series of pelagic, benthic and atmospheric sampling sites within 40 km of Plymouth, UK, that have been sampled by the Plymouth institutes on a regular basis since 1903. This longevity of recording and the high frequency of observations provide a unique combination of data; for example temperature data were first collected in 1903, and the reference station L4, where nearly 400 planktonic taxa have been enumerated, has been sampled on a weekly basis since 1988. While the component datasets have been archived, here we provide the first summary database bringing together a wide suite of the observations. This provides monthly average values of some of the key pelagic and benthic measurements for the inshore site L4 (50∘15.00′ N, 4∘13.02′ W; approx. depth 55 m), the offshore site E1 (50∘02.00′ N, 4∘22.00′ W; approx. depth 75 m) and the intermediate L5 site (50∘10.80′ N, 4∘18.00′ W; approx. depth 58 m). In brief, these data include the following: water temperature (from 1903); macronutrients (from 1934); dissolved inorganic carbon and total alkalinity (from 2008); methane and nitrous oxide (from 2011); chlorophyll a (from 1992); high-performance liquid chromatography (HPLC)-derived pigments (from 1999); <20 µm plankton by flow cytometry, including bacteria (8 functional groups from 2007); phytoplankton by microscopy (6 functional groups from 1992); microplankton and mesozooplankton from FlowCam (6 groups from 2012); Noctiluca sp. dinoflagellate (from 1997); mesozooplankton by microscopy (8 groups from 1988); Calanus helgolandicus egg production rates (from 1992); fish larvae from the Young Fish Trawl survey (4 groups from 1924); benthic macrofauna (4 groups from 2008); demersal fish (19 families from 2008); blue shark, Prionace glauca (from 1958); and 16S alpha diversity for sediment and water column (from 2012). These data have varying coverage with respect to time and depth resolution. The metadata tables describe each dataset and provide pointers to the source data and other related Western Channel Observatory datasets and outputs not compiled here. We provide summaries of the main trends in seasonality and some major climate-related shifts that have been revealed over the last century. The data are available from the Data Archive for Seabed Species and Habitats (DASSH): https://doi.org/10.17031/645110fb81749 (McEvoy and Atkinson, 2023). Making these data fully accessible and including units of both abundance and biomass will stimulate a variety of uptakes. These may include uses as an educational resource for projects, for models and budgets, for the analysis of seasonality and long-term change in a coupled benthic–pelagic system, or for supporting UK and north-eastern Atlantic policy and management.

Comparison of inorganic nitrogen concentrations in airborne particles at inshore and offshore sites in the Yellow Sea (2017–2019): Long-range transport and potential impact on marine productivity

Atmospheric deposition of nitrogen is one of the most important external nutrient sources. We investigated the concentrations of NO3− and NH4+ in airborne particles at both an offshore and an inshore site in the Yellow Sea. At the offshore site, devoid of local sources and located downwind from the highly developed areas of Korea and China, the concentrations of atmospheric particulate NO3− and NH4+ were ∼88 ± 101 nmol m−3 and ∼102 ± 102 nmol m−3, respectively, likely due to the transboundary long-range transport of pollutants. The inshore site showed a concentration ∼2 times higher than the offshore site. Considering not only dry inorganic nitrogen deposition but also wet and organic material deposition, the total atmospheric nitrogen deposition was estimated to contribute roughly 10 % to the new production in the Yellow Sea.

