Surface Seawater Research Articles

Data-driven model based adaptive feedback-feed forward control schemes for open cycle - OTEC process

Open Cycle - Ocean Thermal Energy Conversion (OC-OTEC) is one of the most important renewable energy sources that generate electricity and fresh water from seawater utilizing the temperature gradient between the warm surface seawater and the cold deep seawater. This paper aims to develop non-linear data-driven model-based adaptive Feedback Control (FBC) schemes for the OC-OTEC process to track the output power and a dynamic Feed-Forward Control (FFC) scheme to reject the effects of temperature disturbance on power caused by climate variations in OC-OTEC. The experiments are conducted on a laboratory-scale OC-OTEC experimental setup at the National Institute of Ocean Technology, Chennai. Firstly, linear data-driven models are developed using system identification techniques. Based on the developed models, gain scheduling-based adaptive control schemes are developed: Proportional Integral (PI) control and Model Predictive Control (MPC). Secondly, the closed-loop performances of the developed FBC schemes are analysed under servo and regulatory operations. Furthermore, it is observed from the sensitivity analysis results that the temperature disturbance highly influences output over the manipulated variable. Hence, a dynamic FFC scheme is implemented to reject known disturbance of 1 °C variation in temperature gradient from 18 °C to 19 °C due to Sea Surface Temperature (SST) changes in temperature gradient. The results show that the proposed MPC-based FBC-FF scheme effectively enhances the tracking and disturbance rejection performance compared to the PI-based FBC-FF control scheme with a minimum Integral Square Error (ISE) of 3.055 and Control Effort (CE) of 7.505. This experimental data-based, data-driven modelling and adaptive control research provides a new direction for automating OC-OTEC. Further, these studies will help to develop a rugged and automated upscaling OC-OTEC plant control system with proposed feasible control schemes.

Tritium contents in drinking and surface seawaters before the nuclear power plant planned in Sinop (Türkiye) and their radiological risks on human population.

This study aims to determine the background levels of tritium radioisotope in drinking and seawater samples of Sinop province before the nuclear power plant was established in Sinop. In this context, a total of 174 water samples were collected, these are as follows: nine drinking water samples from the Sinop center and districts and 165 seawater samples from the seacoast from Samsun to Kastamonu. Tritium concentrations in the collected water samples were measured by the liquid scintillation counter. The minimum detectable activity for the method used was found to be 1.48 Bq/L. The tritium concentrations of the seawater and drinking water samples were found in the range of <MDA (minimum detectable activity)-6.29 Bq/L and 2.45-3.17 Bq/L, respectively. In addition, the annual effective dose rates of the people consuming these drinking waters due to the tritium radioisotope were calculated separately for infants, children and adults and found to be 12.12, 16.96 and 35.38 nSv, respectively.

Isoprene Production and Its Driving Factors in the Northwest Pacific Ocean

AbstractMarine isoprene plays a crucial role in the formation of secondary organic aerosol within the remote marine boundary layer. Due to scarce field measurements of oceanic isoprene and limited laboratory‐based studies of isoprene production, assessing the importance of marine isoprene on atmospheric chemistry and climate is challenging. Calculating in‐field isoprene production rates is a crucial step to predict marine isoprene concentrations and the subsequent emissions to the atmosphere. The distribution, sources, and dominant environmental factors of isoprene were determined in the Northwest Pacific Ocean in 2019. The nutrient enrichment in the Kuroshio Oyashio Extension (KOE) surface seawater, driven by the upwelling and atmospheric deposition, promoted the growth of phytoplankton and elevated the isoprene concentration. This was confirmed by observed responses of isoprene to nutrients and aerosol dust additions in a ship‐based incubation experiment, where the isoprene concentrations increased by 70% (t = 4.417, p &lt; 0.001) and 35% (t = 2.387, p &lt; 0.05), respectively. Biogenic isoprene production rates in the deck incubation experiments were positively related to chlorophyll a, temperature, and solar radiation, with an average production of 7.33 ± 4.27 pmol L−1 day−1. Photochemical degradation of dissolved organic matter was likely an abiotic source of isoprene, contributing to approximately 14% of the total production. Driven by high isoprene production and extreme physical disturbance, the KOE showed very high emissions of isoprene of 46.0 ± 13.0 nmol m−2 day−1, which led to a significant influence on the oxidative capacity of the local atmosphere.

