Spatial distribution of bacterioplankton biomass and production in the marginal ice-edge zone of the Weddell-Scotia Sea during austral winter

The influence of the melting of Antarctic sea ice on the planktonic microbial food web and the formation of microalgal blooms was investigated under controlled laboratory conditions in 20 1 microcosms at the onset of austral spring in the southern Atlantic. Experiments were performed with first-year ice and water from the Antarctic Circumpolar Current (ACC) and the ACC-Weddell Gyre Boundary (AWB) at 6" W, a region usually lacking ice-edge blooms in austral spring. The experiments comprised the following simulations: (1) stratification of the water column, (2) seeding of sympagic organisms, (3) inoculation of dissolved organic matter from sea ice and (4) grazing impact of mesozooplankton (Calanojdes acutus). Microcosms were sampled almost daily over a 2 wk period. The samples were analyzed for inorganic nutrient concentrations, prunary and bacterial production, abundances of algae (in the size classes <20 and >20 p), bactend and heterotrophic flagellates (in the size classes < 2 , 2 to 10 and 10 to 20 pm). Additionally, maximum uptake rates of glucose and aminopeptidase activity were measured. Stratification alone did not induce bloom formation within the time scale of the experiments. Simulated seeding of sympagic organisms provoked a strong increase in abundances and activities of auto-and heterotrophic microbes and the development of microalgal blooms (cells >20 pm). Primary and bacterial production was enhanced up to 28-and 24-fold, respectively, compared to the control, while abundances increased by a factor of about 20 for microalgae and 12 for bacteria. Initial h g h activities of auto-and heterotrophs were restricted to sympagic organisms, which maintained their high metabolic rates for several days. Addition of dissolved organic substances mainly stimulated the pelagic bacterial populations. Their production was enhanced up to 12-fold compared to the control, while autotrophs were virtually unaffected. In the presence of mesozooplankton, bacterial blooms occurred but no accumulation of nano-and microalgae. Thus, this region of the Atlantic sector of the Southern Ocean does have a strong potential for the formation of ice-edge blooms, but phytoplankton accumulation is efficiently controlled by grazing activity. Bacterial blooms may be more common during ice melt. These findings agree with remote-sensing data, which show no bloom formation during ice melt in this area.

Section: Resultssupporting

confidence: 92%

How are Antarctic planktonic microbial food webs and algal blooms affected by melting of sea ice? Microcosm simulations

Giesenhagen¹,

Detmer²,

Wall³

et al. 1999

“…Several comprehensive studies of Antarctic bacterioplankton have been performed, yet there is little agreement on the principal factors regulating bacterial growth (Ducklow et al 2001), and very few of these studies encompass winter (Mordy et al 1995, Scott et al 2000. This study found large seasonal variation in bacterioplankton abundance in Antarctic coastal waters that correlated with seasonal changes in the physical and biological environment.…”

Section: Discussionmentioning

confidence: 66%

Seasonal changes in the concentration and metabolic activity of bacteria and viruses at an Antarctic coastal site

Pearce¹,

Davidson²,

Bell³

et al. 2007

Bacteria play a key role in the world's oceans, supporting nutrient remineralisation and mediating carbon transfer. Little is known about annual changes in bacterial concentration, production and metabolism during the extreme seasonal changes in biological productivity in Antarctic waters. We measured rates of bacterial production, concentrations of viruses and bacteria and environmental parameters between February 2004 and January 2005 at an Antarctic coastal site. Concentrations of total bacteria and viruses were obtained using 4', 6-diamidino-2-phenylindole (DAPI) and SYBR Green I (Molecular Probes), respectively. Populations of bacteria in different metabolic states were estimated using vital stains. Concentrations of bacteria with intact or compromised plasma membranes were estimated using BacLight (Molecular Probes) and active cells estimated using 6-carboxyfluorescein diacetate (6CFDA). Our study showed 6CFDA and BacLight gave rapid and ecologically valuable insights into bacterial physiology, production and growth in natural Antarctic communities that were poorly represented by changes in total cell concentrations. Concentrations of total, active and intact bacteria declined rapidly at the end of summer probably owing to viral infection and microheterotrophic grazing. The decline continued over winter, likely owing to substrate limitation, and concentrations only increased after the phytoplankton bloom in spring and summer. Bacterial abundance was positively correlated with particulate organic carbon (POC) and nitrogen (PON), but not dissolved organic carbon (DOC), reflecting the refractory nature of the DOC pool. Only active and intact bacteria were significantly correlated with concentrations of chl a and rates of bacterial production. Furthermore, the obtained rates of [ 3 H]thymidine uptake suggest that bacterial growth rates can be sustained by the populations identified as intact or by active cells alone.

“…Similarly, during winter in the Antarctic, Helmke & Weyland (1995) found very low bacterial production beneath the pack ice. In contrast, Mordy et al (1995) found that bacterial production in water near the ice margin during winter was equivalent to 44% of primary production. This bacterial activity in winter likely reflects the fact that there is some year-round phytoplankton photosynthesis in most of the Southern Ocean, and it is enhanced near the ice edge even in winter (Cota et al 1992).…”

Section: Permanently Cold Watersmentioning

confidence: 70%

“…They include many measurements in water and sediments with an annual temperature range ≤ 4°C. Bacterial metabolic activity in polar waters in winter in the marginal ice zone is sometimes similar to that of summer (Rivkin et al 1989, Mordy et al 1995. In other instances very low rates are seen, although little seasonal temperature change occurred (Griffiths et al 1978, Pomeroy et al 1990, Karl 1993, Carlson et al 1998, Bird & Karl 1999.…”

Section: Permanently Cold Watersmentioning

confidence: 99%

Temperature and substrates as interactive limiting factors for marine heterotrophic bacteria

Pomeroy¹,

Wiebe²

2001

537

385

Active heterotrophic bacterial communities exist in all marine environments, and although their growth rates or respiratory rates may be limited by the interaction of low substrate concentrations with temperatures near their lower limit for growth, temperature and substrate concentrations are rarely considered together as limiting factors. Moreover, attempts to evaluate metabolic limits by both temperature and substrate concentration have sometimes led to confusing conclusions, because, while we can measure dissolved organic carbon (DOC) concentrations in natural waters, much of it is not readily available to heterotrophic bacteria. In spite of this procedural limitation, it can be helpful to regard temperature and substrate concentration as potential limiting factors that interact. In temperate ocean surface waters and estuarine waters, where bacterial growth is often reduced in winter, growth and respiration may be increased experimentally either by raising the temperature or by increasing organic substrate concentrations, providing indirect evidence that the limitation is an effect of temperature on substrate uptake or assimilation. Experimental work with bacterial isolates also has shown a temperature-substrate interaction. In permanently cold polar waters, most heterotrophic bacteria appear to be living at temperatures well below their optima for growth. Nevertheless, bacteria in permanently cold surface waters can achieve activity rates in summer that are as high as those in temperate waters. In sea ice, rates of bacterial production are most often low, even though concentrations of substrates, including free amino acids, are sometimes much higher than they are in seawater. This suggests that at sea ice temperatures heterotrophic bacteria have lowered ability to take up or utilize organic substrates. KEY WORDS: Temperature · Substrates · Heterotrophic bacteria · Limiting factorsResale or republication not permitted without written consent of the publisher