Estuarine Sites Research Articles

Distribution, sorption patterns, and outflows of riverine microplastics-affiliated linear alkylbenzenes and polycyclic aromatic hydrocarbons in a dynamic coastal zone

Microplastics (MPs) pollution has emerged as a global concern. To mitigate the potential threats by MPs, particularly to coastal regions, it is crucial to comprehend the environmental behavior of MPs and their affiliated chemicals. In the present study, we collected floating MPs using a Manta net (0.33 mm mesh size) in a one-year sampling event in 2022 from the eight major estuaries in the Pearl River Delta, China, and also from five coastal sites in August and December in the same year. Nineteen linear alkylbenzenes (∑19LAB) and 16 polycyclic aromatic hydrocarbons (∑16PAH) affiliated with MPs were measured. The mean concentrations of MPs-affiliated ∑19LAB and ∑16PAH were 6710 (range: 3400–12300) and 5310 (range: 817–19,600) ng g−1, respectively, at the estuarine sites, and were 4920 (range: 2400–7600) and 2610 (range: 911–7890) ng g−1, respectively, at the coastal sites. Significant correlations were found between logarithmic MPs–water partition coefficients (log Kpw) and logarithmic suspended particulate matter–water partition coefficients (log Kd) values for LABs and PAHs, indicating analogous partitioning dynamics for MPs and suspended particulate matter with water. The annual riverine outflows were 1170 and 414 g for ∑19LAB and ∑16PAH, respectively. Although the riverine outflows of LABs and PAHs carried by MPs remain negligible compared to those by suspended particulate matter, an upward trend was identified between 2018 and 2022. Notably, the riverine input of LABs and PAHs carried by suspended particulate matter to the coastal ocean decreased from 2005/2006 to 2022, due to a combination of improved technological processes and energy structures.

A potential tool for marine biogeography: eDNA-dominant fish species differ among coastal habitats and by season concordant with gear-based assessments.

Effective ocean management asks for up-to-date knowledge of marine biogeography. Here we compare eDNA and gear-based assessments of marine fish populations using an approach that focuses on the commonest species. The protocol takes advantage of the "hollow curve" of species abundance distributions, with a minority of species comprising the great majority of individuals or biomass. We analyzed new and published teleost eDNA metabarcoding surveys from three neighboring northwest Atlantic coastal locations representing sandy, rocky, or estuary habitat. Fish eDNA followed a hollow curve species abundance distribution at each location-the 10 commonest taxa accounted for more than 90% of eDNA copies. Top ten taxa were designated eDNA-dominant species (eDDS) and categorized as habitat-associated (top 10 in one study) or as shared. eDDS by category were similarly abundant in concurrent bottom trawl and seine surveys. eDDS habitat category profiles correctly classified most (94%-100%) individual eDNA and capture measurements within surveys and recognized estuarine sites in other regional eDNA and seine studies. Using a category metric like that for habitats, eDDS demonstrated strong seasonal turnover concordant with trawl catch weights. eDNA seasonal profiles applied to historical trawl and seine records highlighted known long-term trends in mid-Atlantic fish populations. This study provides evidence that eDNA-abundant fish species differ among coastal habitats and by season consistent with gear-based assessments. Grouping abundant species by category facilitated comparisons among habitats and integration with established surveys. eDNA metabarcoding of dominant fish species potentially offers a useful tool for marine biogeography and ocean monitoring.

Refining Sampling Efforts for Fish Diversity Assessment in Subtropical Urban Estuarine and Oceanic Waters Using Environmental DNA With Multiple Primers

