Spatio-temporal variability of wasting disease symptoms in eelgrass meadows of Brittany (France)

Eelgrass-leaf dynamics and 'wasting disease' symptoms were compared in three meadows of the Brittany shoreline. The agent responsible for these symptoms, Labyrinthula zosterae, was present in these three sites its infestation was highly correlated with leaf-age. To distinguish the periods of increased Labyrinthula infestation from the periods of normal functioning of the plant with none or only few infestations, a procedure based on the association of a wasting index (WI) and leaf-age was developed. This procedure is capable of revealing the phases of early infestation and recession of the 'disease' by comparison of the normal infestation of Labyrinthula which develops only to a minor extent in the oldest leaves of the shoots, The overall seasonal dynamics of leaf production and leaf growth were masked by the local conditions of each Zostera bed. Over the period of study ( 1-2 years), no significant mortality due to labyrinthula was observed. The variability of the WI appeared to depend essentially on the normal life-span of the leaves and local events, and appeared to be asynchronous, However, periods of 'disease' were observed; in which the WI increased from 5-10%. (baseline) to 20-25% (maximum) at the end of the summer, when the leaf surface and leaf numbers were at their maximum. No die-off due to Labyrinthula was found. (C) 2002 Elsevier Science B.V. All rights reserved.