Multiple impacts of microplastics can threaten marine habitat-forming species

Microplastics are recognised as a potential global threat to marine ecosystems, but the biological mechanisms determining their impact on marine life are still largely unknown. Here, we investigated the effects of microplastics on the red coral, a long-lived habitat-forming organism belonging to the Corallium genus, which is present at almost all latitudes from shallow-water to deep-sea habitats. When exposed to microplastics, corals preferentially ingest polypropylene, with multiple biological effects, from feeding impairment to mucus production and altered gene expression. Microplastics can alter the coral microbiome directly and indirectly by causing tissue abrasions that allow the proliferation of opportunistic bacteria. These multiple effects suggest that microplastics at the concentrations present in some marine areas and predicted for most oceans in the coming decades, can ultimately cause coral death. Other habitat-forming suspension-feeding species are likely subjected to similar impacts, which may act synergistically with climate-driven events primarily responsible for mass mortalities.


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All relevant data are included in the main text and in the supplementary information. Raw sequences and additionL dataseta are available at the following links: (https://figshare.com/s/ad48bdf75eebff0721b2 and https://figshare.com/s/6dff1da37178435dc5fa, respectively.

October 2018
For a reference copy of the document with all sections, see nature.com/documents/nr-reporting-summary-flat.pdf Ecological, evolutionary & environmental sciences study design All studies must disclose on these points even when the disclosure is negative. Access and import/export Disturbance We investigated the biological effects of microplastics onì the red coral, a long-living, marine habitat-forming species present in different oceans. Here, we demonstrate that corals can preferentially ingest polypropylene and that the ingested microplastics bioaccumulate, causing multiple biological effects, from feeding impairment to mucus production and altered gene expression. Microplastics can also cause tissue abrasions that alter the coral microbiome, with consequent proliferation of opportunistic bacteria, ultimately leading to coral death. Finally, we show that microplastics ingested by zooplankton are transferred to the corals through predation. The multiple biological effects demonstrated here indicate that the current levels of marine microplastic contamination can already threaten many marine life forms, and are expected to alter marine ecosystem functioning in a wide range of habitats by 2030. Experiments were conducted with simple one-factor or two-factor factorial designs. Mixed models were used to determine the possibility of random effects of experimental tanks, even where treatments were balanced among tanks. Sixty coral branches with similar morphology, and a surface of approximately 2 cm^2 each, were distributed among 12 experimental mesocosms (12 L glass tanks), in order to have 5 coral branches per mesocosm (containing on average, 274 ± 26.4 coral polyps each).
Here, we tested for the first time the effects of microplastic contamination on the key marine habitat-forming species Corallium rubrum, which is a good model species to gather information on the impact of microplastics in a variety of environmental conditions and across different bathymetric ranges. The genus Corallium is present at almost all latitudes from shallow-water to deep-sea habitats and has a great ecological relevance as it is an ecosystem engineer, thus supporting biodiversity and ecosystem functioning.
The experiment was based on 3 replicated mesocosms containing 5 coral branches each per 3 different treatments (3 microplastic mixture concentrations). This sample size was based on the best compromise between statistical relevance ethical issues, given that Corallium rubrum is a endangered IUCN red-listed species. The microplastic mixture was added to the mesocosms in order to mirror the concentrations and composition of dominating polymers reported in marine environment. We used three different concentrations of microplastic mixture. The highest concentrations of microplastics (up to 600 microplastic particles per litre) can reflect future contamination on the basis of estimates obtained by numerical models (Isobe et al. 2019), whereas the low and medium concentrations have been selected to represent highly-contaminated marine habitats, including the areas where the corals were collected (Ligurian Sea, Fossi et al. 2012, 2016. Because coral samples from the same tanks are not independent, we treated tanks as replicates for analyses.
We investigated the responses of C. rubrum in terms of feeding activity and defence mechanisms, the tissue damage due to the physical contact with microplastics, responses at the molecular level (i.e., gene expression and DNA damage), and the influence on the coral-associated microbiome. The experimental approach utilized included microscopy-based analyses ( No data were excluded.
All data are contained in the main text, Supplementary Material and Figshare repository.There were no pilot trials, given the vulnerable status of the study species.
Coral branches within tanks and treatments were selected randomly for analysis.
Blinding was not necessary, but sequence data were obtained without reference to experimental treatments. According to the communication we received from the Italian Ministry of the Environment, the restrictive rules for taxa included in Annex D of Presidential Decree 357/97 (and in the EU Directive n. 2010/63) do not apply to C. rubrum and therefore the collection activities and use for scientific experiments do not require authorization.
The disturbance on the C. rubrum colonies of the Portofino Marine Protected Area was minimized by collecting less than 5% of the coral branches from different colonies located in the same area. Being colonial organisms and with high regeneration potential the minimal sampling of coral branches does not affect the health of donor colonies.