ABSTRACTThe environmental DNA (eDNA) approach is an emerging tool for monitoring marine biodiversity. However, the sampling effort needs optimization according to the site characteristics and target taxonomic groups. In this study, we optimized the eDNA sampling effort in terms of sample volume and number of replicates to monitor the diversity of marine vertebrates (mainly fish) in Hong Kong's subtropical waters that show a gradient of estuarine to oceanic waters. To maximize detection, we used three pairs of metabarcoding primers (12S‐v5, MiFish‐U, and MiFish‐E). We compared vertebrate diversity in 78 water samples, ranging from 1 to 10 L, collected from oceanic and estuarine sites. Metabarcoding yielded a total of 140 vertebrate species, of which 18 were unique to the estuarine site, 66 unique to the oceanic site, and 56 shared between both sites. The detected species were predominantly ray‐finned fish (136 species), and the three primer pairs exhibited differential sensitivity toward different taxa, especially cartilaginous fish and cetaceans. Increasing sampling volume per replicate generally increased the total detected species, average species per replicate, and species coverage, and sampling 3 or 4 × 4 L represented the most efficient sampling effort for the estuarine and oceanic sites, respectively. The diversity analysis revealed that sampling >2 L per replicate reduced variability and improved diversity analysis. The results also showed that a larger sampling volume per replicate increased the probability of detecting endangered, indicator, invasive, and elusive species, with 4 L representing the most efficient volume. This study recommended sampling 4 L per replicate and 3 replicates for estuarine and 4 for oceanic sites, respectively for effectively monitoring marine fish in subtropical waters using the eDNA approach.

Planktonic ciliate communities along an environmental gradient in the Nile Delta (Damietta region, Egypt)

The spatial patterns of planktonic ciliate communities were studied from May to June 2019 in the Nile Delta’s Damietta region, southeastern Mediterranean. The ciliate communities were sampled from twenty-five sites of five stressed domains with spatial gradients of environmental status. A total of 32 ciliate taxa with six dominant species were identified, comprising 21 tintinnids and 11 aloricate ciliates. The abundance and richness of each ciliate group varied geographically and were most strongly influenced by salinity variations; tintinnid ciliates attained high abundance and richness at high salinity sites in the harbour and coastal region and decreased within the estuary upstream. Aloricate ciliates were poorly represented at most sites but were a substantial proportion of upstream estuarine sites. Multivariate/univariate analyses demonstrated that spatial patterns of the ciliate communities were significantly correlated with environmental variables, especially salinity, chlorophyll-a, and nutrients, either alone or in combination with one another. These results indicate that the ciliates can be useful bioindicators in stressed environments while also allowing the detection of impacts on short time scales by rapidly responding to environmental variations.

Microbial ecology of northern Gulf of Mexico estuarine waters.

Estuarine and coastal ecosystems are of high economic and ecological importance, owing to their diverse communities and the disproportionate role they play in carbon cycling, particularly in carbon sequestration. Organisms inhabiting these environments must overcome strong natural fluctuations in salinity, nutrients, and turbidity, as well as numerous climate change-induced disturbances such as land loss, sea level rise, and, in some locations, increasingly severe tropical cyclones that threaten to disrupt future ecosystem health. The northern Gulf of Mexico (nGoM) along the Louisiana coast contains dozens of estuaries, including the Mississippi-Atchafalaya River outflow, which dramatically influence the region due to their vast upstream watershed. Nevertheless, the microbiology of these estuaries and surrounding coastal environments has received little attention. To improve our understanding of microbial ecology in the understudied coastal nGoM, we conducted a 16S rRNA gene amplicon survey at eight sites and multiple time points along the Louisiana coast and one inland swamp spanning freshwater to high brackish salinities, totaling 47 duplicated Sterivex (0.2-2.7 µm) and prefilter (>2.7 µm) samples. We cataloged over 13,000 Amplicon Sequence ariants (ASVs) from common freshwater and marine clades such as SAR11 (Alphaproteobacteria), Synechococcus (Cyanobacteria), and acI and Candidatus Actinomarina (Actinobacteria). We observed correlations with freshwater or marine habitats in many organisms and characterized a group of taxa with specialized distributions across brackish water sites, supporting the hypothesis of an endogenous brackish-water community. Additionally, we observed brackish-water associations for several aquatic clades typically considered marine or freshwater taxa, such as SAR11 subclade II, SAR324, and the acI Actinobacteria. The data presented here expand the geographic coverage of microbial ecology in estuarine communities, help delineate the native and transitory members of these environments, and provide critical aquatic microbiological baseline data for coastal and estuarine sites in the nGoM.IMPORTANCEEstuarine and coastal waters are diverse ecosystems influenced by tidal fluxes, interconnected wetlands, and river outflows, which are of high economic and ecological importance. Microorganisms play a pivotal role in estuaries as "first responders" and ecosystem architects, yet despite their ecological importance, they remain underrepresented in microbial studies compared to open ocean environments. This leads to substantial knowledge gaps that are important for understanding global biogeochemical cycling and making decisions about conservation and management strategies in these environments. Our study makes key contributions to the microbial ecology of estuarine and coastal habitats in the northern Gulf of Mexico. Our microbial community data support the concept of a globally distributed, core brackish microbiome and emphasize previously underrecognized brackish-water taxa. Given the projected worsening of land loss, oil spills, and natural disasters in this region, our results will serve as important baseline data for researchers investigating the microbial communities found across estuaries.

