The quality of seawater needs to be continuously monitored due to its effect on human life and natural ecosystems. However, the balance of the extent, spatial pattern and maintenance costs of marine environmental monitoring remains a challenging issue which is crucial for decision-makers. The main contribution of this work suggests taking advantage of two minimization criteria (TMC: integrating minimization of Kriging variance and minimization of relative error at a given confidence level) to improve the design and optimization of a marine environmental monitoring network. To achieve this purpose, the spatial simulated annealing (SSA) method is applied to identify the best locations for monitoring network optimization. For the case study, phosphate (PO4) is used as an indicator to characterize the seawater quality in northern coastal waters of Zhejiang Province, China. The 122 existing sites have redundancies (about 78 sites) that can be effectively identified and removed to reduce costs with the given relative error (less than 10%) and confidence level (95%). Some new sites can be added and adjusted to improve the quality of costal environmental monitoring based on quantitative analysis. In addition, the relationship between the number of the monitoring sites and monitoring precision is analyzed. The results suggest that the present method using TMC can provide a scientific basis for marine environmental monitoring and management.

This study presents baseline records of trace metals for two commercial shrimps from the inner continental shelf of southeast Brazil (~22°S). Organisms were sampled in 2004, 10 years before the beginning of large port activities in coastal waters. The concentrations of trace metals in muscle tissues (μg.g⁻¹ w.w.) of Xyphopenaues kroyeri and Artemesia longinaris are as follows: Al: 141.57 and 146.71, Fe: 83.17 and 91.68, Zn: 28.69 and 29.70, Cu: 7.19 and 3.94, Mn: 1.47 and 1.72, Pb: 1.14 and 0.60, V: 0.66 and 0.56, Ni: 0.38 and 0.34, Cr: 0.42 and 0.29, and Cd: 0.15 and 0.14, respectively. Significantly higher concentrations of Cu and Pb were recorded for X. kroyeri. In general, the concentrations are below the maximum permissible limits for metals in fishery/food products, as established by the Brazilian Agency for Sanitary Vigilance (ANVISA), except for Pb and Cr. These baseline records are relevant for future monitoring.

The prevalence of microplastics in the sediments of six beaches of the Puducherry coast in India was studied and its correlation to fishing activities and recreational activities was analysed. On an average, 72.03 ± 19.16 microplastic particles/100 g dry weight of sediments is found to be the microplastic abundance in the study. A Strong positive correlation (Pearson's R = 0.92, p = 0.0103) between fishing activity and microplastic abundance and a weak correlation (Pearson's R = 0.04, p = 0.932) between microplastic abundance and recreational activities is found. Majority (65.12%) of the microplastics belongs to the size bracket of 300 μm-1 mm and only 34.88% were large microplastics (>1 mm). The Polymers of the microplastics were identified as Polypropylene, HDPE, LDPE, Polystyrene, Polyurethane etc. using Raman spectroscopy. Microplastic fragments comprise 56.32% of the total particles. In terms of colour of the microplastics, white (26.92%) is the most abundant.

This study measured spatial distribution of marine debris stranded on beaches in South Eleuthera, The Bahamas. Citizen science, fetch modeling, relative exposure index and predictive mapping were used to determine marine debris source and abundance. Citizen scientists quantified debris type and abundance on 16 beaches within three coastal exposures (The Atlantic Ocean, Great Bahama Bank and The Exuma Sound) in South Eleuthera. Marine debris, (~2.5 cm or larger) on each beach was monitored twice between March–May and September–November 2013 at the same locations using GPS. Approximately, 93% of all debris items were plastic with plastic fragments (≤2.5 cm) being the most common. There were spatial differences (p ≤ 0.0001) in plastic debris abundance between coastal exposures. Atlantic Ocean beaches had larger quantities of plastic debris by weight and by meter (m) of shoreline. Stranded plastic may be associated with Atlantic Ocean currents associated with leakage from the North Atlantic sub-tropical gyre.

