Legacy of “New Normal” Plastics and “New Nitrogen” in the Cyanotoxin Footprint in Mangrove Ecosystems

• Published in: Phycology 2023-03, Vol.3 (1), p.106-126
• Main Authors: Gunawardana, Dilantha, Abeysiri, Sashika, Manage, Pathmalal
• Format: Article
• Language: English
• Subjects: cyanobacteria; cyanotoxins; mangrove ecosystems; plastic pollution; plastisphere
• ISSN: 2673-9410; 2673-9410
• DOI: 10.3390/phycology3010007

In a paradigm shift in plastic wastes due to the COVID-19 pandemic, wetlands such as mangroves are threatened by a new form of pollution, plastics, on top of the eutrophication of estuarine waters due to nitrogen and phosphorus wastes/effluents that lead to cyanobacterial proliferation. Both plastic and nutrient pollution lead to prosperity of cyanotoxin-producing cyanobacteria that flourish in both and disperse leading to the detriment of fauna and flora in the mangrove ecosystem due to resulting toxicities. Although cyanotoxins are still a relatively poorly studied phenomenon in mangroves, their presence does create a focus of attention due to biofilm formation and the resultant flotation and sinking properties that are linked to cyanobacterial mats on plastic debris. Sri Lanka, being the first country in the world to conserve all its mangrove wetlands, does have a responsibility to prevent the invasion of plastics to this protected ecosystem, and binding with the Ramsar Convention, precluding plastic waste and their concomitant footprint, is a task at hand to the relative authorities. The path ahead mandates that we study the properties of plastics for cyanobacterial proliferation, biofilm formation, the fates of such plastics (flotation, dispersal and sinking), the cyanotoxin production changes that are attributed—or linked—to plastic pollution and the resultant impacts on mangrove ecosystems. Cyanotoxins are long-lived, and it is paramount that we find the necessary mechanisms to eliminate or curtail their production in mangrove ecosystems while establishing surveillance and monitoring of both the producers and the harmful agents. Cyanobacteria although vehicles for nitrogen fixation and replenishing of nutrients to an N-depleted ecosystem such as the mangroves, could lead to enhancements in cyanotoxins production. However, this phenomenon remains ambiguous and poorly studied in applied phycology in relation to mangroves. “New normal” plastics are lodged mostly on the surfaces of bark, prop roots, and pneumatophores, which are the localities where the highest level of new nitrogen is fixed, and this may lead to the proliferation of N-fixing, cyanotoxin-producing cyanobacteria, which may have repercussions on both flora and fauna of mangroves. Therefore, it is crucial that we monitor plastic pollution and find mechanisms for sanitizing plastics-imprinted mangroves to lessen the harmful footprint resulting from plastic overload.