Environmental DNA metabarcoding reveals fish diversity, community assembly and one invasive species prevalence in a National Park of Liaohe in September

The escalating environmental changes are imposing multiple pressures on biodiversity conservation, thereby, more attention has been paid to fish diversity and community assembly patterns. Fish diversity in Liaohe River has deteriorated significantly due to overfishing, environmental pollution and other reasons, in addition, no fish survey related research has been published in Liaohe National Park in recent years. In order to study the diversity of fish species in the area and to investigate the presence of any invasive species. This study used eDNA metabarcoding to explore the distribution and diversity of fish communities in the Liaohe National Park. The study showed that a total of 54 species of fish from six orders, 14 families, and 39 genera were detected, meantime, the invasive species Lepomis cyanellus was found at two sampling sites. The α-diversity results showed that estuarine sites had the highest species diversity. The spatial structure of fish communities in the upstream and downstream reaches were similar as indicated by non-metric multidimensional scaling. In our study, the fish community is influenced by both deterministic and stochastic processes, with the stochastic processes being the main factor. The potential existence of L. cyanellus in Liaohe National Park might be resulted from aquaculture, ornamental pet trade, other economic fish farming, artificial release. The relatively low number of fish species in this study may be attributed to the limited number of sampling events and sampling sites. In addition to these factors, over exploitation of resources, water pollution, and the invasion of alien species have directly impacted the biodiversity of aquatic life. The results of this study lay a foundation for the future biodiversity investigation in National Parks of China, meantime, the use of eDNA monitoring is crucial to prevent, to control and limit the spreading of invasive species in advance.

The Microphytobenthos are Abundant and Mediate Key Carbon Fluxes in Tropical Mangroves

AbstractThe microphytobenthos (MPB) are known to play important ecological roles in estuarine ecosystems. While tidal flat MPB are widely studied, mangrove MPB are often overlooked due to the common belief that the light-limited environment under the mangrove canopy is not conducive to MPB growth. We assessed the biomass and community characteristics of the MPB in two contrasting mangrove forests (silty substrate and brackish influence versus sandy substrate and oceanic influence), their seasonal photosynthetic performance, as well as their role in mediating porewater carbon flux. Biomass measured as chlorophyll a concentration indicated that MPB abundance was equal, if not higher, in mangroves than on tidal flats. While mangrove sediments fostered an equally rich assemblage of MPB (estimated 23 to 45 genera) as the adjacent tidal flat, the MPB genus composition was different across all habitats, sites, and seasons, indicating the strong environmental influence on MPB assemblages. This study identified porewater salinity, temperature, and pH, as well as irradiance level and surface soil temperature to be accountable for 23.5% of this variation. MPB in all sampling locations were dominated by pennate diatoms, while cyanobacteria were common in the estuarine (as opposed to oceanic) site. Compared to tidal flat MPB, mangrove MPB exhibited photosynthetic performance characteristic of lower light acclimation. A mesocosm experiment using enriched stable isotopes of carbon and nitrogen indicated that a tight coupling exists between mangrove-derived carbon and MPB. Mangrove MPB are abundant and different from tidal flat MPB, and are functional photosynthetic entities with a regulatory role in nutrient cycling in mangrove ecosystems.

The reproductive biology of Ellochelon vaigiensis from the Vietnamese Mekong Delta.

