Biology Reference
In-Depth Information
16.4.4 Macroalgae-Mangrove Interactions
The vast majority of studies focused on mangroves come out of the Indian and
Southwest Pacific Ocean in which water transparency can be low due to high tidal
amplitude and intense terrestrial runoff typical of estuaries and deltas (Kristensen
2008
). This limits subsurface primary productivity and promotes the development
of detrital communities (Kristensen
2008
). Studies coming out of Southeast Asia
(Thailand, Malaysia) and the Indus Delta describe mangrove forests as nutrient
exporting systems that have low epifaunal biodiversity, low macroalgal abundance,
and organically rich sediments (Saifullah and Ahmed
2007
). In this environment,
macrophytes and filter feeding assemblages are extremely limited. As a result,
many of the inhabitants are generalists and opportunists with microalgae and
allochthonous phytoplankton providing an additional and essential source of nitro-
gen (Kristensen
2008
). However, in the Atlantic Ocean and Caribbean Sea tidal
amplitudes are minimal and terrestrial runoff is limited, leading to high water
clarity, allowing for the proliferation of macroalgal and filter feeding communities
within fringe regions (Kieckbusch et al
.
2004
). Therefore, the disproportionate
amount of research coming out of Asia and Australia has led to a skewed perception
of the role of macroalgae within mangrove systems.
16.4.4.1 Abundance and Productivity
The NPP (NPP) of mangrove prop root epiphytes in the Bahamas (8.5
6.4 gC
kg
1
day
1
) has been measured to rival that of nearby seagrass epiphytes (Koch and
Madden
2001
). In the Karachi mangroves of the Indus Delta, Saifullah and Ahmed
(
2007
) have estimated that the algal productivity is much higher than that of the
mangroves themselves. However, the actual biomass of algae growing within some
mangrove systems may be quite low due to light limitation. Nevertheless, their role
in coastal food webs is likely to be consistently significant, owing to their nitrogen
content, which is 10
higher than mangrove tissues (Alongi
1998
). Since decom-
position of mangrove tissues is a slow process, due to its high lignin, cellulose, and
tannin content, it is likely that algae and bacteria provide a significant amount of
nitrogen to the mangrove food web. Therefore, it is probable that any algal tissue
appearing within algae-deficient mangrove habitats is likely to be quickly utilized
by resident fauna (Alfaro
2008
).
In 2001, Koch and Madden attempted to determine the source of nutrients within
oligotrophic lagoons in the Bahamas. They found that total nitrogen and phospho-
rus concentrations were highest within fringe mangrove and seagrass meadow
sediment samples directly adjacent to mangroves, relative to sand flats and open
lagoon seagrass meadows. On a biomass basis, the gross primary production of prop
root macroalgae was twice as high as nearby seagrass epiphytes and their NPP was
even comparable to that of seagrasses. At that time they were unable to identify the
