Light-induced alteration in pigment signature and growth in a tropical surf-zone phytoplankton assemblage (southwestern Bay of Bengal, India)

Abstract

Abstract We present here the first study documenting the variability in growth and pigment signature with fluctuating light in a tropical surf-zone (coastal Bay of Bengal) phytoplankton assemblage. In response to an 8.5 times light cut-off for 3 days, 50% of the particulate organic matter (POC)-based growth rate (μPOC d−1) was maintained. Chlorophyll a (Chla) and light-harvesting pigment (LHP) contents exhibited a reverse trend without increasing POC contents, suggesting that the Chla-based growth rate can be biased under fluctuating light. Certain commonly occurring diatoms like Skeletonema, Leptocylindrus and Chaetoceros exhibited high light preference, whereas another diatom Thalassiosira proliferated at low light. Phytoplankton pigment signature was also monitored on an hourly basis over a day and the lowest LHP contents were associated with the highest photon flux densities, whereas the highest values were noticed during morning and evening hours. The ratio between photo-protective to LHP remained < 0.5, indicating that LHP contents were always greater than photo-protective pigment values and the cells were not severely light stressed. Iron (Fe) supplementation did not alter POC accumulation; photo-protective to LHP ratios also indicated Fe adequacy in this coastal water and the observed variability in the pigment signature was entirely attributed to variable light.