Shallow Coastal Systems Research Articles

Effects of Diel Oxygen Cycling and Benthic Macrofauna on Sediment Oxygen Demand

This field study examined how sediment macroinfauna change patterns of sediment oxygen demand (SOD) throughout a diel oxygen cycle. Sediments with a greater faunal presence would be expected to have greater overall SOD, and at night may alter their behavior and influence SOD depending on their response to low-oxygen stress. Dynamic faunal bioturbation or bioirrigation behavior would also result in corresponding variation in SOD values on short time scales. In situ flow-through benthic metabolism chambers were used to measure SOD at a high temporal resolution in discrete sediment patches. Sediments with more macroinfauna had greater average SOD over the diel cycle, consistent with previous studies. Where more macroinfauna were present, they drove greater SOD during nightly low oxygen, presumably by enhancing their burrowing and irrigation activities. SOD was also more variable on a sub-diel timescale in sediments with more macroinfauna. Sediment oxygen demand is dynamic and highly sensitive both temporally, on very short timescales, and spatially, in terms of resident fauna, and their interaction produces heretofore unaccounted complexity in patterns of SOD particularly in shallow coastal systems. Extrapolations of temporally and spatially limited SOD measurements to a system-wide scale that do not account for the short-term and spatially variable effects of fauna may produce imprecise and misleading estimates of this critical ecosystem function.

Mapping marine habitats in a shallow beach-reef environment combining direct methods and hyperspectral remote sensing

Human occupation of coastal strips generates pressures that can trigger severe degradation processes in marine ecosystems and threaten human livelihoods and the sustainability of the socio-ecological system. In this context, monitoring the conservation status of algal and benthic plant communities, as the basis of coastal ecosystems, is essential for the sustainability of coastal environments. The paper presents a bionomic investigation in a shallow water beach-reef coastal system called Las Canteras, in the Canary Islands (Spain). The work aims to generate a high-resolution mapping, according to standardised rules, of the marine habitats of an area with high ecological value showing signs of severe degradation due to anthropogenic pressure. For this purpose, direct observation techniques were combined with hyperspectral remote sensing techniques. The bathymetric, sedimentological and biological data collected were combined to generate detailed mapping of 13 marine habitats according to the Spanish Inventory of Marine Habitats and Species (IEHEM by its initials in Spanish) classification system. Comparison of these results with previous studies since 1960 shows total regression of the most sensitive species of marine habitats in the Canary Islands, such as Cymodocea nodosa, as well as the decline of sandy substrates which are fundamental for maintenance of the local coastal socio-ecological system.

Eelgrass (Zostera marina L.) populations are threatened by high sea-surface temperatures and impaired waters on Nantucket Island, USA

Eelgrass (Zostera marina L.) is a key foundation species that provides multiple ecosystem services to shallow coastal and estuarine systems in the Northern Hemisphere. It is estimated that, over the last century, up to 50 % of all Z. marina habitat has been lost along the east coast of the USA due to factors including light reduction, eutrophication, and physical disturbance. Warming sea surface temperatures are also believed to be exacerbating losses and the future of this ecosystem is unclear. Here, we assess Z. marina meadows on Nantucket, an island system located 50 km off-shore of Massachusetts, by using common indicators of seagrass plant health and environmental quality. Our results show that Z. marina meadows on Nantucket Island are thermally stressed and light-limited during parts of their peak growing season. This suggests that sea-surface temperatures are a pivotal factor, along with cultural eutrophication, in observed large-scale losses of Z. marina and that further degradation could be expected in the future as the climate continues to warm. Methods from this study may be used by managers as a guide to assess seagrass ecosystem status in degrading systems.

