Investigating factors driving phytoplankton growth and grazing loss rates in waters around Peninsular Malaysia

Abstract

In tropical waters where temperatures are relatively stable, we investigated whether the relationship between phytoplankton growth and grazing loss rate across different habitats around Peninsular Malaysia can be attributed to its eutrophication states. We measured phytoplankton growth (μ) and grazing loss (g) rates in waters off Bachok Marine Research Station (BMRS), located northeast of Peninsular Malaysia. Chlorophyll-a (chl-a) concentration ranged from 2.90 to 15.78 µg/L and was dominated by nano-and micro-phytoplankton (>2 µm in size). Using the Landry and Hassett dilution method, μ at BMRS ranged from 1.02 to 1.58 per day whereas g varied from 0.07 to 0.88 per day. Grazing accounted for 35% of the primary production at BMRS. A systematic review of available data in waters around Peninsular Malaysia, revealed how μ fluctuated over a wide range (0.01–1.80 per day) and correlated with chl a distribution (R2=0.181- P<0.001). However, the relationship was only significant at <9 µg/L chl a for mesotrophic waters and <16 µg/L chl a for eutrophic waters. In contrast, g ranged from 0.00 to 1.01 per day, and correlated with μ at all locations. The g/μ slope ranged from 19% to 84%, and was generally similar for waters around Peninsular Malaysia. However, all the g/μ slopes had a positive y-intercept except for BMRS, and this seemed to suggest the availability of alternative prey supporting grazing at the other stations.