Astill & Lavery: Benthic macroalgae in the Swan-Canning Estuary 
Figure 2. Average (Av.) and maximum (Max.) rainfall (in mm) and river flow (in irF.s' 1 ) recorded for each month between July 1995 and 
April 1997 
25 i 
Aug95 Nov 95 Feb96 May96 Aug 96 Nov 96 Feb 97 May 97 
Figure 3. Macroalgal species number at sites within lower (Q; 0 to 15 km), mid (Q; 15 to 25 km) and upper (H; 25 to 55 km) estuarine 
reaches of the Swan-Canning Estuary 
eight seasonal surveys is provided in Table 1, which 
includes the season in which each species was found. In 
total, 36 species of macroalgae were recorded during the 
study, dominated by chlorophytes (20 species) and 
rhodophytes (12 species). The highest total species 
number recorded in any one season was 20 in spring 
(November 1995) and the lowest was 6 recorded in 
winter (August 1996), the season of highest rainfall and 
river flows (Fig 2). 
Regionally, the highest total species number was 
recorded in the lower estuarine reaches (Fig 3), where 
benthic salinities were over 30 in number in all seasons 
and macroalgal assemblages were dominated by species 
common to the nearby marine environment (Huisman 
2000). Within this estuarine region, species numbers 
varied between 15 and 22 in spring, summer, and 
autumn, falling to between 7 and 12 in winter. The total 
species number was significantly lower in mid- and 
upper-estuarine reaches (Tables 2 and 3). In total, 
between 6 and 11 species were found in the mid- 
estuarine regions of the estuary in all seasons except 
winter (3-5 species), while in the upper reaches 7 to 9 
11 
