Open Coastal Waters Research Articles

Nutrient accumulations in high-saline bottom waters in the eutrophic East China Sea inner shelf

Despite decades of mitigation efforts, eutrophication-induced algal blooms and hypoxia have not significantly decreased globally, possibly due to the legacy effects of eutrophication. The legacy effect has been more explored in inland waters and enclosed estuaries than in open coastal waters. Here, we reanalyzed cruise data from the East China Sea inner shelf to explore the effect of eutrophication on nutrient accumulations in high-saline bottom waters. Our dataset showed elevated nitrate (12.75 ± 6.51 μmol L−1) and phosphate (0.85 ± 0.26 μmol L−1) in high-salinity (salinity>34, temperature < 23 °C) bottom waters during the summer of 2006 to 2013. They were higher than those typically observed in the Taiwan Warm Current Bottom Water by approximately 5.45 ± 6.51, and 0.29 ± 0.26 μmol L−1, respectively. Significant correlations of nitrate with apparent oxygen utilization (AOU) and elevated AOU suggested that organic matter decomposition contributed to increased nitrate in bottom waters under eutrophication conditions. Based on an end-member mixing estimation, we found that the organic matter decomposition accounted for 28% to 37% of the nutrient concentrations in the bottom waters, with a standard deviation of 20%. Results from our mass-balance model indicated that 40–74% of regenerated nutrients are flushed out of the model box set within 95% equilibrium time due to the advection of offshore waters, assuming a residence time of 46.0 to 13.9 days. Based on cruise results in June and August 2009, the net accumulation rates of nitrate, phosphate, and AOU in the Taiwan Warm Current Bottom Water were estimated to be 0.046, 0.0036, and 0.44 μmol L−1 d−1, respectively. Such nutrient accumulations in the water column and the residual nutrients in sediment are crucial legacy nutrients, potentially triggering algal blooms. Conversely, the flushing effect suggests a significant transport of nutrients and other chemical elements to the offshore and open ocean.

Comparing the effect of larval dispersal strategies on morphological versus genetic differentiation in two neotropical fiddler crabs

AbstractThe dispersal mode of estuarine invertebrates has a strong effect on genetic variability and phenotypic expression, potentially maintaining gene flow among widely separated populations or limiting connectivity among close ones. Understanding the dispersal strategies effects can support adequate strategies for environment management and understand the evolutionary history of the studied species. A comparative study on the effect of larval dispersal strategies (export vs retention) along the overall geographic distribution ranges of adult populations of two co‐distributed fiddler crab species was performed. Geometric morphometric techniques were used to evaluate morphological differentiation in the shape of the carapace and major cheliped propodus in 10 populations of Minuca mordax and five populations of Leptuca leptodactyla. Potential genetic differentiation was assessed using DNA sequence data from up to 170 fiddler crab specimens, corresponding to the mitochondrial gene cytochrome c oxidase subunit 1 (COX1). Patterns of genetic and morphological characteristics diverged among populations of both species. In terms of morphology, populations of both species showed intraspecific variation in the shape of the carapace and, to a lesser extent, in the major cheliped propodus. This observed intraspecific variation followed a clear geographic pattern of morphometric differentiation, in which the geographic origin is associated with a phenotypic response to the environmental diversity along the extended Brazilian coast. In contrast, there are shared haplotypes in populations separated by more than 4000 km, but with significant ΦST values among most populations of L. leptodactyla and M. mordax, suggesting a moderate to high level of gene flow. Therefore, it can be concluded that the split of the Central South Equatorial Current has not acted as an efficient long‐term barrier to the dispersal of larvae in both species. In M. mordax, a slight limitation of genetic exchange can be observed between the southernmost populations and the remaining ones. This first evidence of genetic structuring within this widely distributed species is consistent with its documented strategy to retain larvae in the estuarine environments. However, occasional transport of larvae to more open coastal waters seems to maintain stepwise gene flow between neighboring populations. Overall, our results still provide evidence of more pronounced genetic homogeneity in a species with a larval export strategy (L. leptodactyla) compared to a species with a larval retention strategy (M. mordax). This suggests that larval dispersal strategies, coupled with the microhabitat in which the respective species occur, have a noticeable effect on the degree of gene flow. Most likely, these biological aspects are further influenced by the estuarine and coastline geomorphology.

