Effect of nutrient salts eluted from hedoro blocks on growth and survival rate of gametophyte and juvenile Eisenia bicyclis

Abstract

The effects of nutrient salts eluted from artificial algal reef blocks made with sea-bottom sediment (hedoro) and cement to the growth and survival rate of the gametophytes and juveniles of Eisenia bicyclis were investigated. When each sample block was submerged in filtered seawater for 28 days, the nutrient salt content from the hedoro increased with time and, in particular, the amounts of NO₃⁻-N and NO₂⁻-N reached a constant level on day 10. We observed that the lower the cement ratio, the higher the concentrations of eluted NH₄⁺-N and PO₄³⁻-P. The growth of gametophytes as well as juveniles was highest in the elution of the block with the lowest cement ratio of 30%. In contrast, the survival rate of gametophytes and juveniles decreased linearly with time and the survival rate was higher for the hedoro blocks than for the block made of mortar.