Geology Reference
In-Depth Information
Fig. 12.6
.
Changes in the substrate, coverage and composition
of shelf-edge and shelf reefs off Cozumel caused by Hurri-
cane Gilbert.
A:
Overall changes.
B:
Changes in the coverage of calcareous and non-calcareous organisms.
The impact of the hurricane on substrate conditions,
coverage and biotic composition are summarized in
Figs. 12.6 and 12.7. The histograms give an idea of the
overall changes in the reefs studied (Fig. 12.6) and of
the variations in the changes in reefs located in differ-
ent water depths (Fig. 12.7). Major changes with im-
plications for the interpretation of ancient reef destruc-
tions relate to the frequency of hard and soft substrates,
the distribution of sediments, and the abundance of car-
bonate-producing and other organisms.
Statistically
significant results
of the comparison of
the pre-hurricane and the post-hurricane situation are:
• The size and frequency of bare hard bottoms (reef
rocks), not yet resettled by organisms have dramati-
cally increased in shallow subtidal settings (Fig. 12.6A).
These hardground areas were almost doubled in some
reefs as a result of the hurricane (Fig. 12.7A).
• The frequency of sand-sized loose sediment (soft
bottoms) has increased in shelf-edge reefs (Fig. 12.7A)
Fig. 12.7
.
Changes caused by Hurricane Gilbert
in shelf-edge reefs (III), shelf reefs (I and II, isolated patch reefs) and reefs
on the upper slope (15-30 m).
A:
Coverage changes.
B:
Changes in the frequency and coverage of coral morphotypes.
