Samoa gives introduced sea snail a tick for environmental and economic benefits

Three sea snails under a rock ledgeA trio of trochus sea snail under a ledge in a Samoan coral reef (credit Steven Purcell).

A Southern Cross University study has found that a marine snail introduced to the Pacific nation of Samoa, instead of being detrimental to the environment, is proving to be an asset.

Before the snail’s introduction 15 years ago Samoa did not have a naturally-occurring trochus population. In fact, the island nation was one of the last places in the Pacific for the species to be introduced compared with other countries where trochus sea snails had provided an additional shellfish resource for coastal fishers for more than 80 years.

In a new paper, published in the journal Restoration Ecology, Southern Cross University marine researcher Associate Professor Steven Purcell has found no negative ecological effects of the trochus in colonised Samoan coral reefs.

“It’s a story of the amazing colonisation of snails that appears to benefit both the marine environment and the livelihoods of the Samoan people,” Dr Purcell said.

“Unlike examples in Australia – the cane toad, the fox, rabbit and European carp, to name a few, which have been detrimental to native species and habitats – the trochus has shown itself to be a welcome species that can control reef algae while offering a valuable new seafood to coastal people.”

Video transcript

Associate Professor Steven Purcell, Southern Cross University: Here in Samoa the coral reefs have been devastated by coral bleaching over the last 15 years leaving a lot of the previous coral skeletons dead and covered with algae. In the long term that’s likely to decrease the productivity of shellfish fisheries and food availability for people on the coast. But this humble marine snail called trochus has been introduced 15 years ago and has now created populations abundant enough that people are now collecting the animals and selling the meat. Here we’re evaluating stocks and on some reefs the populations are very well-established and other reefs not so much.

Justin Aiafi, Senior Fisheries Officer, Ministry of Fisheries, Samoa: Yes I believe the introduction of trochus has helped our local fishermen in many ways and I’ve seen that some of the fishermen have benefits from the selling of the introduced trochus. More and more people are harvesting trochus for commercial purpose like selling them on the roadside and we have seen the trend that it has been increasing from year to year. I give credit to Australian foreign aid for providing the financial support to make this translocation and bring an introduction of trochus to Samoa which has now benefited many of our local fishermen.

Close transcript

When trochus snails sourced from Fiji and Vanuatu were introduced between 2003 to 2006 the goal was to establish populations that could benefit Samoan village-based fishers, weighed up against potential ecological impacts.

A few years ago the Australian Centre for International Agricultural Research (ACIAR) commissioned Southern Cross University to partner with Samoa’s Ministry of Fisheries in a new study. The aim was to investigate how extensively trochus had colonised Samoan coral reefs and examine subsequent impacts on the environment and people’s livelihoods.

“From a few initial release sites, trochus now can be found around both main islands in Samoa. At many reef sites, populations are abundant, with several hundred animals or more per hectare,” said Dr Purcell.

A vibrant fishery has been established in Samoa, where artisanal village fishers collect them for local consumption and sale by the roadside.”

In recent years, reefs in Samoa and elsewhere in the Pacific have been impacted by coral bleaching and subsequent algal overgrowth. Other studies had shown that trochus can benefit reef systems. Through its feeding, the herbivorous snails graze down this algal overgrowth that can smother young corals or prevent them from attaching on the reef.

“Our data found the introduced trochus in Samoa do not appear to be out-competing the native marine snail species,” said Dr Purcell.

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