Mechanically robust, compressible, and photothermal silane/reduced graphene oxide modified plant fiber sponge for highly efficient cleanup of crude oil spill

Developing solar-assisted self-heating hydrophobic absorbents for efficient cleanup of viscous crude oil spills is attracting attention. However, using a simple, environment-friendly, and scalable fabrication approach to prepare solar-heating absorbent remains a big challenge. Due to the viscosity of crude oil can enormously decrease with increasing temperature, the self-heating absorbent which can in-situ raise the temperature to decrease the viscosity of crude oil shows potential application in accelerating the absorption and recovery of crude oil. Here, a hydrophobic and photothermal reduced graphene oxide and hexamethyldisilane synergistically modified plant fiber sponge (PFS@rGO@HMDS) is developed by an easy and efficient mechanical foaming strategy combined with in-situ vapor and thermal reduction treatment. The obtained PFS@rGO@HMDS exhibits good hydrophobicity (135° in water contact angle), excellent mechanical compressibility and durability, high solar absorption (>97.84 %), and oil absorptive capacity (27.3–52.0 g/g). Benefiting from the excellent photothermal conversion capacity, the surface temperature at the equilibrium of PFS@rGO@HMDS can reach 71.2 °C under 1 sun irradiation to reduce the viscosity of crude oil and realize the rapid crude oil spill remediation. The PFS@rGO@HMDS also can be used in a continual absorbent system to accomplish the ongoing and quick repair of viscous oil spills from the seawater surface, showcasing its enormous potential for use in huge-scale oil spill clean-up and recovery.

Amplified Subsurface Signals of Ocean Acidification

AbstractWe evaluate the impact of anthropogenic carbon (Cant) accumulation on multiple ocean acidification (OA) metrics throughout the water column and across the major ocean basins using the GLODAPv2.2016b mapped product. OA is largely considered a surface‐intensified process caused by the air‐to‐sea transfer of Cant; however, we find that the partial pressure of carbon dioxide gas (pCO2), Revelle sensitivity Factor (RF), and hydrogen ion concentration ([H+]) exhibit their largest responses to Cant well below the surface (&gt;100 m). This is because subsurface seawater is usually less well‐buffered than surface seawater due to the accumulation of natural carbon from organic matter remineralization. pH and aragonite saturation state (ΩAr) do not exhibit spatially coherent amplified subsurface responses to Cant accumulation in the GLODAPv2.2016b mapped product, though nonlinear characteristics of the carbonate system work to amplify subsurface changes in each OA metric evaluated except ΩAr. Regional variability in the vertical gradients of natural and anthropogenic carbon create regional hot spots of subsurface intensified OA metric changes, with implications for vertical shifts in biologically relevant chemical thresholds. Cant accumulation has resulted in subsurface pCO2, RF, and [H+] changes that significantly exceed their respective surface change magnitudes, sometimes by &gt;100%, throughout large expanses of the ocean. Such interior ocean pCO2 changes are outpacing the atmospheric pCO2 change that drives OA itself. Re‐emergence of these waters at the sea surface could lead to elevated CO2 evasion rates and reduced ocean carbon storage efficiency in high‐latitude regions where waters do not have time to fully equilibrate with the atmosphere before subduction.

Spatiotemporal distribution, source analysis and ecological risk assessment of polychlorinated biphenyls (PCBs) in the Bohai Bay, China

As a class of persistent organic pollutants (POPs), the spatial and temporal distribution of polychlorinated biphenyls (PCBs) in seawater is important for environmental assessment. Surface water samples were collected from 35 stations during summer and 36 stations during autumn of 2020 in the Bohai Bay. The concentration, composition, distribution and sources of PCBs were analyzed to assess the ecological impact of PCBs. The average concentration of ∑18PCBs was 124.6 ng/L (range of 28.1–445.5 ng/L) in summer and 122.8 ng/L (range of 21.0–581.4 ng/L) in autumn. PCBs in surface seawater of the Bohai Bay showed high near-shore and low far-shore characteristics, indicating the serious influence of land-based sources such as port activities and river inputs. Proportion analysis showed that Tetra-PCBs and Penta-PCBs were the major constituents in most stations. It was assessed as moderate and high risk (MRQ > 0.1) by mixture risk quotient (MRQ) and concentration addition (CA) model in surface seawater of the Bohai Bay. Principal component analysis (PCA) was used to explain the sources of PCBs in the Bohai Bay. PCBs in the Bohai Bay may come from commercial PCBs and their incineration products, municipal landfills, wood and coal combustion, and industrial activities, etc.

