Effects of natural irradiance fluctuations on the photosynthetic responses of Gymnodinium breve (Karenia brevis) and Thalassiosira pseudonana and hydrographic structure associated with persistent Gymnodinium breve (Karenia brevis) subsurface accumulations

The effects of high and variable natural irradiance on the optical properties and primary productivity of the diatom T. pseudonana and the red tide forming dinoflagellate Gymnodinium breve were examined during deployments of the Self-Contained Underwater Photosynthetic Apparatus (SUPA), a bio-optical instrument capable of measuring productivity and incident light on minute time scales. Nutrient replete, low tight acclimated diatom cultures and relatively high light acclimated dinoflagellate cultures were placed in SUPA in Sarasota Bay under environmental conditions typical for summer. Comparisons made between the productivity responses of the two phytoplankton species show that under in situ irradiance conditions, T. pseudonana showed only a moderate decline in productivity initially and then a rapid acclimation response resulting in vigorous growth and cellular pigment adaptation in contrast to the lack of acclimation seen in G. breve resulting in a decline in net productivity. Estimations of changes in quantum yield throughout the deployment were determined using reconstructed cell specific absorption curves and the SUPA determined values. The importance of diadinoxanthin/diatoxanthin cycling in a photoprotective role is also examined.; Hydrographic features related to the persistence of small-scale G. breve subsurface accumulations, which remained near the entrance of Tampa Bay, were examined by comparing meteorological, hydrographic and coastal water level conditions prior to and during the cruise in an effort to examine the possible accumulation and dissipation and advection of G. breve cells on the west Florida shelf. The initial shelf-wide hydrographic survey, ancillary data and multiple samplings at the persistent patch location provide insight into small scale, near shore dynamics that may contribute to patch development and stability. Results indicate that G. breve was present inshore at the pycnocline where upwelled inner shelf water contacted pulsed coastal bay water. Also, a meteorologically driven rise and fall in sea level resulting in the expulsion of low density, buoyant pulses of coastal bay water was detected in both remotely sensed images and in shipboard determined hydrographic data.