THE EFFECT OF THE GRAZING GASTROPOD BEMBICIUM NANUM ON 
RECOLONIZATION OF ALGAE ON AN INTERTIDAL ROCK PLATFORM 
Hal Braley 1 , Trevor A. Anderson 1 ’ 3 and G. P. Quinn 2 
department of Biological Sciences, Deakin University, Geelong, Victoria 3217 
department of Botany and Zoology, Monash University, Clayton, Victoria 3168 
3 Address for reprints 
Braley, H., Anderson, T. A. & Quinn, G. P., 1991:06:30. The effect of the grazing gas¬ 
tropod Bembicium nanum on recolonization of algae on an intertidal rock platform. 
Proceedings of the Royal Society of Victoria 103 (1): 13-16. ISSN 0035-9211. 
The predominant organisms found in the littoral zone of a rock platform at Aircys Inlet, 
Victoria, were surveyed in autumn 1989. The predominant algal species was the brown alga 
Hormosira banksii , while the predominant invertebrate herbivore was Bembicium nanum. 
The abundances of H. banksii and B. nanum were negatively correlated. B. nanum had a 
significant effect on recolonization of the ephemeral brown alga Scytosiphon lomentaria but 
there was no effect on recolonization of H. banksii or of the green alga Enteromorpha intes- 
tinalis. 
MANY RECENT studies have described the 
structure of intertidal communities (Cubit 1984, 
Lubchenco 1980, 1983, Lubchenco & Cubit 
1980, Underwood 1980, 1984, Underwood & 
Jernakoff 1981). Many of these studies have 
shown that the structure of an intertidal algal 
community is affected by both the physical en¬ 
vironment (including such factors as immer¬ 
sion) and by grazing, which may eliminate algae 
above a certain level on the shore (Jernakoff 
1983, Steneck 1982, Underwood 1980). Whilst 
many experiments have examined competition 
between intertidal herbivores (Fletcher & 
Creese 1985, Fletcher & Underwood 1987, 
Quinn & Ryan 1989, Underwood 1984), rela¬ 
tively few have examined specific algal-herbi¬ 
vore interactions (Hunter & Hunter 1983, Un¬ 
derwood 1980, Underwood & Jernakoff 1981) 
and fewer still have been conducted in Vic¬ 
toria. 
An initial survey of a rocky intertidal platform 
at Aireys Inlet, Victoria, showed a significant 
negative correlation between the density of the 
littorinid snail Bembicium nanum and the abun¬ 
dance of the predominant algal species Hormo- 
sira banksii. Previous studies have observed that 
this littorinid snail grazes micro and ephemeral 
algae (Quinn & Ryan 1989, Undemood 1980, 
1984). A study was conducted to examine the 
effects of the presence of B. nanum upon the 
recolonisation of H. banksii and two species of 
ephemeral algae, Enteromorpha intestinalis and 
Scytosiphon lomentaria. 
STUDY SITE AND METHODS 
The study site was a sandstone and clay inter¬ 
tidal platform located at Aireys Inlet, Victoria. 
The platform extends from the sublittoral zone 
to the high water mark. 
Initial Survey 
An initial study was conducted to determine the 
abundance and total number of algae and herbi¬ 
vores present. Twenty one-metre square quad¬ 
rats were selected randomly and the organisms 
within the quadrats counted. Correlation analy¬ 
ses were then performed between the number of 
plants present and the number of herbivores 
(Zar 1984). 
Major Study 
Twenty areas each measuring 200 x 200 mm 
were randomly selected over the rock platform. 
The substratum within these areas was cleaned 
to bare rock by scraping with a metal implement 
and scrubbing vigorously with a domestic scrub¬ 
bing brush. The experimental areas were then 
bounded by a layer of antifouling paint (25% 
CuS0 4 ). Nineteen B. nanum (the maximum 
density of B. nanum found) were placed into 
each of 10 areas (inclusion) whilst all benthic 
herbivores were excluded from the remaining 10 
areas (exclusion). 
The enclosures were monitored weekly (or as 
close as tides and weather would permit) for 
13 
