Physical and cellular impact of environmentally relevant microplastic exposure on thermally challenged Pocillopora damicornis (Cnidaria, Scleractinia).

Microplastic pollution is an increasing threat to coral reefs, which are already strongly challenged by climate change-related heat stress. Although it is known that scleractinian corals can ingest microplastic, little is known about their egestion and how microplastic exposure may impair corals at physiological and cellular levels. In addition, the effects of microplastic pollution at current environmental concentration have been little investigated to date, particularly in corals already impacted by heat stress. In this study, the combined effects of these environmental threats on Pocillopora damicornis were investigated from a physical and cellular perspective. Colonies were exposed to three concentrations of polyethylene microplastic beads (no microplastic beads: [No MP], 1 mg/L: [Low MP]; 10 mg/L: [High MP]), and two different temperatures (25 °C and 30 °C) for 72 h. No visual signs of stress in corals, such as abnormal mucus production and polyp extroflection, were recorded. At [Low MP], beads adhered to colonies were ingested but were also egested. Moreover, thermally stressed colonies showed a lower adhesion and higher egestion of microplastic beads. Coral bleaching was observed with an increase in temperature and microplastic bead concentration, as indicated by a general decrease in chlorophyll concentration and Symbiodiniaceae density. An increase in lipid peroxidation was measured in colonies exposed to [Low MP] and [High MP] and an up-regulation of stress response gene hsp70 was observed due to the synergistic interaction of both stressors. Overall, our findings showed that heat stress still represents the main threat to P. damicornis, while the effect of microplastics on coral health and physiology may be minor, especially at control temperature. However, microplastics could exacerbate the effect of thermal stress on cellular homeostasis, even at [Low MP]. While reducing ocean warming is critical for preserving coral reefs, effective management of emerging threats like microplastic pollution is equally essential.

Biodegradable Zein-Based Biocomposite Films for Underwater Delivery of Curcumin Reduce Thermal Stress Effects in Corals.

Massive coral bleaching episodes induced by thermal stress are one of the first causes of coral death worldwide. Overproduction of reactive oxygen species (ROS) has been identified as one of the potential causes of symbiosis breakdown between polyps and algae in corals during extreme heat wave events. Here, we propose a new strategy for mitigating heat effects by delivering underwater an antioxidant to the corals. We fabricated zein/polyvinylpyrrolidone (PVP)-based biocomposite films laden with the strong and natural antioxidant curcumin as an advanced coral bleaching remediation tool. Biocomposites' mechanical, water contact angle (WCA), swelling, and release properties can be tuned thanks to different supramolecular rearrangements that occur by varying the zein/PVP weight ratio. Following immersion in seawater, the biocomposites became soft hydrogels that did not affect the coral's health in the short (24 h) and long periods (15 days). Laboratory bleaching experiments at 29 and 33 °C showed that coral colonies of Stylophora pistillata coated with the biocomposites had ameliorated conditions in terms of morphological aspects, chlorophyll content, and enzymatic activity compared to untreated colonies and did not bleach. Finally, biochemical oxygen demand (BOD) confirmed the full biodegradability of the biocomposites, showing a low potential environmental impact in the case of open-field application. These insights may pave the way for new frontiers in mitigating extreme coral bleaching events by combining natural antioxidants and biocomposites.

Effects of polypropylene nanofibers on soft corals.

Current information regarding the effects of both micro- and nano-plastic debris on coral reefs is limited; especially the toxicity onto corals from nano-plastics originating from secondary sources such as fibers from synthetic fabrics. Within this study, we exposed the alcyonacean coral Pinnigorgia flava to different concentrations of polypropylene secondary nanofibers (0.001, 0.1, 1.0 and 10 mg/L) and then assayed mortality, mucus production, polyps retraction, coral tissue bleaching, and swelling. The assay materials were obtained by artificially weathering non-woven fabrics retrieved from commercially available personal protective equipment. Specifically, polypropylene (PP) nanofibers displaying a hydrodynamic size of 114.7 ± 8.1 nm and a polydispersity index (PDI) of 0.431 were obtained after 180 h exposition in a UV light aging chamber (340 nm at 0.76 Wˑm-2ˑnm-1). After 72 h of PP exposure no mortality was observed but there were evident stress responses from the corals tested. Specifically, the application of nanofibers at different concentrations caused significant differences in mucus production, polyps retraction and coral tissue swelling (ANOVA, p < 0.001, p = 0.015 and p = 0.015, respectively). NOEC (No Observed Effect Concentration) and LOEC (Lowest Observed Effect concentration) at 72 h resulted 0.1 mg/L and 1 mg/L, respectively. Overall, the study indicates that PP secondary nanofibers can cause adverse effects on corals and could potentially act as a stress factor in coral reefs. The generality of the method of producing and assaying the toxicity of secondary nanofibers from synthetic textiles is also discussed.

Phthalates bioconcentration in the soft corals: Inter- and intra- species differences and ecological aspects.

The bioconcentration of dimethyl phthalate (DMP) diethyl phthalate (DEP) dibutyl phthalate (DBP) butyl benzyl phthalate (BBzP), di-(2-ethy hexyl) phthalates (DEHP), mono-butyl phthalate (MBP), mono-benzyl phthalate (MBzP), mono-(2-ethy hexyl) phthalate (MEHP) in the soft corals Coelogorgia palmosa, Sinularia sp., Sarcophyton glaucum, and Lobophytum sp. was investigated. Specimens were cultured in a microcosm environment built-up at the Genova Aquarium and analyses were carried out by in vivo SPME-LC-MS/MS. The distributions of the phthalates among the four surveyed species resulted significantly different. Calculated bioconcentration factors (BCFs) showed values spanning over two orders of magnitude, from a minimum of log10 BCFDEP = 1.0 in Sarcophyton glaucum to a maximum of log10 BCFDBP = 3,9 calculated for Coelogorgia palmosa. Moreover, the calculated BCFs of the long chain phthalates resulted up to three orders of magnitude lower than theoretically predicted (from logKow), whereas BCF of short chain phthalates resulted higher. This, together with the detection of phthalic acid monoesters, suggests the presence of species-specific different metabolic transformation among the surveyed soft coral species that involve DEHP.