284
2010). Coral reefs in turn dissipate wave energy and create favorable conditions for
the growth of seagrasses and mangrove ecosystems (Birkeland 1985; Ogden 1988).
Here we briefly summarize the physical and biogeochemical relationships between
coral reefs and associated landscapes such as seagrass meadows and mangrove forests. We also explain the shift of reef flats from coral communities to macroalgal
communities (“phase shift”) and the implications of this shift to changes in biogeochemical cycles.
10.3.1 Relationship Between Coral Reefs and Seagrass Beds
Lamb et al. (2017) showed recently that when seagrass meadows are present in a
reef ecosystem there is a 50% reduction in the relative abundance of pathogens
potentially capable of causing diseases in humans and marine organisms. Their field
surveys showed that disease levels in more than 8000 reef-building corals located
adjacent to seagrass meadows were lower by a factor of two compared to corals at
sites without adjacent seagrass meadows.
Biogeochemical interactions between seagrasses and corals have recently been
proposed. Unsworth et al. (2012) found that 83% of seagrass meadows in the IndoPacific have a positive NPP and can increase seawater pH, which could buffer coral
reef calcification against future ocean acidification. Future laboratory and field
work should quantify the buffering capacity of seagrass relative to ocean
acidification.
Coral reefs in turn serve as physical buffers against oceanic currents and waves,
creating a suitable environment for seagrass beds over geologic time (Moberg and
Folke 1999). However, as Saunders et al. (2014) suggested, this shelter effect can be
threatened by increases of water depth in the lagoon (or moat) from sea-level rise.
They indicate that the rates of carbonate accretion typical of modern reef flats (up to
3 mm year
−1
) will not be sufficient to maintain suitable conditions for reef seagrasses in the future. These climate change (i.e. ocean acidification and sea-level
rise) impacts on connected coral reef–seagrass landscapes should be considered
when planning conservation efforts.
10.3.2 Relationships Between Coral Reefs and Mangrove
Forests
Mangrove forests act as natural filters to trap fine sediments and improve water clarity (Fig. 10.5; Duke and Wolanski 2001). Mangrove forests typically occur in turbid
waters where the turbidity mainly comes from a terrestrial catchment. When the
catchment still has natural forests, grasslands, or freshwater wetlands, mangroves
can filter the turbid water, and any remaining slightly turbid water does not reach
A. Watanabe and T. Nakamura
2010). Coral reefs in turn dissipate wave energy and create favorable conditions for
the growth of seagrasses and mangrove ecosystems (Birkeland 1985; Ogden 1988).
Here we briefly summarize the physical and biogeochemical relationships between
coral reefs and associated landscapes such as seagrass meadows and mangrove forests. We also explain the shift of reef flats from coral communities to macroalgal
communities (“phase shift”) and the implications of this shift to changes in biogeochemical cycles.
10.3.1 Relationship Between Coral Reefs and Seagrass Beds
Lamb et al. (2017) showed recently that when seagrass meadows are present in a
reef ecosystem there is a 50% reduction in the relative abundance of pathogens
potentially capable of causing diseases in humans and marine organisms. Their field
surveys showed that disease levels in more than 8000 reef-building corals located
adjacent to seagrass meadows were lower by a factor of two compared to corals at
sites without adjacent seagrass meadows.
Biogeochemical interactions between seagrasses and corals have recently been
proposed. Unsworth et al. (2012) found that 83% of seagrass meadows in the IndoPacific have a positive NPP and can increase seawater pH, which could buffer coral
reef calcification against future ocean acidification. Future laboratory and field
work should quantify the buffering capacity of seagrass relative to ocean
acidification.
Coral reefs in turn serve as physical buffers against oceanic currents and waves,
creating a suitable environment for seagrass beds over geologic time (Moberg and
Folke 1999). However, as Saunders et al. (2014) suggested, this shelter effect can be
threatened by increases of water depth in the lagoon (or moat) from sea-level rise.
They indicate that the rates of carbonate accretion typical of modern reef flats (up to
3 mm year
−1
) will not be sufficient to maintain suitable conditions for reef seagrasses in the future. These climate change (i.e. ocean acidification and sea-level
rise) impacts on connected coral reef–seagrass landscapes should be considered
when planning conservation efforts.
10.3.2 Relationships Between Coral Reefs and Mangrove
Forests
Mangrove forests act as natural filters to trap fine sediments and improve water clarity (Fig. 10.5; Duke and Wolanski 2001). Mangrove forests typically occur in turbid
waters where the turbidity mainly comes from a terrestrial catchment. When the
catchment still has natural forests, grasslands, or freshwater wetlands, mangroves
can filter the turbid water, and any remaining slightly turbid water does not reach
A. Watanabe and T. Nakamura