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Aside from the positive role of CCA in coral recruitment, Vermeij et al . ( 2011 )
have reported that mixed communities of CCA ( Porolithon spp. and Hydrolithon
spp.) are capable of suppressing macroalgal growth and recruitment of the green
macroalgae Ulva fasciata, based on studies conducted on a coral reef area in
Hawai'i. Likewise, Birrell et al . ( 2005 ) have highlighted the negative impact of
the association of macroalgal turfs and sediments have on coral recruitment of
Acropora millepora found in the Orpheus Islands of the GBR. The results of that
study indicated that sediment addition and algal turfs are capable of reducing coral
settlement, although the effects of different algal turfs varied. In some cases, algal
turfs inhibited coral settlement while other turfs inhibited settlement only when
combined with sediments. Their results are suggestive of the need to study the
impacts of similar associations to further understand the role of CCA in securing
long-term resilience and recovery of coral reefs.
16.4.2 Macroalgae-Seagrass Interactions
In low nutrient environments, seagrasses and slow-growing macroalgae constitute a
dominant regime in stable coastal waters. Seagrass habitats are important nurseries
for commercially important fish species found within seagrasses and adjacent
habitats such as coral reefs and mangroves (Dorenbosch et al . 2005 ). Within
seagrass meadows macroalgae contribute to substrate complexity, act as a vital
food resource for grazers, and have a significant influence on the cycling of
nutrients. In nutrient-rich locations, macroalgal epiphytes are capable of achieving
the same level of productivity as their seagrass hosts (Uku 2005 ). Some calcareous
algae generate such immense quantities of CaCO 3 that entire beaches are
constructed from the sand that they produce (Muzuka et al . 2005 ). However,
enrichment of coastal waters can encourage the proliferation of algal blooms and
initiate a breakdown in the balance of the system, resulting in decreased seagrass
coverage (McGlathery 2001 ; Hauxwell et al . 2003 ; Lapointe et al . 2004 ).
Macroalgae may provide short-term spatial heterogeneity and an enriched trophic
resource, thereby appearing to be beneficial for invertebrate community diversity;
however, they are often ephemeral and thus represent a threat to long-term biodi-
versity, relative to more permanent substrates, such as seagrasses (Cardosoa et al.
2004 ). Three distinct types of macroalgae (Epiphytic, Drift, and Calcareous Algae)
have an important influence on the seagrass environment and thus dictate the
structure of the following section.
16.4.2.1 Seagrass Epiphytes
In the tropics, epiphytic macroalgae are abundant and play a major ecological role
in several habitats (see also Chap. 11 by Potin). In the Western Indian Ocean,
macroalgal epiphytes constitute the most abundant group of epiphytes and can
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