Culture Studies of Halodule wrightii Aschers. Edaphic Requirements

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Abstract
Growth rates of H. wrightii Aschers. were compared during laboratory culture on artificial sediments containing varying amounts of soluble sulfide and Fe, but similar amounts of N, P and Mn. Moderate levels of H2S (.apprx. 0.5 mM) and very low levels of soluble Fe (0.5-2.0 .mu.g/ml) in the sediment water correlated with maximal Halodule growth rates. Interstitial water-soluble Fe > 20 .mu.g/ml appeared to inhibit Halodule growth, possible by interfering with S metabolism or limiting the availability of P to the plants. Excess phosphate, but not Mn, added to the sediments containing low H2S levels counteracted some degree of Fe inhibition. Sediment H2S concentrations > 1 mM were also correlated with decreased growth rates, verifying that a poised level of H2S between 0.2-1.0 mM favored Halodule growth. The methodology described is proposed for laboratory culture studies of other seagrasses.