Dissolved Carbohydrate Dynamics in the Sea

Abstract

Dissolved polysaccharide (PCHO), monosaccharide (MCHO) and total carbohydrate (TCHO) have been determined at two to four hour intervals in three marine environments, and related to several other chemical and biological parameters, to study the dynamics and biological interactions of dissolved carbohydrate (CHO). Six vertical CHO arid dissolved organic carbon (DOC) profiles from a preliminary study across the North Atlantic were compaired with those of particulate ATP (< 3 um and > 3 um size fractions), chlorophyll a phaeopigments and dissolved oxygen. Carbohydrate peaks were associated with accumulations of > 3 um organisms which were low in chlorophyll a possibly indicative of collections of protozooplankton. A total of ten follow up diel studies in an enclosed salt marsh and a 13 m3 simulated estuarine ecosystem (MERL tank) show evidence of biologically mediated CH0 fluctuations. During five of the six marsh studies, PCHO underwent periods of sustained accumulation commencing in the late morning or early afternoon and continuing through at least two sampling periods into the early evening. Accumulations during this time period seem to be related to the rate of primary production. They may result from the release of recently synthesized PCHO from phototrophs since their magnitude was a significant multiple linear function of daily solar radiation and mean daily temperature for the six studies spanning all seasons. Similar periods of sustained release were not found in the MERL tank but a significant direct correlation between the rates of change of PCHO and phaeopigments in the combined data from all four tank studies suggests that zooplankton excretion was an important source of PCHO. Bacterioplankton counts and PCHO levels, in one study, varied directly in the late morning and inversely through the afternoon and evening, indicating that the bacteria were active and able to respond rapidly and control the natural PCHO concentrations on a time scale of a few hours. Data from two stations in the western Sargasso Sea, sampled at three or four hour intervals while following a drogued buoy, indicate that in-situ CHO concentrations were closely related to the phototrophic nanoplankton (PNAN), heterotrophic nanoplankton (HNAN) and heterotrophic bacterioplankton (HBAC) populations determined by epifluorescence microscopy. Significant inverse correlations of PCHO and of TCHO with PNAN numbers were found in two diel data sets from off the Carolina coast. Off central Florida, TCHO and/or PCHO were significant multiple linear functions of PNAN, HBAC and sometimes HNAN counts. Partial regression coefficients for PNAN