Connectivity

Principle 4: Maintenance of ecological connectivity among and between habitats.

Connectivity refers to the extent to which populations are linked by the exchange of eggs, larval recruits, juveniles or adults. It also refers to the ecological linkages associated with adjacent and distant habitats. Connectivity within and between protected areas is important for maintaining diversity, fish stocks, and especially important for maintaining ecological resilience.

A network of MPAs should maximize connectivity between individual MPAs to ensure the protection of ecological functionality and productivity. Connectivity and ecological linkages include:

  • Connections through regular larval dispersal in the water column between and within MPA sites
  • Regular settlement of larvae from one MPA to another
  • Marine life in their home range, from one site to another
  • Connections of linked habitats such as coral reefs and seagrass beds, or among mangrove and seagrass nursery areas and coral reefs

Connectivity between protected areas and areas open to fishing is also critically important to support local fisheries through spillover of adults, juveniles, and larvae to fished areas.  ref

Design Recommendations

Sizing

Apply minimum sizes to protected areas within the network

  • Apply minimum sizes to marine reserves, depending on which species require protection, how far they move, and if other effective management is in place outside reserves (e.g., 0.5-1 km and 5-20 km across). ref
  • Marine reserves should be more than twice the size of the home range of focal species (in all directions).
  • If the objective is to protect all species, then it is important to have large areas (smaller areas can provide benefits for some species that don’t move very far); for biodiversity protection, the recommended size is 10-20 km long.  ref
  • Where larval dispersal patterns and/or adult movement patterns of particular target species are known, this information can also inform decisions about ideal sizes of protected areas.
  • Protect key habitats used by focal species throughout their lives (e.g., for home ranges, nursery areas and fish spawning aggregations) in marine reserves, and ensure reserves are spaced to allow for movements among them (e.g., ontogenetic habitat shifts, spawning migrations).  ref
  • Include whole ecological units (e.g., offshore reefs) in marine reserves.

Spacing

Apply a variety of spacing distances between protected areas within the network

  • Space marine reserves 1–15 km apart, with smaller reserves closer together.
  • For temporal closures of any kind: Other types of protected areas (e.g., spatial gear or access restrictions) might be quite large in extent (e.g., throughout the management area), and so it may not make sense to have specified “distances” between them. However, if other permanent protected areas are isolated “islands” of protection, then the same spacing rules (and rationale) apply as no-take areas.

Location

  • Larval sources are temporally variable and difficult to identify. So if there is a strong, consistent, unidirectional current, a greater number of marine reserves should be located upstream relative to fished areas.  ref 
  • Ensure that MPAs are located in habitats that focal species use.  ref

Shape

Use square or circular shapes for MPAs subject to considerations of compliance (e.g. including using landmarks)

  • Use compact shapes (e.g., squares or circles rather than elongated ones) for MPAs subject to considerations of compliance (e.g. including using landmarks).
  • Square and circles allow for limited adult spillover, which helps maintain the integrity of the protected areas and, therefore, the sustainability of their contribution to fisheries production, biodiversity and ecosystem resilience. Other shapes (e.g. long and thin) may facilitate more spillover to fished areas.
  • The shape of an MPA is a critical factor in effective delineation and enforcement. MPAs with regular shapes can be delineated by lines of latitude and longitude and are more easily enforceable. MPAs of irregular shapes are not easily identifiable or enforced and should be avoided.

Many fish, invertebrates and corals release numbers of eggs and young into the open ocean. The pelagic larvae can remain floating or moving through ocean currents for hours, days, or even months, traveling distances of 1-1000s of km prior to settling.

Many factors influence larval dispersal that act synergistically. Factors influencing larval dispersal include:

  • Larval behavior: swimming speed and directional capabilities of larvae are considered to be highly species-specific
  • Larval duration: amount of time larvae spend in the open ocean is also species-specific; ranging from hours to months, and typical pelagic duration is 28-35 days ref
  • Food resources: amount of available food during the pelagic duration
  • Predators encountered: predators affect survival, condition and growth rates
  • Influences of currents or other oceanographic factors

Recent studies also show huge variability in larval dispersal distances, and lower dispersal distances than previously thought (e.g., 100m to 1km to 30 km). ref  For example, larval dispersal distance in coral reef fishes tend to be 5-15km and self-recruitment is common. ref  Therefore, reserve spacing should be < 15 km with smaller reserves spaced more closely.

