Biology Reference
In-Depth Information
(grazing and competition) conditions (Berner
1990
). We therefore describe the
zonation using examples from a Caribbean fringing reef, a Pacific Atoll, and a
Barrier reef.
On Cura¸ao in the Caribbean, van den Hoek et al
.
(
1978
) described the vertical
distribution of reef macroalgae and distinguished seven different algal
communities. The narrow eulittoral zone is inhabited by cyanophytes, turfs, and
smaller macroalgae. In the top part of the surf area, the seaweed community is
composed of
Ulva
and the brown seaweeds
Giffordia duchassaigniana
and
Sphacelaria tribuloides
, whereas in the deeper part the brown seaweed
Sargassum
polyceratium
and the red algae
Hypnea musciformis
and
Laurencia
spp. dominate.
In the sublittoral zone on the platform, from the surf area down to 3 m deep is a
shallow reef occupied by coral rubble fragments aggregated by the crustose red alga
Porolithon pachydermum
and macroalgal turfs. The foliose brown seaweed
Lobophora variegata
forms a girdle-like vegetation at 30-38 m deep and the
erect
Sargassum polyceratium
occurs from 15 to more than 65 m depth. Many
shade adapted species are present in this zone reaching to depths of 55-65 m,
including the green macroalgae
Udotea
and
Caulerpa
species and numerous red
algae. Crustose red algae reach into the deep where the reef terminates and a sandy
plateau forms at a depth of 75-90 m.
Womersley and Bailey (
1969
) described the zonation of macroalgae in the
Solomon Islands on four types of coral reefs, with differences in hydrodynamic
activity. The seaward rim consists of crustose coralline algae, mainly
Lithophyllum
and corals, and behind this the coralline alga
Porolithon onkodes
dominates. On
shallow intertidal rubble near the island shore, crustose and endolithic green algae
and cyanobacteria dominate.
Studies of the algal assemblages on the GBR have shown marked latitudinal,
cross-shelf, and within-reef variations in composition and abundance (Wismer et al
.
2009
). In contrast to midshelf and outer-shelf reefs, inshore or coastal reefs typi-
cally have abundant and conspicuous macroalgal communities (Diaz-Pulido et al
.
2007
). The reef flat zone in particular is often dominated by dense and highly
productive beds of large fleshy brown macroalgae, predominantly
Sargassum
(e.g., McCook
1997
; Schaffelke and Klumpp
1997
).
16.3.4 Seasonal Dynamics
Varying weather conditions throughout the year have a strong influence on the
abundance of macroalgae in tropical regions. In particular, lower temperatures and
the influx of nutrient-rich freshwater during the rainy season can cause a significant
increase of algal biomass. For example, in Kenya epiphyte coverage on seagrasses
can double or triple during the shift from the NE monsoon (warm temperatures, less
rain, and light winds) to the SE monsoon (cool temperatures, heavy rains, and
strong winds) (Uku and Bj
ork
2005
). In Florida, researchers observed an increase of
epiphyte biomass during the rainy season so extreme that it became three times
€
