Existing mitigations to address deterioration in water clarity associated with human activities are based on responses from single seagrass species but may not be appropriate for diverse seagrass assemblages common to tropical waters. We present findings from a light experiment designed to determine the effects of magnitude and duration of low light on a mixed tropical seagrass assemblage. Mixed assemblages of three commonly co-occurring Indo-West Pacific seagrasses, Cymodocea serrulata, Halodule uninervis and Halophila ovalis were grown in climate-controlled tanks, where replicate pots were subjected to a gradient in light availability (0.9–21.6 mols PAR m−2 day−1) for 12 weeks. Increased shading resulted in declines in growth and changes in cellular and photosynthesis responses for all species, although time-scale and magnitude of response were species-specific. Applying management criteria (e.g. thresholds) relevant to one species may under- or over-estimate potential for impact on other species and the meadow as a whole.

Benthic indicators are important tools for the classification of coastal and transitional water bodies. The aim of the work was to assess for the first time the Environmental Status (ES) of Slovenian transitional waters, comparing the following biotic indices: richness, Shannon-Weaver diversity, AMBI, M-AMBI, BENTIX and BITS indices. A total of 13 stations were sampled with a Van Veen grab, in three ecosystems in the northern Adriatic. Samples were sieved and sorted, invertebrates identified and counted. The anthropogenic impact was estimated with professional judgement. Richness and diversity showed a good response to anthropogenic pressure. Conversely, indices based on sensitivity/tolerance groups did not showed a clear distinction between more and less impacted ecosystems. In particular BENTIX underestimated the ES, while with BITS there was a overestimation. The best evaluation was obtained with M-AMBI, because even if based on a sensitivity/tolerance approach, it considered also the structural aspect of the community.

The first report on the emergence of microplastic in Malaysian marine waters was documented in this study. Water samples were collected from two regions, namely Kuala Nerus and Kuantan port, as the representatives of different anthropogenic activities. Identification of microplastic was performed based on physical characteristics (colour, shape, density) and chemical characterisation (ATR-FTIR analysis) for a functional group of polymers. Fragment type, black or grey colour and high density (>1.02 g cm−3) of microplastic were the most prevalent characteristics found in both areas. Two principal components (density and colour) rendered explained about 95.3% (Kuantan) and 95.6% (Kuala Nerus) of the total variance. Six possible polymer materials were identified, namely polyester, polystyrene, polyamide, polyvinyl chloride, polypropylene, and polyethylene. The findings of the study provided good baseline information on marine debris issue in Malaysia.

Using ¹³C/¹²C, ¹⁵N/¹⁴N and ¹⁸O/¹⁶O isotopes, the trophic relationship and growth estimation were analyzed in gastropods Nassarius siquijorensis, Murex trapa and Turritella bacillum and their potential food sources and predators in summer and winter from estuarine and oceanic environments in subtropical Hong Kong. Results of δ¹³C and δ¹⁵N values and isotopic mixing model revealed N. siquijorensis and M. trapa were one trophic level higher than T. bacillum, in which its main food source was particulate organic matter (POM) whereas N. siquijorensis largely consumed POM and polychaetes and M. trapa also preyed on other gastropods. Crabs were the major predator of gastropods. Organisms collected from oceanic waters were more ¹³C enriched than from estuarine waters, reflecting different carbon food sources from marine or terrestrial origin. The δ¹⁸O profile from shell carbonate suggested these gastropods were one to two years old. T. bacillum exhibited faster summer growth than the other two species.

Large seaweed cultivation has proven an effective means to inhibit harmful microalgae at experimental scales and battle eutrophication in Chinese coastal waters, but essentially there is a lack of field-scale studies to explore the underlying mechanism. Here we present a 1.5-year-long time series of particulate organic matter (POM) and settling particulate matter (SPM) concentrations from an integrated aquaculture of Gracilaria lemaneiformis off the coast of Nan'ao Island, South China from April 2014 to August 2015. The microscopic examination and geochemical characteristics show that the POM mainly consisted of microalgae. The mean POM concentration increased 99.8%, 71.2%, 45.8% and 111.9% at the four sampling sites during the non-cultivation period, while decreased 25.5%, 17.3%, 12.2% and 20.3%, respectively, during the seaweed cultivation period. These results suggest that the large scale seaweed cultivation can remove excess nutrients and inhibit microalgal growth, thereby contributing to the improvement of coastal marine aquaculture environment.

