Biology Reference
In-Depth Information
the genera
Caulerpa
and
Halimeda
have been well studied and experiments have
shown that their chemical composition deters both parrotfishes and sea urchins
alike (Schupp and Paul
1994
). Brown algae are known to utilize polyphetanolic
compounds as deterrents along with terpenoids, which are commonly present in the
order Dictyotales (Pereira and Da Gama
2008
). Red macroalgae possess a great
variety of secondary metabolites and the genus
Laurencia
has been widely studied
for this reason (Blunt et al
.
2007
).
The study of chemical defenses of macroalgae has been widely investigated for
over two decades and most of the research has been focused on their utilization
against grazers (fishes, sea urchins, and gastropods) and their effect on coral
species. For example, from their experiments conducted in the Caribbean and
tropical Pacific, Rasher and Hay (
2010
) provide evidence that five of seven
seaweeds (71%) caused bleaching of the coral species
Porites porites
in Panama.
While in Fiji, three of eight species (38%) caused bleaching of
Porites cylindrica
.
Seaweeds were observed to damage corals via abrasion, shading, or lipid-soluble
allelopathic compounds transferred through direct contact. The effects of a lipid-
soluble extract from various species of macroalgae (
Ochtodes secundaramea,
Dictyota bartayresiana, Lobophora variegata, Halimeda opuntia, and Amphiroa
fragillisima
in Panama) caused significant coral bleaching and suppression of
photosynthetic efficiency in assays using both intact seaweeds and chemical
extracts. The two species that did not cause bleaching in any of the two assays
were
Padina perindusiata
and
Sargassum
spp. These results illustrate how
overfishing of herbivorous fish, capable of suppressing undesirable macroalgae,
will inevitably result in an increase of direct coral-algae contacts and further impair
corals through allelopathic interactions. Major gaps still persist concerning the
ecological role that macroalgal secondary metabolites play apart from feeding
deterrence (Pereira and Da Gama
2008
).
16.4.1.3 Providers of Spatial Refuge
Persistence of unpalatable macroalgae on coral reefs can be facilitated by spatial
refuges and associational assemblages. An associational refuge is one in which a
host species provides protection that enhances the survival of associate species
(Bittick et al
.
2010
). These interactions are becoming increasingly recognized as
important drivers of ecosystem function. Smith et al
.
(
2010b
) have found that
patches of the green algae
Caulerpa sertularioides
found in reef areas of Uva
Island in Panama can persist due to their association with an epiphytic cyanobacte-
rium (
Lyngbya majuscula
). The cyanobacterial epiphytes on
C. sertularioides
thalli
provide protection from herbivory for both upright assimilators and stolons.
Similarly, associational defenses provided by cyanobacteria have been reported to
be responsible for the 5-year persistence of the highly palatable alga
Acanthophora
spicifera
on the Uva Island reef (Fong et al
.
2006
). On the coral reefs of Moorea,
French Polynesia, Bittick et al
.
(
2010
) observed that aggregations of the brown
macroalga
Turbinaria ornata
provide mechanical and chemical refuge from
