Journal of the Royal Society of Western Australia, 87(1), March 2004 
species were recorded, although lower numbers of 1 to 2 
species were found in winter. An exception to this 
generally low species number in the upper estuarine 
reaches was in November 1996 when 7 species were 
found in this estuarine region. 
The total number of macroalgal species found during 
these surveys was 36, with the highest number recorded 
in any one season (spring) being 20 (Tables 2 and 3). 
These species numbers indicate a relatively diverse 
macroalgal community compared to other south-western 
Australian estuaries. For example, Hillman et al (2000) 
listed only 13 macroalgal species from multiple surveys 
of the Leschenault Inlet between 1984 and 1993. The 
Leschenault Inlet also receives freshwater input from two 
rivers, the Collie and Preston Rivers, with an artificial 
connection to the ocean. Since construction of the 
Wellington Dam on the Collie River, freshwater input to 
the system has been significantly reduced, causing 
salinities within the Inlet to be marine throughout most 
of the year, and hypersaline in the northern end of the 
system. As reported here for the Swan-Canning System, 
the macroalgal assemblages in Leschenault Inlet were co¬ 
dominated by rhodophytes and chlorophytes, with the 
predominant species being Gracilaria sp and Chaetomorpha 
linum, respectively. Similarly, Lukatelich ct al. (1984) 
recorded 8 macroalgal species in Wilson Inlet, primarily 
chlorophytes. In contrast, Phillips & Lavery (1997) found 
40 macroalgal species in Waychinicup Estuary, 
dominated by phaeophytes and rhodophytes. 
Waychinicup Estuary is a small system (1.3 km in length) 
that has a strong tidal influence with a small, but 
consistent freshwater input. These hydrodynamic 
characteristics result in both vertical and horizontal 
variations in salinity within the estuary, with surface 
salinities at the head of the estuary as low as 22, and 
salinities at the mouth of the estuary effectively marine 
(34). As found in the current survey of the Swan-Canning 
Estuary, it was also in the lower reaches of Waychinicup 
Estuary, where extensive hard substratum is present, that 
most of opportunistic macroalgal species recorded during 
the investigation were recorded. 
Allender (1981) first reviewed the macroalgal species 
of the Swan-Canning Estuary in 1968 over a one-year 
period. Allender surveyed benthic macroalgal 
communities present in the photic zone within the lower 
25 km of the system. In total, he recorded 29 species 
comprising 11 chlorophytes and 14 rhodophytes, the 
majority of which he recognised as marine. As such, he 
proposed that the distribution of macroalgae along the 
horizontal axis of the estuary was strongly affected by 
the penetration of marine waters and the physiological 
tolerance of these species to freshwater inflows during 
winter. Accordingly, he found that the maximum 
horizontal distribution of species was during summer 
and the minimum was during winter. Allender (1981) 
proposed that macroalgal species in the Swan-Canning 
Estuary could be categorised as either annuals or 
perennials, depending upon whether the plants survived 
the winter season, and concluded that seasonal and 
temporal patterns in macroalgal communities of the 
system were largely due to the penetration and duration 
of marine waters into the estuary. 
The present study provided preliminary identification 
of spatial and temporal patterns present in the 
macroalgal assemblages of the Swan-Canning Estuary, 
evidenced by the presence and absence of individual 
species according to season and estuarine region. In 
particular, highest species numbers were encountered in 
summer and autumn in the lower estuarine region, areas 
and times of high salinity and hard limestone substrate. 
Outside of these seasons and region, the number of 
macroalgal species was far fewer, mostly unattached 
macroalgae growing over soft sediments dominated by 
the species Gracilaria comosa. 
Figure 4. Macroalgal species number at (a) hard and (b) soft substrate sites within lower (Q- 0 to 15 km), mid (□; 15 to 25 km) and 
upper (■; 25 to 55 km) estuarine reaches of the Swan-Canning Estuary 
12 