Temperature amplification and marine heatwave alteration in shallow coastal bays

Shallow coastal ecosystems are threatened by marine heatwaves, but few long-term records exist to quantify these heatwaves. Here, 40-year records of measured water temperature were constructed for a site in a system of shallow bays with documented heatwave impacts and a nearby ocean site; available gridded sea-surface temperature datasets in the region were also examined. Water temperatures at both sites increased significantly though bay temperatures were consistently 3-4°C hotter in summer and colder in winter and were more variable overall, differences not captured in high-resolution gridded sea-surface temperature datasets. There was considerable overlap in heatwave events at the coastal bay and ocean sites. Annual heatwave exposure was similar and significantly increased at both sites while annual heatwave intensity was significantly higher at the bay site owing to the high variance of the daily temperature anomaly there. Event frequency at both sites increased at a rate of about 1 event/decade. Future simulations indicate all heatwave metrics increase, as do days above 28°C, a heat stress threshold for seagrass. Ocean temperatures on the U.S. mid-Atlantic margin have rarely exceeded this threshold, while summer bay temperatures commonly do, allowing ocean exchange with coastal bays to provide thermal relief to bay ecosystems. This will have changed by 2100, creating a thermal environment that threatens seagrass communities in these systems. Documenting such change requires development of long-term water temperature records in more shallow coastal systems.

Microphytobenthic impact on benthic pelagic nutrient exchange in temperate shallow estuaries

Microphytobenthos (MPB) form a light-sensitive “nutrient filter” between sediment and bottom water in shallow coastal systems and the MPB activity is believed to have important implications for nutrient availability in such systems. We quantified this light-driven control on nutrient fluxes by analyzing benthic flux measurements from >3000 sediment cores sampled in five Danish estuaries. Light responses and the seasonality of benthic primary production (BPP), benthic nutrient fluxes and the MPB impact on these fluxes showed that MPB significantly intercepted fluxes of ammonium (NH4+), nitrate (NO3−) and dissolved silica (DSi) both under light and dark conditions. Phosphate (PO43−) fluxes were only significantly intercepted in light. The microphytobenthos had a large relative impact on nutrient fluxes during spring and a weaker impact in the autumn, despite significant photosynthetic activity of the MPB at this time of the year. The proportion of the annual sediment-water flux impacted by MPB reached maximum values of 65%, 73%, 89% and 96% for NH4+, NO3−, PO43− and DSi, respectively. The relative impact depended on the magnitude of the base fluxes and the relative impact increased with light availability at the stations above a threshold of 5% light at the seafloor. This documents that changing light regimes alter the MPB control on nutrient dynamics in shallow systems.

An in situ benthic chamber system for improved temporal and spatial resolution measurement of sediment oxygen demand

AbstractIn shallow coastal systems, sediments are exposed to dramatic and complex variability in environmental conditions that influences sediment processes on short timescales. Sediment oxygen demand (SOD), or consumption of oxygen by sediment‐dwelling organisms and chemical reactions within sediments, is one such process and an important metric of aquatic ecosystem functioning and health. The most common instruments used to measure SOD in situ are batch‐style benthic chambers, which generally require long measurement periods to resolve fluxes and thus do not capture the high temporal variability in SOD that can be driven by dynamic coastal processes. These techniques also preclude linking changes in SOD through time to specific features of the sediment, for example, shifts in sediment faunal activities which can vary on short time scales and can also be affected by ambient oxygen concentrations. Here we present an in situ semi‐flow through instrument to repeatedly measure SOD in discrete areas of sediment. The system isolates patches of sediment in replicate benthic chambers, and measures and records oxygen decrease for a short time before refreshing the overlying water in the chamber with water from the external environment. This results in a sawtooth pattern in which each tooth is an incubation, providing an automated method to produce direct measurements of in situ SOD that can be directly linked to an area of sediment and related to rapid shifts in environmental conditions.