Dissolved organic carbon leaching from microplastics and bioavailability in coastal ecosystems

The dissolved organic carbon (DOC) leached from two types of microplastics (polyethylene and polypropylene) frequently found in coastal areas were evaluated in situ. Subsequently, the bioavailability of leached DOC was assessed for microbial inocula from different coastal communities (i.e., estuarine and open-coastal waters, river-mouth waters and seagrass beds). Leached DOC was largely biodegradable (as much as 85 %). However, seagrass beds and river-mouth waters exhibited lower DOC utilization efficiency than estuarine and open-coastal waters, probably because of differences in their microbial communities. The labile/recalcitrant ratio of DOC leached from plastic was similar under illuminated and dark conditions, whereas DOC leached from polyethylene, rather than DOC leached from polypropylene, was preferentially used by microbial communities. We estimated that as many as 21,000 metric tons of DOC leached from plastics may be released into ocean annually. Our results support the need to consider the potential impacts of coastal plastic pollution on microbial communities, including consideration of the trophic webs and coastal carbon cycle.

Infection with swim bladder nematode Anguillicola crassus in relation to European eel growth, age, and habitat along the German Baltic coast.

One possible reason for the European eel (Anguilla anguilla) population decline is the neozoan eel swim bladder nematode Anguillicola crassus. To investigate whether the prevalence of A. crassus and the associated swim bladder pathology is related to eel habitat, growth rate, and age, 728 yellow eels from 6 habitats differing in salinity and located along the German Baltic coast were examined between 2005 and 2009. The prevalence of A. crassus varied between habitats, ranging from 9 to 57%. Infection prevalence and the percentage of eels with a damaged swim bladder were significantly higher in inner coastal waters compared to more saline open coastal water. In infected eels, 1 to 32 adult and preadult individuals of A. crassus were observed. The mean infection intensity varied between habitats from 2 to 7 nematodes per eel but did not significantly differ between inner and open coastal waters. Infection prevalence and intensity decreased significantly with age when all open coastal waters and all habitats were combined. Both the lower prevalence of A. crassus and the swim bladder damage of older eels and of eels originating from open coastal water habitats suggest that these eels have a higher fitness for spawning migrations than eels from inner coastal waters. The present study underlines the importance of eel screening on a sufficiently small geographical scale for the accurate estimation of eel recruitment and the identification of priority areas that are likely to produce healthy silver eels.

Meteorological Satellite Observations Reveal Diurnal Exceedance of Water Quality Guideline Thresholds in the Coastal Great Barrier Reef

The Great Barrier Reef (GBR) is a marine protected area subject to natural and anthropogenic disturbances. Water quality is critical for the health and protecting resilience of GBR coral ecosystems against the synergistic and cumulative pressures of tropical cyclones, marine heat waves, and outbreaks of crown-of-thorns starfish. The concentration of Total Suspended Solids (TSS) is a key water quality parameter measured at multiple spatio-temporal scales from in situ probes to satellite observations. High TSS concentrations can adversely impact coral and seagrasses on the inshore GBR. We present diurnal TSS derived from Himawari-8 Geostationary satellite observations at 10 min frequency and demonstrate its applicability for improved monitoring of GBR water quality. Diurnal TSS obtained from Himawari-8 observations were compared to TSS computed from in situ bio-optical measurements at the Lucinda Jetty Coastal Observatory (LJCO). The coastal waters at LJCO experience diurnal variability of TSS (~7 mg L−1), where magnitude peaks followed the slack tides, and the largest diurnal changes were associated with freshwater discharge residuals from the wet season. Exceedance maps revealed that TSS is above guideline thresholds in the open coastal and mid-shelf waters for ~60% of the valid monthly observations, including during dry season months.

High resolution modeling of aluminium transport in a fjord estuary with focus on mean circulation and irregular flow events