The Squaretail mullet, Ellochelon vaigiensis, is a commercial fish species distributed throughout the Indo-Pacific region. This species tolerates wide variations in salinity, having been reported from both freshwater and marine habitats. Although economically significant, there is little information on its reproduction, especially in the Vietnamese Mekong Delta (VMD), where it is heavily extracted. Our study elucidates the breeding pattern, seasonality, first length at maturity, as well as potential and relative fecundity of this species. Fish specimens were collected by trawl nets from November 2020 to October 2021 at four estuarine sites within the VMD. We found this species to be a synchronous spawner, with peaks in reproductive activity from June to September. In the populations we surveyed, there was significant dominance of males (1.26:1.00) based on 942 fish samples (526 males and 416 females). The length at 50% maturity for females was significantly higher than for males at all sites and ranged from 10.6 to 19.3 cm. The diameter of the eggs examined for this species exhibited slight variation, from 0.43 to 0.54 mm. The potential fecundity ranged from 246,254 ± 35,878 to 411,970 ± 54,370 eggs, corresponding to female length and weight of 26.7-32.6 cm and 102.97-234.19 g, respectively. Relative fecundity values were highest at Thanh Phu, Ben Tre (6388 ± 605 eggs), and Dong Hai, Bac Lieu (6461 ± 637 eggs), followed by Tran De, Soc Trang (4729 ± 408), and were found to be lowest at Duyen Hai, Tra Vinh (3117 ± 223 eggs). Information on reproductive behavior in this species has far-reaching impacts on sustainable extractions, stock conservation, and aquaculture.

Estimating the Seasonality of Bent-Nose Clam (Macoma nasuta) Harvesting at a 3,000-Year-Old Ancestral Ohlone Site (CA-ALA-11) on the San Francisco Bay

ABSTRACT This article investigates the harvest month for bent-nose clams (Macoma nasuta) at CA-ALA-11, an estuarine site in the modern-day city of Alameda along the San Francisco Bay. The archaeological deposit in which the clam shells were recovered dates primarily to the Early Period (3,350–2,550 cal BP) and Early-Middle Transition (2,550–2,150 cal BP), although some activity continues through 2,650 BP. Season of harvest estimates for clams offers insight into Indigenous use of estuarine resources and the degree of sedentism or length of habitation at this locality. Water salinity varies predictably in San Francisco Bay, from annual lows in winter to highs in summer. We used oxygen isotopes (δ18O) to estimate season of harvest by sampling at the intact terminal growth edge of the shell, which records salinity at the time of harvest. Three additional samples represent earlier periods of shell growth. Results show that while clams comprise a minority of the shellfish harvested, clamming took place between January and August, with a marked peak in mid-winter (February). There is no evidence for fall harvesting, which suggests that people were either not living at CA-ALA-11 during this time or focused on acquiring other seasonally available foods. We compare these results to previously published data on seasonality of clam harvesting from five other San Francisco Bay area sites.

Evaluating environmental DNA detection of a rare fish in turbid water using field and experimental approaches.

Detection sensitivity of aquatic species using environmental DNA (eDNA) generally decreases in turbid water but is poorly characterized. In this study, eDNA detection targeted delta smelt (Hypomesus transpacificus), a critically endangered estuarine fish associated with turbid water. eDNA sampling in the field was first paired with a trawl survey. Species-specific detection using a Taqman qPCR assay showed concordance between the methods, but a weak eDNA signal. Informed by the results of field sampling, an experiment was designed to assess how turbidity and filtration methods influence detection of a rare target. Water from non-turbid (5 NTU) and turbid (50 NTU) estuarine sites was spiked with small volumes (0.5 and 1 mL) of water from a delta smelt tank to generate low eDNA concentrations. Samples were filtered using four filter types: cartridge filters (pore size 0.45 μm) and 47 mm filters (glass fiber, pore size 1.6 μm and polycarbonate, pore sizes 5 and 10 μm). Prefiltration was also tested as an addition to the filtration protocol for turbid water samples. eDNA copy numbers were analyzed using a censored data method for qPCR data. The assay limits and lack of PCR inhibition indicated an optimized assay. Glass fiber filters yielded the highest detection rates and eDNA copies in non-turbid and turbid water. Prefiltration improved detection in turbid water only when used with cartridge and polycarbonate filters. Statistical analysis identified turbidity as a significant effect on detection probability and eDNA copies detected; filter type and an interaction between filter type and prefilter were significant effects on eDNA copies detected, suggesting that particulate-filter interactions can affect detection sensitivity. Pilot experiments and transparent criteria for positive detection could improve eDNA surveys of rare species in turbid environments.

