In June 2012, production was measured and compared among Zostera marina stands with different shoot sizes and stand structures, at a total of seven stations in three Z. marina beds in the Seto Inland Sea, Japan. Production per shoot depended on the shoot size, and was larger (50.9 - 73.2 mg DW shoot -1 d-1) at the stands in the bed of Ikuno-shima Is. (Hiroshima Pref.; Aki-Nada Sea), where large shoots formed stands with lower densities, than at stands in the bed of Heigun-jima Is. (Yamaguchi Pref.; Suo-Nada Sea) (7.7 - 27.4 mg DW shoot -1 d-1) where small shoots exhibited higher densities. Though the areal production estimated was compensated by shoot density, it was still larger at the bed of Ikunoshima Is. (2.89-5.38 g DW m-2 d-1) than at Heigun-jima Is. (1.63 - 2.56 g DW m-2 d-1). Sediment characteristics were quite different between the two Z. marina beds and considered to affect the stand structures and productivity, i.e., the sediment at Ikuno-shima Is. was muddy and rich in organic matter and the sediment at Heigun-jima Is. was dominated by sand indicating severer physical conditions induced by waves.
In Aba-shima Is. (Hiroshima Pref.; Aki-Nada Sea), the third research site, the Z. marina bed was on the way of recovery after catastrophic damage due to heavy grazing of rabbitfish (Siganus fuscescens) which had occurred in autumn of 2011, and young shoots developed from seeds forming a patchy stand with a low shoot density and biomass. Though the production was lowest (0.60 g DW m-2 d-1), the turnover of the biomass was higher (6.5 % d-1) at the stand in Aba-shima Is. than values (1.7-3.3% d-1) at the other two beds.