Microphytobenthic biomass, species composition and environmental gradients in the mangrove intertidal region of the Andaman Archipelago, India

Abstract

Monthly sampling in mangrove intertidal sediments of Andaman Archipelago was carried out during a 1-year study (January to December, 2013) in order to analyse the spatial and temporal distribution of microphytobenthos (MPB) and MPB biomass (sediment chlorophyll-a (chl-a)) in the surficial layer 0-1 cm. The MPB community was mainly composed of diatoms. The MPB biomass concentration in surface sediment (0-1 cm) ranged from 0.7 to 16.98 μg cm. Population density of benthic diatoms varied from 78 to 224 ind cm. This study identified 41 diatom taxa (27 pennate diatoms, 14 centric diatoms) in the sediment, and among all the diatom taxa, we distinguished few true planktonic species-Coscinodiscus centralis, Coscinodiscus marginatus, Leptocylindricus danicus, Planktoniella sol, Thalassiosira decipiens, Thalassionema nitzschioides and Thalassiothrix longissima. Overall, a high percentage of diatoms were pennate (81%) as opposed to centric. Based on benthic diatom abundance, species composition and distribution, MPB assemblages of sampling stations were grouped into two distinct clusters: one with St. 1 and St. 3 and another one with St. 2 and St. 4. Canonical correspondence analysis (CCA) revealed seasonality as the most important factor determining variability in diatom species composition among sampling sites. There was a distinct seasonal pattern in MPB biomass distribution and benthic diatom cell density during monsoon and post-monsoon seasons. Our results suggest that among various physical and chemical variables studied, greater levels of overlying water nutrients and sediment textures significantly correlated and were conducive factors for MPB. This is the first detailed study on the MPB from these mangrove sediments, providing benchmark data for future studies about these remote groups of Andaman and Nicobar Islands.

Benthic microalgae offset the sediment carbon dioxide emission in subtropical mangrove in cold seasons

“…The significant relationship between sediment Chl a concentration and diatom density in this study suggested the diatoms as an important component of the microphytobenthos community. This was consistent with other findings that the diatoms were the most important component of the microphytobenthos assemblages of estuarine mudflats and mangroves (McLusky ; Thornton et al ; Balasubramaniam et al ). The Nitzschia and Gyrosigma genera represented the majority of diatoms in the microalgal film in winter, while Nitzschia and Coscinodiscus were the dominant genera of the mangrove microalgae film in spring in this study.…”

“…The range of Chl a concentration in the cold seasons, 0.61–4.74 μ g cm −2 , in this study fell within the ranges reported in other intertidal areas (Pinckney et al ; Liu et al ; Balasubramaniam et al ). The significant relationship between sediment Chl a concentration and diatom density in this study suggested the diatoms as an important component of the microphytobenthos community.…”

“…The microphytobenthos consists of unicellular eukaryotic algae, cyanobacteria, and chemoautotrophic archea that grow within the upper several millimeters of illuminated sediments (Macintyre et al ). It has been suggested that the production of benthic microalgae as the dominant microphytobenthos in intertidal sediments (Thornton et al ; Miyatake et al ; Balasubramaniam et al ) is generally low or undetectable in mangroves due to light limitation resulting from shading by the tree canopy, inhibition by sediment organic compounds such as tannins, and nutrient limitation that may also play a role (Alongi ; Gattuso et al ). However, not all the mangroves have low microphytobenthos coverage and microphytobenthos could have high abundance in dwarf mangrove (Leopold et al ) or form conspicuous microbial mat or biofilm in mangroves where sufficient light penetrates to the sediment surface (Kristensen and Alongi ; Lovelock ).…”

Tolerance of tropical marine microphytobenthos exposed to elevated irradiance and temperature

“…Some can protect themselves physiologically against the damaging effects of exposure (Blanchard et al, 2004;Perkins et al, 2010) by dissipating the excess energy absorbed by light-harvesting centers, a process S. Salleh and A. McMinn: Impact of irradiance and temperature on microphytobenthos known as non-photochemical quenching (NPQ), while others can move vertically in the sediment, adjusting their position to minimize irradiance (Consalvey et al, 2004a;Perkins et al, 2010;Cartaxana et al, 2013). For instance, in a study by Mouget et al (2008) it was shown that benthic diatoms with a high migratory capacity could experience high photosynthetic activity without any evidence of photodamage, while non-migratory taxa showed a significant depression in photosynthetic activity, which was caused by high irradiance and/or UV-B.…”

“…Similarly, benthic diatoms inhabiting sediment surfaces in estuaries are usually able to recover from extreme temperatures and light photoinhibition caused by tidal changes, since photoinhibition is only rarely recorded in these communities (Defew et al, 2004;Lee and McMinn, 2013;Perkins et al, 2006). Furthermore, many have the ability to migrate vertically, hence positioning themselves within the sediment at a depth that provides shading from excess irradiance and provides an optimal light environment for their photosynthetic activities (Cartaxana et al, 2011;Mouget et al, 2008;Perkins et al, 2010).…”