The Photophysiology of Benthic Diatoms in the Intertidal Flats of Pulau Pinang (Malaysia)

Abstract

The in-situ photosynthetic activity in tropical intertidal benthic diatom in response to environmental variation was assessed in this study by measuring chlorophyll fluorescence. The investigation was carried out during the lowest tide in January (non-rainy day) and February 2013 (post-rainy day) at two sampling sites (A and B) from each selected location (Pantai Jerejak, Teluk Bahang and Tanjung Bungah, Pulau Pinang, Malaysia). Samples of surface sediment (top 0.5 cm) were collected, and chlorophyll a extracted as biomass estimation. Assessments of the photosynthetic activity of benthic diatoms were made using a pulse-amplitude modulated (PAM) fluorometer. Fifty-three species were identified, representing 27 genera from the three studied locations. Both locations showed similarities in species diversity and abundance. Two-way ANOVA showed no significant differences (p = 0.430) in species richness (Margalef Index) among sampling locations, with an average value of 6.33±0.247. Both intertidal flats were dominated by Cocconeis, Navicula, Actinoptychus, and Diploneis. The community has low maximum quantum yields, Fv/Fm (ranging from 0.170 to 0.340) and is often light-limited (Photoacclimation Index, Ek, ranging from 67.96 to 236.71 mol photons m-2 s-1). The relative electron transport rate (rETRmax) was low, with values ranging from 3.45 to 35.51 across three sampling locations. Fluctuation in salinity has caused a decrease in photosynthetic activity. This study suggests that the low values indicated a poorly adapted benthic microalgal community that is constantly light-limited. However, time-series data is needed to determine the ability of these communities to adapt to the changing environment.