Biology Reference
In-Depth Information
cause of this nutrient gradient, but they suggested remineralization by bacteria,
nutrient mobilization, and even delivery of metabolic wastes by fishes that migrate
between habitats during the day.
Recently, a great deal of debate has been focused on whether or not mangrove
systems are a source of nutrients for adjacent benthic and pelagic food webs
(Kieckbusch et al
.
2004
; Bouillon et al
.
2008
). Of course, the retention of organic
material within mangroves is completely dependent upon the tidal regimes of the
area. For example, from their studies in Thailand, Kristensen (
2008
) suggests that
the main source of organic matter in mangrove systems is derived from the
mangroves themselves and that macroalgae contribute very little to the organic
pool. Conversely, researchers in the Indus Delta argue that epiphytic algae are
an important source of energy within the mangrove environment (Saifullah and
Ahmed
2007
). However, Bouillon et al
.
(
2002
) have provided evidence from
studies in India, suggesting that there is very little export of this material to adjacent
habitats. According to stable isotope analysis of benthic invertebrates in neighbor-
ing habitats, the labile organic matter that is exported from the mangroves is not
consumed in significant quantities by faunal assemblages. Instead, grazers outside
of the mangrove system prefer to consume local sources of algae which are likely to
have a higher content of nitrogen. In fact, they argue that the primary production of
mangrove epiphytes in Karachi is higher than that of mangrove trees. Therefore,
caution must be taken when reviewing the literature and an understanding that each
mangrove system is likely to be unique based upon hydrodynamics and algal
communities.
16.4.5 Distribution of Macroalgae Within Mangroves
The mangrove systems of the Atlantic Ocean and Caribbean Sea are quite distinct
from those of Asia and Australia, especially in the context of the importance of
macroalgae. A recent study revealed that the most abundant epiphytes growing on
mangrove prop roots in Panama were sponges and macroalgae (
Caulerpa
verticillata
and
Halimeda
spp.) (Diaz and R
utzler
2009
). Sponges and macroalgae
clearly compete for space on prop roots, with algae occasionally dominating where
elevated sun exposure tips the balance in favor of algal dominance. In Belize,
macroalgae only dominate where deforestation and dredging have recently
occurred (Diaz and R
€
utzler
2009
). These two disturbances promote the suspension
of fine sediments that negatively impact all filter feeders (sponges and ascidians),
presenting the resulting macroalgal blooms with a competitive advantage.
Within mangrove habitats, algae growing on vertical surfaces are subject to an
array of extremely variable conditions such as submersion and exposure, light,
nutrients, temperature, and salinity. These challenging conditions have brought
about the evolution of mangrove-specific algae. A survey of macroalgae growing
on the pneumatophores of the mangroves of Karachi in the Indus Delta revealed a
collection of 14 species belonging to Chlorophyta, Phaeophyta, and Xanthophyta
€
