The head of a citizen-based conservation group has warned that horseshoe crabs on the Tsuyazaki tideland in Fukuoka Prefecture are declining sharply.

Marine life expert Mari Shuno spends every summer on the tideland in the city of Fukutsu researching the animals under the harsh sun. This is because they only become active during the summer.

Last year, she confirmed that only a few of the horseshoe crabs had laid eggs, compared with 141 in 2005.

Shuno said the construction of breakwaters near the tideland in 2006 might be driving the decline.

"Horseshoe crabs have been here since before we were born. We must preserve this tideland for future generations."