Anthropogenic sedimentation is a major contributor to the worldwide decline in coral cover. Resuspension of benthic material can exacerbate the threat to corals, but evidence of vertical sediment gradients is limited. Here, we installed sediment traps at 10, 20, 30, 40, and 50 cm above the substrate at three equatorial reef sites for three months and determined the dry mass, particle size, and biogeochemical composition of the material collected. As the trap mouth height increased from 10 to 50 cm, dry mass decreased as sediments became finer, poorer in carbonate, and richer in silicate. Despite among-site differences in collected sediment, this vertical gradient was present in all trap arrays, likely driven by resuspension mechanisms on seabed sediments. These results have implications for coral vertical ecology and underline the importance of standardising sediment collection protocols.

Understanding the distribution of trace elements in Ocellated icefish (Chionodraco rastrospinosus), one of fish species with lacking hemoglobin from the family Channichthyidae and distributes in a very limited area at the south Scotia Sea, will help understand their physiological composition and conserve this vulnerable population; however, information on this topic is extremely limited. This study examines trace elements (two essential elements, copper [Cu] and zinc [Zn], and two non-essential elements, cadmium [Cd] and lead [Pb]) in C. rastrospinosus and provides for the first time baseline data on elemental distribution in four tissues of C. rastrospinosus in the northern Antarctic Peninsula (NAP). The element concentrations showed the following trends: Zn > Cu > Pb > Cd in muscle and stomach and Zn > Cu > Cd > Pb in intestine and liver. Among all tissues, muscle had the lowest element concentrations. The average Zn level is 70.81 ± 28.91 μg g⁻¹ dry weight (DW) in C. rastrospinosus muscle, which is higher significantly than average levels of Cu (0.56 ± 0.41 μg g⁻¹ DW), Pb (0.29 ± 0.33 μg g⁻¹ DW) and Cd (0.12 ± 0.05 μg g⁻¹ DW). Zn and Cd concentrations in the stomach and intestines were significantly positively correlated. C. rastrospinosus could be a useful bioindicator for monitoring variability in trace elements dynamics in NAP and the environmental variability in this region.

This study was a baseline with quantitative data of marine litter along the Gulf of Nicoya, Costa Rica. The objective of the study was to quantify marine litter and its association with human activities in this estuarine gulf. A total of fourteen sandy beaches were cataloged by the degree of urbanization, tourism intensity, beach cleaning programs, and tributary rivers as possible drivers of marine litter presence. The items of the marine litter were separated and weighted by type. Analysis by the clean coastal index (CCI) and multivariate statistics were applied to find spatial patterns in marine litter in the gulf. On beaches with the highest touristic activity, cigarette butts and straws were the main components. Locations with river plume influence, less frequent cleanup, or waste cans showed more bottles, plastic parts, and sanitary waste than beaches in other conditions. A beach in a fisherman town had recently utilized plastic bags, household goods, and boat parts in the marine litter. A wildlife refuge beach showed only small plastic and coffee foam cup fragments that came with currents from other points in the estuary. River basin management, solid waste disposal programs, and environmental education to avoid single-use items combined with correct waste disposal are needed to reduce marine litter in tropical countries focused on ecological tourism.

Globally, nutrient river discharges drive water quality of coastal ecosystems, and excess nutrients can cause eutrophication impacts. The Grijalva-Usumacinta River System (GURS) discharges in the southern Gulf of Mexico (SGoM) and it is the second largest riverine input to the Gulf. To study how contrasting GURS freshwater flow between rainy and dry seasons affects nutrients concentrations in the receiving coastal ecosystem, we evaluated nutrient variability in the water column during both seasons. High inorganic nutrients and total phosphate outline the rivers discharge plumes during rainy season, and were significantly higher than during the dry season throughout the study area, suggesting contrasting seasonal nutrient discharge of the GURS to coastal waters. On average the GURS discharged 141,123 t N yr⁻¹ 6893 t P yr⁻¹ and 928,904 t Si yr⁻¹ to SGoM. These results contribute with a nutrient baseline in the SGoM that could be useful for GURS decision-makers.

Ocean acidification resulting from increased CO₂ and pollution from land-sourced toxicants such as copper have been linked to coral cover declines in coastal reef ecosystems. The impacts of ocean acidification and copper pollution on corals have been intensively investigated, whereas research on their effects on coral endosymbiont Symbiodiniaceae is limited. In this study, reproduction, photosynthetic parameters, nutrient accumulation and metabolome of Symbiodiniaceae Cladocopium goreaui were investigated after a weeklong treatment with acute CO₂-induced acidification and copper ion. Acidification promoted algal reproduction through increased nutrients assimilation, upregulated citrate cycle and biomolecular biosynthesis pathway, while copper exposure repressed algal reproduction through toxic effects. The combined acidification and copper exposure caused the same decline in algal reproduction as copper exposure alone, but the upregulation of pentose phosphate pathway and the downregulation of aromatic amino acid biosynthesis. These results suggest that copper pollution could override the positive effects of acidification on the symbiodiniacean reproduction.