Environmental impact assessments of trace metals and radionuclides in estuarine waters will benefit from numerical transport models that can provide detailed and accurate predictions of concentrations of harmful physico-chemical forms of contaminants at adequate spatial and temporal resolution. Aiming to study the potential of aluminium (Al) exposure to biota, a transport model (OpenDrift) including dynamic speciation and transformation processes was improved and applied, using three-dimensional hydrodynamic flow fields from a numerical ocean model (ROMS) at high horizontal resolution (32 m). Al transport and concentration was computed along the Sandnesfjorden Fjord, south-eastern Norway, from river outlet to open coastal waters. Validation of the circulation model with 29 hydrographic profiles from Sandnesfjorden showed substantial improvements compared to previous studies due to optimized model configuration (salinity overestimation decreased from >7 psu to <4 psu). Modeled Al data compared well with observed surface Al concentration from 12 locations and the along-fjord decreasing trend in Al-concentration was well reproduced (error ratios were <2 in Sandnesfjorden). Except in the channel area, both salinity and Al concentration estimates lie well within the expected variability. However, the transport modeling gave a more detailed site-specific picture of the Al concentration, suggesting more scattered and variable fields than indicated by observational data (variations of a factor 3–4 over short spatiotemporal scales). Reversed flow events (surface flow into the fjord) caused considerable mixing and redistribution of water masses, affecting both horizontal mixing of river discharges with coastal water as well as vertically as surface water mixed with deeper water masses. These blocking events strongly changed properties and distribution of the water masses giving rise to local and short-term high Al-exposure episodes (variations of a factor of 10 over a 12 h period) in the fjord that may pose risks to biota and therefore should be taken into account in impact and risk assessments.

Novel Insights into Agar Metabolism in Marine Heterotrophic Bacteria

Agar is a key structural polysaccharide of red macroalgae which provides a rich habitat for marine heterotrophic bacteria in marine ecosystems. Marine agarolytic bacteria, that can use agar as the sole carbon source, are distributed in diverse marine environments from open coastal waters to the gut of marine herbivores. Agarolytic bacteria employ a combination of carbohydrate-active enzymes (CAZymes) for the depolymerization of agar. Extensive studies on the genomic architecture of the agarolytic bacteria suggested that genes encoding these CAZymes are arranged in polysaccharide utilization loci (PUL). Agar hydrolyzing enzymes (agarases) are categorized into; β-agarase (GH16, GH50, GH86, and GH118), α-agarase (GH96), neoagarooligosaccharide hydrolase (GH117), and agarolytic β-galactosidase (GH2). The molecular functionality, structural elements, and catalytic mechanisms of agarases belonging to different GH families show unique characteristics. L-AHG, one of the main constituents in agar, is a rare monosaccharide and its metabolic pathway is exclusively found in marine agarolytic bacteria. Recent trends in the agarolytic systems are mostly focused on the sequence data to visualize the universal agarolytic enzyme repertoire and the evolution of the agarolytic pathway in marine heterotrophic bacteria. In addition, increasing attention is paid to understanding the oligosaccharide transport mechanisms and transcriptional regulation of genes in PUL. In this review, we will cover a comprehensive overview of genomic architecture, structural and functional analysis of agar hydrolyzing enzymes, and agar metabolism in marine heterotrophic bacteria.

Increased oceanic dimethyl sulfide emissions in areas of sea ice retreat inferred from a Greenland ice core

Ocean phytoplankton are an important source of dimethyl sulfide, which influences marine cloud formation. Model studies suggest that declines in Arctic sea ice may lead to increased dimethyl sulfide emissions, however observational support is lacking. Here, we present a 55-year high-resolution ice core record of methane sulfonic acid flux, an oxidation product of dimethyl sulfide, from the southeast Greenland Ice Sheet. We infer temporal variations in ocean dimethyl sulfide emissions and find that springtime (April–June) fluxes of methane sulfonic acid correlate well with satellite-derived chlorophyll-a concentration in the Irminger Sea. Summertime (July–September) methane sulfonic acid fluxes were 3 to 6 times higher between 2002–2014 than 1972–2001. We attribute this to sea ice retreat day becoming earlier and a coincident increase in chlorophyll-a concentration in the adjacent open coastal waters.

Developing Philippine Coastal and Oceanic Aquaculture for Food Security and Livelihood Generation

The fisheries of the Philippines are dominated by aquaculture, the farming of animals and plants for food and other products. With declining fish stocks in marine waters because of overfishing and habitat degradation, more than 1.7 million small fisherfolk dependent on fishing for their livelihood are among the country’s “poorest of the poor”. More than 70% of the total aquaculture production comes from coastal aquaculture with the farming of seaweeds, oysters, and mussels in open coastal waters (&lt;200 m deep) and milkfish and other fishes in pens and floating cages. Oceanic aquaculture, farming in the deep sea (&gt;200 m), is still in its infancy in the country. Mariculture parks such as the Panabo City Mariculture Park in Davao del Norte are a model for an integrated approach to sustainable coastal aquaculture. Expansion of coastal aquaculture in the country requires the dissemination of improved varieties of seaweeds to farmers and management of the ‘ice-ice” disease. Meanwhile, for the cage culture of milkfish and species, the establishment of more hatcheries/nurseries and the development of efficient and cost-effective feeds are needed. The creation of a Department of Fisheries and Aquatic Resources is endorsed to give more support and attention for the further development and sustainability of the country’s coastal and oceanic aquaculture for food security and livelihood generation.

