SYNCHRONOUS FLOWERING OF ESTUARINE SEAGRASS MEADOWS

A hierarchical sampling scheme was used to describe variation in the t iming and intensity of flowering of multiple meadows of two species of seagrasses: Posidonia australis and Zostera capricorni. Sampling was stratified across a range of spatial scales: among sites and depths (P . australis only) within individual meadows, among meadows within the same estuary and among estuaries separated by tens of kilometres on th e coastline of Central New South Wales, Australia. Four surveys of P. australis were undertaken between 1992 and 1994. Surveys of Z. caprico rni were done over a single reproductive season; between September 199 2 and March 1993. Flowers of P. australis were found only in August 19 93, when they were present in all nine of the meadows examined. Densit ies of flowering shoots varied significantly among estuaries and at sm aller spatial scales within individual meadows. The timing of this unu sual flowering event coincided with unseasonably cool autumnal water t emperatures. Reproductive shoots of Z. capricorni were also recorded i n each of the nine meadows surveyed, but the timing and magnitude of p eak abundance varied widely among estuaries and exhibited considerable patchiness within individual meadows. The results suggest that the ti ming and intensity of flowering of Z. capricorni and P. australis are affected by processes that operate over at least three spatial scales. Initiation of flower production appears to be triggered by regional ( tens to hundreds of kilometres) changes in environmental conditions, s uch as water temperature or photoperiod, whereas the abundance of flow ers varied significantly among estuaries and may be influenced more by both meso-scale (kilometres) processes within estuaries and by local conditions within each meadow (metres to tens of metres). (C) 1998 Els evier Science B.V.