The delivery of nutrients to the surface of marine algae can be controlled by the local hydrodynamic regime: in higher flow velocities, the Diffusive Boundary Layer (DBL) at the uptake surface is thinner, which can increase the flux of dissolved chemicals to the algal surface. If the primary productivity of an alga is controlled by the availability of a dissolved chemical, increased water flow should result in greater primary productivity due to increased chemical flux. To test the hypothesis that increased water flow will increase Photosystem II kinematics (PSII) in the green alga Caulerpa we used a Diving Pam Fluorometer to measure the maximum relative electron transport rate (Pmax), Saturation Irradiance (Ik), Non-photochemical quenching (NPQ), the light limited slope of photosynthesis vs. irradiance curve (α) and photo-chemical quenching (qP) and compared these measured values among treatments of varying flow speeds in a portable laboratory flume. We also measured the influence of water flow on values of Pmax, Ik, α , qP and NPQ in the field. Results showed that in C. racemosa collected from Tampa bay, and tested in a laboratory flume, values of Pmax and Ik were positively correlated to increase water flow, possibly indicating mass-transfer limitation. C. mexicana, collected from the Florida Keys, showed a decrease in values of Pmax, and Ik with increasing water velocity in flume experiments, indicating that the increased flow was resulting in physiological stress. This result was supported with field measurements for C. sertularioides, which showed a negative correlation between Pmax and flow velocity and Ik and flow velocity.