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.
ABSTRACT. We report the results of a 3 yr study on 2 tidal creeks in the northwest corner of the lndus River delta (Pakistan) mangrove ecosystem. We measured light (extinction coefficients), nutrients (nitrate, nitrite, phosphate, silicate and ammonium), chlorophyll a (chl a), suspended load, primary productiv~ty (I4C uptake] and phytoplankton species In Isaro and Gharo Creeks. There was no clear seasonal cycle in any of the 5 nutrients in either of the 2 tidal creeks. NO3 ranged from l to 8 PM, NH, from 2 to 15 pM, Si04 from 3 to 20 pM, and PO, from 0.2 to 2 pM (except when it was undetectable during a bloom in lsaro Creek in June). Hence, nitrogen and silicate do not limit primary productivity, but during a large bloom phosphate may become limiting When phosphate samples were reanalyzed without removing the sed~ment (no filtration), phosphate concentrations were about 25 D/o higher. This suggests that phosphate is adsorbed to sediment particles and could potentially be biologically available. There was a high suspended load (100 to 180 mg 1-') because the sediments were fine (silt and clay) and they were kept suspended by high tidal currents (0.5 to 1.5 m S-') caused by tidal ranges of up to 4 m during spring tldes in these shallow (3 to 9 m deep) creeks. Hence, extinction coefficients were very high (1 to 2 m-') and the 1% light depth ranged from < l m in August (the rainy season) to about 4 m in January and February. Consequently, primary productivity appeared to be light-limited throughout the year.Chl a ranged from 1 to 4 pg 1-' with occasional blooms up to 40 pg I-'. Primary productivity ranged from 0.2 to over 1 g C mw2 d-' in lsaro Creek. There was no apparent seasonal cycle in chl a or primary productivity. Phytoplankton species were predominantly large centric diatoms which were presumably kept in suspension by tidal currents. Since nutrients are rarely limiting, there is an export of nutrients from the creeks to the coastal area which may stimulate phytoplankton productivity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.