Coral Reef Carbonate Chemistry Reveals Interannual, Seasonal, and Spatial Impacts on Ocean Acidification Off Florida

AbstractOcean acidification (OA) threatens coral reef persistence by decreasing calcification and accelerating the dissolution of reef frameworks. The carbonate chemistry of coastal areas where many reefs exist is strongly influenced by the metabolic activity of the underlying benthic community, contributing to high spatiotemporal variability. While characterizing this variability is difficult, it has important implications for the progression of OA and the persistence of the ecosystems. Here, we characterized the carbonate chemistry at 38 permanent stations located along 10 inshore‐offshore transects spanning 250 km of the Florida Coral Reef (FCR), which encompass four major biogeographic regions (Biscayne Bay, Upper Keys, Middle Keys, and Lower Keys) and four shelf zones (inshore, mid‐channel, offshore, and oceanic). Data have been collected since 2010, with approximately bi‐monthly periodicity starting in 2015. Increasing OA, driven by increasing DIC, was detected in the mid‐channel, offshore, and oceanic zones in every biogeographic region. In the inshore zone, however, increasing TA counteracted any measurable OA trend. Strong seasonal variability occurred at inshore sites and included periods of both exacerbated and mitigated OA. Seasonality was region‐dependent, with greater variability in the Lower and Middle Keys. Elevated pH and aragonite saturation states (ΩAr) were observed in the Upper and Middle Keys, which could favor reef habitat persistence in these regions. Offshore reefs in the FCR could be more susceptible to global OA by experiencing open‐ocean‐like water chemistry conditions. By contrast, higher seasonal variability at inshore reefs could offer a temporary OA refuge during periods of enhanced primary production.

Short-term responses of macroinvertebrate assemblages to the “ten-year fishing ban” in the largest highland lake of the Yangtze basin

The rapid decline of freshwater biodiversity caused by overfishing has led to the implementation of a series of conservation measures, including fishing bans. However, existing studies have mostly focused on the effects of fishing bans on economically important species, while impacts on freshwater macroinvertebrates in lake ecosystems have been rarely studied. This study used a before-and-after methodology to determine the short-term effects of the “ten-year fishing ban” on the macroinvertebrates of the Dianchi Lake, the largest highland freshwater lake in the upper Yangtze basin, between 2015 and 2022. Following the fishing ban, the overall macroinvertebrate species richness (median [interquartile]) across sites increased from 4 [2–6] to 5 [4–7]. The total density increased from 128 [80–272] to 212 [140–325] n/m2. The median biomass increased from 0.18 [0.08–0.41] to 0.51 [0.26–2.36] g/m2. In particular, the Chironomidae density in the offshore sites increased from 16.00 [0.00–32.00] to 33.30 [16.00–48.00] n/m2, and the biomass increased from 0.03 [0.00–0.09] to 0.16 [0.07–0.22] g/m2. Within the inshore sites, the aquatic insect density increased from 4 [1.33–15.33] to 56 [22.00–86.67] n/m2. The Malacostraca density increased from 34.67 [11.67–95.33] to 110 [53.33–223.33] n/m2, and the biomass increased from 0.43 [0.11–1.00] to 1.48 [0.50–2.00] g/m2. Two endangered Margarya species were rediscovered at multiple sites compared to the pre-fishing ban period. A significant change in macroinvertebrate community structure across the lake was observed, which can be largely attributed to the fishing ban. The immediate increase in species richness, density, and biomass of most macroinvertebrate species suggests a combination of effects from both reduced exploitation pressure and lessened disturbances on lake habitats. The findings indicate that the fishing ban is beneficial for the recovery of most macroinvertebrate species in freshwater lakes.

Bleaching, mortality and lengthy recovery on the coral reefs of Lord Howe Island. The 2019 marine heatwave suggests an uncertain future for high-latitude ecosystems

