Abundance of Ruppia megacarpa Mason in a seasonally variable estuary

The aim of this paper was to assess how much of the variation in abundance of Ruppia megacarpa within Wilson Inlet, Western Australia, could be attrib uted to variations in conductivity, turbidity, depth, dissolved oxygen, pH and temperature of the water column (hydrological variables). R. megacarpa was collected from six sites within Wilson Inlet, a bar built estuary in so uthwestern Australia. Hydrological variables were measured and seasonal var iation assessed using non-metric Multi-Dimensional Scaling (non-metric MDS) . Canonical Correlation Analysis (CCA) was used to determine correlations b etween Ruppia abundance and these hydrological variables, for the same time period and with a lag time of 2, 4 and 6 months. Strong seasonal patterns in hydrological variables in Wilson Inlet were related to seasonal rain and the annual winter opening of the channel to the ocean by the local council . Conductivity, turbidity and depth were related to approximately 40% of th e variation in R. megacarpa abundance. Morphological plasticity is hypothes ized to be an important component of the unexplained 60% of variation in R. megacarpa abundance. Strongest relationships between R. megacarpa abundanc e and individual hydrological variables were over different time periods: t urbidity was directly related; depth with a lag of 2 months; and conductivi ty with a lag of 4 months. This study confirms that in a variable estuarine system there is a strong relationship between hydrological and biological variables. (C) 1999 Academic Press.