Relevance of bacterioplankton abundance and production in the oligotrophic equatorial Indian Ocean

Abstract

Bacterioplankton abundance and production, chlorophyll a (Chl a) concentrations and primary production (PP) were measured from the equatorial Indian Ocean (EIO) during northeast (NEM), southwest (SWM) and spring intermonsoon (SpIM) seasons from 1°N to 5°S along 83°E. The average bacterial abundance was 0.52 ± 0.29, 0.62 ± 0.33 and 0.46 ± 0.19 (· 10 8 cells l -1 ), respectively during NEM, SWM and SpIM in the top 100 m. In the deep waters (200 m and below), the bacterial counts averaged *0.35 ± 0.14 · 10 8 cells l -1 in SWM and 0.39 ± 0.16 · 10 8 cells l -1 in SpIM. The 0-120 m column integrated bacterial production (BP) ranged from 19 to 115 and from 10 to 51 mg C m -2 d -1 during NEM and SWM, respectively. Compared with many open ocean locations, bacterial abundance and production in this region are lower. The bacterial carbon production, however, is notably higher than that of phytoplankton PP (BP:PP ratio 102% in SWM and 188% in NEM). With perpetually low PP (NEM: 20, SWM: 18 and SpIM: 12 mg C m -2 d -1 ) and Chl a concentration (NEM: 16.5, SWM: 15.0 and SpIM: 20.9 mg m -2 ), the observed bacterial abundance and production are pivotal in the trophodynamics of the EIO. Efficient assimilation and mineralization of available organics by bacteria in the euphotic zone might serve a dual role in the ultra-oligotrophic regions including EIO. Thus, bacteria probably sustain microheterotrophs (micro-and meso-zooplankton) through microbial loop. Further, rapid mineralization by bacteria will make essential nutrients available to autotrophs.

Oceanography and the base of the pelagic food web in the southern Indian Ocean

“…Published data on bacterial production in the Indian Ocean are scarce. Leaving out the highly productive Station 7-8, observed rates of bacterial production ranged from 0.12-1.4 mg C m 23 day 21 in the upper 100 m (average 0.38 + 0.33 mg C m 23 day 21 ), which is similar to an average production of 0.39 + 1.13 mg C m 23 day 21 obtained for non-bloom conditions in a recent study in the equatorial Indian Ocean (range: 0.004 to 4.70 mg C m 23 day 21 , Fernandes et al, 2008). The highly elevated bacterial production in the photic zone at Station 7-8 reflected a strong bacterial response to the postphytoplankton bloom conditions.…”

Latitudinal δ13C and δ15N variations in particulate organic matter (POM) in surface waters from the Indian ocean sector of Southern Ocean and the Tropical Indian Ocean in 2012

“…Previous studies in the oligotrophic equatorial Indian Ocean have indicated greater contribution of heterotrophic bacterial production to the biological production (Fernandes et al, 2008;Ramaiah et al, 2009). Selective mineralization of POM resulting in preferential removal of nitrogen rich compounds by heterotrophic bacteria is fairly well-known in marine environments (Eadie and Jeffrey, 1973;Harvey et al, 1995;Kolasinski et al, 2012).…”

The Composition and Primary Metabolic Potential of Microbial Communities Inhabiting the Surface Water in the Equatorial Eastern Indian Ocean

“…Previously, researchers characterized the abundance, diversity, and functions of bacteria in the Indian Ocean by isolation of the cultivable species [26,27]. Recently, studies on environmental microbes were performed from water columns and sediments [28][29][30][31][32][33][34]. Wang et al (2016) and Qian et al (2018) provided an extensive depiction of bacteria in their environmental context [28,31].…”