Oceanic thermal anomalies are increasing in both frequency and strength, causing detrimental impacts to coral reef communities. Water temperatures beyond the corals optimum threshold causeing coral bleaching and mass mortality, impacting our global coral reef ecosystems, including marginal high-latitude reefs. Coral bleaching and mortality were observed at the southernmost coral reef, Lord Howe Island Marine Park, during the summer of 2019, coinciding with anomalously high sea surface temperatures across the reef system from January-April. Here we document the extent of coral impacts within the Lord Howe Island lagoonal reef and the recovery from bleaching eight-months later. Significant differences in bleaching prevalence were observed across the lagoonal coral reef, ranging from 16 to 83% across offshore and inshore reef regions and with variable onset timing. Coral mortality of up to 40% was recorded in the reef’s most severely impacted near-shore area. The four most dominant species, Stylophora pistillata, Pocillopora damicornis, Porites spp. and Seriatopora hystrix, were the most susceptible to bleaching, with all coral colonies found either bleached or dead at the most affected inshore site during and following peak heat stress. Interestingly, during the eight-months following bleaching, there was no evidence of bleaching recovery (i.e., re-establishment of symbiosis) at the offshore lagoonal site. However, there was a significant increase in the abundance of healthy coral colonies at the inshore site, suggesting the recovery of the surviving bleached corals at this site. Importantly, we found no evidence for bleaching or mortality in the Acropora spp. and minimal bleaching and no mortality in Isopora cuneata during the study period, typically highly susceptible species. Given the isolation of high-latitude reefs such as Lord Howe Island, our results highlight the importance of understanding the impacts of bleaching, mortality and bleaching recovery on coral population structure and resilience of high-latitude coral reefs.

Macroalgal cover on coral reefs: Spatial and environmental predictors, and decadal trends in the Great Barrier Reef.

Macroalgae are an important component of coral reef ecosystems. We identified spatial patterns, environmental drivers and long-term trends of total cover of upright fleshy and calcareous coral reef inhabiting macroalgae in the Great Barrier Reef. The spatial study comprised of one-off surveys of 1257 sites (latitude 11-24°S, coastal to offshore, 0-18 m depth), while the temporal trends analysis was based on 26 years of long-term monitoring data from 93 reefs. Environmental predictors were obtained from in situ data and from the coupled hydrodynamic-biochemical model eReefs. Macroalgae dominated the benthos (≥50% cover) on at least one site of 40.4% of surveyed inshore reefs. Spatially, macroalgal cover increased steeply towards the coast, with latitude away from the equator, and towards shallow (≤3 m) depth. Environmental conditions associated with macroalgal dominance were: high tidal range, wave exposure and irradiance, and low aragonite saturation state, Secchi depth, total alkalinity and temperature. Evidence of space competition between macroalgal cover and hard coral cover was restricted to shallow inshore sites. Temporally, macroalgal cover on inshore and mid-shelf reefs showed some fluctuations, but unlike hard corals they showed no systematic trends. Our extensive empirical data may serve to parameterize ecosystem models, and to refine reef condition indices based on macroalgal data for Pacific coral reefs.

Restoration and coral adaptation delay, but do not prevent, climate-driven reef framework erosion of an inshore site in the Florida Keys

For reef framework to persist, calcium carbonate production by corals and other calcifiers needs to outpace loss due to physical, chemical, and biological erosion. This balance is both delicate and dynamic and is currently threatened by the effects of ocean warming and acidification. Although the protection and recovery of ecosystem functions are at the center of most restoration and conservation programs, decision makers are limited by the lack of predictive tools to forecast habitat persistence under different emission scenarios. To address this, we developed a modelling approach, based on carbonate budgets, that ties species-specific responses to site-specific global change using the latest generation of climate models projections (CMIP6). We applied this model to Cheeca Rocks, an outlier in the Florida Keys in terms of high coral cover, and explored the outcomes of restoration targets scheduled in the coming 20 years at this site by the Mission: Iconic Reefs restoration initiative. Additionally, we examined the potential effects of coral thermal adaptation by increasing the bleaching threshold by 0.25, 0.5, 1 and 2˚C. Regardless of coral adaptative capacity or restoration, net carbonate production at Cheeca Rocks declines heavily once the threshold for the onset of annual severe bleaching is reached. The switch from net accretion to net erosion, however, is significantly delayed by mitigation and adaptation. The maintenance of framework accretion until 2100 and beyond is possible under a decreased emission scenario coupled with thermal adaptation above 0.5˚C. Although restoration initiatives increase reef accretion estimates, Cheeca Rocks will only be able to keep pace with future sea-level rise in a world where anthropogenic CO2 emissions are reduced. Present results, however, attest to the potential of restoration interventions combined with increases in coral thermal tolerance to delay the onset of mass bleaching mortalities, possibly in time for a low-carbon economy to be implemented and complementary mitigation measures to become effective.

