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Understanding scleractinian coral microplastic ingestion: calcification, size limits, and retention
Citation:
Hankins, C., A. Duffy, AND K. Drisco. Understanding scleractinian coral microplastic ingestion: calcification, size limits, and retention. Sixth International Marine Debris Conference, San Diego, CA, March 12 - 16, 2018.
Impact/Purpose:
The prevalence of microplastics (<5mm) in the marine environment has been of increasing concern in the past decade. Microplastics have been shown to be ingested by aquatic organisms but the physical and toxic effects of ingestion of microplastics in marine organisms, including coral, are not well understood. In order to learn of potential impacts of microplastics, research must first be conducted to investigate responses of scleractinian corals in the presence of microplastic. This research seeks to define minimum/maximum size ranges in which corals will ingest, how long microplastic remain within coral tissue, and microplastic effects on coral calcification. This research is being conducted under a RARE grant with Region 2 and supports SSWR's task 3.01D-03c: Land use effects on marine and estuarine coastal resources.
Description:
The prevalence of microplastics (<5mm) in the marine environment has been of increasing concern in the past decade. Microplastics have been shown to be ingested by aquatic organisms, however the physical and toxic effects of microplastic ingestion in marine organisms, including coral, are not well understood. Two laboratory experiments were conducted on cultured coral species, Montastraea cavernosa and Orbicella faveolata. The first experiment measured calcification rates of corals exposed to three sizes of cured microplastics: 90-106 µm, 425-500 µm, and 850-1000 µm. Both species ingested all size classes, however, O. faveolata did not retain many of the 425-500 or 850-1000 µm size range. Calcification was measured by using the alkalinity anomaly principle per experimental chamber. Calcification was qualitatively lower in corals exposed to microplastics, however there was no significant difference from control treatment. This may be explained by potential species-specific retention times (time coral retained microplastic within tissue) and an artifact of exposing both species at the same time as the amount of microplastics recovered was greater in M. cavernosa than in O. faveolata fragments. Hence, a second experiment was performed to determine retention times of various, uncured size classes (425-500 µm, 850-1000 µm, 1.7-2.0 mm, and 2.4-2.8 mm) of microplastic in individual fragments of M. cavernosa and O. faveolata. The largest size range ingested by both M. cavernosa and O. faveolata was 2.4-2.7 mm, with ingestion rates of 100% and 20%, respectively. Approximately 12 hours after ingestion O. faveolata retained more of the 425-500 µm, 850-1000 µm, and 1.7-2.0 mm size ranges compared to M. cavernosa, however, only M. cavernosa retained any 2.4-2.8 mm microplastics (26.7%). At 48 hours, the majority of microplastics (82% or greater) were released by both species. It is clear that there are varying responses of ingestion rates and retention times for different coral species. These results are the first step to providing threshold values for better land-based management practices, especially around coral reef habitats. Future research will seek to define species-specific calcification effects and identify which size range of microplastics, if any, are microplastics that are retained within coral polyps.