14 
H. BRALEY, T. A. ANDERSON AND G. P. QUINN 
eight weeks between mid April and early June 
1989. On each visit, where necessary, animals 
were replaced in test areas. The number of plants 
and algal species were recorded at each visit, and 
colour photographs were taken at fortnightly in¬ 
tervals to aid analysis of algal abundance. Vari¬ 
ation in the mass of organic material in each 
experimental area was determined at the end of 
the experimental period. The central four centi¬ 
metre square portion of each experimental area 
was scraped with a razor blade and the scrapings 
dried at 50° C for 24 hours. After weighing to the 
nearest 0.1 mg, the scrapings were ashed at 550° 
C for 24 hours and re-weighed. The loss in 
weight was attributed to organic matter. Analy¬ 
sis of variance was performed on log-trans¬ 
formed plant numbers and on log-transformed 
dry weights of organic matter found after 8 
weeks in test versus control area. 
RESULTS 
Initial Survey 
Table 1 shows the abundance of predominant 
organisms in the littoral zone of the rock plat¬ 
form. The alga Hormosira banksii was the pre¬ 
dominant species, covering 100% of the sub¬ 
stratum in the lower zones, but becoming patchy 
Species 
Mean 
SE 
Hormosira banksii 
159.0 
32.8 
Ulva lactuca 
2.8 
Corallina spp. 
1.2 
i.L 
08 
Siphonaria diemenensis 
63.9 
17? 
Austracochlea constrict a 
3.7 
1 4 
Bembicium nanum 
98.8 
28.5 
Table 1. Abundance of predominant organisms found 
on the rock platform (number of organisms present/ 
m 2 , n = 20). 
and sparse in the higher zones. Small amounts of 
Viva lactuca and Corallina spp. were found but 
no Scytosiphon lomentaria or Enteromorpha in- 
tes final is were found in this survey. The most 
numerous herbivore present was B. nanum av¬ 
eraging 98.8 animals/m 2 and reaching densities 
up to 473 animals/m 2 in some areas'^ The pul- 
monate limpet Siphonaria diemenensis was also 
found in large numbers. A significant negative 
correlation was recorded between II. banksii 
and B. nanum (r = —0.705, df = 18, P < 
0.001). No other significant correlations were 
found. 
Major Study 
The ephemeral species S. lomentaria and E. in- 
testinalis were the dominant recolonising algae 
H. banksii E. intestlnalls S. lomentaria Organic matter 
Fig. 1. Abundance of algae and dry weight of organic matter after 8 weeks following clearing of experimental 
areas in inclusion (diagonal rule) versus exclusion (stipple) areas. NB, analysis of//, banksii not performed due 
to the large number of null values; * = significant value of p (p < 0.05); inclusion = areas containing B. nanum: 
exclusion = areas where B. nanum excluded. 
