AN ESTIMATION OF NET PRODUCTION-RATE OF EELGRASS ZOSTERA-MARINA AT YANAI BAY DURING SPRING AND SUMMER

The net production of eelgrass Zostera marina in tidal flats at Yanai Bay in the Seto Inland Sea, Japan, was estimated from seven field surveys using a marking method from April to July 1982. The increase of actual leaf length observed was corrected by the addition of assumed increases which had been washed away in the interval between surveys. The net production in the overground part was obtained by converting the corrected increase of leaf length into dry weight. The net production in the underground part was obtained from the weight increase of biomass during the investigation. The net production rates in overground and underground parts were 2.3 and 0.4 g dry wt./m2 . day, respectively. The net organic productions of the former and latter parts were 8.0 and 6.6 times greater than the biomass at the start of the investigation, respectively. The production rates of eelgrass beds in the infralittoral zone at Yanai Bay were estimated as 7.4 and 2.7 g dry wt./m2 . day for the former and latter parts, respectively.