Prokaryote communities along a source-to-estuary river continuum in the Brazilian Atlantic Forest.

The activities of microbiomes in river sediments play an important role in sustaining ecosystem functions by driving many biogeochemical cycles. However, river ecosystems are frequently affected by anthropogenic activities, which may lead to microbial biodiversity loss and/or changes in ecosystem functions and related services. While parts of the Atlantic Forest biome stretching along much of the eastern coast of South America are protected by governmental conservation efforts, an estimated 89% of these areas in Brazil are under threat. This adds urgency to the characterization of prokaryotic communities in this vast and highly diverse biome. Here, we present prokaryotic sediment communities in the tropical Juliana River system at three sites, an upstream site near the river source in the mountains (Source) to a site in the middle reaches (Valley) and an estuarine site near the urban center of Ituberá (Mangrove). The diversity and composition of the communities were compared at these sites, along with environmental conditions, the former by using qualitative and quantitative analyses of 16S rRNA gene amplicons. While the communities included distinct populations at each site, a suite of core taxa accounted for the majority of the populations at all sites. Prokaryote diversity was highest in the sediments of the Mangrove site and lowest at the Valley site. The highest number of genera exclusive to a given site was found at the Source site, followed by the Mangrove site, which contained some archaeal genera not present at the freshwater sites. Copper (Cu) concentrations were related to differences in communities among sites, but none of the other environmental factors we determined was found to have a significant influence. This may be partly due to an urban imprint on the Mangrove site by providing organic carbon and nutrients via domestic effluents.

Storms mobilize organophosphate esters, bisphenols, PFASs, and vehicle-derived contaminants to San Francisco Bay watersheds.

In urban to peri-urban watersheds such as those surrounding San Francisco Bay, stormwater runoff is a major pathway by which contaminants enter aquatic ecosystems. We evaluated the occurrence of 154 organic contaminants via liquid chromatography coupled to tandem mass spectrometry, including organophosphate esters (OPEs), bisphenols, per- and polyfluoroalkyl substances (PFASs), and a suite of novel urban stormwater tracers (SWCECs; i.e., vehicle-derived chemicals, pesticides, pharmaceuticals/personal care products, benzothiazoles/benzotriazoles). Time-averaged composite sampling focused on storms in highly developed watersheds over four wet seasons, with complementary sampling in less-urban reference watersheds, near-shore estuarine sites, and the open Bay. Of the targeted contaminants, 68 (21 SWCECs, 29 OPEs, 3 bisphenols, 15 PFASs) were detected in ≥10 of 26 urban stormwater samples. Median concentrations exceeded 500 ng L-1 for 1,3-diphenylguanidine, hexa(methoxymethyl)melamine, and caffeine, and exceeded 300 ng L-1 for 2-hydroxy-benzothiazole, 5-methyl-1H-benzotriazole, pentachlorophenol, and tris(2-butoxyethyl) phosphate. Median individual PFAS concentrations were <10 ng L-1, with highest concentrations for PFHxA (180 ng L-1), PFOA (110 ng L-1), and PFOS (81 ng L-1). In six of eight urban stormwater samples analyzed for 6PPD-quinone (a tire rubber-derived transformation product), concentrations exceeded coho salmon acute toxicity thresholds, suggesting (sub)lethal impacts for sensitive species. Observed concentrations were generally significantly higher in highly developed watersheds relative to reference watersheds, but not statistically different in near-shore estuarine sites, suggesting substantial transient exposure potential at stormwater outfalls or creek outflows. Results emphasized the role of stormwater in contaminant transport, the importance of vehicles/roadways as contaminant sources, and the value of monitoring broad multi-analyte contaminant suites to enable comprehensive source and toxicity evaluations.