Evolutionary Dynamics of Two Classes of Repetitive DNA in the Genomes of Two Species of Elopiformes (Teleostei, Elopomorpha).

The order Elopiformes includes fish species of medium to large size with a circumglobal distribution, in both the open sea, coastal, and estuarine waters. The Elopiformes are considered an excellent model for evolutionary studies due to their ample adaptive capacity, which allow them to exploit a range of different ecological niches. In this study, we analyzed the karyotype structure and distribution of two classes of repetitive DNA (microsatellites and transposable elements) in two Elopiformes species (Elops smithi and Megalops atlanticus). The results showed that the microsatellite sequences had a very similar distribution in these species, primarily associated to heterochromatin (centromeres and telomeres), suggesting these sequences contribute to the chromosome structure. In contrast, specific signals detected throughout the euchromatic regions indicate that some of these sequences may play a role in the regulation of gene expression. By contrast, the transposable elements presented a distinct distribution in the two species, pointing to a possible interspecific difference in the function of these sequences in the genomes of the two species. Therefore, the comparative genome mapping provides new insights into the structure and organization of these repetitive sequences in the Elopiformes genome.

Consistency of thresholds for eutrophication assessments, examples and recommendations

International harmonisation of management goals for eutrophication processes in coastal waters, requiring reduction of discharges and depositions of nutrients and organic matter, needs coordinated assessments and measures. This is especially necessary in open areas, connected by currents and mixing processes with trans-boundary exchanges. Management goals, defined nationally as local thresholds for nutrients and chlorophyll-a, had been applied recently (2006–2014) within international eutrophication assessments in the North Sea (OSPAR) and Baltic Sea (HELCOM). Consistency of thresholds for nitrogen nutrients and chlorophyll-a concentrations is tested by mixing diagrams and correlations between nitrogen nutrients (total and inorganic nitrogen) and chlorophyll-a. Results indicate mean consistent relations, but single deviations as in the continental coastal water of the North Sea surpassed means by a factor up to 5 for chlorophyll-a in relation to inorganic nitrogen. Thresholds differed across national borders significantly. Correlations of thresholds and assed data reflect the degree of regional deviations by comparison. Consistency of regionally applied thresholds can be achieved stepwise, by application of regionally correlated means, by adaptation to mixing and parameter relations, and finally by relations of thresholds to natural background concentrations. By this, consistency of international assessments can be improved generally, allowing coordinated management of open coastal waters.

Response of Aquatic Organisms Communities to Global Climate Changes and Anthropogenic Impact: Evidence from Listvennichny Bay of Lake Baikal

