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account for as much as 40% of the fresh weight of seagrass shoots (de la Torre-
Castro et al . 2008 ; Uku and Bj
ork 2001 ). In a Bahamas lagoon, the rates of net
primary production (NPP) for seagrass epiphytes (5.2
1.4 gC kg 1 day 1 ) have
been measured at approximately 40% of the NPP of the seagrasses themselves
(Koch and Madden 2001 ). In highly enriched waters, it is not uncommon for
seagrass-associated macroalgae to reach abundances higher than 0.5 kg m 2 and
obtain canopy heights greater than 0.5 m (McGlathery 2001 ).
In Kenya, encrusting red coralline algae are the first to colonize seagrass leaves,
establishing a purchase upon which subsequent epiphytes may settle, such as the
green algae Cladophora spp. and red algae Ceramium spp. (Uku 2005 ). This
succession of algal groups follows a consistent and predictable community gradient
along the vertical length of seagrass leaves, which is likely determined by light
exposure (Uku 2005 ). Of course, leaf colonization by epiphytes inevitably exacts a
toll on the host. Dixon ( 2000 ) determined that epiphytes covering seagrass leaves
can be responsible for reducing as much as 33.1% of available PAR. However,
studies in the tropical waters of Eastern Africa provide evidence that shading by
epiphytes has no effect on overall photosynthetic output of Thalassodendron
ciliatum shoots (Uku 2005 ). It seems that T. ciliatum compensate for the lost
PAR by maintaining photosynthetic activity in older epiphyte covered leaves
while increasing the production of new leaves capable of higher photosynthetic
activity.
In the presence of excessive nutrient concentrations, seagrasses may respond to
smothering epiphytes by increasing their growth rate (Ferdie and Fourqurean 2004 ).
Nutrient-enrichment studies have revealed decreased carbon reserves in the
rhizomes of seagrasses in the presence of excessive concentrations of nitrate and
ammonium (Invers et al. 2004 ). The unbalanced metabolism caused by this type of
enrichment can result in a significant loss of nonstructural carbohydrates which
allows seagrasses to persist during unfavorable conditions. Koch and Madden
( 2001 ) observed surge growth and N -storage in macroalgal seagrass epiphytes
during enrichment studies, indicating an adaptive trait that allows for a competitive
advantage when nutrients are limiting.
Epiphytes constitute an important food resource for seagrass herbivores and
omnivores. In Zanzibar, the majority of commercially important fish species found
within seagrass habitats, ranging fromherbivores, piscivores, and invertebrate feeders,
were found to graze directly on seagrasses and epiphytes (de la Torre-Castro et al.
2008 ). It seems that the higher nitrogen content of epiphytes and their resident
invertebrates is an important supplement to nitrogen-poor seagrass diets. Various
species of herbivorous parrotfish and surgeonfish collected from the seagrass beds
of Cura¸ao were found to have diets consisting primarily of seagrass epiphytes
(filamentous algae) and leaves (Nagelkerken and van der Velde 2004 ). From their
work with manipulative studies in Florida, Baggett et al . ( 2010 ) suggest that increased
grazing of epiphytes by herbivores (isopods, amphipods, gastropods, and caridean
shrimps) compensates for increased coverage during nutrient-enrichment treatments.
Recent studies in temperate seagrasses suggest that herbivorous invertebrates exert a
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