A baseline assessment of coastal pH variability in a temperate South African embayment: implications for biological ocean acidification research

Compared with the open ocean, knowledge of pH variability in coastal waters is rudimentary, especially in Africa. This is concerning as quantifying local pH conditions is critical when assessing the response of coastal species to future ocean acidification scenarios. The objective of this study was to capture some of the variability in pH at scales and sites relevant to coastal marine organisms in a South African temperate embayment (Algoa Bay, Indian Ocean). We used a sampling approach that captured spatial (at a resolution of ∼10 km), monthly and diel (24-hour) variability in pH and associated physical and biological parameters at offshore and shallow inshore sites in Algoa Bay. We found that pH and associated parameters (temperature, calculated pCO2, chlorophyll a) varied over space and time in Algoa Bay. The range in pH was 0.30 units at offshore sites and 0.46 at inshore sites, and the average pH was 8.10 (SD 0.06) and 8.10 (SD 0.13) at these sites, respectively, which is typical for coastal environments. Our results showed that both biological factors (at the offshore sites) and salinity (at the inshore sites) may influence temporal and spatial variability in pH. We also identified a shallow inshore site with high levels of macroalgal growth that had consistently higher average daytime pH levels (8.33 [SD 0.07]), which may serve as an ocean acidification refuge for coastal marine species. This is the first comprehensive pH-monitoring study to be implemented in a nearshore coastal area in Africa and provides recommendations for monitoring in other understudied regions.

Monitoring cetacean occurrence and variability in ambient sound in Scottish offshore waters

The characterisation of marine soundscapes allows observation of spatiotemporal distribution of vocalising species and human activities, which can inform an assessment of their interactions. Such data are important for monitoring the ecological status of marine habitats. The Scottish Atlantic Frontier is an important habitat for a variety of cetacean species. Historic whaling has heavily impacted several species inhabiting these waters and current comprehensive information about seasonal occurrence and distribution is lacking for all species. This study presents year-round passive acoustic monitoring data from ten sites in this understudied region. The three most offshore sites were examined for baleen whale vocalisations, and four species were regularly detected. Fin whale detections peaked from October to January and were at their lowest during May and June. Humpback whale song was detected as early as January but showed a strong seasonal peak in March and April. In contrast, minke whales were detected regularly throughout the year but with a peak in detections from October to November, when sei whales were also detected. All monitoring sites showed frequent occurrence of odontocete echolocation clicks and whistles. Comprised mainly of delphinid vocalisations, whistles and clicks were detected on an almost-daily basis among the offshore sites, with a slight reduction in detections from May to July particularly among the more inshore sites. Ambient sound levels (root-mean-square sounds pressure level; SPL) varied by site and season in relation to species presence, anthropogenic contributions, and environmental conditions. Monthly median SPL across the array varied up to 18 dB within 1/3-octave bands. Throughout the year, variability in median SPL was lowest in the higher frequency bands (>10 kHz), while highest variability was found between January to July in specific lower frequency bands (<1 kHz). Results from this study demonstrate the value of passive acoustic data in providing novel baseline information about cetacean occurrence and distribution in Scottish offshore habitats where data are limited and outdated. The results will feed into statutory reporting on underwater noise, support the identification and designation of future marine protected areas for cetaceans, and help guide management of future human-marine mammal interactions in Scottish offshore waters.

