Marine Ecology Enhancement Fund – Impact of microplastics on the Chinese horseshoe crab in Hong Kong western waters

The Marine Ecology Enhancement Fund, set up by Airport Authority Hong Kong, supports a team from The Hong Kong Polytechnic University and City University of Hong Kong that studies the ecological risks of microplastics for Chinese horseshoe crabs.

Horseshoe crabs are often seen in soft sand or mud in the shallow coastal waters of Hong Kong’s western waters, including the endangered Chinese horseshoe crabs. However, evidence shows that the western waters have been polluted by microplastics in recent years, how would this impact the Chinese horseshoe crabs which live in local mudflats?

Dr. Cheung Siu-gin, Associate Professor, Department of Chemistry, City University of Hong Kong, said, “The Chinese horseshoe crab is a very special creature. With a history of more than 400 million years, it is also called a “living fossil”. Recently, the Chinese horseshoe crab was listed as an endangered species, so there’s an urgent need for us to protect it.”

The team collected sediment samples at five investigation sites.　Different types of microplastics were then identified from the samples. Preliminary study discovered that the size of microplastics ranged from about 31 to 5,000 micrometre. Of the five sites, Shui Hau had the most serious case of suspected microplastic pollution, the average amount of microplastics found being 6 to 14 times higher than other sites.

Dr. James Fang, Assistant Professor, Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, said, “We have found that PET – a common type of plastic that can be found in plastic bottles, containers and tableware – is abundant in Hong Kong waters.Microplastics are so small that Chinese horseshoe crabs often eat them by mistake. If they eat too much, their digestive systems will be blocked and they may die.”

The project team also exposed artificially bred juvenile Chinese horseshoe crabs to three types of microplastics commonly found in the western waters of Hong Kong to study their physiological responses.

Results of the study showed that the crabs’ growth rates in terms of weight and size prosomal width were 3% to 7% less in the environment containing microplastics, while their mobility and intention to move were up to 60% lower, compared to crabs not exposed to microplastics.

“We found that microplastics like PET have harmful effects on Chinese horseshoe crabs. PET makes Chinese horseshoe crabs less active. This means they are less able to find food and escape from predators. It has also been learned that PET increases the mortality rate of Chinese horseshoe crabs. These findings are very important – and alarming,” said Dr. Fang.

The results of this research project provide important baseline data for the Government and other organisations to help them implement conservation policies and programmes for the Chinese horseshoe crabs.

Professor Paul Lam, Chairperson of Marine Ecology Enhancement Fund Management Committee, said, “when we were considering funding for this project, we saw that it was an ecological conservation initiative that required very thorough scientific research. The results of this study are significant. They have clearly shown the impact of microplastics on endangered Chinese horseshoe crabs. We hope this project can also raise public awareness about the importance of environmental conservation.”

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