Two new species of Cymbasoma (Multicrustacea: Copepoda: Monstrilloida: Monstrillidae) from the North Atlantic

ABSTRACT Monstrilloid copepods are protelean endoparasites of benthic invertebrates. Their adult free-living stage is chiefly found in the plankton of shallow coastal systems, estuaries and coral reefs; there are no previous records of monstrilloids from deeper marine habitats including epipelagic or mesopelagic waters. Two new species of the monstrilloid copepod genus Cymbasoma Thompson, 1888 are described based on adult females incidentally captured by an epibenthic sledge operated at a depth range of 118–302 m off north-west Iceland and the Norway Channel. Cymbasoma norvegicum sp. nov. is distinguished by a combination of characters including a long, constricted anal somite, bilobed fifth legs with long inner lobe, antennules with fused segments, and first antennule segment unarmed. Cymbasoma pedroi sp. nov. has a pair of rounded posterolateral protuberances on the genital somite, fused fifth legs lobes, and an anteriorly produced, ornamented forehead. Both species are considered new members of the Cymbasoma rigidum species group, widely distributed in different geographic areas but not previously known from epi-mesopelagic depths. The finding of these new species represents the first discovery of monstrilloids at epi-mesopelagic depths in the Pacific Ocean and it significantly adds to our knowledge of this copepod order, thus highlighting their potentially high yet unstudied diversity in deeper waters. http://www.zoobank.org/urn:lsid:zoobank.org:pub:C05EEC28-9936-41CB-BC9E-D990AE53B3B1

Modeling Coastal Water Clarity Using Landsat‐8 and Sentinel‐2

AbstractUnderstanding and attributing changes to water quality is essential to the study and management of coastal ecosystems and the ecological functions they sustain (e.g., primary productivity, predation, and submerged aquatic vegetation growth). However, describing patterns of water clarity—a key aspect of water quality—over meaningful scales in space and time is challenged by high spatial and temporal variability due to natural and anthropogenic processes. Regionally tuned satellite algorithms can provide a more complete understanding of coastal water clarity changes and drivers. In this study, we used open‐access satellite data and low‐cost in situ methods to improve estimates of water clarity in an optically complex coastal water body. Specifically, we created a remote sensing water clarity product by compiling Landsat‐8 and Sentinel‐2 reflectance data with long‐term Secchi depth measurements at 12 sites over 8 years in a shallow turbid coastal lagoon system in Virginia, USA. Our satellite‐based model explained ∼33% of the variation in in situ water clarity. Our approach increases the spatiotemporal coverage of in situ water clarity data and improves estimates from bio‐optical algorithms that overpredicted water clarity. This could lead to a better understanding of water clarity changes and drivers to better predict how water quality will change in the future.

A regional analysis of tide-surge interactions during extreme water levels in complex coastal systems of Aotearoa New Zealand

Tide-surge interaction (TSI) is a critical factor in assessing flooding in shallow coastal systems, particularly in estuaries and harbours. Non-linear interactions between tides and surges can occur due to the water depth and bed friction. Global investigations have been conducted to examine TSI, but its occurrence and impact on water levels in Aotearoa New Zealand (NZ) have not been extensively studied. Water level observations from 36 tide gauges across the diverse coast of NZ were analysed to determine the occurrence and location of TSI. Statistical analysis and numerical modelling were conducted on data from both inside and outside estuaries, focusing on one estuary (Manukau Harbour) to determine the impact of TSI and estuarine morphology on the co-occurrence rate of extreme events. TSI was found to occur at most sites in NZ and primarily affects the timing of the largest surges relative to high tide. There were no regional patterns associated with the tide, non-tidal residual, or skew-surge regimes. The strongest TSI occurred in inner estuarine locations and was correlated with the intertidal area. The magnitude of the TSI varied depending on the method used, ranging from -16 cm to +27 cm. Co-occurrence rates of extreme water levels outside and inside the same estuary varied from 20% to 84%, with TSI modulating the rate by affecting tidal amplification. The results highlight the importance of investing in a more extensive tide gauge network to provide longer observations in highly populated estuarine coastlines. The incorporation of TSI in flooding hazard projections would benefit from more accurate and detailed observations, particularly in estuaries with high morphological complexity. TSI occurs in most sites along the coast of NZ and has a significant impact on water levels in inner estuarine locations. TSI modulates the co-occurrence rate of extreme water levels in estuaries of NZ by affecting tidal amplification. Therefore, further investment in the tide gauge network is needed to provide more accurate observations to incorporate TSI in flooding hazard projections.

