Coral Reefs: A Reef Resilience Toolkit Module

Adaptation

Seagrass Meadows

One coastal habitat that may benefit from increased CO2 concentrations is seagrass meadows. Seagrasses are carbon limited but are able to extract carbon for photosynthesis. Experiments have demonstrated that increased carbon availability resulted in higher photosynthetic rates2. Seagrass beds located near corals may provide a short-term local buffer from the effects of ocean acidification on these coral reefs because the uptake of CO2 in the water column by seagrass through photosynthesis during the day may slow the rising of the carbonate saturation state in the water3.

Seagrass (Halophila decipiens) in O`ahu, Hawai`i. Photo © Katie Laing

Because mitigation strategies are not viable options on local and regional scales, adaptation strategies must become management priorities. Habitats that are likely to be resilient under relatively acidic conditions should receive conservation priority to maintain ecosystem functions and services. Reef and associated habitat types that are more likely to be resistant with increased carbon dioxide and acidification include:

• Reefs in carbonate rich areas
  Examples are those that include raised reefs and limestone islands, extensive reef flats, patch reef and coral head complexes, and carbonate sediment deposits.
• Well-flushed reefs
  In most reef lagoons, the release of CO2 through calcification exceeds the uptake of CO2 through primary production. Reefs that are well flushed with seawater are consistently exposed to higher aragonite saturation states that support calcification.
• Reefs with dense seagrass meadows
  The net effect on increasing CO2 on seagrass ecosystems will likely be increased seagrass biomass and productivity. It is possible that an increase in total seagrass area will lead to more favorable habitat and conditions for associated organisms1.
• Reef habitats rich in macroalgae
  Algal turfs are thought to benefit calcification because during sunlight hours, they photosynthesize and reduce carbon dioxide levels from the water column, thereby raising the saturation state.

When designing MPA networks, it is critical to consider the above mentioned habitat types, which may be resilient to ocean acidification impacts.