A comprehensive study on ecological insights of Ulva lactuca seaweed bloom in a lagoon along the southeast coast of India

Abstract

Ulva lactuca, commonly known as sea lettuce is a green macroalgae (chlorophyta) and its uncontrolled proliferation forms a bloom, which causes ecological imbalances and adversely impacts brackishwater ecosystems. Algal bloom can harm the environment and aquatic organisms, but it can also be beneficial if harvested and utilized for industrial purposes. A massive bloom of green macroalgae was observed in the Muttukadu lagoon, located along the southeast coast of India in the Bay of Bengal. A comprehensive study was taken up to assess the spatial distribution, proximate, nutrients, minerals, heavy metals, and factors inducing the bloom. For this study, high-resolution satellite images (Sentinel 2) were used. The spatial distribution of seaweed was mapped using Floating Algae Index (FAI), Modified Floating Algae Index (MFAI), Normalized Difference Red Edge (NDRE) Index and Seaweed Index (SI) models. Results were validated using the MAVIC 3 pro drone and field survey. The SI model was found to be more accurate compared to other models. The bloom exhibited notable temporal dynamics, with peak coverage observed in the last week of May 2023 with a spread area of about 100.05 ha, the bloom intensity was found to be high till the last week of June 2023, after which it gradually declined. The proximate composition (%) of Ulva lactuca showed the moisture content is about 80.00 ± 2.98, crude protein 24.17 ± 1.80, crude lipid 0.81 ± 0.05, Total Ash 37.45 ± 1.44, Fiber (8.92 ± 0.41), and Acid Insoluble Ash (16.18 ± 1.16). The mineral concentration was in the order Ca > Na > Mg > K > P. Iron (Fe) was observed to be high compared to other micronutrients, with a concentration of 1164.40 mg/kg. Rich nutrients and low heavy metal concentration significantly can boost the selling cost of Ulva lactuca providing livelihood support for the coastal fisherfolk.