Biology Reference
In-Depth Information
16.4.1.5 Competition
Competition is an important force influencing the structure of coral reef
communities and its effects can impact all stages of a coral colony's life cycle
(Lirman
2001
; Nugues and Bak
2006
; Foster et al
.
2008
; Ritson-Williams et al.
2010
; Vermeij et al
.
2011
). Macroalgae are known to compete with corals using
different strategies which include the occupation of settlement substrate (Birrell
et al
.
2005
; Vermeij
2006
), physical disturbance (e.g., abrasion, shading, smother-
ing) (McCook et al
.
2001
; Box and Mumby
2007
), allelopathy (Gross et al.
2003
;
Kuffner et al.
2006
; Foster et al
.
2008
), and direct transmission of pathogenic
microbes (Vermeij et al
.
2009
). This competitive interaction is often species
specific and capable of causing different levels of stress on coral species, potentially
leading to coral mortality (Jompa and McCook
2002
,
2003
). In the Caribbean, Box
and Mumby (
2007
) determined that
Lobophora variegata
and
Dictyota pulchella
inhibited coral growth on juvenile
Agaricia
spp. and
L. variegata
through shading
and abrasion. In Hawaii, Vermeij et al
.
(
2009
) found that algal-induced microbes
can cause mortality of the planular larvae of
Montipora capitata
. This effect on
corals may be related to the ability of some algae to exude organic compounds that
enhance rapid microbial growth, causing hypoxia and the reduction of larval
resistance via the hampering of the coral's defense mechanisms against opportunis-
tic microbes.
Although competition between macroalgae and corals has received significant
attention from marine researchers, more evidence is still required in order to
determine if algal growth is a cause rather than a consequence of coral mortality
(McCook et al
.
2001
). More information is also needed concerning the interaction
between coral larvae, macroalgae, and microbes in order to improve reef restoration
techniques (Vermeij et al
.
2009
).
16.4.1.6 Facilitation of Coral Recruitment
CCA have been identified as facilitators of settlement and metamorphosis of a
variety of marine invertebrate larvae as well as coral larvae (Ritson-Williams et al
.
2010
; Vermeij et al.
2011
). CCA and coral interactions are known to be species
specific, since corals have displayed different degrees of specificity in their require-
ment for CCA to induce successful settlement and metamorphosis. For example, an
experiment conducted in the Caribbean (Belize) revealed that both
Acropora
palmata
and
Acropora cervicornis
have higher rates of metamorphosis on the top
surfaces of the CCA species
Hydrolithon boergesenii
and/or
Titanoderma
prototypum
than on
Porolithon pachydermum (
Ritson-Williams et al
.
2010
).
Further observations in the field (after 6 weeks) showed 15% survival of
transplanted
A. palmata
recruits on both
T. prototypum
and
H. boergesenii
, and
only 13% of A.
cervicornis
recruits on
T. prototypum
. These results suggest that
CCA and settling coral polyp interactions can be species specific and also highlight
the importance of benthic community composition for successful coral recruitment.