Simple SummaryLake Baikal is ranked first among the world’s lakes in terms of freshwater reserves (23,000 km3). It is a UNESCO World Heritage Site, and its biota is represented by unique fauna and flora, with endemics accounting for more than 60%. What is happening in the Baikal ecosystem in recent decades due to global climate change and anthropogenic impacts? In this paper, we studied this issue on the example of one of the few open bays on the western shore of Lake Baikal, as well as of some remote areas. It has been found that the plankton composition is dominated by thermophilic species; the role of endemic species in the formation of total biomass is decreasing, which confirms the ecosystem’s response to climate warming. As a result of human activity, filamentous algae bloom suppresses endemic algae species and reduces mollusk proportion. The coastal zone of Lake Baikal is taking on the features of common shallow freshwater lakes due to the predominance of cosmopolitan and widespread Palearctic species. It is necessary to monitor the Baikal ecosystem in the changing climate and to strengthen control over human activities on the shores of the lake.Recent studies have revealed how the freshwater biota of Lake Baikal responds to climate change and anthropogenic impacts. We studied phyto- and zooplankton, as well as phyto- and zoobenthos, in the open coastal waters of the southern basin of the lake and of Listvennichny Bay. A total of 180 aquatic organism taxa were recorded. The response of the Baikal ecosystem to climate change can be traced by changes in the species composition of planktonic communities of the lake’s open coasts in summer. The key species were thermophilic the Anabaena lemmermannii P. Richt. (Fij = +0.7) blue-green algae, the Asplanchna priodonta Gosse (Fij = +0.6) rotifers in 2016, the Rhodomonas pusilla (Bachm.) Javorn. (Fij = +0.5) cold-loving algae, and the Cyclops kolensis Lilljeborg (Fij = +0.9) copepods in the past century. The proportion of Chlorophyta decreased from 63% to 17%; the Cyanophyta increased from 3% to 11% in the total biomass of phytoplankton; and the proportion of Cladocera and Rotifera increased to 26% and 11% in the biomass of zooplankton, respectively. Human activity makes an additional contribution to the eutrophication of coastal waters. The Dinobryon species, the cosmopolitan Asterionella formosa Hass. and Fragilaria radians Kütz., dominated phytoplankton, and filamentous algae, Spirogyra, dominated at the bottom in the area with anthropogenic impact. The trophic level was higher than at the unaffected background site: the saprobity index varied from 1.45 to 2.17; the ratio of eutrophic species to oligotrophic species ranged from 1:2 to 3:1, and the ratio of mesosaprobiont biomass to endemics biomass ranged from 2:1 to 7:1. Currently, the boundaries of eutrophication zones of shallow waters in Lake Baikal are expanding, and its coastal zone has acquired features typical of freshwater bodies of the eutrophic type.

Laminaria kelps impact iodine speciation chemistry in coastal seawater

Kelp (Laminaria digitata) uses iodide as a unique inorganic antioxidant to protect its surface and apoplastic space against reactive oxygen species such as ozone, hydrogen peroxide and superoxide, with implications for atmospheric and marine chemistry as well as regional climatic processes. If kelp is covered by seawater, this results in iodide leaching into surrounding sea water. In this study, the influence of the kelps Laminaria digitata, L. hyperborea, L. ochroleuca and Saccharina latissima on iodine speciation chemistry was explored at two sites in Oban (Argyll, Scotland) and Roscoff (Brittany, France) based on diver-operated in situ sampling. Seawater samples were subsequently analysed voltammetrically, accompanied by determination of extractable iodine concentrations in the tissues of the thalli surveyed by ICP-MS. The main result is that iodide concentrations in the vicinity of kelp thalli are strongly enhanced, especially at low tide, while iodate concentrations are decreased in comparison to open coastal water and open ocean concentrations.

Estimation of Bathymetry and Benthic Habitat Composition from Hyperspectral Remote Sensing Data (BIODIVERSITY) Using a Semi-Analytical Approach

The relevant benefits of hyperspectral sensors for water column determination and seabed features mapping compared to multispectral data, especially in coastal areas, have been demonstrated in recent studies. In this study, we used hyperspectral satellite data in the accurate mapping of the bathymetry and the composition of water habitats for inland water. Particularly, the identification of the bottom diversity for a shallow lagoon (less than 2 m in depth) was examined. Hyperspectral satellite data were simulated based on aerial hyperspectral imagery acquired above a lagoon, namely the Vaccarès lagoon (France), considering the spatial and spectral resolutions, and the signal-to-noise ratio of a satellite sensor, BIODIVERSITY, that is under study by the French space agency (CNES). Various sources of uncertainties such as inter-band calibration errors and atmospheric correction were considered to make the dataset realistic. The results were compared with a recently launched hyperspectral sensor, namely the DESIS sensor (DLR, Germany). The analysis of BIODIVERSITY-like sensor simulated data demonstrated the feasibility to satisfactorily estimate the bathymetry with a root-mean-square error of 0.28 m and a relative error of 14% between 0 and 2 m. In comparison to open coastal waters, the retrieval of bathymetry is a more challenging task for inland waters because the latter usually shows a high abundance of hydrosols (phytoplankton, SPM, and CDOM). The retrieval performance of seabed abundance was estimated through a comparison of the bottom composition with in situ data that were acquired by a recently developed imaging camera (SILIOS Technologies SA., France). Regression coefficients for the retrieval of the fractional species abundances from the theoretical inversion and measurements were obtained to be 0.77 (underwater imaging camera) and 0.80 (in situ macrophytes data), revealing the potential of the sensor characteristics. By contrast, the comparison of the in situ bathymetry and macrophyte data with the DESIS inverted data showed that depth was estimated with an RSME of 0.38 m and a relative error of 17%, and the fractional species abundance was estimated to have a regression coefficient of 0.68.

