Coral Reefs: A Reef Resilience Toolkit Module

Resistant Characteristics

Representation of reef communities or coral types that display resistance to bleaching is a vital component of an MPA, and should be afforded high levels of protection, and should be buffered within larger management areas. If a coral reef is resistant, it is more likely to withstand environmental fluctuations or unexpected catastrophes. These resistant communities can play a critical role in reef survival, by providing the larvae to recruit and enable recovery of affected areas.

Exposed coral heads at low tide frequently display resistant characteristics. Photo © Great Barrier Reef Marine Park Authority

Resistance Factors in Coral Reefs

Determinants of resistance to bleaching have been identified in some coral communities and species. For example, coral communities that are exposed to extreme conditions on a regular basis (e.g., shallow water or intertidal corals) maintain a higher resistance to bleaching than other non-exposed corals. The following list of resistance factors1 in coral communities should be considered in any MPA design.

• Physical factors that reduce temperature stress

  Localized upwelling of cool water

  Areas adjacent to deep water

  Regular exchanges (cooler waters replace warm water)

• Physical factors that enhance water movement and flush toxins

  Permanent strong currents (eddies, gyres, tides)

  Wind topography (narrow channel, peninsulas and points)

  High wave energy

  High tidal range

• Physical factors that decrease light and radiation stress

  Shade (from high land profile, undercut coastlines or reef structure)

  Steep slope from coral assemblages and structure

  Presence of naturally turbid water

  Cloud cover

• Factors that correlate with bleaching tolerance

  Exposure to elevated water temperatures (warmer waters in shallow back-reef lagoons)

  Frequent exposure and emergence at low tide

• Indirect indicators of bleaching tolerance

  High diversity and abundance of reef species

  Wide range of coral colony sizes and species distribution

  History of coral survival after bleaching

Considering the above mentioned resistance factors, the following guidelines are recommended:

1. Survey MPAs and their adjacent areas for the presence of environmental factors that cause bleaching resistance, and identify coral communities protected by them.
2. For resistant coral communities inside established MPAs, consider securing high levels of protection for them by revising zone boundaries, or establishing special zones to encompass these sites.
3. For resistant coral communities outside established MPAs, consider extending MPA boundaries to incorporate these sites, if feasible, or creating new MPAs to include them.