Spatiotemporal variation of dissolved oxygen concentration in the northern Gulf of Mexico during the period of 1992–2017

Dissolved oxygen (DO) concentration is an important index of ocean systems. In this study, spatiotemporal variations in DO were analyzed in the northern Gulf of Mexico (NGM) for the period of 1992–2017. Temporal variation involves annual, monthly, and seasonal variations. The spatial scope ranged from the sea surface to 1000 m depth. The results show that: (1) DO decreased from 1992 to 2017 with a brief increase; (2) clear seasonal variation characteristics of DO were presented, and the seasonal average DO was relatively low in summer; (3) the monthly average trends of sea surface DO in different years were relatively consistent; and (4) with increasing water depth from seawater surface to 1000 m, the average DO of 1992 to 2017 tended to decrease and then increase. The results aim at shedding some light on the assessment of DO change in the NGM over the past quarter century.

Spatial distribution, partitioning, and ecological risk assessment of benzotriazoles, benzothiazoles, and benzotriazole UV absorbers in the eastern shelf seas of China

Benzotriazoles (BTRs), benzothiazoles (BTHs), and benzotriazole UV stabilizers (BUVs) have attracted increasing attention due to their ubiquity in the environment, toxicity, and potential ecological risks. However, information on their distributions in the ocean is scarce. In this study, BTRs, BTHs, and BUVs were firstly determined in the surface seawater, sea-surface microlayer (SML), suspended particulate matter (SPM), and sediments of the Yellow Sea (YS) and East China Sea (ECS). The spatial distributions of BTRs, BTHs, and BUVs in the YS and ECS showed offshore decreasing trend in their concentrations, indicating that terrestrial inputs from runoff and rivers had important influences on their distributions. The organic carbon normalized partition coefficients (log Koc) of target contaminants in surface seawater-SPM (3.06–4.16 L/g) and bottom seawater-sediment (2.55–4.82 L/kg) systems were determined. SPM showed greater sorption capacities for most target contaminants than the sediment. The burial capacities of BTHs, BTRs, and BUVs from SPM to surface sediments were evaluated using their respective log Kow values and their sedimentary fluxes in the YS and ECS were quantified. BTRs, BTHs, and BUVs were enriched in the SML, with the enrichment extents of the suspended particulate phase being obviously lower than those of the dissolved phase. The ecological risks of BTRs, BTHs, and BUVs were evaluated using the risk quotient (RQ) method, which showed no toxic risk to aquatic organisms throughout the water phases, but high risk in nearshore sediments.

Beadlet anemone: A novel bio-indicator of microplastic pollution in the marine environment

Extensive usage of plastic in different industries and household usage has degraded to microplastic due to environmental conditions over the last year. While several researchers conducted the determination of microplastic (MP) bioaccumulation from rivers to stormwater, except for some filter-feeding species used as a bioindicator, to achieve a holistic approach to the fate of MPs in the marine system, sea anemone was used as an indicator. Microplastics were extracted from surface seawater, sediment, and sea anemones from the same sampling area and characterized. The extracted MPs were confirmed by confocal micro-Raman spectroscopy, and the morphology of the MPs was investigated by scanning electron microscopy (SEM). The results showed that the accumulation of microplastics and the type of polymer, shape, colour, and size of these persistent pollutants varied in sediment, surface water, and sea anemone. The abundance of MPs was different, and grey-coloured MPs were detected at a relatively higher level in sea anemones, from 8.7 to 13.3%, and more minor MPs (less than 0.5 mm) at 43.4–56.8% were detected in sea anemones among the sampling stations. In terms of polymer type, there are relatively more types of polymers classified in sea anemones among the sampling stations (six different types of polymers). These results indicated that the utilization of sea anemones as a bioindicator for MPs could be a critical factor in a better understanding of their pathway in the marine ecosystem. This study proved that analysing sea anemones as an indicator could offer a reliable, fast, and time-saving approach for detecting microplastic accumulation in marine systems.