An evolutionary estuarine incursion: molecular differentiation and niche separation in Bornean Indothais snails (Rapaninae, Muricidae)

AbstractEcological and biogeographic information for marine gastropods has lagged behind taxonomic, molecular and phylogenetic information, limiting understanding of evolutionary processes. We investigated niche separation and speciation in rapinine whelks that represent a rare deep estuarine penetration by muricid gastropods. We studied the genetic and ecological differentiation of four Indothais morphotypes, distributed along a salinity gradient in Brunei (Borneo, South East Asia). Our molecular analyses, based on three mitochondrial genes (COI, 12S rRNA and 16S rRNA) and one nuclear gene (28S rRNA), revealed three species having the following relationship [Indothais rufotincta (Tan &amp; Sigurdsson, 1996), [I. javanica (Philippi, 1848), [I. gradata (Jonas, 1846)]]]. This pattern coincided with their salinity-related distributions, such that I. rufotincta occurred alone in the open coastal waters, and I. javanica and I. gradata extended into the upper estuary. This suggests speciation through divergent selection and local adaptation, specifically synapomorphic low salinity tolerance by I. javanica and I. gradata. The observed intertidal vertical separation where the species co-occur suggests competitive exclusion of the others by the most-recently evolved I. gradata. This species also showed greatest morphological and genetic variation, and unique niche expansion involving feeding on both hard surface and muddy sediment organisms. Our study presents a novel hypothesis for the speciation of these snails.

Fjordic Lagoons of the Barents Sea as Models for Study of the Dynamics of Coastal Communities with Alien Red King Crab (Paralithodes camtschaticus, Decapoda, Lithodidae)

Benthic communities of the semi-isolated deep fjordic Linjalampi and Sisajarvi lagoons in the apex part of Ambarnaya Bay, Varanger fjord, Barents Sea, are affected by the limited water exchange and wave action in combination with other abiotic and biotic factors. Among the biotic factors, the presence of a numerous group of red king crab (Paralithodes camtschaticus) that naturalized in the southern part of the Barents Sea in the second half of the 20th century may play a particularly important role. The median density of juvenile and adult crabs in the lagoons (42.5–52 specimens/1000 m2 in most years of observation) is comparable to their density in the neighboring open parts of the Varanger fjord. A narrow and shallow strait connecting the lagoons with the sea may restrict crab migrations between these habitats. Thus, adult crabs are present in the lagoons in the seasons when they migrate from the coast to greater depths in their usual habitats. The food chains starting from phytoplankton and macrophytes to benthic predators, red king crabs, spider crabs (Hyas araneus), and hermit crabs (Pagurus pubescens) have been studied using stable isotope analysis. The trophic level of adult king crabs in the lagoons (2.88) is lower than that of both spider crabs (3.16–3.42) and those king crabs that occur in the open part of the coastal area (3.44). This indicates differences in the feeding habits of crabs in the lagoons and in the open coastal waters. The food chain kelp–sea urchins–red king crabs typical for the coastal zone in the Barents Sea is not expressed in the food web of the lagoons. The low abundance and distribution patterns of sea urchins may be due to their consumption by red king crabs over a long period. Although fjordic Linjalampi and Sisajarvi lagoons are full marine water bodies, they are similar to continental lakes in some characteristics. In particular, the conditions in the lagoons make them convenient models for the study of the long-term dynamics of communities and ecosystems.

Succession of a phytoplankton and mesozooplankton community in a coastal area with frequently occurring algal blooms

We examined seasonal succession in a phytoplankton and mesozooplankton community in open coastal waters with frequently occurring harmful algal blooms. Chlorophyll a (Chl a) concentration was positively related to the N/P/Si ratio, suggesting that nitrate is a major limiting nutrient for phytoplankton biomass increase. Heterotrophic red Noctiluca, but not toxic dinoflagellate, abundance showed a negative trend with both Chl a and mesozooplankton abundance. The phytoplankton community showed a clear seasonal succession, with an increased abundance of dinoflagellates in the summer community (June–September), which was distinctive from the autumn–winter–spring community (October–May) that was dominated by diatoms. A mesozooplankton community shift followed, with a lag of a couple of months, in the late August to December community that was associated with subtropical copepods. The other community from February to August is associated with marine cladocerans. Although the most dominant mesozooplankton of year was copepod at a rate of over 70%, coexisting gelatinous plankton such as appendicularians and Noctiluca, which may compete with copepods for prey could affect to copepod production in the region.

