Mud Banks along the southwest coast of India are not too muddy for plankton

Abstract

Considering Alappuzha Mud Bank in the southern Kerala coast as a typical case of biologically productive Mud Banks that form along the southwest coast of India during the Southwest Monsoon (June - September), the present study addresses several pertinent missing links between the physical environment in Mud Banks and their influence on plankton stock. This study showed that very strong coastal upwelling prevails in the entire study domain during the Southwest Monsoon, which manifests itself in the form of significantly cool, hypoxic and nitrate-rich waters surfacing near the coast. The upwelled water persisting throughout the Southwest Monsoon period was found to have fuelled the exceptionally high phytoplankton stock in the entire study area, including the Mud Bank region. Having accepted that Mud Banks are special because of the calm sea surface conditions and relatively high turbidity level in the water column around them, the present study showed that except at points close to the sea bottom, turbidity level in the Alappuzha Mud Bank was below the critical level to inhibit the plankton stock. The suspended sediments that form in the Mud Bank occasionally could be attributed to the disturbance of the bottom fluid muddy layer and their vertical spurts.

Ecological responses of autotrophic microplankton to the eutrophication of the coastal upwelling along the Southwest coast of India

“…Upwelling along the southwest coast of India enriches the coastal waters with a high concentration of essential nutrients facilitating an increase in phytoplankton biomass (Bhattathiri et al 1996;Qasim 1982;Madhupratap et al 1990;Jyothibabu et al 2008;Karnan et al 2017a;Karnan et al 2020). This enhancement in autotrophs biomass during the Southwest Monsoon is well imprinted in satellite imageries of chlorophyll-a as well, but information about the dominant phytoplankton behind such a biomass increase is limited (Jyothibabu et al 2010(Jyothibabu et al , 2018aKarnan et al 2017a).…”

Characteristics of Mudbanks along the Southwest Coast of India

“…In most of the studies on the entire west coast, the Southwest Monsoon period is the most productive time because of the proportionate availability and replenishment of nutrients [27,21,58,59]. Also, except at points close to the sea bottom, the turbidity level in the Alappuzha Mudbank was below the critical level to inhibit the plankton stock [60]. The research output in sediment dynamics, biogeochemical processes like sulfate reduction/nitrogen cycle and metal enrichment/ contamination in the coastal sediments in three distinct depositional milieus like estuaries, mangroves, and mudbanks in India were reviewed by and found these regimes as highly productive [61].…”

Early Miocene marine ostracodes from southwestern India: implications for their biogeography and the closure of the Tethyan Seaway

“…Based on the associated benthic foraminiferan fauna, which is characterized by mesophotic taxa (Brigulio and Rögl, 2018; Rögl and Brigulio, 2018), it has been recently suggested that the seagrass fauna was transported from seagrass beds, which grew in ~20–30 m water depth, down to 60–70 m water depth (Brigulio et al, 2018). This paleobathymetric reconstruction, however, has to be taken with caution because it does not consider the attenuation of light in seagrass canopies (e.g., Hedley et al, 2014) and turbid coastal waters along southern Kerala (Jyothibabu et al, 2018).

Figure 1.( 1 ) Locality maps and stratigraphic summary.

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