Preliminary study on the impact of South-West monsoon on the abundance and diversity of seaweeds in Dikwella algal bed, Southern Sri Lanka

Marine macro algae (seaweeds) are macroscopic, multicellular benthic marine algae that are important natural resources found throughout the world, including Sri Lanka. This study reveals the diversity of seaweeds found at the Dikwella algae bed at the beginning of South-West monsoon (March -April) and the end (October-November) during 2019. The random quadrat method was used to collect the data from 30 sampling locations in the first and last weeks of each month. The Shannon wiener diversity index (H) was used to calculate the diversity of recorded algae species, while the abundance of each species was calculated based on the total algal percentage coverage in all quadrates. Standard identification guides were used to identify the algal species. Results revealed that 42 algal species presented from 20 different families in the field. The average total percentage cover of algae species on the bed prior to the monsoon and after the monsoon period was 68.06% and 98.66%, respectively. The increased coverage could be attributed to the wave actions and ambient environmental conditions received for algae growth during the monsoon season. Ulva lactuca had the highest abundance before the monsoon followed by Sargassum sp. and Chaetomorpha antennina had the lowest abundances followed by Cladophora herpestica. After the monsoon, the highest algal abundance was Sargassum sp. followed by U. lactuca while the lowest abundance was Padina minor followed by Hypnea pannosa. Regardless of the monsoon effect, Sargassum sp. was found to be the dominating species in the algae bed during both periods. However, after the monsoon season, the percentage coverage was higher. As a result, it can be suggested that the South-West monsoon showed a significant impact on the availability and diversity of seaweeds in the Dikwella algal bed in 2019.