Connectivity among populations of reef species is primarily, (or for sessile species exclusively), due to dispersal during larval life. For the majority of reef species that have been studied, demographic connectivity has been shown to act on scales of up to tens of kilometers, rather than on scales of hundreds of kilometers or more. This local-scale pattern of self-recruitment and connectivity among reefs has implications for the sizes required for MPAs within a network, and may indicate that even small MPAs may be self-sustaining. Additionally, recent research on the Great Barrier Reef demonstrates that well protected marine reserve networks can make a significant contribution to the replenishment of fish populations both within the reserve and also on adjacent fished reefs. ref

Adult movement is generally at a smaller scale than larval movement. Adult species movement patterns vary greatly among species. To protect a range of species within the MPA, a range of adult movement patterns needs to be considered in the MPA network design. The amount of protection an MPA provides for a species depends (to some degree) on movement habits and distances of the individual (both as adult and larvae).  ref

If adults move widely, the ocean neighborhood is large and diffuse. If adults are sessile, then the ocean neighborhood might be small and distinct.

Fish movement Diagram

Gombos et al. 2013 ref; modified from Maypa 2012 ref

Connectivity is important for supporting ecological processes (e.g., herbivory) that promote reef resilience. For example, connectivity between coral reefs and mangroves can increase grazing of herbivorous fish on adjacent reefs. ref Herbivorous fish remove algae, and therefore, can promote coral growth and reef resilience. Mangroves in the Caribbean have been shown to increase the resilience of offshore coral reefs in response to disturbances such as hurricane damage. ref After a disturbance event on a reef, macroalgae may out-compete corals for space, so maintaining healthy populations of fish that eat algae is critical for coral reef recovery. Mangroves support increased biomass of fish that eat macroalgae; thus, connectivity between mangroves and reefs can help corals recover from disturbance and enhance their rates of recovery. ref

linked habitats

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 (click diagram for larger version). Photos: Top left and right © S. Summerhays; middle left © D. Obura; middle right © NOAA; bottom left © A. Reid; bottom right © 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 fish.
  • Corals in naturally turbid, deeper lagoons may display higher resistance to bleaching than corals of the same species in clear waters over barrier reefs.

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 (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 refer to Managing Mangroves for Resilience to Climate Change (pdf, 1.9M).

  • 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.
  • Mangroves can provide intermediate nursery habitat between seagrass beds and patch reefs that increase the survival of young fish, thus mangroves can strongly influence the community structure of fish on adjacent coral reefs. ref
  • Research in the Caribbean demonstrated that the biomass of several commercially important fish species more than doubled when adult habitat was connected mangroves, reinforcing the need for conservation efforts to protect connected corridors of mangroves, seagrass beds and coral reefs. ref More recent studies in Australia also demonstrate that connectivity between reefs and mangroves in reserves promotes the abundance of harvested fish species. ref
mangroves present and absent

The figures illustrate how connectivity between seagrass beds, mangroves, and coral reefs can affect the size and density of fish (e.g., grunts and parrotfish). Top – Mangroves Present: Red letter “A” shows juvenile grunts, once reaching a given size in a seagrass bed, moving to mangroves (B). The mangroves serve as an intermediate nursery habitat before the fish migrate to patch reefs (C), and fish biomass is significantly enhanced on patch reefs (C), shallow forereefs (D), and Montastrea reefs (E). Some fish (F), such as certain species of parrotfish, Scarus guacamaia, are dependent on mangroves and are not seen where mangroves are absent. Bottom – Mangroves Absent: If the mangroves are not present, then fish move directly from the seagrass to the patch reefs, appearing on patch reefs (G) at a smaller size and at lower density, thus more vulnerable to predation. Modified from Mumby et al. 2004. Source: Peter Mumby

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.

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 and Ecological Processes

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. Photo © Jason Valdez/Marine Photobank

Recent studies discuss the importance of incorporating connectivity into conservation planning. ref These case studies demonstrate how ecological processes (e.g., connectivity among habitats) can be integrated into decision support tools such as reserve selection algorithms (e.g., MARXAN) to help improve the performance of protected areas. Such efforts are important to help managers integrate ecosystem-based management into the design of marine protected areas.

For the latest guidance on integrating larval dispersal and movement patterns of coral reef fishes into the design of marine reserves, click here.

Resources

Larval Dispersal And Movement Patterns Of Coral Reef Fishes, And Implications For Marine Reserve Network Design

Designing Marine Protected Area Networks To Address The Impacts Of Climate Change

Designing Marine Protected Area Networks to Achieve Fisheries, Biodiversity, and Climate Change Objectives in Tropical Ecosystems: A Practitioner Guide (pdf, 4.9M)

Biophysical Principles for Designing Resilient Networks of Marine Protected Areas to Integrate Fisheries, Biodiversity and Climate Change Objectives in the Coral Triangle (pdf, 3.3M)

The Science of Marine Reserves

NOAA National Marine Protected Areas Center

Rules of Thumb for MPA Network Design

Preserving Reef Connectivity: A Handbook for Marine Protected Area Managers

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Last updated May 4, 2016

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