Microplastics Presence in Rhizophora mangle Roots throughout Fishponds and Open Coasts in Moloka'i, Hawaii

Abstract

Microplastics (MP) are an emerging global contaminant that has drawn the attention of many researchers in the last few decades due to their growing environmental threats. Pieces of plastic smaller than 5 mm, they are specifically a high cause for concern in marine environments as their small size allows them to flow from inland into the ocean. Through this movement, MPs have been found in all marine ecosystems and ingested by hundreds of marine species often mistaking them for food. Labeled as one of the most threatened ecosystems, mangrove forests are already a large sink for a variety of contaminants now including MPs as they may be trapped within the sediment by mangroves' unique aerial roots. As mangroves grow in coastal zones, these contaminants are often anthropogenic coming from both land and marine-based activities. Fishing activities have recently begun to be researched and associated with MP abundance, but one type of fishing, fishponds, has had no research done to understand MPs' presence. Fishponds are a tool used for a specific kind of seawater farming that take advantage of and utilizes the natural resources of the ocean's tidal movements to control the exchange of water and sediment build-up. This study focused on the fishponds spread throughout the island of Moloka'i Hawaii to evaluate the effect fishpond presence has on microplastics in Moloka'i Hawaii. The combination of mangrove roots' ability to trap sediment and fishponds' use of the ocean to control sediment flow may have an impact on the MP presence at these sites compared to open coasts. Therefore this study was conducted to evaluate how MPs found in the mangrove roots of Moloka'i, Hawaii are affected by the presence of fishponds versus along the open coast. Four to five hour digestions at 50°C using Sodium hypochlorite were used to digest the organic matter of collected root samples, separated as coarse and fine roots. No statistical significance was observed for coarse or fine roots between open coasts and fishponds (p-values of 0.4723 and 0.7812).