The interplay between short-term, mild physicochemical forcing and plankton dynamics in a coastal area

Abstract

Two intensive surveys were conducted in the coastal waters of Barcelona (northwest Mediterranean) to assessshort-term variations of biological parameters in relation to environmental conditions. Surveys lasted 1 week,with three to four samplings per day, and were carried out in autumn and spring. Rather than exploring extremeevents, we aimed to study the effects of regular low or moderate perturbations, such as meteorological fronts, onthe dynamics of the system. We focused on two attributes: wave height, as a proxy for mechanical energy enteringthe system, and nutrient inputs, whose variability in total load and relative composition is a central characteristicof coastal areas. The effects of the temporal coupling or uncoupling of both factors were examined. Suddennutrient fluxes uncoupled from water motion tended to favor bacteria and heterotrophic nanoflagellates, whiletheir concurrence with some water column mixing shaped a favorable scenario for large autotrophs. Ultimately,these two distinct biological responses pointed toward two main disturbance scenarios: episodes of nutrientenrichment uncoupled from mixing, mostly related to episodic water spills from the nearby city that contributedto high relative loads of ammonium and organic compounds; and episodes of increased wind caused by passingweather fronts that promoted some water column mixing and the entrainment of nutrients from bottom sedimentsor from adjacent water masses. © 2013, by the Association for the Sciences of Limnology and Oceanography, Inc.