High contribution of picophytoplankton to phytoplankton biomass in a shallow, eutrophic coastal sea

We explored picophytoplankton in the surface (0 m) and bottom (2.3–8.7 m) layers of a shallow (<10 m) eutrophic coastal system (Isahaya Bay, Japan). We found that picophytoplankton (principally Synechococcus) constituted the major phytoplankton in spring and summer. The chlorophyll a (chl.a) concentration in the 0.7–2.0-μm picophytoplankton fraction (hereinafter ‘pico-sized chl. a’) and picophytoplankton abundance in Isahaya Bay were higher than those in other eutrophic coastal waters. The pico-sized chl. a concentration and the picophytoplankton abundance counted with an epifluorescence microscope was up to 49.31 μg L−1 and 1.9 × 106 cells mL−1, respectively. Higher contributions of pico-sized chl. a to the total chl. a were evident in summer (up to 63.5%), relative to spring (up to 32.1%), at both depths. Picophytoplankton abundance and the pico-sized chl. a concentration was positively correlated with water temperature and dissolved inorganic phosphorus (DIP) concentrations. Thus, both temperature and DIP may be major controllers of picophytoplankton in Isahaya Bay. The pico-sized chl. a concentration and picophytoplankton cell number at the bottom layer were positively correlated with those in the surface layer, suggesting that picophytoplankton in bottom layers may have sunk from the surface layers. The results imply that the picophytoplankton affects the biogeochemical processes in the bottom of Isahaya Bay more than previously thought. This may be true not only for this estuary but also for other eutrophic coastal seas.

Establishing biologically relevant sediment organic matter thresholds for estuaries and embayments of the Southern California Bight, USA

• Thresholds for sediment TOC and TN were predictive of healthy, intact macrobenthic communities. • Decline in macrobenthos condition with increasing gradients of sediment organic matter. • Thresholds were consistent with other coastal ocean sites in Northern Hemisphere. • First study to put forth sediment TN thresholds protective of benthic community condition. • Thresholds could be used as a guideline in the management of eutrophication stressors. Estuaries, lagoons, and embayments are key components of the coastal ecosystem and they are pervasively exposed to a variety of stressors – the most common of which is eutrophication. In shallow water coastal systems, eutrophication typically manifests as shifts in sediment oxygen horizons and accumulation of toxic reduced compounds in the porewater, which have direct, negative effects on the benthic fauna that live in these sediments. To catalog, prevent, and remediate these stressors, the coastal zone management community has expressed a need to identify targets for biostimulatory compounds and products in the environment that are protective of biological integrity of coastal waters. In response to this need, the present study identified and validated a series of sediment total organic carbon (TOC) and total nitrogen (TN) concentrations associated with changes in macrobenthic community composition across the estuaries and embayments of the Southern California Bight (SCB). Using data from a regional monitoring program, benthic community condition, quantified using the M-AMBI condition assessment index, was modelled as a function of TOC or TN concentration using logistic regression. Then, we evaluated eutrophication thresholds at concentrations corresponding to several relative probabilities (from 0.6 to 0.8), reflecting a range of policy makers’ potential tolerance for risk of failing to meet biointegrity goals. Organic matter thresholds were extracted from the regressions that were predictive of healthy macrobenthic community condition at a 0.8 probability (1.23 mg g −1 TN, 15.51 mg g −1 TOC), 0.7 probability (2.58 mg g -1 TN, 22.9 mg g −1 TOC), or 0.6 probability (3.68 mg g −1 TN, 28.96 mg g −1 TOC) – as an illustration of how these types of stressor response models could be used to set targets for management of these ecosystems. These thresholds were subsequently validated by applying them to data held back from the model creation and by comparing them to taxon-specific inflection points identified from TITAN changepoint analysis of the macrobenthic/TOC/TN calibration data. The different TOC and TN thresholds correctly classified between 67 and 86% of the validation samples, with most of the misclassifications being instances of low organic matter concentration but poor community condition (i.e., false positives). The TOC thresholds identified from our Southern California dataset fell within a similar range (10–35 mg g −1 ) that has been linked to benthic community impacts from a variety of coastal ocean sites across the Northern Hemisphere. The consistency in thresholds across multiple habitats and different types of biota is suggestive of a general, quantitative threshold for organic matter accumulation in near shore sediment habitats and could be useful for informing the management of coastal ecosystems and setting targets biostimulatory stressors in these systems.