Metagenomic analysis of microbial communities and antibiotic resistant genes in the Tijuana river, and potential sources

The Tijuana River is a transborder river that flows northwest across the border from Baja California in Mexico into Southern California before discharging into the Pacific Ocean. The river is frequently contaminated with raw sewage due to inadequate sanitary infrastructure in Tijuana. To assess the type and degree of microbial contamination, water samples were collected monthly from a near-border and an estuarine site from August 2020 until May 2021. A portion of each sample was used for epifluorescent microscopy and DNA was extracted directly from the rest for shotgun metagenomic sequencing. After sequence quality checking and processing, we used the rapid taxonomic identifier tool Kaiju to characterize the microbial diversity of the metagenomes and matched the sequences against the Comprehensive Antibiotic Resistance Database (CARD) to examine antimicrobial resistance genes (ARGs). Bacterial and viral-like particle (VLP) abundance was consistently higher in the near-border samples than in the estuarine samples, while alpha diversity (within sample biodiversity) was higher in estuarine samples. Beta-diversity analysis found clear compositional separation between samples from the two sites, and the near-border samples were more dissimilar to one another than were the estuarine sites. Near-border samples were dominated by fecal-associated bacteria and bacteria associated with sewage sludge, while estuarine sites were dominated by marine bacteria. ARGs were more abundant at the near-border site, but were also readily detectable in the estuarine samples, and the most abundant ARGs had multi-resistance to beta-lactam antibiotics. SourceTracker analysis identified human feces and sewage sludge to be the largest contributors to the near-border samples, while marine waters dominated estuarine samples except for two sewage overflow dates with high fecal contamination. Overall, our research determined human sewage microbes to be common in the Tijuana River, and the prevalence of ARGs confirms the importance of planned infrastructure treatment upgrades for environmental health.

High resolution dissolved heavy metals in sediment porewater of a small estuary: Distribution, mobilization and migration

Identifying the distribution features, mobilization mechanisms and migration processes of heavy metals (HMs) in estuarine sediments is essential to predict their potential toxicity risk and for following contamination remediation. In this study, high-resolution dialysis (HR-Peeper) and a sequential extraction procedure were employed to determine the porewater dissolved iron (Fe), manganese (Mn), arsenic (As), chromium (Cr), vanadium (V), selenium (Se), molybdenum (Mo), nickel (Ni), zinc (Zn) and their geochemical species fractions in sediments of the Xixi River Estuary, Xiamen, China. The results showed that at estuarine sites with high TOC and TS content, sulfate reduction is the main diagenetic pathway of OC degradation and directly inhibits the reduction of Fe/Mn oxides. The mobility of most HMs in porewater profiles was influenced by multiple factors, such as the adsorption-desorption by Fe/Mn oxides, HM-sulfide co-precipitation, and the degradation of OM under different redox conditions. However, no environmental correlation and control factors of Ni and Zn have been found. In addition, the profile-averaged distribution of most HMs showed a seaward increasing trend, probably due to the severe industrial wastewater discharge and increasing salinity responsible for the competitive adsorption of HM ions. The overall positive fluxes of all HMs, together with the higher positive diffusion fluxes of some HMs such as Mn, Cr, V and Zn, suggest that the HMs mobility in small estuarine sediments should be seriously reconsidered due to its high contamination potential.

Integrating chemical and biological data by chemometrics to evaluate detoxification responses of a neotropical bivalve to metal and metalloid contamination

Mangroves represent a challenge in monitoring studies due to their physical and chemical conditions under constant marine and anthropogenic influences. This study investigated metals/metalloids whole-body bioaccumulation (soft tissues) and the risk associated with their uptake, biochemical and morphological detoxification processes in gills and metals/metalloids immobilisation in shells of the neotropical sentinel oyster Crassostrea rhizophorae from two Brazilian estuarine sites. Biochemical and morphological responses indicated three main mechanisms: (1) catalase, superoxide dismutase and glutathione played important roles as the first defence against reactive oxygen species; (2) antioxidant capacity against peroxyl radicals, glutathione S-transferase, metallothionein prevent protein damage and (3) metals/metalloids sequestration into oyster shells as a mechanism of oyster detoxification. However, the estimated daily intake, target hazard quotient, and hazard index showed that the human consumption of oysters would not represent a human health risk. Among 14 analysed metals/metalloids, chemometrics indicate that Mn, As, Pb, Zn and Fe overload the antioxidant system leading to morphological alterations in gills. Overall, results indicated cellular vacuolization and increases in mucous cell density as defence mechanisms to prevent metals/metalloids accumulation and the reduction in gill cilia; these have long-term implications in respiration and feeding and, consequently, for growth and development. The integration of data from different sites and environmental conditions using chemometrics highlights the main biological patterns of detoxification from a neotropical estuarine bivalve, indicating the way in which species can cope with metals/metalloids contamination and its ecological consequences.

