Communities Structure of Reef Corals
Fig. 7.9. Average size of common corals (D
diameter in cm) in different zones of fringing
reef off Eilat, Red Sea: 1 Acropora
hemprichi; 2 Montipora lobata; 3 Stylophora
pistillata; 4 Porites lutea; 5 Echinopora
lamellosa. (After Loya 1972)
269
.ll
75
12
8
~ ~----~~----~--~~
Rer Outez *-1,." 8-72,." 7J-!!m2U-JUm
Jfo~e ~~~e Reef seope
diameter and several tens of years of age often dominate (Isdale 1984;
Cameron and Endean 1985). The mortality rates of corals in their
communities also vary in different reef zones depending upon the level of
physical stress (Connell 1973). In young colonies with their projective area
below 40cm 2 it is the highest - up to 10-20% year-I. In average sized
colonies (40-80cm 2 ) it is 3 to 10%, and in larger colonies 1-5% year-I.
The average number of coral colonies per meter varies between 20-40 sp.
with the percentage of bottom surface covered by them being 40-80% (Fig.
7.10). On reef flats this number is usually less: 5-20 sp. Maximal numbers of
colonies could be found in deeper zones of reef slopes - up to 60sp. m- 2 .
Most often a large part of the colonies in communities belong to 2-4
dominating species, which might occupy up to 50% of the total area covered
by corals (Table 7.8). On many reefs a significant or even larger part of
coral colonies in communities could be represented by octocorals, which
may comprise there 60 to 90% of their total number (Jaap 1985).
Table 7.10. Age of coral colonies on some reefs in the GBR area; N - total number of
colonies counted; A - their average age, years; G - their average growth rate (diameter),
cm, year- 1 (After Connell 1973)
Corals
G
Position of reef
Heron Island
Low Isles
N
A
N
A
Acropora
4.6
32
6.5
7.
2.5
Montipora
6.8
12
4.5
7
2.5
Porites
2.0
27
9.5
5
11.5
Pocillopora
6.7
4
5.5
Psammocora
4.6
3
4.5
Missive coral species (average for 11 sp.)
1.3
73
7.5
Sum (average) for all species studied
75
6.5
96
7.5