Influence of Rising Water Temperature on the Temperate Seagrass Species Eelgrass (Zostera marina L.) in the Northeast USA

Sea surface temperature (SST) has increased worldwide since the beginning of the 20th century, a trend which is expected to continue. Changes in SST can have significant impacts on marine biota, including population-level shifts and alterations in community structure and diversity, and changes in the timing of ecosystem events. Seagrasses are a group of foundation species that grow in shallow coastal and estuarine systems, where they provide many ecosystem services. Eelgrass, Zostera marina L., is the dominant seagrass species in the Northeast United States of America (USA). Multiple factors have been cited for losses in this region, including light reduction, eutrophication, and physical disturbance. Warming has the potential to exacerbate seagrass loss. Here, we investigate regional changes in eelgrass presence and abundance in relation to local water temperature using monitoring data from eight sites in the Northeastern USA (New Hampshire to Maryland) where a consistent monitoring protocol, SeagrassNet, has been applied. We use a hurdle model consisting of a generalized additive mixed model (GAMM) with binomial and beta response distributions for modeling eelgrass presence and abundance, respectively, in relation to the local summer average water temperature. We show that summer water temperature one year prior to monitoring is a significant predictor of eelgrass presence, but not abundance, on a regional scale. Above average summer temperatures correspond to a decrease in probability of eelgrass presence (and increased probability of eelgrass absence) the following year. Cooler than average temperatures in the preceding year, down to approximately 0.5°C below the site average, are associated with the highest predicted probability of eelgrass presence. Our findings suggest vulnerability in eelgrass meadows of the Northeast USA and emphasize the value of unified approaches to seagrass monitoring, conservation and management at the seascape scale.

Response of Living Benthic Foraminifera to Anthropogenic Pollution and Metal Concentrations in Saronikos Gulf (Greece, Eastern Mediterranean)

The Saronikos Gulf, including the industrial zone of Elefsis Bay, is subjected to a variety of urban and industrial impacts that significantly contribute to environmental degradation. Benthic foraminifera comprise a significant component of meiobenthic communities and they are widely used as reliable indicators for the determination of the natural environmental and anthropogenic impact in shallow coastal systems. The present study analyses the living benthic foraminifera composition and its relation to environmental parameters such as grain size, organic carbon content, and heavy metal concentrations, from the surficial sediment layer collected in the Elefsis Bay and the Inner Saronikos Gulf in February 2016. Canonical correspondence analysis and Spearman’s rho correlation show that the foraminiferal species composition is significantly influenced by the increase of organic carbon and Cu, Pb, Zn content. In particular, a relatively low diversity fauna dominated by the stress-tolerant species Ammonia tepida, Bulimina elongata, Bulimina marginata, and Nonionella turgida occurs in the restricted environment of the Elefsis Bay, demonstrating the negative environmental impact caused by the relatively elevated organic carbon and heavy metal contents.

