Biology Reference
In-Depth Information
to the predominant idea that abundant macroalgae indicate compromised reef
health, no indications were found that conflicted with the existing definition of
“pristine” oligotrophic reef systems (Littler et al
.
2010a
).
Turf algal assemblages can provide the majority of the primary productivity on a
coral reef (Adey and Steneck
1985
; Fricke et al.
2011
). These assemblages are
multispecies associations, characterized by undifferentiated upright axes and a
rapid turnover (Carpenter et al.
1985
). Although inconspicuous, they occur almost
everywhere on reefs where space is available (Littler and Littler
1984
; Steneck and
Dethier
1994
). Although they are fast growing, fleshy macroalgae often outcompete
with them for limited light and space (Hay
1981
). Algal turfs are able to persist
under intense herbivory and physical stress in areas where other algae are continu-
ously excluded. Their high productivity rather than their standing crop maintains
the high standing stocks of grazers characteristic of coral reefs (Hatcher
1988
;
Carpenter
1986
; McCook et al.
2001
). In deep and shallow reef zones, where
grazing pressure is low, frondose algae rather than turfs commonly dominate
(Van den Hoek et al
.
1978
; Vuki and Price
1994
).
Crustose coralline algae (CCA) play three important roles on coral reefs: (1)
limestone formation, (2) the consolidation of loose substrates (Fabricius and Dea'th
2001
), and (3) primary production (Littler and Littler
1984
). In shallow waters they
can build massive carbonate structures on reef crests despite the typically turbulent
conditions (Adey and Vassar
1975
). Due to their unpalatable nature, coralline algae
are more resistant to grazing and therefore survive well in areas where grazing
intensity is high.
Fleshy frondose macroalgae are mainly composed of tropical fucoids like
Sargassum
,
Turbinaria
, and
Cystoseira
. They often dominate on shallow reef
flats and crests of inner reefs or in deeper fore reef zones and are generally absent
from mid and outer shelf reefs (Vuki and Price
1994
; McCook
1996
).
Sargassum
species are often dominant in terms of biomass and canopy cover, due in part to
their high productivity (Vuki and Price
1994
; McCook
1996
; Schaffelke
and Klumpp
1997
). Foliose macroalgae are seasonal opportunists and can be
found in areas less dominated by canopy-forming macroalgae (Schaffelke and
Klumpp
1997
). Due to high biomass turnover, reefs with a high cover of large
Phaeophyta are often regarded as detritus-driven ecosystems (Schaffelke and
Klumpp
1997
).
16.3.3 Zonation
The zonation and distribution of macroalgae is highly variable, which complicates
extrapolations between similar habitats and across habitat types within regions and
between different parts of the world. The distribution and zonation of macroalgae is
strongly dependent on the structure of the habitats which is formed by historical
(geology: reef types), abiotic (nutrients,
temperature, and light), and biotic
