Unusual mass shoreward movement of bivalve (Mollusca) Donax scortum Linnaeus along the coastal waters off Calicut - South Eastern Arabian Sea

67-72Eutrophication and oxygen depletion are the major factors influencing the responses of benthic organisms in coastal ecosystems. Along the coastal waters of South Eastern Arabian Sea a mass shoreward movement of bivalve Donax scortum (locally referred as “eranthu”) occurred during end phase of summer monsoon upwelling. Possible reasons for this shoreward movement points to the low dissolved oxygen (0.25 ml L-1) in the bottom waters. Intense blooms of large dinoflagellate species, Noctiluca scintillans were observed a week prior to this event along these coastal waters and the crashing related decaying might have resulted in lower DO values in the region. The study discuss on the deleterious effects of hypoxic conditions caused by summer monsoon algal blooms on benthic fauna of South Eastern Arabian Sea

Unusual mass shoreward movement of bivalve (Mollusca) Donax scortum Linnaeus along the coastal waters off Calicut - South Eastern Arabian Sea

Eutrophication and oxygen depletion are the major factors influencing the responses of benthic organisms in coastal ecosystems. Along the coastal waters of South Eastern Arabian Sea a mass shoreward movement of bivalve Donax scortum (locally referred as “eranthu”) occurred during end phase of summer monsoon upwelling. Possible reasons for this shoreward movement points to the low dissolved oxygen (0.25 ml L-1) in the bottom waters. Intense blooms of large dinoflagellate species, Noctiluca scintillans were observed a week prior to this event along these coastal waters and the crashing related decaying might have resulted in lower DO values in the region. The study discuss on the deleterious effects of hypoxic conditions caused by summer monsoon algal blooms on benthic fauna of South Eastern Arabian Sea

Occurrence of potentially toxic cyanobacteria

Microcystis aeruginosa is a potentially toxic bloom-forming freshwater cyanobacterium, usually found in eutrophic water bodies worldwide. The present study reports the occurrence of Microcystis aeruginosa and its bloom in freshwater ponds along central Kerala (south India). Monitoring of cyanobacterial blooms was conducted from May 2019 to February 2020 along the aquatic ecosystems of central Kerala and the M. aeruginosa blooms were recorded from two freshwater ponds of Kochi. Massive blooms of M. aeruginosa was observed during the period prior to summer monsoon (May) with an abundance of 1.17 × 106 cells L‑1 (Station 1) and during early summer (February) latter being more thick scum (2 × 108 cells L‑1) with high chlorophyll a. Dense aggregates of M. aeruginosa scums were more prevalent during the periods characterised by higher Surface Water Temperature (SWT). The nutrient characteristic pattern of the study area showed the abundance of M. aeruginosa correlated very well with higher dissolved nitrate (96.7 μmol L‑1) and phosphate (19.88 μmol L‑1) concentrations. Thus in the stable freshwater ponds with higher SWT and nutrients were the major factors influencing the growth and abundance of the cyanobacteria M. aeruginosa. Toxicological studies conducted revealed that the Microcystis bloom was hepatotoxic, inflicting fish mortality.The occurrence of M. aeruginosa bloom in two freshwater ponds along central Kerala has been addressed along with the variations in the hydrobiological characteristics of the ecosystem during bloom and non-bloom conditions of the species. Histological studies highlight hepatotoxicity of M. aeruginosa signifying regular monitoring of bloom events in these ecosystems