Photo: Parguera by Simon Pittman

Coastal communities depend on a healthy coral reef ecosystems for food, clean water, commerce, and culture. These reefs are also home to a rich diversity of tropical fish and other vibrant species. Among the range of threats posed to coral reefs, warming ocean due to climate change is among the most concerning.

Dr Lisa Wedding

A new study led by Dr Lisa Wedding (pictured left), Assistant Professor at the School of Geography and the Environment, uses remotely sensed LiDAR (light detection and ranging) data to illuminate coral reef complexity and biodiversity.

Published in Remote Sensing in Ecology and Conservation, the research uses a new approach of combining 2D and 3D seascape models to accurately identify complex reef structure, and the populations of fish living within them. Creating cost effective and accurate spatial methods of identifying coastal “hotspots” is an essential step in the creation of effective management plans for marine protection and conservation.

“Mapping and placing value on reef areas that represent important biodiversity hotspots are important for coastal communities that rely on healthy reef fish populations for food, tourism and culture. This information can help to inform urgently needed management actions to sustain healthy reefs and healthy coastal communities,” said research lead Lisa Wedding.

The team took to their SCUBA gear and dove on 625 coral reef sites in order to inform their models. The divers tallied the type and length of each reef fish species viewed. These nearshore locations varied in habitat types (such as coral reef and sea grass beds), marine conservation efforts (studying areas in and outside of marine-protected areas) along with mixed human impacts and shoreline exposures.

They then harnessed satellite data to create 2D habitat maps at each site. While used widely in the past, using 2D satellite data for coral reef mapping has limitations, as only planimetric (or horizontal) areas of habitats are accounted for rather than the total complex 3D structure. In the case of coral reefs, elaborate habitat configurations indicate higher potential for biodiversity, a chief indicator of a healthy ecosystem.

The team turned to a technology called light detection and ranging (LiDAR), a remote sensing tool that uses light in the form of a pulsed laser to measure variable distances. This allowed them to create 3D models, bringing to life the true complexity of the coral reef seafloor. Equipped with this information, the researchers were able to create predictive models of the reef fish community, based on the collected habitat data. Surprisingly, the most effective model was a combination of the 2D and 3D LiDAR satellite data, which most accurately predicted coral reef fish diversity, biomass and density.

“We found that 2D characterization of the seafloor does not capture the intricate relationships between reefs and fish communities, and the application of LiDAR in this work helps to advance seascape ecology theory and application in the third dimension,” said Wedding.

Seascape ecology is an emerging applied science that focuses on understanding the consequences of spatial patterns in the ocean and is the topic of a new book Seascape Ecology edited by Simon J. Pittman, co-authored by Lisa M. Wedding, and published by Wiley.

The researchers also noted that marine protected areas consistently experienced higher fish diversity and biomass. Meaning management of fisheries plays a fundamental role in marine conservation and should not be overlooked. This also suggests that creating marine protected areas where complex 3D reef structures exist may be key in establishing more resilient ocean ecosystems, able to recover more quickly from future bleaching events or other damaging forces.

“Understanding the seascape from a 3D perspective offers great potential to advance our knowledge of coral reefs,” Wedding said. “LiDAR remote sensing allows us to capture the intricate 3D vertical structure of coral reefs and understand where habitats have high conservation value to inform future ocean planning efforts. Our research supports the design of marine protected areas in these locations, which should be a management priority, as habitat complexity can enhance reef resilience and recovery.”

"LiDAR remote sensing allows us to capture the intricate 3D vertical structure of coral reefs and understand where habitats have high conservation value to inform future ocean planning efforts".

Dr Lisa Wedding