Exploring the mechanisms of microplastics incorporation and their influence on the functioning of coral holobionts.

Project Rationale

Recent studies have determined that >4 million tons of plastic enter the oceans each year, which are progressively broken down by natural conditions generating fragments < 5mm in size that are known as microplastics. The effect that these particles are having on coastal ecosystems such as coral reefs is currently a subject of considerable debate.

Microplastics have been found in the mouth and among the mesenteries of coral polyps collected from reef regions as well as in plankton tows in reef waters, demonstrating that in coral reefs, microplastics are present in the food chain but also that corals might act as long-term sink of these particles through adhesion to their surface (Huang et al. 2020).

However, the effect of ingestion or incorporation of microplastics on the functioning of these habitat-founding organisms, is less clear. Experiments under controlled conditions have shown that after a short time of exposure to plastic particles, corals exhibit cleaning mechanisms (mucus production), ingestion and/or passive overgrowth (Reichert et al., 2021). This results in some cases in negative effects on health, such as increased bleaching and tissue necrosis. However, our own preliminary data shows that over long-term exposure to microplastics, coral functioning is not adversely affected, emphasizing the gap in our understanding of coral incorporation, accumulation and overall response to microplastics.

This project aims to use a combination of advanced laboratory study and novel analytical approaches to plug this knowledge gap to determine the impact of microplastic pollution on coral health and reveal the mechanisms of microplastic incorporation into the coral holobiont. 

Methodology

This project aims to: (a) Maintain different coral species exposed to different plastic treatments under tightly controlled conditions. Species will be chosen to include a range of growth morphologies and rate: Acropora sp (fast growing, branching), Porites sp (Slow growing, massive), Montipora sp (fast growing, plate forming), Euphyllia sp (slow growing, large polyps). (b) Identify and quantify plastics in coral tissue samples (both coral animal and symbiont) using a novel approach based upon Coherent Anti-Stokes Raman Spectroscopy (CARS; e.g. Takahashi et al., 2021). (c) define what the effects of microplastics are on key physiological functioning of the coral holobiont (symbiont photosynthesis, host tissue growth, symbiont densities, density and composition of the skeleton), and (d) to identify what partner/s of the symbiosis is/are involved in the long-term quantitative accumulation of particles in different coral species with different morphologies and growth rates.

All coral experiments will be carried out in the mesocosms of the Coral Reef Laboratory in the School of Ocean and Earth Science. The CARS analysis will be performed in the School of Chemistry. 

Training

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the School of Chemistry and the School of Ocean Science. Specific training will include:

·        husbandry, monitoring of physiological parameters of live corals maintained under carefully controlled environments.

·        Analysis of tissue and skeleton composition and structure.

·        Coherent anti-Stokes Raman scattering (CARS) microscopy.

Opportunities exist for the student to attend national and international meetings and conferences (e.g. International Coral Reef Symposium) to present their work.