The Seasonal Keeling Oscillation in Atmospheric pCO2 is Caused by Variation in Seawater Surface Temperature

The Seasonal Keeling Oscillation in Atmospheric pCO2 is Caused by Variation in Seawater Surface Temperature

Metatranscriptomic responses and microbial degradation of background polycyclic aromatic hydrocarbons in the coastal Mediterranean and Antarctica

Although microbial degradation is a key sink of polycyclic aromatic hydrocarbons (PAH) in surface seawaters, there is a dearth of field-based evidences of regional divergences in biodegradation and the effects of PAHs on site-specific microbial communities. We compared the magnitude of PAH degradation and its impacts in short-term incubations of coastal Mediterranean and the Maritime Antarctica microbiomes with environmentally relevant concentrations of PAHs. Mediterranean bacteria readily degraded the less hydrophobic PAHs, with rates averaging 4.72 ± 0.5 ng L h−1. Metatranscriptomic responses showed significant enrichments of genes associated to horizontal gene transfer, stress response, and PAH degradation, mainly harbored by Alphaproteobacteria. Community composition changed and increased relative abundances of Bacteroidota and Flavobacteriales. In Antarctic waters, there was no degradation of PAH, and minimal metatranscriptome responses were observed. These results provide evidence for factors such as geographic region, community composition, and pre-exposure history to predict PAH biodegradation in seawater.

Dichlorodiphenyltrichloroethane (DDT) and Dichlorodiphenyldichloroethylene (DDE) levels in air and surface sea waters along the Antarctic Peninsula

Persistent organic pollutants (POPs) are widespread worldwide, even reaching polar regions. Among POPs, dichlorodiphenyltrichloroethane (DDT) and their metabolites have been reported scarcely in the Antarctic environment. Here we report the levels of p,p′-DDT, o,p′-DDT, p,p′-DDE, and o,p′-DDE in air and water samples collected during austral summer 2009. The levels found ranged from 0.25 to 4.26 pg m−3 in the atmospheric samples while in the water samples ranged from 0.07 to 0.25 pg L−1. These concentrations were within the range of the reported concentrations in the last 20 years in Antarctica. However, the source ratio showed that most of p,p′-DDT comes from fresh applications and Dicofol formulations. The back-trajectories estimated for the air masses revealed that most of the p,p′-DDT came from the continental Antarctic peninsula and surrounding waters. The diffusive exchange direction showed that Antarctic surface waters are the final sink of the studied compounds during the survey period.

Coral Reveals a Transition in Sources of Seawater Vanadium From Submarine Groundwater Discharge to Upwelling in the Northern South China Sea

AbstractIn recent decades, vanadium (V) levels in the environment have dramatically increased and will continue to rise alarmingly in the future. Conventional methods for assessing oceanic V typically only involved the collection of seawater and sediments, which significantly limited our understanding of the dynamics of oceanic V and its relationship to environment and climate. Here, the interannual temporal variations in surface seawater V levels in the northern South China Sea, were reconstructed utilizing a 137‐year record of V/Ca ratios from Porites lutea coral from Xiaodonghai Bay off Sanya. We observed that anthropogenic activities had a limited impact on the V levels of surface seawater in the study area, whereas V variability exhibited significant disparities across different time periods. Precipitation‐related submarine groundwater discharge (SGD) recharge was the primary driver of V variation prior to 1990, with tropical cyclones (TCs) playing a detectable role in total precipitation during this period. Conversely, changes in surface seawater V levels after 1990 were predominantly linked to increasingly intense upwelling driven by summer winds. The recharge processes in unconfined groundwater systems within the study area might generate favorable oxic and alkaline conditions, which facilitated mineral dissolution and/or desorption reactions that elevated V concentrations along the groundwater flow path, which were recorded in coral skeletal V/Ca ratios. This study confirmed the seawater V was dominated by SGD and upwelling near Sanya, providing essential evidence for comprehending the geochemical behavior of V and the impact of ocean‐atmospheric climate interactions on long‐term variations in seawater V levels.

Vibrio methylphosphonaticus sp. nov., a methylphosphonate-decomposing bacterium isolated from surface seawater in the Xisha Islands, PR China.