Characterizing the Flow Regime in Brook Trout Incubation Habitats and Implications for Management in a Hydro‐Regulated River

AbstractThe operation of dams, diversions, and power generation facilities unavoidably influence the ecological function of rivers. We evaluated vertical and horizontal hydraulic gradients and subsequent water temperature changes in the hyporheic zone of a spawning area for Brook Trout Salvelinus fontinalis in a managed Lake Superior tributary in Ontario, then conducted a laboratory‐based experiment to show the impact of cold shock during incubation on the timing of larval emergence and survival. Upwelling groundwater was observed at the spawning area during the monitoring period (October 28, 2016, to January 11, 2017); hyporheic water temperatures remained above 3.7°C, whereas ambient river temperature above the substrate fell to 1.5°C until water was released from the upstream control dam. After the release event, water level increased by 0.9 m over the spawning area, and within 24 h, vertical and horizontal flow gradients were reversed in the hyporheic zone; downwelling conditions were observed for 30 h between surface and hyporheic water 1.8 m below substrate, and hyporheic water temperature decreased in unison. Hyporheic temperatures at shallow inshore sites fell below 1°C for more than 53 h. In the laboratory, applying a worst‐case scenario of dam‐induced cold shock on Brook Trout redds using historic monitoring records (i.e., <1.0°C for 40 h), we found no appreciable effect on survival and development timing of incubating Brook Trout eggs compared with a control group. Survival from fertilization to hatching was high for both treatment and control groups (>90%) and lower from fertilization to emergence (55%). Overall, our results suggest that standard winter operating procedures on a Lake Superior tributary had little impact on Brook Trout egg survival and development time to hatching and emergence; however, our findings also suggest that staged winter discharges would lessen the reversal of flow in the hyporheic zone and the magnitude of temperature changes experienced at Brook Trout redds.

Microclimate predicts kelp forest extinction in the face of direct and indirect marine heatwave effects.

Marine heatwaves threaten the persistence of kelp forests globally. However, the observed responses of kelp forests to these events have been highly variable on local scales. Here, we synthesize distribution data from an environmentally diverse region to examine spatial patterns of canopy kelp persistence through an unprecedented marine heatwave. We show that, although often overlooked, temperature variation occurring at fine spatial scales (i.e., a few kilometers or less) can be a critical driver of kelp forest persistence during these events. Specifically, though kelp forests nearly all persisted toward the cool outer coast, inshore areas were >3°C warmer at the surface and experienced extensive kelp loss. Although temperatures remained cool at depths below the thermocline, kelp persistence in these thermal refugia was strongly constrained by biotic interactions, specifically urchin populations that increased during the heatwave and drove transitions to urchin barrens in deeper rocky habitat. Urchins were, however, largely absent from mixed sand and cobble benthos, leading to an unexpected association between bottom substrate and kelp forest persistence at inshore sites with warm surface waters. Our findings demonstrate both that warm microclimates increase the risk of habitat loss during marine heatwaves and that biotic interactions modified by these events will modulate the capacity of cool microclimates to serve as thermal refugia.

Comparative analysis of bacterial communities in the sediment and seawater environments from marine large yellow croaker cages (Zhejiang coast, China)

Bacterial community plays a vital role in the open-oceanic aquaculture ecosystem, and its stability is crucial for maintaining the health of mariculture fish. However, there are no reported studies on microbial communities in the culture environment of marine fish cages. In this study, bacterial community composition and diversity of seawater and sediment habitats from 5 large yellow croaker cage farms were first investigated by 16S rRNA-based high-throughput sequencing. The composition of bacterial communities was visualized at the phylum and genus levels. Meanwhile, biological and ecological functions were also predicted. The bacterial diversity observed at 3 inshore sampling sites was higher in seawater groups than that in sediment groups. The alpha diversity indices were influenced by the geographic location, especially the inshore site Yueqing (YQ), showing higher values than other sampling sites. The pathogenic bacteria were prevalent in the aquaculture environments, and probiotics showed a relatively low proportion by comparing the potential pathogens. Our study provides baseline data on bacterial communities and diversity in the open-oceanic environments of cage-culture large yellow croaker.

