Fragmentation of large plastic debris into smaller particles results in increasing microplastic concentrations in the marine environment. In plastic debris fragmentation processes, the influence of biological factors remains largely unknown. This study investigated the fragmentation of expanded polystyrene (EPS) debris by polychaetes (Marphysa sanguinea) living on the debris. A large number of EPS particles (131 ± 131 particles/individual, 0.2–3.8 mm in length) were found in the digestive tracts of burrowing polychaetes living on EPS debris. To confirm the formation of microplastics by polychaetes and identify the quantity and morphology of produced microplastics, polychaetes were exposed to EPS blocks in filtered seawater under laboratory conditions. Polychaetes burrowed into the blocks and created numerous EPS microplastic particles, indicating that a single polychaete can produce hundreds of thousands of microplastic particles per year. These results reveal the potential role of marine organisms as microplastic producers in the marine environment.

Trace elements in organisms are normally higher in well-developed coastal areas than on oceanic islands. Few studies have used seaweeds as their sentinels on islands. This study established background levels of trace elements (As, Cd, Pb, Zn, Cu and Hg) for four seaweed species (Dictyopteris delicatula and Canistrocarpus cervicornis, brown algae; Ceratodictyon variabile and Palisada perforata, red algae) from Trindade, an oceanic Brazilian island, and verified potential differences associated to distinct environmental conditions. Spatial differences were not detected for As, Hg and Cd in samples, although the highest concentrations of these elements were observed in brown seaweeds. The highest Zn, Pb and Cu concentrations in seaweeds from the only inhabited beach may be a signal of the onset of human footprints on this still pristine, remote island. By comparison with background described in the literature, concentrations of trace elements in seaweeds were low, thus, allowing them to be considered reference levels.

Inappropriate disposal of plastic debris has led to the contamination of marine habitats worldwide. This debris can be ingested by organisms; however, the extent to which chewing and gut transit modifies plastic debris is unclear. Detritivores, such as amphipods, ingest and shred natural organic matter and are fundamental to its breakdown. Here we examine ingestion and shredding of plastic carrier bags by Orchestia gammarellus. A laboratory experiment showed these amphipods shredded plastic carrier bags, generating numerous microplastic fragments (average diameter 488.59μm). The presence of a biofilm significantly increased the amount of shredding, but plastic type (conventional, degradable and biodegradable) had no effect. Subsequent field observations confirmed similar shredding occurred on the strandline. Rates of shredding will vary according to amphipod density; however, our data indicates that shredding by organisms could substantially accelerate the formation microplastics in the environment.

The anthropogenic pressure in recent years has driven us to investigate the environmental quality at 22 stations in Parangipettai by collecting seawater samples monthly from 2014 to 2015. The sampling stations were grouped into three different environments, namely, Vellar Estuary (VE), Coleroon Estuary (CE), and Open Sea (OS). Factor analysis showed a total variance of 65.63% and exhibited a strong factor loading for atmospheric temperature (0.914), water temperature (0.917), ammonia (0.767), inorganic phosphate (0.897), total phosphorus (0.783), and phytoplankton (0.829). The index value showed water quality was good in OS (74.18), whereas it was moderate in VE (69.73) and CE (68.47). The visual model developed using Geographical Information System (GIS) displayed a spatial pattern of water temperature and phytoplankton dispersion in a distinct manner. The results obtained through multivariate analysis and GIS-based model are imperative to establish reference for a comparative study with other similar ecosystem for better planning and management of tropical seawaters.

Very intense internal tides take place in Indonesian seas. They dissipate and affect the vertical distribution of temperature and currents, which in turn influence the survival rates and transports of most planktonic organisms at the base of the whole marine ecosystem. This study uses the INDESO physical model to characterize the internal tides spatio-temporal patterns in the Indonesian Seas. The model reproduced internal tide dissipation in agreement with previous fine structure and microstructure observed in-situ in the sites of generation. The model also produced similar water mass transformation as the previous parameterization of Koch-Larrouy et al. (2007), and show good agreement with observations. The resulting cooling at the surface is 0.3°C, with maxima of 0.8°C at the location of internal tides energy, with stronger cooling in austral winter. The cycle of spring tides and neap tides modulates this impact by 0.1°C to 0.3°C. These results suggest that mixing due to internal tides might also upwell nutrients at the surface at a frequency similar to the tidal frequencies. Implications for biogeochemical modelling are important.

In the present study, we analyzed the influence of untreated sewage exposure on carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic composition and several biochemical responses in the barnacle Balanus glandula. The main objective was to evaluate whether changes in stable isotopes signature do reflect biochemical sub-lethal effects in a sewage influence gradient. Stable isotopes analysis showed differences in isotope signatures between close sewage influence and distant sites, being δ¹³C signatures stronger than that of δ¹⁵N. Regarding biochemical effects, although organisms close to the effluent would be clearly exposed to contaminants (increased GST activity) the oxidative stress would not be too evident (peroxidases and ACAP not affected). The most affected physiological aspect was the digestive one, reflected in increased alkaline proteases and lipases activities. A clear relation between δ¹⁵N and GST activity was found, showing to δ¹⁵N as an indicator of potential exposure to chemical contaminants.

The purpose of this study was to quantify phosphorus bioavailability and various forms of this element in surface sediments of the southern Caspian Sea. To do, sediment samples were collected from different depths in autumn 2015 using a Van Veen Grab. Phosphorus forms were recognized by a sequential extraction procedure (SEDEX). Results revealed that the range of total phosphorus (TP) was between 431ppm and 594ppm with a mean value of 535.25±45.05ppm. Organic phosphorus (OP) ranged from 62 to 99ppm and contributed 14.85±2.21% of total phosphorus in average. The contents of loosely phosphorus, iron-bound phosphorus, authigenic phosphorus and detrital phosphorus varied 35–55ppm, 50–94ppm, 125–189ppm and 152–217ppm, respectively. Generally, inorganic phosphorus (IP) was between 365 and 522ppm which comprised 81.9–88.53% of total phosphorus. Findings showed levels of different phosphorus forms in a descending order: detrital P>Authigenic P>Organic P>Fe-P>Loosely P. Bioavailable phosphorus concentration was between 153ppm and 240ppm and consisted 37.21±3% of total phosphorus. Based on molar ratio of TOC/OP, organic matter obtained from the studied stations suggested a terrestrial origin.

Based on a survey conducted from June to July 2013, aragonite saturation state variation and control in the river-dominated marginal BoHai and Yellow seas were investigated. Surface water Ωarag ranged from 2.0–3.8, whereas subsurface water Ωarag was generally lower than 2.0. Temperature changes had a strong influence on Ωarag through induced CO2 solubility changes in seawater. Riverine freshwater input decreased Ωarag in the Changjiang and Yalu river estuaries, but induced higher Ωarag in the Yellow River estuary. Biological processes had opposite effects on Ωarag, whereby elevated biological production led to the highest Ωarag in the South Yellow Sea surface water, whereas net community respiration/remineralization induced low Ωarag in subsurface water. Stratification affected the level and scale of low Ωarag in subsurface water. By the year 2100, surface water with Ωarag > 2.0 will disappear except for the Yellow River estuary, and most of the subsurface water will develop substantial aragonite undersaturation.