A Gram-stain-negative, facultative anaerobic, methylphosphonate-decomposing, motile by a polar flagellum and rod-shaped marine bacterium, designated S4B1T, was isolated from the surface seawater collected from the Yongle Atoll (Xisha Islands, PR China). The pairwise alignment showed the highest sequence similarity of 97.5 and 96.6 % to Vibrio aestuarianus subsp. cardii 12_122_3T3T and Vibrio atypicus HHS02T, respectively. Phylogenetic analysis based on 16S rRNA gene and the phylogenomic analysis of single-copy genes showed that strain S4B1T belonged to the genus Vibrio and formed a close branch with Vibrio qingdaonensis ZSDZ65T. Growth of strain S4B1T occurred at 4-30 °C (optimum, 28 °C), at pH 6.0-8.0 (optimum, pH 7.0) and in the presence of 2-7 % (w/v) NaCl (optimum, 3 %). The predominant fatty acids (>10 %) were C16 : 0, iso-C16 : 0 and summed feature 3 (C16 : 1 ω7c or/and C16 : 1 ω6c). The DNA G+C content of the assembled genomic sequence was 44.3 mol%. Average nucleotide identity (ANI) values between S4B1T and its reference species were lower than the threshold for species delineation (95-96 %), in which its highest ANI value with V. qingdaonensis ZSDZ65T was 87.0 %. In silico DNA-DNA hybridization further showed that strain S4B1T had less than 70 % similarity to its relatives. On the basis of the polyphasic evidence, strain S4B1T is proposed to represent a novel species of the genus Vibrio, for which the name Vibrio methylphosphonaticus sp. nov. is proposed. The type strain is S4B1T (=KCTC 92311T=MCCC 1K06168T).

Spatial distribution and pollution assessment of heavy metals in surface and bottom water along the eastern part of the Egyptian Mediterranean coast

Seawater contamination with heavy metals (HMs) as a result of anthropogenic activities is a global challenge due to its negative impacts on marine environments and coastal communities. This study investigates the distribution of HMs (Fe, Zn, Cu, Mn, Cd, Ni and Co) and assesses the quality of surface and bottom seawater. Samples were collected in winter 2020 and summer 2021 from eleven sectors along the eastern Egyptian Mediterranean Sea coast. The water quality was evaluated using Water Quality Index (WQI), Metal Index (MI), heavy metal pollution index (HMI) and Metal Pollution index (MPI). The results indicated that, Eastern Harbour, Abu-Qir and Port Said sectors were polluted with HMs. Based on Two-Way ANOVA test there was seasonal variation for dissolved HMs (Zn, Ni, Cd and Mn in bottom layer and Cu in surface layer), while, (Cd, Co, Cu, Zn and Mn (in bottom layer)) revealed spatial differences among sectors.

Accessing the intrinsic factors of carbonyl index of microplastics: Physical and spectral properties, baseline correction, calculation methods, and their interdependence

Carbonyl index (CI) is a measure of the degradation status of microplastics. While many studies address environmental factors of microplastic degradation, intrinsic factors like physical properties, spectral properties, baseline correction, and CI calculation methods are less explored. This research focused on these aspects using surface seawater samples. We found that color and shape have limited dependence on particle size or signal-to-noise ratio (SNR). Baseline correction can significantly alter CI values, with the direction of the shift depending on the methods used. Additionally, most CI values before and after baseline correction and those calculated using different methods tend to be strongly correlated. Using the selected CI calculation methods, we found that CI values varied significantly by shape and color. CI's relation to the similarity between the sample and its pristine form suggests an alternative degradation measure. Our findings emphasize the need for standardized CI calculation methods.

Infestation of cultivated Pacific oysters by shell-boring polychaetes along the US West Coast: Prevalence is associated with season, culture method, and pH

Shell-boring polychaetes have contributed to the collapse of several mariculture operations around the world. These pests burrow into the shells of bivalves, creating mud blisters that are unappealing to consumers and which make oysters less valuable on the half-shell market. The US Pacific region produces 38% of the farmed shellfish in the US, making it important to understand the prevalence and drivers of parasite infestation in this region. We sampled Pacific oysters (Crassostrea gigas; n = 4158) from 35 shellfish farms over four seasons (two winters and two summers) in four states (northern California (CA), Oregon (OR), Washington (WA), and Alaska (AK)) to document the prevalence of shell-boring polychaetes. We extracted worms from infested oysters and used mitochondrial (CO1, n = 139) and nuclear (18S rRNA, n = 224) markers to determine species identities. To identify the environmental correlates that were associated with infestation, we pooled environmental data from seven monitoring stations in Washington. We assessed whether seawater surface temperature (SST), salinity, and pH were associated with shell-boring polychaete infestation. Our sampling confirmed the presence of Polydora websteri in the study region, in addition to four other species of shell-boring polychaetes and seven unidentified haplotypes. The mean prevalences across all shell-boring polychaete species ranged from 23 to 45% across seasons between states. In general, prevalence was higher in the winter and among oysters cultured on the bottom versus in tumbled bags, but these results varied across states. We also found greater infestation by shell-boring polychaetes at less acidified sites (pH = 8–8.2). This work is the most comprehensive dataset to characterize shell-boring polychaetes along the US West Coast, providing an important baseline of prevalence, species distribution, and environmental associations.

