Understanding Larval Connectivity to Strengthen Marine Protected Area Networks in South and Southeast Asia

Effective marine protected area (MPA) networks depend on ecological connectivity, yet larval dispersal patterns across South and Southeast Asia have remained poorly understood and rarely incorporated into management. Under the ASEAN ENMAPS Project, a regional biophysical modelling study was conducted to assess larval connectivity across four Large Marine Ecosystems—the Bay of Bengal, South China Sea, Sulu–Celebes Sea, and Indonesian Seas—and within selected pilot MPAs. By integrating ocean circulation models with larval dispersal simulations and reef habitat data, the study generated connectivity matrices and source–sink maps that identify reefs critical to sustaining population connectivity. Results show that self-recruitment is dominant in many reef systems, connectivity is highly uneven and seasonally driven, and larval exchange frequently crosses national boundaries. The experience demonstrates how larval connectivity modelling can function as a practical decision-support tool for strengthening MPA network design, supporting ecosystem-based management, and fostering regional and transboundary cooperation in complex marine systems.

The project Effectively Managing Networks of Marine Protected Areas in Large Marine Ecosystems in the ASEAN region (ASEAN ENMAPS) aims to improve MPA network management in key Large Marine Ecosystems across Indonesia, the Philippines, and Thailand. It applies science-based strategies to conserve biodiversity and sustain fisheries. The project also aims to strengthen governance, build the capacity of stakeholders, promote knowledge sharing, and advance sustainable financing for long-term conservation. ASEAN ENMAPS is implemented by the United Nations Development Programme through the funding of the Global Environment Facility, and with the ASEAN Centre for Biodiversity as the executing agency.

The coral reef systems of South and Southeast Asia are among the most biologically diverse in the world, yet they are increasingly threatened by overfishing, coastal development, and climate change. Many MPAs in the region were established based on administrative or site-specific considerations, with limited incorporation of ecological connectivity.

Key challenges included:

• Limited empirical data on larval dispersal across large spatial scales;
• Highly dynamic circulation systems driven by monsoons, straits, and throughflows;
• Fragmented marine management across national jurisdictions;
• Uneven reef distribution, particularly in the Bay of Bengal.

Without understanding how larvae move among reef systems, MPA networks risk being ecologically isolated and less resilient to disturbance.

Designing effective networks of marine protected areas (MPAs) requires understanding how marine populations are connected through larval dispersal. In South and Southeast Asia, this ecological connectivity spans national boundaries and diverse oceanographic settings, yet has historically been difficult to quantify and operationalise for management.

Under the project Effectively Managing Networks of Marine Protected Areas in Large Marine Ecosystems in the ASEAN Region (ASEAN ENMAPS), a regional biophysical modelling study was undertaken to assess larval connectivity across four Large Marine Ecosystems (LMEs) and within selected pilot MPAs. By integrating ocean circulation models with larval dispersal simulations, the study produced connectivity matrices and source–sink maps that identify reefs critical to sustaining regional connectivity.

This experience demonstrates how larval connectivity modelling can serve as a practical decision-support tool for strengthening MPA network design, improving spatial planning, and supporting ecosystem-based and transboundary marine management.

APPROACH AND METHODS

The project applied a biophysical larval connectivity modelling approach that combined physical oceanography with biological assumptions on larval behaviour.

Key elements included:

• Ocean circulation data from the Copernicus Marine Environment Monitoring Service (CMEMS) global model at 1/12° resolution;
• Downscaled hydrodynamic models (1/24° to 1/48° resolution) using the SURF-NEMO platform for selected pilot sites;
• Larval dispersal simulations using the Connectivity Modeling System, with larvae represented as particles with a defined planktonic duration and settlement window;
• Coral reef habitat data from the Allen Coral Atlas to define larval source and sink areas.

Connectivity matrices were generated for each LME and pilot site and translated into source and sink potential maps, enabling identification of reefs that act as key larval exporters, receivers, or both.

Pilot sites included nationally and regionally significant MPAs such as Wakatobi National Park, Kepulauan Togean National Park, Turtle Islands Wildlife Sanctuary, and multiple ASEAN Heritage Parks.

KEY RESULTS AND INSIGHTS

Across LMEs and pilot sites, the modelling revealed that:

• Self-recruitment is dominant in many reef systems, highlighting the importance of local protection;
• Connectivity is uneven, with certain reefs functioning as critical sources or sinks depending on circulation patterns;
• Seasonality matters, as monsoon-driven circulation strongly influences dispersal direction and intensity;
• Geographic configuration influences resilience, with enclosed or semi-enclosed systems exhibiting stronger internal connectivity than high-energy throughflow areas.

At the regional scale, larval exchange frequently crossed national boundaries, reinforcing the ecological basis for cooperative marine management.

WHAT WORKED WELL

• Scalable modelling design: The same framework supported both basin-scale and site-specific analyses.
• Use of open and transferable tools: Scripts, datasets, and GIS layers can be reused and updated as new data become available.
• Clear management outputs: Connectivity matrices and source–sink maps were readily interpretable by planners and decision-makers.
• Capacity-building potential: The approach lends itself to training and replication by national agencies and research institutions. 

LESSONS LEARNED

1. Connectivity matters, but context matters more. The same MPA design principles cannot be uniformly applied across LMEs with very different oceanographic and geographic characteristics.
2. Source reefs are strategic assets. Protecting reefs with high source potential can enhance resilience well beyond their immediate boundaries.
3. Scale alignment is critical. Regional connectivity patterns must be matched with local-scale management actions to be effective.
4. Models enable dialogue. Even with uncertainties, connectivity outputs provide a shared scientific basis for cross-sectoral and transboundary discussions.

This experience is directly relevant to other IW-supported projects seeking to operationalise ecological connectivity in marine spatial planning. The approach can be replicated by:

• Applying the modelling framework to other LMEs or seascapes;
• Integrating connectivity outputs into MPA network design, zoning, and fisheries management;
• Using connectivity results to support regional agreements and cooperative management mechanisms.

Future enhancements may include coupling connectivity models with climate scenarios, genetic data, or network-analysis tools to further strengthen decision-making.

Larval connectivity modelling provides a powerful, science-based foundation for designing resilient MPA networks in complex marine systems. When embedded within regional cooperation frameworks, it can help bridge the gap between ecological processes and practical marine governance.