Dynamics of seagrass stability and change

To the casual observer, seagrass meadows often appear to be uniformlandscapes with limited structure. Belying this appearance, seagrass meadows contain considerable structure and dynamics (cf. den Hartog, 1971). Seagrass meadows, at any one time, consist of a nested structure of clones, possibly fragmented into different ramets, each supporting a variable number of shoots. Thus, although apparently rather static, seagrass meadows are highly dynamic landscapes maintained through the continuous recruitment of new clones to the meadow, and the growth and the turnover of the shoots they contain. Therefore, the intense dynamics of seagrass ecosystems results from the combination of processes operating at various scales, which-if balanced-maintain a rather stable ecosystem. Often, however, the various processes responsible for meadow dynamics are either unbalanced or out of phase due to either natural causes or anthropogenic effects. Such imbalances result in changes in the meadows, which are sometimes readily evident, such as the case in catastrophic seagrass declines or are so subtle as to even elude quantification, such as may be the case in the gradual decline of slow-growing seagrass species (e.g. Marbà et al., 2003).