Located within the subtropical convergence zone, the Hawaiian archipelago is subject to high debris loads. This paper represents the first study to determine the spatial and temporal trends of floating macro debris quantities and polymer composition within Maui County waters. Ocean surveys were conducted from 2013 to 2017 and collected 2095 debris items of which 90% were plastic. Attempts to categorize items by source resulted in only 6% likely from land, 12% from ocean-based sources, 50% from either land or ocean, and 32% from unknown sources. Results found a multi-step process for debris accumulation, with temporal trends linked to survey day and year and spatial trends linked to ocean processes. High- and low-density polyethylene and polypropylene accounted for the majority of polymer types. The results of this study demonstrate minimal debris in Maui originates from land/local sources, and the importance of baseline data to guide further research and mitigation measures.

Gelatinous zooplankton including jellyfishes, pyrosomes, and salps serve as important prey items for a number of marine species; however, relatively few studies have examined contaminant concentrations in these animals. Scyphozoans (Aurelia sp., Chrysaora colorata, C. fuscescens, and Phacellophora camtschatica) and Thaliaceans (Pyrosoma sp.) were collected from 2009 to 2011 from Monterey Bay National Marine Sanctuary and analyzed for total mercury and selenium concentrations. In general, mercury (0.0001–0.0016 μg/g wet weight) and selenium (0.009–0.304 μg/g wet weight) concentrations of the sampled organisms were low; however, the two Pyrosoma sp. had total mercury and selenium concentrations that were one order of magnitude higher than the Scyphozoans. There was a significant positive relationship between mercury and selenium concentrations in jellyfishes and pyrosomes, suggesting a potential detoxification mechanism in these lower trophic level organisms. This study provides evidence that trophic transfer of mercury and selenium likely occurs through ingestion of gelatinous prey.

Based on field observations in the summer of 2006 and long-term series data, this paper investigates the spatiotemporal variations of hypoxia and associated physical-biogeochemical driving mechanisms in the Bohai Sea (BS), China. Results show that the benthic hypoxic zone is mainly distributed in the “V”-shaped trough region in the western BS, and it tends to form two hypoxic centers which generally correspond to the bottom cold-water core. The regional difference in the intensity of stratification has a significant impact on the spatial distribution of hypoxia. The relatively weak stratification and the mesoscale anticyclonic eddy in the central shoal of the BS weaken the connectivity between the southern and northern hypoxic zones. Organic matter decomposition contributes to hypoxia and results in corresponding nutrient pool with a “dual (southern and northern)-core” structure. Intensified eutrophication is the main drive for decreasing in bottom dissolved oxygen and expansion of hypoxic zone in the BS.

Knowledge on microplastic (MP) ingestion by cetaceans is difficult to obtain. We infer the potential for MP uptake by cetaceans from the occurrence of MP in prey species. First, we reviewed information on whale prey species, focussing on common minke (Balaenoptera acutorostrata) and sei whale (B. borealis), for which the most comprehensive quantitative datasets exist. Second, evidence of MP ingestion by their prey species was reviewed. We found common minke whales forage opportunistically on fish from various families: Ammodytidae, Clupeidae, Gadidae, Engraulidae and Osmeridae. Sei whales mostly feed on copepods, Engraulidae, Clupeidae and Scombridae. High levels of MP contamination are reported for Scombridae in the Atlantic and Engraulidae in the Northwest Pacific Ocean. Copepods exhibit low levels of MP ingestion in the Northeast Pacific Ocean. Species-specific prey preferences and feeding strategies imply different cetaceans have varied potential for MP uptake, even if they feed in similar geographic areas.

Information about coral community response to bleaching on Indian reefs is much more limited compared with Indo-Pacific reefs, with no understanding of algal symbionts. We investigated a reef in Palk Bay to understand the coral community response to 2016 bleaching event and to reveal dominant symbiont type association in four common coral genera. Out of 508 colonies surveyed, we found 20.9% (106) mortality in 53.8% (n = 290) of bleached corals. We found differential bleaching and recovery pattern among coral genera. Bleaching was most prevalent in Acropora (86.36%), followed by Porites (65.45%), while moderate to no bleaching was recorded in Favites 5.88%, Symphyllia 51.11% and Favia 55.77%, Platygyra 41.67%, Goniastrea 41.83%. Pre-bleaching and post bleaching samplings revealed changes in dominant symbiont type following bleaching only in Acropora (Cladocopium, Clade C to Durusdinium Clade D) while no such changes were found in other coral genera hosted Clade D. This is the first observation of coral symbiont diversity in the Indian reef.