Ecologists from the School of Biological Sciences (SBS) and the Swire Institute of Marine Science (SWIMS) at The University of Hong Kong (HKU) have uncovered serious ecological threats linked to the introduction of hybrid groupers into the coastal waters of Hong Kong, a practice often associated with religious ‘mercy release’ ceremonies.Their research reveals that the Tiger Grouper-Giant Grouper hybrid (TGGG), commonly referred to as the Sabah grouper, disrupts local marine ecosystems by taking advantage of specific ecological niches and may emerge as a dominant predator.
This study is groundbreaking as it is the first to employ advanced DNA metabarcoding techniques to investigate the diet of this hybrid species, highlighting the pressing need for public awareness and conservation efforts to address unintended ecological consequences. The results have been published in the journal Reviews in Fish Biology and Fisheries.
The TGGG is a hybrid created through aquaculture by crossing the Tiger Grouper (Epinephelus fuscoguttatus) with the Giant Grouper (Epinephelus lanceolatus). Known for its large size and fast growth, it is frequently found in Hong Kong’s fish markets. Its low cost and impressive size have made it a favoured option for local mercy release practices, where animals are set free into the wild as a form of spiritual merit. However, this seemingly kind gesture carries significant ecological repercussions.
To investigate the potential ecological impacts of releasing hybrid groupers into Hong Kong’s coastal waters, the research team utilised DNA metabarcoding to study the diet of the TGGG. Being the first to use this method for examining the dietary patterns of this hybrid species, the team extracted and sequenced DNA from the hybrid’s stomach contents, enabling them to identify its prey, even if it was fully digested or fragmented. This innovative technique offers a comprehensive and precise understanding of the hybrid’s dietary habits and its role within local marine ecosystems.
The research revealed that the TGGG is a powerful predator with a unique diet, consuming a variety of prey species that are not usually targeted by native species, such as fish, crustaceans, and cephalopods. By taking advantage of wider ecological niches and areas within the ecosystem that are underutilised, the TGGG disrupts local food chains and is likely to flourish, establishing itself as a leading predator.
“Our findings show that the TGGG is not just another introduced species, it has the potential to significantly disrupt trophic dynamics and reshape coastal ecosystems,” said Professor Celia Schunter of HKU SBS and SWIMS, the study’s lead investigator.
The researchers caution that the TGGG’s rapid growth, significant size, and lack of natural predators in Hong Kong’s waters make it an exceptionally competitive species. These characteristics, along with the presence of unoccupied ecological niches, pose a considerable threat to the stability of marine biodiversity in Hong Kong’s coastal environments. Additionally, the study highlights how mercy release practices contribute to the introduction of non-native species like the TGGG into local waters.
The researchers underscored that educating the public and implementing stricter conservation measures are vital for reducing the ecological harm caused by mercy release and other human activities. These initiatives are crucial for maintaining the health of Hong Kong’s marine ecosystems.
[image: Released through the religious practice of mercy release, the Tiger Grouper-Giant Grouper hybrid (TGGG), also known as the Sabah grouper, now swims in Hong Kong waters, affecting the balance of marine ecosystems. Credit: Arthur Chung.]