Comparative Food Web Analysis of Two Peruvian Bay Systems Along a Latitudinal Gradient: Resource Use and the Environmental Envelope

The coast of Peru lies within the tropics under the influence of the cold, nutrient-rich waters of the Humboldt Current and the interannual onslaught of the El Niño phenomenon. The Peruvian upwelling system is exceptionally productive and is comprised of subsystems at different scales along the coast. We aimed to understand the differences between two shallow coastal systems along a latitudinal gradient: Sechura Bay in the north (at the convergence of Humboldt and tropical waters) and Independencia Bay in the central-south (under typical upwelling conditions). We compared their biodiversity, trophic dynamics, community energetics, resource use and underlying abiotic conditions. Our analysis revealed that over the past two decades, Sechura has shown a warming trend, while Independencia has maintained its cold water conditions. Chlorophyll concentrations have risen significantly in both systems, higher values in Sechura suggesting there is an increase in local pressures that could lead to eutrophication. Trophic models of the La Niña 07/08 period revealed that both systems are bottom-up driven with high biomass and production at the lower trophic levels, though top-down controls were also shown, particularly in Sechura. While primary productivity was similar in both systems, differences were found in the structure and size of energy flows. More cycling and higher transfer efficiency were found in Independencia, where phytoplankton-based food chains played the main role in the overall dynamic. In contrast, the detritus food chain appears to be more relevant for energy flow in Sechura. Differences in biota and flow structure relate to the systems’ environmental conditions, i.e., more diverse warm-water species in the north and mostly cold water adapted species (mainly invertebrate filter-feeders and their predators) in the central-south. Catches in both systems were dominated by the diving fisheries and comprised mostly scallops (bottom-cultured), snails and fish in Sechura, and mussels, clams, crabs and fish in Independencia. Overall, system indicators suggest that Sechura is a comparatively less developed system. Independencia shall likely maintain its general highly productive system features, whereas Sechura will continue to be more frequently disturbed by El Niño and ongoing human-driven activities, reducing its overall stability and functionality. In the context of climate change, acknowledging these differences is essential for future adaptive management regimes.

Assessment of Groundwater Flow Dynamics Using MODFLOW in Shallow Aquifer System of Mahanadi Delta (East Coast), India

Despite being a biodiversity hotspot, the Mahanadi delta is facing groundwater salinization as one of the main environmental threats in the recent past. Hence, this study attempts to understand the dynamics of groundwater and its sustainable management options through numerical simulation in the Jagatsinghpur deltaic region. The result shows that groundwater in the study area is extensively abstracted for agricultural activities, which also causes the depletion of groundwater levels. The hydraulic head value varies from 0.7 to 15 m above mean sea level (MSL) with an average head of 6 m in this low-lying coastal region. The horizontal hydraulic conductivity and the specific yield values in the area are found to vary from 40 to 45 m/day and 0.05 to 0.07, respectively. The study area has been calibrated for two years (2004–2005) by using these parameters, followed by the validation of four years (2006–2009). The calibrated numerical model is used to evaluate the net recharge and groundwater balance in this study area. The interaction between the river and coastal unconfined aquifer system responds differently in different seasons. The net groundwater recharge to the coastal aquifer has been estimated and varies from 247.89 to 262.63 million cubic meters (MCM) in the year 2006–2007. The model further indicates a net outflow of 8.92–9.64 MCM of groundwater into the Bay of Bengal. Further, the outflow to the sea is preventing the seawater ingress into the shallow coastal aquifer system.

