The life history strategy of the temperate seagrass Posidonia australis (Brown) Hook. f. in South Eastern NSW

Abstract

An intensive study was conducted on Posidonia australis (Brown) Hook f in south east Australia. Three sites were studied intensively (16 times a year for two years) these being in Quibray Bay (sites 1 & 2) and Port Hacking (Site 3). Site 4 in Jervis Bay and site 5 at Bonna Point in Quibray Bay were studied less intensively (four times a year for two and one year respectively). Variables examined included shoot density, leafing rate, leaf number, unit leaf weight, leaf biomass per shoot as well as biomass production of leaf, sheath, rhizome, root and reprod'u'ctive structures. Correlations between seasonal variations in these parameters were established with water temperature, light intensity and rainfall. A procedure was developed and employed which estimated net leaf production without causing major damage to the study populations. This procedure also allowed estimation of several leaf production variables for the first time. The effects of stress and disturbance on meristem activity were examined. The correlation between leaf production and standing stock was established and the suitability of using seasonal changes in leaf standing stock or biomass values to estimate production seasonality was examined. The applicability to P. australis of two procedures that indirectly estimate the plastochron was also investigated.

Among the P. australis studied, significant seasonal variation occurred in unit leaf weight (mg * cm'l), total leaf biomass, leaf and rhizome biomass production, plastochron interval, and leaf and non-leaf production. The rates of most production variables peaked in late spring with minimal values recorded in early to mid-winter. Seasonal changes in relative leaf growth rate, leaf and rhizome production of P. australis shoots, highly correlated with changes in water temperature and light intensity. Mean total shoot biomass production ranged from 2.33 to 4.74 g * m'2 * day".