Estimation of light requirement for the growth of Zostera marina in central Japan

Abstract

The present study was designed to estimate the critical light intensity required for growth of Zostera marina and that which determines its depth limit. Seeds of Z. marina collected at Matsunase, Ise Bay, Mie Prefecture, central Japan were germinated and grown to young plants of 10 cm in length. The young Z. marina were cultured for 1 week in various water temperatures, and their photosynthesis and respiration were measured under various photon irradiances. The daily compensation point was estimated by a mathematical model based on photosynthetic activity and diurnal changes in solar irradiance. The estimated daily compensation point of young Z. marina was 5.7% of sea surface. The depth limit was determined by the Beer–Lambert law concerning the relative solar irradiance on the sea surface and the extinction coefficient. Almost all previous studies report a shallower growing depth of Z. marina than the present result, but the lowest reported data agreed well with the current estimated depth limit. Therefore, the mathematical model in the present study can estimate the production and critical growing depth of Z. marina. The results suggest that the compensation depth is controlled mainly by the solar irradiance reaching the Z. marina beds.

Estimation of light requirement for growth of Zostera japonica cultured seedlings based on photosynthetic properties

“…Generally, the extinction coefficient (k) is 0.1-0.2 in the open sea, 0.2-0.5 in the inner sea, and[0.5 in the turbid inner sea [31].…”

“…When P(I) = 0, I = I c , i.e., the light compensation point. The seasonal daily compensation points of the Z. japonica were estimated based on the photosynthesislight relationship fitted by the equation and the diurnal changes in PPFD in each season, according to Abe et al [31]. Water temperatures examined in this study were representative of the four seasons, namely 10°C, winter; 15, 20°C, spring/autumn; and 25°C, summer.…”

“…Water temperatures were controlled by using an improved type of temperature-gradient culture [19,20,[34][35][36][37]. For the photosynthesis and respiration experiments, six to nine samples of whole Z. japonica seedlings were used, and the photosynthetic and respiratory activities were measured with an improved type of differential gas volumeter [27,29,31,[38][39][40][41][42][43][44] on the 6th day in culture. Photosynthesis and respiration were measured at eight different PPFDs (0, 12.5, 25, 50, 100, 200, 400, and 800 lmol photons m -2 s -1 ) generated using a projector lamp (Master HI-LUX 1000 W; RikagakuSeiki, Tokyo, Japan).…”

“…Thus far, many studies have been carried out on the light requirements of Zostera marina [22,25,26,28,[30][31][32]; however, there are no studies on Zostera japonica in this regard.…”

“…Light condition is one of the most important factors in the growth of marine plants including seagrasses [25][26][27][28][29][30][31]. Thus far, many studies have been carried out on the light requirements of Zostera marina [22,25,26,28,[30][31][32]; however, there are no studies on Zostera japonica in this regard.…”