Macroalgal Forests and Sea Urchin Grazing, Madeira Case Study

Infographic of the Madeira demonstration site
Infographic of the Madeira demonstration site

Case Study Components

Assessment
Planning and Design
Implementation
Monitoring and Evaluation
Sharing and Communication

Introduction to the site

Location: 32. 7607 N, 16.9595 W

Observed climate change impacts

Loss of macroalgae forests due to overpopulation of sea urchins

CLIMAREST Objectives

Restore macroalgae forests

Features of Madeira

Includes inhabited islands of Madeira and Porto Santo, and the uninhabited islands of Desertas and Selvagens

Submerged habitats characterized by rocky reefs and sandy bottoms, with occassional seagrass patches

Unique blend of temperate and tropic species, typical of subtropical regions

Map indicating Madeira island, located southwest of Portugal. 

Driving Factors and Motivations

The restoration of macroalgal forests in Madeira is driven by concerns over their decline due to multiple stressors, including

  • overgrazing by sea urchins
  • habitat degradation
  • anthropogenic climate change
  • coastal development

These forests are vital to the island’s shallow marine ecosystems offering habitat, food, and nursery grounds that support marine biodiversity and ecosystem resilience.

A healthy macroalgal forest can support local fisheries, improve water quality and contribute to carbon sequestration.

Aims of restoration efforts
  • enhance ecological function, by re-establishing canopy forming species
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Assessment Phase

Key Criteria for Site Selection

Accessibility of site

Availability of ecological data from previous studies

Strong local support from nearby dive centers as key stakeholders

<em> An initial ecological assessment was conducted at each site to establish a baseline for monitoring restoration success. These methods formed a robust foundation for evaluating ecological changes over time.
An initial ecological assessment was conducted at each site to establish a baseline for monitoring restoration success. These methods formed a robust foundation for evaluating ecological changes over time.
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Planning and Design Phase

Primary Objective: Increase native macroalgae cover (Sargassum spp.) using forestation techniques

Control D. africanum densities through targeted culling
Cull when populations exceed 0.3 individuals / m2. Maintain densities below ecological threshold of 0.5/ m2 -(Gizzi et al., 2021) 
Enhance algal recruitment and increase cover by at least 15% at each site
Sites located in and out of Marine Protected Areas (MPA) to evaluate the role of protective measures

Permits

Regional Institute for Nature Conservation and Forests (IFCN)

  • Two-year license for marine protected area sites 
  • Used for three month monitoring program 
  • Information needed: planned diving activities, names of divers

IFCN online forms

  • Completed before each survey
  • Information needed: Location, date, hours, number of divers, and the license plate registration of the boat supporting the activities 

Captaincy of the Port of Funchal

  • Special permit needed to deploy modular eco-concrete seawalls

Relevant EU regulations

EU Nature Restoration Law

  • Sets legally binding targets for restoration of degraded ecosystems
  • Member States are required to restore at least 20% of EU land and sea areas by 2030

Habitats Directive (92/43/EEC)

  • Requires strict protection and conservation measures for Natura 2000 sites

Marine Strategy Framework Directive (2008/56/EC)

  • Mandates achieving Good Environmental Status (GES) of marine waters 

Developing Project Protocols

Steps and factors considered when developing the protocol of the demonstration site
Steps and factors considered when developing the protocol of the demonstration site
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Implementation Phase

Implementation Process

Collect fertile material

Gather fertile branches/receptacles from natural Sargassum populations

Process in lab for zygotes

Extract zygotes for cultivation

Seed zygotes

Plant zygotes on substrate units of nature-based materials such as natural rock, terracotta, and ceramic

Culture substrates

Culture algae under controlled conditions to promote germling growth

Transplant to Modular Artificial Reef Structure (MARS) units

Transfer juvenile algae to MARS units at restoration sites

Submerge MARS units at restoration sites

Coordinate the submerging process with local dive centres and relevant local authorities

Each of the four sites host three MARS, resulting in...

meters squared of restorative actions
Over
meters squared of monitored sea area

Monitoring and Data Collection Process

Methods for data collection

Scientific

    • Photoquadrats and point counts for sessile and benthic organisms
    • Underwater visual census (UVC) along fixed transects to assess mobile fauna

Citizen Science Monitoring of 24 pre-selected species and their abundance using the Dive Reporter App

Ecological indicators measured

Species Diversity

Species Abundance

Species Density

Image of which factors were monitored and at what intervals of time.
Image of which factors were monitored and at what intervals of time.
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Ongoing Management, Monitoring, and Evaluation Phase

Initial results from the demonstration site

Restoration Challenges

Mass Mortality Event
A sudden mass mortality event in 2022 decimated D. africanum urchin populations across all sites, eliminating grazing as a variable. The lack of D. africanum grazing has likely been beneficial for algae growth, however we were unable to compare the effects of reducing grazing vs. increasing algae recruitment vs. a combination of both.
Permit Timeline
Obtaining the necessary permits for fieldwork and restoration activities took significantly longer than expected. This caused delays in the implementation schedule but did not prevent the completion of planned actions.
Lack of Donor Populations
The lack of large donor populations has limited the extent and scale of the transplantation activities. Despite the setbacks, the core restoration activities were carried out successfully, though timelines were adjusted to accommodate administrative requirements and natural ecological changes.

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Sharing and Communication

<em> Map of Madeira island with locations of stakeholder engagement
Map of Madeira island with locations of stakeholder engagement
Click on the diagram above to learn more about who was engaged throughout the restoration project!
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For a more detailed PDF of the Madeira Case Study, click here!

Additional resources:

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