Oyster and Barnacle Recruitment Dynamics on and Near a Natural Reef in China: Implications for Oyster Reef Restoration

Oysters and barnacles are dominant inhabitants of natural and restored oyster reefs around the world, and high areal coverage of barnacles at natural or restored reefs commonly decreases substrate accessibility for oyster settlement. The overall understanding of oyster and barnacle recruitment dynamics provides invaluable information on site selection and strategies employed for oyster reef restoration. This study documented the temporal and spatial patterns of oyster and barnacle recruitment on and near the largest natural intertidal oyster reef (Liyashan) in China during 2019–2020. The oyster Crassostrea sikamea recruitment appeared as a continuous process from June through late November or early December, with the peak in August. Greater recruits of oyster spat occurred on the sheltered inshore at the upstream of the natural oyster reef than on the reef and the nearby open coast (p < 0.05). The barnacle recruitment extended from spring to early winter, with mid-spring and mid-summer peaks. Conversely, higher barnacle recruitment appeared on the natural oyster reef and the nearby open coast than on the sheltered inshore. Across all the monitoring sites, the cumulative recruits of oysters in each of 2019 and 2020 was negatively correlated with those of barnacles (p < 0.05). The inshore sites (SH1 and SH2) with high oyster recruitment and low barnacle recruitment should be recognized as the natural spatfall sites for the natural oyster reef restoration. The separation in the recruitment peak between the oyster and the barnacle indicated that August was the most favorable window for capturing oyster spat through substratum addition to the water around the natural reef.

Genetic population structure of summer flounder Paralichthys dentatus using microsatellite DNA analysis

Summer flounder Paralichthys dentatus supports one of the most valuable commercial and recreational fisheries along the Atlantic Coast of the U.S. However, in recent decades the management of this species has proven to be one of the most contentious for any exploited marine resource in the region. A coastwide catch quota is imposed annually for summer flounder of which 60% is allocated to the commercial fishery and 40% to the recreational fishery. The allocation is further divided among the individual coastal states from North Carolina to Massachusetts based on their landings in the 1980s. This process, based on political jurisdictions, does not consider the species’ biological stock structure. Previous genetic studies (allozyme, mtDNA, and SNPs) provided contradictory results regarding the possible population structure of summer. To address this issue, we used DNA microsatellite analysis at 9 loci to define the coastwide population structure of summer flounder. In total, 1182 specimens were analyzed from 18 collection sites. Most collections were from the Continental Shelf during the fall-winter spawning season. These were supplemented with additional samples from inshore waters from North Carolina to Florida, and inshore sites which support significant recreational fisheries at Nantucket Shoals, Massachusetts and Fire Island, New York. The overall level of genetic differentiation in pairwise comparisons between collections was very low, mean FST= 0.001. There was no evidence of genetic differentiation between collections from north and south of Cape Hatteras. Our microsatellite results are consistent with an earlier SNP study which failed to find significant allelic heterogeneity among coastwide collections of summer flounder. However, a subset of pairwise FST comparisons between some collections proved statistically significant. Furthermore, in STRUCTURE analysis we found evidence of two genetic clusters within the species’ northern landings area, however, this finding was not supported by DPAC analysis. We conclude that summer flounder most likely constitute a single population along their entire Atlantic Coast distribution.

Switch of Bacteria Community Under Oxygen Depletion in Sediment of Bohai Sea

Regular oxygen depletion is occurring every summer in the depression area of the Bohai Sea. The community structure and potential functions of microbes in expanding marine hypoxic area are of great importance due to their roles in biogeochemical cycling. In this study, the diversity and distribution of bacteria based on 16S rRNA gene in sediment along an inshore-offshore transect across the oxygen-depletion area in the Bohai Sea was investigated in June, July and August of 2018 by employing high-throughput sequencing. Results revealed that the bacteria community was dominated by Proteobacteria (42.67%), Actinobacteria (14.13%), Chloroflexi (13.02%), Acidobacteria (8.01%), and Bacteroidetes (6.30%). During oxygen depletion, the bacteria community from inshore site A3 subjected to dramatic variation from June to August, but the composition tended to be stable in sites from the depression area along the transect. Distinct switch of bacteria from aerobic to anaerobic group was observed when the DO concentration <4.2 mg/L, typically represented by dominance of Anaerolineaceae in August sample. Further, KEGG prediction by PICRUSt confirmed the variations by showing significant difference in functional pathways, especially the nitrogen metabolisms, before and after DO depletion (p < 0.05). These variations could be influenced by depth, NO2– concentration and DO availability based on RDA analysis. The details in diversity and composition of bacteria under continually observation provide insights into both instant and long-term response of bacteria community to oxygen depletion, and the distinct functional switch under this process expands our knowledge on the metabolic character of bacteria in worldwide hypoxia areas.

