Linked Habitats

Ocean habitats are connected through changes in habitat utilization of juvenile and adult organisms, and through the transfer of materials and nutrients. For demographic connectivity to contribute to the resilience of coral reefs, it must function beyond the box of no-take MPAs. Specifically, management must improve nursery habitats on or near reefs and enhance the reproductive output of ecologically important species throughout the coral reef ecosystem.

Top left: Exposed at low tide, corals on reef flats often exhibit stress tolerance and may resist bleaching. Top right: Back-reef lagoons often experience wide temperature fluctuations. Corals in these areas may exhibit acclimatization to temperature stress. Middle left: Adjacent seagrass beds and sand flats serve as feeding grounds and nursery areas for coral reef species. Middle right: Adjacent mangrove habitats are linked to coral reef systems through the flow of matter, energy, and organisms. Bottom left: The reef ecosystem extends beyond its physical boundary to include the neighboring habitats with which it interacts, especially seagrass beds, back-reef lagoons, and mangroves which provide important fish nurseries. All these linked habitats need to be considered and managed as parts of a single functional unit. Bottom right: Reef zones. Photos: Top left and right © S. Summerhays; middle left © D. Obura; middle right © NOAA; bottom left © A. Reid. Reef zones (click image for larger version) courtesy NOAA CoRIS

The following adjacent habitat types should be considered in the design of the MPA network:

Reef Flats

Corals on reef flats and upper reef crests exposed at low tides often exhibit stress tolerance, and may resist or recover rapidly from bleaching. They will be important providers of larvae that may settle in dead areas and aid their recovery.

Reef flats often provide vital nurseries for reef fishes that will move onto the reef and help reestablish communities affected by bleaching.
Nitrogen and organic materials produced on reef flats, or transported from there in the form of feces of herbivorous fishes and other organisms, contribute valuable nutrients to the reef community. The transfer of materials aids in the overall functioning and recovery of the system.

Back-reef Lagoons

Coral assemblages in back-reef lagoons, especially shallow lagoons behind fringing reefs, are routinely exposed to wide temperature fluctuations. Consequently, the corals may exhibit some acclimatization to temperature stress and resistance to bleaching.

Back-reef lagoons can serve as important nurseries for fishes.
Corals in naturally turbid, deeper lagoons may display higher resistance to bleaching than corals of the same species in clear waters over barrier reefs.

Design Tip

The following MPA design principles are recommended to address connectivity among adjacent habitat types:

Adjacent habitats contribute different types and quantities of larvae to reef systems, and may exhibit different susceptibility to bleaching. Therefore, it is important to identify these reefs and include multiple examples of each in the protected area, when possible.
Connectivity within reefs is an important determinant of MPA zone and boundary locations. For example, consider placing no-take areas that include areas of high resistance to bleaching up-current to sites with lower resistance, to facilitate their recovery by larval recruitment.
Connectivity among reefs is an important determinant of MPA network design. A network of MPAs should be designed so that each MPA is linked together by prevailing currents, to facilitate the recovery of damaged areas and the maintenance of biodiversity through larval exchange.
Based on the construction of metapopulation models that incorporated 3 types of spatial variability in dispersal associated with retention zones, the specific pattern of population persistence depended on the size and number of reserves and demographic parameters, but self persistence was always more likely for reserves in the retention zone. Thus, placing an MPA in a retention zone (e.g. estuary, bay) to promote population persistence is advisable.1

The Ridges to Reefs approach to conservation includes managing reef ecosystems and terrestrial habitats in a single integrated management framework. Photo © S. Kilarski/TNC

Seagrass Beds and Sand Flats

Seagrass beds and sand flats surrounding coral reefs are important feeding grounds for nocturnal feeding fishes, such as snappers and grunts, which take shelter on reefs by day. After feeding in the seagrass beds and sand flats, the fish return to the reef, and deposit nutrients (in the form of feces) to the reef food web, and contribute to the growth and recovery of reef communities.

Mangroves

The generally turbid waters and shading effect of mangroves may reduce the susceptibility of adjacent corals to bleaching. For more information and guidance on resilience and mangroves please refer to Managing Mangroves for Resilience to Climate Change (download pdf, 1,842k).

Mangroves also serve as nursery areas for juveniles of certain reef fishes (e.g., groupers, parrotfishes, and snappers)
When in close proximity to reefs, mangroves can provide feeding grounds to fishes that take shelter on the reefs.
Mangroves introduce fixed nitrogen and organic detritus into the coral reef food chain, as do reef flats and seagrass beds.

Beaches and Dunes

Coastlines are dynamic zones. Disturbances to these areas can cause beach erosion, alteration of the natural cycle of accumulation and erosion of sand along the shore, increased turbidity of inshore waters, or even smother living reefs with excessive sediment.

Managing Linked Habitats

While watersheds are not obvious or easy candidates to include in coral reef MPAs, they may be connected to reefs by streams and coastal currents. Damaging activities in a linked watershed will need to be controlled by a “ridge to reef” approach to MPA planning, or by coastal zone management approaches that complement MPA planning and management.

Linked habitats need to be considered and managed as part of a single functional unit. An integrated approach to coastal management can address complex ecological linkages between distant habitats, fisheries, recreation, research, and ecosystem functioning in a coordinated and complementary method.