MEPS 329:23-42 (2007)  -  doi:10.3354/meps329023

ABSTRACT: Photosynthetic parameters and community respiration were measured throughout 3 seasons at 8 stations in central and western Long Island Sound during 2002 and 2003. Light-dark bottle oxygen change was measured in a photosynthesis–irradiance (P–I) series for water from the mixed layer, and respiration was measured for surface, pycnocline, and near bottom water. P–I curves were fitted numerically to calculate biomass-specific rates of maximum photosynthesis at light saturation (P^B_m), photosynthetic efficiency at low irradiance (α^B) and plankton community respiration (R_c). The temporal and spatial variability of these fitted parameters, the derived parameter I_k, and the concentration of phytoplankton pigments were described in relation to each other and to environmental factors. Concentrations of chlorophyll (chl) and phaeopigments (phaeo), and R_c reached maxima in summer and significantly decreased seaward along the length of the Sound. Photosynthetic parameters also reached maxima in summer, however there was no significant spatial variability. In surface waters, the average (±SD) of P^B_m (1.3 ± 0.4 mmol O₂ [mg chl]^–1 h^–1) demonstrated the lowest variability, compared to chl (6.9 ± 4.9 mg m^–3), phaeo (3.5 ± 2.5 mg m^–3), α^B (10.9 ± 5.4 µmol O₂ [mg chl]^–1 h^–1 [µE m^–2 s^–1]^–1), I_k (132.6 ± 71.9 µE m^–2 s^–1), and R_c (1.4 ± 0.9 mmol O₂ m^–3 h^–1). Chl and P^B_m both varied with total daily insolation and with average irradiance of the photic zone, while P^B_m was also correlated with temperature. Although P^B_m and chl increased during summer, their peaks did not occur simultaneously. Temporal trends in α^B were less clear-cut than for P^B_m and chl, but α^B was correlated with light properties of the water column. Plankton community respiration was high in surface waters and decreased with depth. Based on the relationship between R_c and chl, algal-related rates of respiration (R_a) were estimated at ~50% of total plankton community respiration. Our results do not support the common method of estimating algal respiration based on P^B_m.

KEY WORDS: Productivity · Primary production · Respiration · Oxygen · Chlorophyll · Phytoplankton community · Long Island Sound