First Pliocene fish otolith assemblage from the Gulf Coastal Plain, Dauphin Island, Mobile County, Alabama, USA

ABSTRACT The first Pliocene teleostean otoliths from the Gulf Coastal Plain are described from Dauphin Island, Mobile County, Alabama, USA. The 250 otolith specimens, mainly sagittae, were obtained from shell hash dredged from an offshore Pliocene unit deposited onshore as part of recent beach nourishment. Analysis of the otoliths revealed 22 species from 11 teleostean families. Sciaenid fishes dominate the assemblage and account for 79.6% of the total specimens, while the other 10 families (including indeterminates) comprise approximately 20% of the total. Comparison to modern biological and ecological requirements for the fishes represented by the otoliths suggest a shallow (0–20 m) neritic environment with some brackish and rare deep-water influence. Several of the most abundant taxa indicate shallow, soft bottom estuarine habitat with upstream oligohaline creeks (0.5 to 5.0 ppt salinity) serving as primary nursery area. However, the percentage of marine-only species may indicate more interaction with open estuary and shallow coastal areas and subtropical waters. The lack of invertebrate settlement on the otoliths likely indicates limited surface residence-time. All 22 taxa recovered from the Dauphin Island site are highly significant since they represent the first Pliocene occurrences of these taxa within the Gulf Coastal Plain of North America.

Growth rates of Gracilariopsis longissima, Gracilaria bursa-pastoris and Chondracanthus teedei (Rhodophyta) cultured in ropes: implication for N biomitigation in Cadiz Bay (Southern Spain)

Cultures of three native macroalgal species (Gracilariopsis longissima, Gracilaria bursa-pastoris and Chondracanthus teedei) were developed in open coastal waters of a shallow, potentially eutrophic bay in Southern Spain. Experimental trials to assess the technical feasibility of seaweed cultivation and nitrogen biofiltration potential were conducted between October 2014 and December 2015. Seaweeds were cultivated using submersible rafts in five periods of 9 weeks to identify the most suitable seasons and culture duration (3, 6 or 9 weeks). Using generalized linear models (GLMs), the most relevant environmental factors controlling the growth of the three seaweeds were identified. Maximum net growth rates varied between 1.39% day−1 in C. teedei (winter, 6 weeks) and 4.71% day−1 in G. longissima (autumn, 3 weeks). Overall, the best period to cultivate seaweeds in Cadiz Bay was from mid-winter to early summer. No clear effects of duration of the culture were observed for C. teedei and G. bursa-pastoris. Short culture periods of 3 weeks were more suitable for G. longissima. Tissue N contents generally were lower than the critical quota, and GLMs suggested a critical role of N limiting seaweed growth in this bay. Dissolved inorganic nitrogen was biofiltered from winter to early summer and revealed G. bursa-pastoris as the main biomitigator of nitrogen (up to 80 mg N m−1 month−1 in spring). This species also showed positive growth rates virtually during the entire study period and was the most suitable species for cultivation in this area.

Upwelling Bays: How Coastal Upwelling Controls Circulation, Habitat, and Productivity in Bays

Bays in coastal upwelling regions are physically driven and biochemically fueled by their interaction with open coastal waters. Wind-driven flow over the shelf imposes a circulation in the bay, which is also influenced by local wind stress and thermal bay-ocean density differences. Three types of bays are recognized based on the degree of exposure to coastal currents and winds (wide-open bays, square bays, and elongated bays), and the characteristic circulation and stratification patterns of each type are described. Retention of upwelled waters in bays allows for dense phytoplankton blooms that support productive bay ecosystems. Retention is also important for the accumulation of larvae, which accounts for high recruitment in bays. In addition, bays are coupled to the shelf ecosystem through export of plankton-rich waters during relaxation events. Ocean acidification and deoxygenation are a concern in bays because local extrema can develop beneath strong stratification.