Soft Coral Dominated Reefs
Across the Indo-Pacific, coral reefs are undergoing profound transformations.
As human-induced stressors increase and environmental conditions become more variable, reef ecosystems are shifting. In many places, hard coral communities are being replaced by soft coral assemblages, a trend that challenges our understanding of how reefs function and recover.
understanding soft coral impacts to guide coral reef conservation and restoration
In 2024, Molly Blyth, a postgraduate researcher from the University of Plymouth, conducted fieldwork in North Sulawesi to study these transitions. Under the supervision of Dr. Miriam Reverter, and with support from Coral Eye, Molly investigated how and why soft coral–dominated reefs emerge, and what their rise means for the future of reef conservation and restoration.
Investigating Shifts in Reef Composition
The first part of the study focused on documenting benthic community structure (the organisms living on the seafloor) across various sites around Bangka Island and Bunaken National Park. These surveys, carried out with a team of University of Plymouth students, contribute to a long-term monitoring program initiated in 2020 by Dr. Reverter and Prof. Peter Schupp (University of Oldenburg, Germany).
By collecting comparable data over time, researchers are building a clearer picture of how reef composition changes, from coral cover and soft coral diversity to the frequency of reefs now dominated by soft coral species.
The second part of the research focused on species interactions, specifically, how soft corals compete with hard corals for space and light.
Using both ecological surveys and manipulative field experiments, Molly examined five target soft coral species: Xenia viridis, Sclerophyton procera, Conglomeratusclera coerulea, Sarcophyton sp., and Capnella imbricata. In the field, she recorded natural interactions, noting when soft coral colonies were in contact with hard corals and whether overgrowth or visible tissue damage occurred at the interaction front.
At the Coral Eye house reef, controlled experiments were then set up to observe these interactions under monitored conditions. Fragments of soft and hard corals were transplanted side by side on metal frames in shallow water, allowing researchers to document the early stages of competition.
Results revealed clear signs of bleaching and tissue damage in hard coral fragments at contact points with certain soft coral species, indicating that some species are capable of inflicting direct harm. These findings provide new insight into the competitive strategies of soft corals and their potential to alter reef structure.