Integrated multi-trophic aquaculture with sugar kelp and oysters in a shallow coastal salt pond and open estuary site.

Sustainable aquaculture includes the aquaculture of non-fed crops that provide ecosystem services including nutrient extraction and water quality improvement. While shellfish are the most farmed sustainable aquaculture crops in the USA, shellfish farmers in the northeastern US have an interest in diversifying their crops and incorporating seaweeds into their farms. In this study, we worked with oyster farmers to investigate the potential for farming sugar kelp, Saccharina latissima, across different environmental regimes in coastal Rhode Island USA. Kelp seed spools were outplanted at two time points in the fall/winter of 2017 and 2018 at four sites and cultivated until harvest the following spring. Kelp performance (length, width, yield), tissue content, and nutrient extraction were determined for each line in each year; oyster growth was also measured monthly for one year at each site. We found that kelp could successfully grow in both shallow coastal lagoons and estuarine sites, although the timing of planting and placement of sites was important. Lines that were planted earlier (as soon as water temperatures<15°C) grew longer and yielded more biomass at harvest; overall, kelp blade yield ranged from 0.36 ± 0.01 to 11.26 ± 2.18 kg/m long line. We report little variation in the tissue quality (C:N) of kelp among sites, but differences in biomass production led to differences in nutrient extraction, which ranged from 0.28 ± 0.04 to 16.35 ± 4.26 g nitrogen/m long line and 8.93 ± 0.35 to 286.30 ± 74.66 g carbon/m long line. We found extensive variability in kelp growth within and between lines and between years, suggesting that crop consistency is a challenge for kelp farmers in the region. Our results suggest that, as there is a lower barrier in terms of permitting (versus starting a new aquaculture farm), it may be a worthwhile investment to add sugar kelp to existing oyster farms, provided they have suitable conditions. At current market rates of US$0.88-$3.30 per kg, farmers in southern New England have the potential to earn US$2,229 per 60 m longline. While seaweed aquaculture is growing, considerable barriers still exist that prevent wide-scale kelp aquaculture adoption by existing aquafarmers.

Environmental DNA metabarcoding revealed the impacts of anthropogenic activities on phytoplankton diversity in Dianchi Lake and its three inflow rivers.

Phytoplankton diversity is closely related to environmental variables and has been widely used in ecological health assessment of rivers and lakes. Combining advantages of DNA-based identification and high-throughput sequencing technology, environmental DNA (eDNA) metabarcoding permits a new measurement for biodiversity monitoring in aquatic ecosystems. However, it had rarely been used to explore the variability and similarity of phytoplankton diversity between lake and its inflow rivers and the effects of environmental variables on phytoplankton. This study utilized eDNA metabarcoding to investigate the spatial distribution of phytoplankton and the impacts of environmental variables on the phytoplankton diversity in Dianchi Lake (one of the most polluted urban lakes in China) and its main inflow rivers (Panlong River, Baoxiang River, and Chai River). A total of 243 distinct phytoplankton taxa were detected, covering 9 phyla, 30 classes, 84 orders, and 132 families, and the taxonomic richness of rivers was higher than that of Dianchi Lake. Distinct biodiversity patterns (e.g., community structure, dominant taxon, ɑ-diversity) were exhibited among Dianchi Lake and its three inflow rivers, but similar biodiversity patterns were also observed in Dianchi Lake and the estuarine sites. The patterns of phytoplankton diversity were closely related to environmental variables, which were associated with pollution sources from different anthropogenic activities (e.g., urbanization, water diversion, industrial and agricultural activities). The primary environmental variables correlated with phytoplankton diversity varied in different habitats. The total phosphorus (TP) and chemical oxygen demand (COD) positively correlated with the phytoplankton community structures in Dianchi Lake, whereas negatively correlated in Panlong River and Baoxiang River. The total nitrogen (TN) positively correlated with the phytoplankton community structures in Baoxiang River and Chai River but negatively correlated in Dianchi Lake. Overall, this study provides insights on the phytoplankton diversity monitoring and the conservation of its diversity and healthy management of Dianchi Lake.

