Inter-tidal Ecology at Narrow Neck Reef — Dellow 
367 
petition, within narrower limits, from other 
animal communities, in particular those 
formed by the common rock oyster, Saxostrea 
glomerata, and by tubicolous polychaetes like 
Hermella spinulosa and Vermilia carinifera. 
Chamaesipho and E. modestus owe their 
ubiquitous nature to their ability to reproduce 
in large numbers throughout the year (Moore, 
1943) and to their wide tolerance with re- 
spect to their substrates. 
d. Saxostrea Consociation (Fig. 9) 
Vertical range: 6. 5-3. 5 feet. Between 
M.S.L. and M.L.W.N. 
Exposure: 53-20 per cent. 
Saxostrea glomerata occurs in a conspic- 
uous belt, both upper and lower boundaries 
of which are sharply delimited. A species 
most consistent with regard to vertical range, 
Saxostrea shows relatively little variation in 
pattern of distribution in response to factors 
such as wave action, light incidence, and 
angle of slope of the substrate (Doty, 1946). 
The consociation usually gives way above 
and below to a balanoid community. On the 
main reef, however, which is nowhere higher 
than 6 feet, the oyster forms the uppermost 
belt. 
The few associated species are nearly all 
animals. The gastropod Lepsiella scobina 
causes much damage by boring holes with 
its radula through the shell of the oyster, 
which it extracts in pieces. Powell (1947) 
records that Lepsiella can pierce an oyster 
shell in 45 minutes. 
4. Hermella — Vermilia Association 
Vertical range: 5. 5-2.8 feet. From just 
below M.S.L. to just above M.L.W.M. 
Exposure: 42-10 per cent. 
Hermella spinulosa (d) 
Chamaesipho columna (a) 
C odium adhaerens (f) 
Gelidium caulacantheum (o) 
Vermilia carinifera (d) 
Elminius modestus (a) 
Centro cer as clavulatum (o) 
Fig. 9- Saxostrea glomerata consociation on a heavily eroded ledge near St. Leonard’s Point. 