Analysis of phytoplankton variations and community structure in Kuwait Bay, Northwestern Arabian Gulf

Environmental vicissitudes cause short-term variability in plankton dynamics. The effect would be more pronounced in shallow, semi-enclosed tidal coastal systems. Here, we analyzed diurnal fluctuations in coastal phytoplankton and environmental factors in relation to seasonal tidal cycles (October 2016, Fall and February–March 2017, Winter) in a sub-tropical coastal embayment (Kuwait Bay) in the northwestern Arabian Gulf. Water-column profiles were obtained for chlorophyll, photosynthetically active radiation (PAR), salinity, temperature, and dissolved oxygen. Winter was characterised by relatively cold, well‑oxygenated, nutrient-rich, and high saline waters than the fall. Nutrient levels were high during low tide and low during high tide. High-performance liquid chromatography (HPLC) analysis of phytoplankton marker pigments revealed the presence of twelve different phytoplankton functional groups. Diatoms and dinoflagellates were the most dominant groups with significant surface-bottom differences during both seasons. The phytoplankton biomass (Chl a) was the highest during the low light hours of the day with apparent day-night differences. The picoplankton community was mainly represented by the autotrophs Synechococcus (in Fall) and picoeukaryotes (in winter) with clear seasonal patterns. Compared to picoautotrophs, picoheterotrophic biomass was relatively high during winter. This study revealed that light availability and tidal mixing are the factors regulating variability in the phytoplankton community composition and biomass (Student’'s t-test, two-tailed; (P ≤ 0.1) in Kuwait Bay. High-resolution monitoring programs are essential to capture the natural variability of phytoplankton and its implication on the biogeochemistry of the shallow tide-dominated coastal systems.

Brief Episodes of Nocturnal Hypoxia and Acidification Reduce Survival of Economically Important Blue Crab (Callinectes sapidus) Larvae

Many shallow coastal systems experience diel fluctuations in dissolved oxygen (DO) and pH that can intensify throughout the summer season and expose estuarine organisms to repeated episodes of coastal hypoxia and acidification. In temperate regions, larval release of the economically important blue crab Callinectes sapidus occurs in the summer, and while the earliest stage (zoea I) larvae are susceptible to persistent low DO and low pH conditions, their sensitivity to diel fluctuations is unknown. Here, a series of short-term (≤96 h) experiments were conducted to investigate the survival of C. sapidus zoea I larvae exposed to a range of diel cycling hypoxic and acidified conditions and durations. Two experiments comparing a diel cycling DO/pH treatment (fluctuating from ∼30% air saturation to ∼103% averaging ∼66%/and from pH ∼7.26 to ∼7.80 averaging ∼7.53) to a static low DO/pH treatment (∼43%/∼7.35), a static moderate DO/pH treatment (∼68%/∼7.59), and a static control treatment (∼106%/∼7.94) indicated that survival in the diel cycling treatment was significantly lower than the moderate treatment (p &amp;lt; 0.05) by 75 and 48% over 96 and 48 h, respectively, despite comparable mean experimental DO/pH values. Three other experiments aimed at identifying the effective minimum duration of low DO/low pH to significantly depress larval survival under diel cycling conditions revealed that 8 h of low DO/low pH (∼28%/∼7.43) over a 24-h diel cycle consistently decreased survival (p &amp;lt; 0.05) relative to control conditions by at least 55% regardless of experimental duration (72-, 48-, and 24-h experiments). An increase in DO beyond saturation to supersaturation (160%) and pH beyond normocapnic to highly basified (8.34) conditions during the day phase of the diel cycle did not improve survival of larvae exposed to nocturnal hypoxia and acidification. Collectively, these experiments demonstrate that diel cycling does not provide newly hatched C. sapidus larvae a temporal refuge capable of ameliorating low DO/pH stress, but rather is more lethal than chronic exposure to comparable average DO/pH conditions. Given that larvae exposed to a single nocturnal episode of moderate hypoxia and acidification experience significantly reduced survival, such occurrences may depress larval recruitment.