Decreased Photosynthetic Efficiency in Response to Site Translocation and Elevated Temperature Is Mitigated with LPS Exposure in Porites astreoides Symbionts

Coral reefs have been detrimentally impacted causing health issues due to elevated ocean temperatures as a result of increased greenhouse gases. Extreme temperatures have also exacerbated coral diseases in tropical reef environments. Numerous studies have outlined the impacts of thermal stress and disease on coral organisms, as well as understanding the influence of site-based characteristics on coral physiology. However, few have discussed the interaction of all three. Laboratory out-planting restoration projects have been of importance throughout impacted areas such as the Caribbean and southern Florida in order to increase coral cover in these areas. This study analyzes photosynthetic efficiency of Porites astreoides from the lower Florida Keys after a two-year reciprocal transplant study at inshore (Birthday reef) and offshore (Acer24 reef) sites to understand acclimation capacity of this species. Laboratory experiments subjected these colonies to one of three treatments: control conditions, increases in temperature, and increases in temperature plus exposure to an immune stimulant (lipopolysaccharide (LPS)) to determine their influence on photosynthetic efficiency and how stress events impact these measurements. In addition, this study is a continuation of previous studies from this group. Here, we aim to understand if these results are static or if an acclimation capacity could be found. Overall, we observed site-specific influences from the Acer24 reef site, which had significant decreases in photosynthetic efficiencies in 32 °C treatments compared to Birthday reef colonies. We suggest that high irradiance and lack of an annual recovery period from the Acer24 site exposes these colonies to significant photoinhibition. In addition, we observed significant increases in photosynthetic efficiencies from LPS exposure. We suggest host-derived antioxidants can mitigate the negative impacts of increased thermal stress. Further research is required to understand the full complexity of host immunity and symbiont photosynthetic interactions.

Environmental Filtering by pH and Salinity Jointly Drives Prokaryotic Community Assembly in Coastal Wetland Sediments

Understanding the microbial community assembly is an essential topic in microbial ecology. Coastal wetlands are an important blue carbon sink, where microbes play a key role in biogeochemical cycling of nutrients and energy transformation. However, the drivers controlling the distribution patterns and assembly of bacterial and archaeal communities in coastal wetland are unclear. Here we examined the diversity, co-occurrence network, assembly processes and environmental drivers of bacterial and archaeal communities from inshore to offshore sediments by the sequencing of 16S rRNA gene amplicons. The value of α- and β-diversity of bacterial and archaeal communities generally did not change significantly (P> 0.05) between offshore sites, but changed significantly (P< 0.05) among inshore sites. Sediment pH and salinity showed significant effects on the diversity and keystone taxa of bacterial and archaeal communities. The bacterial and archaeal co-occurrence networks were inextricably linked with pH and salinity to formed the large network nodes, suggesting that they were the key factors to drive the prokaryotic community. We also identified that heterogeneous and homogeneous selection drove the bacterial and archaeal community assembly, while the two selections became weaker from offshore sites to inshore sites, suggesting that deterministic processes were more important in offshore sites. Overall, these results suggested that the environmental filtering of pH and salinity jointly governed the assembly of prokaryotic community in offshore sediments. This study advances our understanding of microbial community assembly in coastal wetland ecosystems.