Spatial distribution of potentially toxic metals (PTMs) and their accumulation in mangrove Avicennia officinalis L. were studied along 8 locations in and around Sundarban mangrove wetland, India. Among 8 locations, S3 (Chemaguri) and S5 (Ghushighata) showed higher concentration of PTMs (Cd, Cr, Cu, Ni, Pb, Zn) characterized by higher enrichment factors (3.45–10.03), geo-accumulation indices (0.04–1.22), contamination factors (1.14–3.51) and pollution load indices (1.3–1.45) indicating progressive deterioration of estuarine quality and considerable ecotoxicological risk. Metal concentration in A. officinalis leaves showed significant correlation with sediment metals implying elevated level of bioaccumulation. Significant statistical correlation between photosynthetic pigments (Chlorophyll a, Chlorophyll b), antioxidant response (free radical scavenging and reducing ability) and stress enzymatic activity (Peroxidase, Catalase, Super-oxide dismutase) of A. officinalis with increasing metal concentration in the contaminated locations reflects active detoxification mechanism of the plant. The study indicates the potentiality of biomonitoring metal pollution using studied biochemical markers in mangrove habitats.

The dramatic increase of microplastics (plastic fragments <5 mm) in marine environments is a problem that has attracted public attention globally. Within the different types of microplastics, microfibres are the least studied (size <1 mm). We examined 51 female scats from a population in Northern Patagonia. Our results showed no presence of microplastic particles, however 67% of them showed a remarkable abundance of microfibers, which until now had only been reported in animals fed in captivity. As a result of this work we propose that the examination of scats from South American Fur Seal and also other pinnipeds could be an efficient tool to monitor environmental levels of microfibres and maybe microplastics in the environment due to the easy recognition of the animals and their scats.

The behavioural responses of migrating humpback whales to an air gun, a small clustered seismic array and a commercial array were used to develop a dose-response model, accounting for the presence of the vessel, array towpath relative to the migration and social and environmental parameters. Whale groups were more likely to show an avoidance response (increasing their distance from the source) when the received sound exposure level was over 130 dB re 1 μPa²·s and they were within 4 km of the source. The 50% probability of response occurred where received levels were 150–155 dB re 1 μPa²·s and they were within 2.5 km of the source. A small number of whales moving rapidly close to the source vessel did not exhibit an avoidance response at the highest received levels (160–170 dB re 1 μPa²·s) meaning it was not possible to estimate the maximum response threshold.

Eight beach/dune systems located along the Atlantico Department, Caribbean coast of Colombia were surveyed to determine litter influences over its scenic quality. Application of the Coastal Scenic Evaluation System (CSES) categorized these systems into two of the five available classes. Five of the investigated beach/dune systems belong to Class IV, while three systems correspond to V. Classes I, II and III were not found. Along these beach/dune systems, a total amount of 1908 litter items were collected with average abundances of 4.2 items/m2. Currently, 82% of surveyed sites are under an unacceptable condition of cleanness. User's habits as well as bad litter management practices are directly responsible for the decline of scenic quality of the Atlantico Department beach/dune systems. Litter management must be centered on strategies to eliminate or minimize litter sources. Specific remedial actions need to be defined and developed.

This study assesses the presence of microplastic litter in the contents of the gastrointestinal tract of 26 commercial and non-commercial fish species from four difference habitats sampled along the Saudi Arabian coast of the Red Sea. A total of 178 individual were examined for microplastics. In total, 26 microplastic fragments were found. Of these, 16 being films (61.5%) and 10 being fishing thread (38.5%). FTIR analysis revealed that the most abundant polymers were polypropylene and polyethylene. Parascolosps eriomma species sampled at Jazan registered the highest number of ingested microplastic. This fish species is benthic and feeds on benthic invertebrates. Although differences in the abundance of microplastic ingestion among species were not statistically significant, a significant change was observed when the level of ingestion of microplastics particles was compared among the habitats. The higher abundance of microplastics particles may be related to the habitats of fish and the presence of microplastics debris near the seabed. The results of this study represent a first evidence that microplastic pollution represents an emerging threat to Red Sea fishes, their food web and human consumers.