Measuring seagrass photosynthesis: methods and applications

Early studies on seagrass photosynthesis (e.g. Drew 1978) usually began by explaining that seagrasses are relatively primitive monocotyledons, closely related to freshwater plants but able to live in the marine environment. Presently, many introductions start by highlighting the importance of seagrasses in overall marine productivity and their subsequent economical importance (e.g. Duarte & Cebrián 1996, Costanza et al. 1997, Duarte & Chiscano 1999). This shift of emphasis indicates the evolution of seagrass perception in global biological science and reflects the contribution of the increasing number of physiological and ecophysiological studies dealing with this plant group. Seagrass photosynthesis was, until recently, most commonly measured in laboratory experiments, usually by incubating leaf segments in closed chambers and determining initial and end O2 values, or by following continuous O2 evolution in the chambers with Clark-type electrodes. These methods have provided most of the fundamental information on seagrass responses to factors such as light, temperature and nutrients (comprehensively reviewed by Lee et al. 2007) and on the mechanisms of carbon uptake and fixation by these plants (Beer et al. 2002). However, they are extremely intrusive, as they involve plant removal from the natural environment and a high degree of manipulation (Beer et al. 2001). In situ measurements of photosynthetic activity in seagrasses were made possible after the development