Significance of bacteria in the flux of organic matter in the tidal creeks of the mangrove ecosystem of the Indus River delta, Pakistan

Abstract

We studied bacterial blomass and production in 3 t~d a l creeks (Isaro, Gharo and Ph~ttl Creeks) in the mangrove forests in the Indus R~ver delta, Pakistan, to assess the signif~cance of bacteria-mediated carbon fluxes in the creek ecosystem. Bacterial biomass, bacterial carbon production (BCP) and primary productivity (PP) were measured periodically for over a year during 1991-92. BCP was high, generally 50 to 300 pg C 1-' d-l. Despite such high BCP, bacterial abundance remained between 1 X 106 ml-' and 4 X 106 ml-' (20 to 80 p g C I-') indicating tight coupling between bacter~al production and removal. Specific growth rates generally ranged from 1 to 7 d.' but the rate reached 24 d.' during a phytoplankton bloom, apparently a red tide, and this was an unprecedented growth rate for a natural assemblage The abundance of attached bacteria exhlblted a large variation, ranglng from 4 to 9 2 % (mean 35 2 21 ",,, n = 41) in Isaro Creek and from 14 to 84 "L. (mean 37 -t 28%,, n = 10) in Gharo Creek Bacterial production due to attached bacteria was 73 to 96'Y" of the total Thus, a major fract~on of BCP may have been directly ava~lablc to m.etazoan grazers. BCP was generally much higher than net PP, the yearly integrated average BCP/13P for all sites was 2.0. Thus, the growth of bacteria, attached and free, probably represented the major pathway of the production of high quality (low C:N) biomass potentially available to the grazers. Average yearly integrated bacterial carbon demand (BCD), estimated conservatively by assuming a 30-0 growth efficiency for all sites, was 6.9 times net PP. Thus, the creek water columns were strongly and persistently net heterotrophic. Data integrated over the entire study period show that even if all phytoplankton production was utilized by bacteria it would satisfy only 7 to 20':0 of the BC:D; the remaining 80 to 93% of BCD would be met by reduced carbon from other sources. Phytoplankton production was l~g h t limited due to high turbidity and, apparently, the majority of BCP could be supported by the input of mangrove detritus. Estimates of utilizable dissolved organic carbon (UDOC) in selected samples were 97 to 656 pg C I-', indicating that In order to sustain the measured BCD (643 + 671 pg C I-' d-') the UDOC pool would turnover in < l d to a few days. Limited data suggest that bacterial production was carbon rather than N or P limited. consistent w~t h sustained high levels of Inorganic N and P in the surface water. Since mangrove detr~tus provides most of the energy for bacterial production, which in turn is a significant source of high quality lood for grazers, particularly via ingestion of attached bacteria, w e predict that the ongoing destruction of mangrove forests in the Indus delta and elsewhere could have a major impact on mangrove ecosystem structure and functioning and the production of economically important flsh and shrimp in mangrove creeks.

Fatty acids as tracers of organic matter in the sediment and food web of a mangrove/intertidal flat ecosystem, Okinawa, Japan

“…The material produced, mainly leaves, enriches the bottom litter (Fleming et al 1990). The decompostion rate of the litter and the quality of the resulting particulate organic matter and nutrients may depend on which mangrove species the leaves come from (Tam et al 1990), on biotic factors such as bacterial activity (Bano et al 1997), and on edaphic effects such as tidal range and temperature (Slim et al 1997).…”

Abundance and production of particle-associated bacteria and their role in a mangrove-dominated estuary

“…The abundance of PAB in the Mandovi estuary was 2 to 4 times more than that reported in temperate waters (Hoch et al 1995, Berger et al 1996) and the adjacent Zuari estuary (De Souza et al 2003). However, it was lower than the highly organic rich Hudson and Indus River delta estuaries (Bano et al 1997, Sanudo-Wilhelmy & Taylor 1999. Although the quantitative POM content of the particles was low, its quality was high with a POC:PON ratio of 5.5 to 7.3.…”

“…Fukuda et al (1998) concluded from their study that a factor of 30.2 ± 12.3 fg C cell -1 would be applicable for coastal bacterial assemblages. In a study on estuaries from Indian regions, Bhaskar & Bhosle (2008) ) in Pakistan (Bano et al 1997). Earlier studies (Simon et al 1990, Smith et al 1992, Grossart & Simon 1998) measured aggregate-associated bacterial production by pooling several aggregates.…”

Les microorganismes dans le maintien de l’équilibre et la réhabilitation des écosystèmes de mangrove pollués par les hydrocarbures. Revue bibliographique

“…Ainsi, la dégradation du matériel végétal dans les écosystèmes de mangroves produit des détritus qui peuvent être définis comme de la matière organique en phase de décomposition. Les détritus sont riches en énergie et contiennent une grande population microbienne active (Bano et al, 1997). En plus des bactéries et des champignons, d'autres organismes peuvent également coloniser le matériel végétal et contribuer à la formation des détritus (D'Croz et al, 1989).…”

“…Elles traitent la plupart des flux d'énergie et de nutriments, et agissent comme un puits de carbone. Par exemple, dans les écosystèmes de mangroves semi-arides, les bactéries sont attachés aux particules des sédiments et transforment la plupart des nutriments de l'écosystème (Bano et al, 1997). En consommant du carbone organique dissous présent dans les eaux interstitielles, les populations bactériennes dans les sédiments de mangrove empêchent l'exportation de cette forme de carbone vers les écosystèmes adjacents (Alongi et al, 1989).…”