Benthic jellyfish dominate water mixing in mangrove ecosystems

Water mixing is a critical mechanism in marine habitats that governs many important processes, including nutrient transport. Physical mechanisms, such as winds or tides, are primarily responsible for mixing effects in shallow coastal systems, but the sheltered habitats adjacent to mangroves experience very low turbulence and vertical mixing. The significance of biogenic mixing in pelagic habitats has been investigated but remains unclear. In this study, we show that the upside-down jellyfish Cassiopea sp. plays a significant role with respect to biogenic contributions to water column mixing within its shallow natural habitat ([Formula: see text] m deep). The mixing contribution was determined by high-resolution flow velocimetry methods in both the laboratory and the natural environment. We demonstrate that Cassiopea sp. continuously pump water from the benthos upward in a vertical jet with flow velocities on the scale of centimeters per second. The volumetric flow rate was calculated to be 212 L⋅h-1 for average-sized animals (8.6 cm bell diameter), which translates to turnover of the entire water column every 15 min for a median population density (29 animals per m2). In addition, we found Cassiopea sp. are capable of releasing porewater into the water column at an average rate of 2.64 mL⋅h-1 per individual. The release of nutrient-rich benthic porewater combined with strong contributions to water column mixing suggests a role for Cassiopea sp. as an ecosystem engineer in mangrove habitats.

Imprints of sea surge and municipal activities on non-potability of groundwater in shallow coastal sandy aquifer system of Lagos State, Southwestern Nigeria

Coastal areas are usually characterized by a high human population with attendant groundwater pollution through increased salinization from varied sources. This study was done to assess the pollution status, suitability of groundwater and associated hydrogeochemical processes of the shallow sandy aquifer near the coastal section of Lagos State, Southwestern Nigeria. A total of fifty-nine hand-dug wells were randomly selected, from which water samples were collected and subjected to physicochemical and statistical analyses. Water quality indices (Pollution Index of Groundwater (PIG) and Irrigation quality indices) and Chloro-Alkaline Indices (CAI 1&2) were calculated while plots of Gibbs and Piper diagrams as well as factor analysis were also carried out. The order of abundance of dissolved ions were Na > Ca > Mg > K for cations and HCO3>Cl > SO4>NO3 for anions. Presently, there appears to be no pollution threat to the groundwater, and the bulk of the samples are found fit for agricultural use. Rock weathering, ion exchange, occasional sea surge and municipal contamination activities constitute the geochemical processes affecting the groundwater quality in the study area. It could be postulated that consistent activities of sea water surge and municipal contamination might impair the groundwater quality of the sandy aquifers in the nearest future.

Ecological consequences of sea level rise and flood protection strategies in shallow coastal systems: A quick-scan barcoding approach

Shallow coastal ecosystems have high ecological value and contribute to flood protection. Their stability is, however, sensitive to the amount and rate of future sea level rise (SLR), their ability to trap sediment which allows them to grow with rising sea level, and human response to SLR. So far, studies have focused on assessing SLR impacts using resource-intensive tools. Here, we present an approach for a first-order assessment and easily accessible ‘barcode’ visualization to rapidly assess potential impacts of both SLR and adaptation strategies on coastal ecosystems in a spatially explicit way. Our approach relates habitat types (ecotopes) to water level, morphology and salinity, allowing users to determine shifts in spatial arrangements of ecological zones under different SLR rates and strategies. We illustrate this approach for a transect in the Dutch Wadden Sea. We find that beyond a critical rate of SLR, major changes in ecotope distribution are projected to occur as this part of the Wadden Sea starts to drown due to insufficient sediment import. Even larger impacts arise from adaptation strategies. Closing the barrier islands will turn the Wadden Sea into a freshwater lake-system with the absence of intertidal areas, infilling of channels and bank erosion. A strategy that allows for inland migration of the shoreline, results in a deep tidal basin with large subtidal habitats, and a shifted intertidal zone. Our case study shows that the barcoding approach provides a rapid, quantitative and spatially explicit overview of the potential implications for coastal ecosystems under different SLR scenarios, adaptation strategies and time horizons. This can then be used to screen adaptation strategies before going into a more comprehensive analysis. The barcode visualization allows for easy dissemination of potential ecological impacts to a broad community.