Coral Reefs: A Reef Resilience Toolkit Module

Larval Dispersal

Many fish, invertebrates and corals release great 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.

Coral larval dispersal patterns can be used to estimate distance ranges for consideration in the MPA design. Photo © E. Hickerson, NOAA

The distance and the patterns of larval dispersal are influenced by several factors which act synergistically over the pelagic larval duration including:

• 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 days1
• 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

Consider Larval Dispersal in MPA Design

The specific pattern of larval dispersal of any particular species is not as important for the MPA network design as the sum of all the patterns of larval dispersal for all the species of concern. Generally, various species in a community display a range of larval dispersal distances; these distances can be evaluated to estimate MPA sizes and spacing that may accommodate the dispersal distances of either focal species, or the broadest range of species. The key is to consider and include the range of dispersal distances for all species of interest.

The following MPA design principles are recommended to address larval dispersal:

• To compensate for constantly changing ocean conditions, which have impacts on larval dispersal patterns, MPAs should be located in a wide variety of places in relation to the prevailing currents.
• In areas where currents are complex (e.g., eddies or reverse flows), an even spread of MPA locations is recommended.
• In areas where currents are strongly directional, MPAs sited in upstream locations will be more likely to support recruitment to the rest of the management areas than those in downstream locations.
• A network of MPAs linked to each other by prevailing currents will facilitate the recovery of damaged areas, and the maintenance of biodiversity through larval exchange.
• Provide for connectivity at a wide range of dispersal distances (within and between patches), emphasizing distances ‹ 20–30 km4.