Coral reefs face numerous threats, from climate change to pollution. Underwater robotics play a crucial role in monitoring these delicate ecosystems, using advanced sensors and cameras to assess coral health, map reef structures, and track changes over time.

Robots also support restoration efforts by identifying suitable transplant sites and placing coral fragments. Their ability to access deep or hazardous areas and collect long-term data makes them invaluable tools for protecting and restoring these vital marine habitats.

Threats to coral reefs

Anthropogenic and natural stressors

• Climate change causes rising ocean temperatures leading to coral bleaching events where corals expel symbiotic algae and become more susceptible to disease and mortality
• Ocean acidification, caused by increased absorption of atmospheric carbon dioxide, reduces availability of calcium carbonate for coral skeleton formation and weakens reef structures
• Overfishing disrupts delicate balance of coral reef ecosystems by removing key herbivorous fish species that control algal growth and maintain coral dominance
• Pollution from land-based sources (agricultural runoff, sewage, plastic waste) introduces excess nutrients, toxins, and physical debris that harm coral health and water quality
• Physical damage from storms or human activities (boat anchoring, destructive fishing practices) can directly impact coral colonies and reef structures

Role of underwater robotics in monitoring coral health

• Remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) provide non-invasive means to monitor coral reef health and assess impacts of various threats
  • Equipped with high-resolution cameras, sensors, and sampling devices to collect data on coral cover, species diversity, water quality, and physical damage
  • Access deeper or more hazardous reef areas that may be difficult for human divers to survey safely and efficiently
• Long-term monitoring using underwater robotics helps track changes in reef health over time and evaluate effectiveness of conservation and restoration efforts
• Data collected by underwater robots informs management decisions and supports development of targeted strategies to mitigate threats and promote coral reef resilience

Coral reef mapping

Acoustic and optical sensors

• Multibeam sonar systems mounted on underwater vehicles emit sound waves and analyze returning echoes to generate high-resolution bathymetric maps of seafloor and reef structures
• Side-scan sonar creates detailed images of seafloor and detects features (coral colonies, sand patches, rubble zones)
• Underwater photogrammetry involves taking overlapping images of reef from different angles using high-resolution cameras mounted on ROVs or AUVs and using software to stitch images together into 3D model
• Underwater hyperspectral imaging maps distribution of different coral species and assesses their health based on unique spectral signatures

Visual surveys and water quality monitoring

• Video footage or still images captured by underwater vehicles used to assess coral cover, species composition, and signs of stress or damage
  • Standardized protocols (Reef Check, Atlantic and Gulf Rapid Reef Assessment) ensure consistent data collection and analysis
• Underwater vehicles equipped with water quality sensors measure parameters (temperature, salinity, pH, dissolved oxygen) that are important indicators of coral reef health
• Combining visual surveys and water quality data provides comprehensive assessment of reef condition and helps identify potential stressors or areas of concern

Coral reef health assessment

Metrics of reef health and diversity

• Coral cover, expressed as percentage of total reef area, is common indicator of reef health estimated from visual surveys or photogrammetry data
• Species richness, or number of different coral species present, determined from visual surveys or by analyzing images and video footage
• Species evenness, or relative abundance of different coral species, calculated using diversity indices (Shannon's diversity index, Pielou's evenness index)
• Benthic community composition, including relative abundance of corals, algae, and other organisms, assessed using point-intercept or random point count methods on images or video footage

Data analysis and long-term monitoring

• Coral health evaluated by analyzing prevalence of bleaching, disease, or physical damage in survey data and comparing indicators across different sites or time periods
• Multivariate statistical techniques (principal component analysis, non-metric multidimensional scaling) identify patterns and relationships in complex reef survey data
• Long-term monitoring data from repeated surveys tracks changes in reef health and diversity over time and assesses impacts of stressors or conservation interventions
• Comparing data from different reef sites or regions helps identify spatial patterns and prioritize areas for conservation or restoration efforts

Robotics for coral reef restoration

Supporting restoration efforts

• High-resolution mapping and 3D modeling of restoration sites using underwater vehicles identifies suitable locations for coral transplantation based on factors (substrate type, water depth, current flow)
• Underwater vehicles equipped with manipulators or specialized tools collect coral fragments for transplantation or precisely place coral colonies onto reef substrate
• Monitoring survival, growth, and health of transplanted corals using underwater vehicles allows for non-invasive, long-term assessment of restoration success without frequent human diver interventions
  • Photogrammetry and visual surveys track changes in coral cover, size, and condition over time
  • Water quality sensors ensure environmental conditions remain suitable for coral growth
• Underwater robots maintain restored reef areas by removing invasive species (algae, crown-of-thorns starfish) that may threaten survival of transplanted corals

Evaluating effectiveness and guiding future efforts

• Comparing data from restored and natural reef sites using underwater vehicle surveys evaluates effectiveness of restoration techniques and informs adaptive management strategies
• Cost-benefit analysis assesses economic and ecological advantages of using underwater robotics in coral reef restoration compared to traditional human diver-based methods
• Successful case studies of underwater robotics applications in coral reef restoration projects worldwide provide evidence for their effectiveness and guide future restoration efforts
• Integrating underwater robotics into coral reef restoration programs can improve efficiency, reduce costs, and increase scalability of restoration efforts to help mitigate impacts of climate change and other stressors on these vital ecosystems