Distribution Characteristics of Microplastics in Surface Seawater off the Yangtze River Estuary Section and Analysis of Ecological Risk Assessment.

Microplastics are widespread in the oceans as a new type of pollutant. Due to the special geographical environment characteristics, the Yangtze River estuary region become hotspot for microplastics research. In 2017 and 2019, surface seawater microplastics samples were collected from five stations off the Yangtze River estuary during four seasons (spring, summer, autumn, and winter). The abundance and characteristics of microplastics in seawater were researched. The results showed that microplastics widely existed in surface seawater; the average abundance of microplastics in seawater was (0.17 ± 0.14) items/m3 (0.00561 ± 0.00462) mg/m3; and accounting for 80% of the total plastic debris, the abundance of microplastics was at moderately low levels compared to national and international studies. The particle size of most microplastics was between 1 mm to 2 mm, accounting for 36.1% of the total microplastics. The main shapes of microplastics were fiber, flake, and line, accounting for 39.5%, 28.4%, and 20.8%, respectively. Polypropylene, polyethylene terephthalate, and polyethylene were the main components of microplastics, accounting for 41.0%, 25.1%, and 24.9%, respectively. Yellow, green, black, and transparent were the most common colors, accounting for 21.9%, 19.6%, 16.5%, and 15.7%, respectively. This study shows that the spatial distribution of microplastics in the surface waters off the Yangtze River estuary shows a decreasing trend from nearshore to farshore due to the influence of land-based inputs, hydrodynamics, and human activities; the distribution of microplastics has obvious seasonal changes, and the level of microplastic pollution is higher in summer. The potential ecological risk of microplastics in the surface waters off the Yangtze River estuary is relatively small.

Chemodynamics of Polycyclic Aromatic Hydrocarbons and Their Alkylated and Nitrated Derivatives in the Yellow Sea and East China Sea.

The occurrence of continuously released polycyclic aromatic hydrocarbons (PAHs) in marginal seas is regulated by hydrological and biogeochemical processes; however, scarce knowledge is about their derivatives in marine environments. In this study, the dissolved and particulate PAHs and their alkylated/nitrated derivatives (A-PAHs/N-PAHs) in surface seawater of the southwestern Yellow Sea (YS) and northwestern East China Sea (ECS) during September 2022 were comprehensively discussed. Results confirm higher levels of Σ26PAHs (9.3-70 ng/L) and Σ43A-PAHs (13-76 ng/L) than Σ20N-PAHs (0.80-6.6 ng/L). The spatial heterogeneity of contaminants was regulated by substantial riverine runoff and ocean currents. Lagrangian Coherent Structure analysis further revealed the existence of a transport barrier at the shelf break of the southwestern YS where contaminants hardly crossed and tended to accumulate. The relationship between dissolved compounds and chlorophyll a indicated both biodegradation and the biological pump contributed to the depletion of PAHs and A-PAHs from surface seawater while the biological pump was the major driver for N-PAHs, despite their complicated water-particle partition behavior due to variations in physicochemical properties in the presence of nitro groups. Source identification demonstrated that pyrogenic and petrogenic sources dominated the YS and ECS, respectively, while photochemical transformations appeared more active in the YS.

Isolation and characterization of polyhydroxyalkanoate-degrading bacteria in seawater at two different depths from Suruga Bay.

Polyhydroxyalkanoate (PHA) is a highly biodegradable microbial polyester, even in marine environments. In this study, we incorporated an enrichment culture-like approach in the process of isolating marine PHA-degrading bacteria. The resulting 91 isolates were suggested to fall into five genera (Alloalcanivorax, Alteromonas, Arenicella, Microbacterium, and Pseudoalteromonas) based on 16S rRNA analysis, including two novel genera (Arenicella and Microbacterium) as marine PHA-degrading bacteria. Microbacterium schleiferi (DSM 20489) and Alteromonas macleodii (NBRC 102226), the type strains closest to the several isolates, have an extracellular poly(3-hydroxybutyrate) [P(3HB)] depolymerase homolog that does not fit a marine-type domain composition. However, A. macleodii exhibited no PHA degradation ability, unlike M. schleiferi. This result demonstrates that the isolated Alteromonas spp. are different species from A. macleodii. P(3HB) depolymerase homologs in the genus Alteromonas should be scrutinized in the future, particularly about which ones work as the depolymerase.