Basin-specific pollution and impoundment effects on greenhouse gas distributions in three rivers and estuaries

Large uncertainties exist regarding the combined effects of pollution and impoundment on riverine greenhouse gas (GHG) emissions. It has also been debated whether river eutrophication can transform downstream estuaries into carbon sinks. To assess human impacts on the riverine and estuarine distributions of CO2, CH4, and N2O, two source-to-estuary surveys along three impounded rivers in Korea were combined with multiple samplings at five or six estuarine sites. The basin-wide surveys revealed predominant pollution effects generating localized hotspots of riverine GHGs along metropolitan areas. The localized pollution effect was pronounced in the lower Han River and estuary adjacent to Seoul, while the highest GHG levels in the upper Yeongsan traversing Gwangju were not carried over into the faraway estuary. CH4 levels were elevated across the eutrophic middle Nakdong reaches regulated by eight cascade weirs in contrast to undersaturated CO2 indicating enhanced phytoplankton production. The levels of all three GHGs tended to be higher in the Han estuary across seasons. Higher summer-time δ13C-CH4 values at some Nakdong and Yeongsan estuarine sites implied that temperature-enhanced CH4 production may have been dampened by increased CH4 oxidation. Our results suggest that the location and magnitude of pollution sources and impoundments control basin-specific longitudinal GHG distributions and estuarine carryover effects, warning against simple generalizations of eutrophic rivers and estuaries as carbon sinks.

The importance of blue carbon as a food source to oysters (Saccostrea cucullata) inside a tropical pristine Australian estuary

This study investigated the importance of blue carbon (carbon captured from the atmosphere by algae, mangrove and seagrass leaves) as a component of particulate organic matter (POM) along the pristine King George River (Kimberley region, Australia), and how this modulates the diet of common suspension feeding bivalves (Mussels: Brachidontes sp. and Oysters: Saccostrea cucullata). These species utilise a range of different carbon sources (e.g., mangrove and seagrass detritus and plankton), which dictate the composition of locally available POM), which could then be used to evaluate shifts in consumer diet away from blue carbon within the estuary, to an increasing reliance on marine phytoplankton in offshore areas. The differences in δ13C of different organs (i.e., mantle, gill and adductor muscle) of oysters further affirm a greater discrepancy between ‘slow-turnover’ muscle and ‘fast-turnover’ gill and mantle tissue at offshore sites, when compared to inner estuarine sites.

A Synopsis of Introduced and Native Seaweeds from 14 Open Coastal and Estuarine Sites within Southern Maine and New Hampshire, U.S.A.

Floristic studies of introduced and native seaweed populations from 14 open coastal and estuarine sites within southern Maine and New Hampshire were documented between 1965 and 2017. A total of 186 seaweed taxa were recorded, including 15 introduced (8.1%) and 171 native (91.9%) species. The highest species diversity (123 taxa) occurred at the open coastal Seapoint Beach site in Kittery, Maine, and an estuarine tidal rapid site at Dover Point, New Hampshire, with 106 taxa. The numbers of introduced species per site ranged from 2–11. The percent occurrence patterns for the 15 introduced seaweeds were highly variable, with Codium fragile subsp. fragile and Ulonema rhizophorum being restricted to single sites (7%), Melanothamnus harveyi occurring at 12 sites (86%), and Agarophyton vermiculophyllum and Dasysiphonia japonica at 13 sites (93%). The geographical origins and initial collection dates for the 15 introduced taxa were highly variable, with their initial collections ranging from 1848 (M. harveyi) to 2007 (D. japonica). Codium fragile subsp. fragile had the most protracted period between its initial occurrence at Orient Point, New York, in 1957 and in northern New England 40 years later (i.e., 1997). By contrast, several other introduced taxa had rapid geographic expansions within five years. The numbers and abundance of introduced species in the Gulf of Maine have increased dramatically between 1986 and 2017, with nine recorded in 1986 and 15 in 2017. Two native warm-water red algae (Agardhiella subulata and Gelidium crinale) showed sudden northward expansions during 2016 and 2017, respectively. Their presence may be associated with global warming, which is presently occurring at an alarming rate within the Gulf of Maine and exceeds many areas within the world.