Dynamics of bacterioplankton abundance and production in seagrass communities of a hypersaline lagoon

Abstract

The significance of bacterioplankton in the flow of carbon and energy and in trophic dynamics of the upper Laguna Madre, Texas (USA), was estimated by measuring bacterioplankton abundance and production over an 18 mo period and over several diel cycles. Bacterioplankton production was estimated from incorporation rates of thymidine (DNA synthesis) and leucine (protein synthesis). These independent inhces of bacterial growth were generally in agreement and yielded nearly identical annual estimates of bacterial production (25.24 g C m-2 yr-' based on thymidine and 25.12 g C m-' yr-I based on leucine). Assuming a 30 % growth efficiency, the annual bacterioplankton growth could be supported by 15 % of the total primary production (seagrasses and phytoplankton), 17 % of the above-ground production of the dominant seagrass, Halodule wrigh~, or 103 % of the phytoplankton production. Bactenal abundance was high throughout the year, often exceeding 1 X 10'' cells I-'. Bacterioplankton production varied seasonally and over the diel cycle, with maximal values during warmer months and dunng daytime. Although changes in water temperature could account for some of this variation, shifts in the quantity and quality of the organic substrates supporting bacterial growth appeared to be the major factors regulating the variations in bacterioplankton production. Bacterioplankton in the Laguna Madre are a large and rapidly growing source of biomass potentially available for higher trophic levels. If this biomass is efficiently used by grazers, bacteria may be a major 'link' between seagrass production and secondary producers in the Laguna Madre ecosystem.

Enhanced bacterioplankton production and respiration at intermediate salinities in the Mississippi River plume

“…a n d rates of TdR and Leu incorporation have been reported to covary in a variety of aquatic systems (McDonough et al 1986, Kirchman & Hoch 1988, Chin-Leo & Benner 1991. In the present study, rates of TdR and Leu incorporation were significantly correlated (p = 0.0001) during summer and winter.…”

“…All radioactive substrates were from New England Nuclear (Boston, MA, USA). The nucleic acid and protein fractions were separated in all samples as described by Chin-Leo & Benner (1991) to test for the possible non-specific incorporation of TdR into protein.…”

Dissolved organic carbon cycling in a subtropical seagrass-dominated lagoon

“…This is surprising considering bacterial production in the water column of seagrass beds is relatively high and has been found to vary diurnally, suggesting that bacterial activity is related to seagrass photosynthesis (Moriarty & Pollard 1982, Chin-Leo & Benner 1991. Diurnal variation in bacterioplankton production was found in Laguna Madre and only about 10 to 20% of this change could be attributed to changes in water temperature (Chin-Leo & Benner 1991). Shifts in the quantity and quality of DOM, related to light-mediated processes such as seagrass or algal exudation, were proposed to be responsible for enhanced bacterial production during daylight hours (Chin-Leo & Benner 1991).…”

“…Direct grazing on living seagrass tissues has been found to be relatively minor, and this is attributed to the abundance of structural polysaccharides and phenolic compounds in seagrasses (Thayer et al 1975, Morgan 1980, Mann 1988. The transfer of seagrass C to secondary production is thought to occur primarily through detritus-based food webs (Robertson et al 1982, Chin-Leo & Benner 1991, Peduzzi & Herndl 1991. Microorganisms, utilizing dissolved organic matter (DOM) released through macrophyte exudation, leaching and decomposition (Benner et al 1986, Findlay et al 1986, are considered a primary conduit in the transfer of this organic matter to higher trophic levels (Tenore 1977).…”

The decomposition characteristics of the seagrass <i>Thalassia hemprichii</i> in Okinawa, Japan

“…This is most likely due to additional consumption by benthic animals, such as; crabs, gammarids and sphaeromatids. These small animals ap- Zepp et al 1998;Chin-Leo and Benner 1991;Mans et al 1998;Ziegler and Benner 2000), substrate composition (Boer 2000), water depth, and waves Romaro 1997, 1996) impact the process of plant litter decom position. In this study, the large variation of organic carbon and nitrogen contents at St.1 may be caused by the unstable environmental condition without seagrasses.…”