You are here:
PHYTOPLANKTON DYNAMICS IN A GULF OF MEXICO ESTUARY: TIME SERIES OF SIZE STRUCTURE, NUTRIENTS, VARIABLE FLUORESCENCE AND ALGAL PHOSPHATASE ACTIVITY
Citation:
Juhl, A. R. AND M C. Murrell. PHYTOPLANKTON DYNAMICS IN A GULF OF MEXICO ESTUARY: TIME SERIES OF SIZE STRUCTURE, NUTRIENTS, VARIABLE FLUORESCENCE AND ALGAL PHOSPHATASE ACTIVITY. Presented at Gulf Estuarine Research Society, New Orleans, LA, May 15-17, 2002.
Description:
Relationships between phytoplankton dynamics and physiology, and environmental conditions were studied in Santa Rosa Sound, Florida, USA, at near-weekly intervals during 2001. Santa Rosa Sound is a component of the Pensacola Bay estuary in the northern Gulf of Mexico. Parameters measured included temperature, salinity, inorganic nutrients, and size-fractionated chlorophyll. Phytoplankton variable fluorescence parameters were measured to evaluate their potential for assessing in situ phytoplankton nutrient status. Algal phosphatase (Pase) activities were used to examine relative phosphorus stress. During the study, dissolved inorganic nitrogen (DIN, mostly as NH4) concentrations ranged <0.5-5.2 uM, dissolved inorganic phosphorus (DIP) concentrations ranged <0.03-0.3 uM, and dissolved silica (DSi) concentrations ranged 6-32 uM. DIN and DSi negatively correlated with salinity, suggesting that rainfall and runoff were primary sources. Chlorophyll concentrations peaked during spring (10-15 ug/L), then dropped about 50% and remained low through summer and fall. Phytoplankton size structure typically was evenly distributed between large (>5 um) and small (<5 um) size fractions, except in late summer/fall when small cells often dominated. Maximum quantum yield of chlorophyll fluorescence (Fv/Fm) for the bulk community varied from 0.54 to 0.62 with lowest values during spring. Fv/Fm was more strongly related to DIP than DIN. The high values of bulk Fv/Fm suggested a phytoplankton community in balanced growth with respect to nutrients. However, a companion study found that nutrient additions always stimulated phytoplankton growth, suggesting that at least a portion of the community was nutrient limited. The large size fraction consistently had higher FV/Fm values, although the difference was usually small. Lower Fv/Fm in the small fractions may indicate greater nutrient stress. However, abundant cyanobacteria could have biased Fv/Fm in the small fraction towards low values. Chlorophyll-normalized Pase activity positively correlated with DIN concentration, suggesting that phytoplankton were driven towards P stress when DIN was supplied. In general, parameters related to phytoplankton physiology varied little and
suggested a community acclimated to ambient conditions.