Interactions between microplastic (MP) and fine-grained suspended sediment in natural waters are important for the environmental fate of plastic particles. Estuaries are transitional areas between freshwater and open marine systems and are recognized as important accumulation zones for MPs. However, there is a knowledge gap on the processes driving the sedimentation of MPs in estuaries, especially with regard to positively buoyant MPs. Here we show from settling tube experiments that positively buoyant and non-spherical MP HDPE particles in different size-fractions (63–500 μm) and concentrations (1 and 5 mg l⁻¹) rapidly flocculate and settle with natural fine-grained sediment in natural seawater. Our results demonstrate that flocculation is a key process for the vertical transport of MP in estuaries. The implication is that land-based sources of positively buoyant HDPE MP transported by rivers will likely settle and accumulate in estuarine environments and thereby increase the concentration of MP in the benthic zone.

Ocean warming is an extreme environment event that has profound and lasting impacts on Symbiodiniaceae. However, their response mechanisms to elevated temperature exposure are poorly understood. In this study, the physiological and transcriptional responses of Effrenium voratum (Symbiodiniaceae) to ocean warming were examined. After exposure to 30 °C, no significant variations in growth, chlorophyll a, or photosynthetic and respiration rates were observed, while a higher temperature (34 °C) significantly reduced these physiological measurements. Meanwhile, lipid content and fatty acid composition were altered at high temperature (i.e., elevated degree of fatty acid saturation). Such biochemical constituents likely contributed to the mitigation of the negative effects of elevated temperatures. Furthermore, higher expression levels of genes related to the synthesis and elongation of fatty acids were detected at high temperature. The adjustment of lipids and fatty acid composition may be a potential mechanism by which E. voratum may survive under future global warming. The adjustment of lipids and fatty acid composition may be a potential mechanism by which E. voratum acclimate to future global warming.

The interaction between microplastics (MPs) and suspended sediment (SS) is important for the environmental fate of MPs. This study explored the interaction of MPs with SS and the vertical migration behavior of MPs in sediment-bearing turbulence. The turbulent shear flow caused MPs to aggregate. This aggregation resulted in a rapid increase in particle size, which peaked when the shear rate was 19.94 s⁻¹, and then declined with a further increase in the shear rate. Compared to large MPs, small MPs were more prone to aggregation, which formed heterogeneous aggregate MPs-SS in sediment-bearing turbulence. Owing to the formation of heterogeneous aggregates, small MPs had a much higher settlement rate in sediment-bearing turbulence than in sediment-free turbulence. MPs in bottom sediments may resuspend owing to turbulent shear flow acting on sediments, causing secondary pollution. These results provide new insights into the aggregation, settlement, and resuspension behaviors of MPs in natural waters.

The water-sediment partitioning of flumequine and florfenicol, two antibiotics used in salmon aquaculture is a critical driver of their fate and environmental impact. Batch experiments, were carried out using pure water or seawater, with or without sediment, and at summer and winter temperatures of Chilean fjords. Log Kd (partition between water and sediment) of florfenicol in seawater varied from 0.62 ± 0.69 to 0.67 ± 0.13, and Log KOC (partition between water and organic fraction of sediment) from 2.15± 0.29 to 2.19 ± 0.13. Difference between KOC and the octanol-water partition constant (KOW) showed that for florfenicol, adsorption onto the surface of particles was more significant than the absorption driven by hydrophobicity whilst hydrophobic absorption was a major driver of flumequine sorption. Flumequine Log Kd (0.92 ± 0.25 to 1.36 ± 0.10) and Log KOC (from 2.44 ± 0.25 to 2.89 ± 0.10) demonstrated its greater affinity than florfenicol to particles and potential accumulation into marine sediments.

Coastal agricultural practices are often located in catchments upstream of ecologically important aquatic systems. Here, we investigate the occurrence of pesticides in a coastal creek flowing into a habitat-protected area within the Solitary Islands Marine Park, Australia. Water samples were collected from six sites along a creek transect during three sampling periods. Samples were analysed for 171 pesticide analytes, including organochlorines, organophosphates, herbicides, and fungicides. Five insecticides, two herbicides, and two fungicides were detected. The neonicotinoid imidacloprid was detected at 5 out of 6 sites, with concentrations reaching 294 μg L⁻¹, the highest yet detected in Australian waterways. The organophosphate insecticide dimethoate was detected at 4 sites, which occurred at the 2nd highest detected concentration in the study (12.8 μg L⁻¹). The presence of these pesticides in the aquatic environment downstream of horticulture in this and other regions may have serious implications for stream biota and ecologically important marine ecosystems.