The effect of temperature on development and reproduction in Chorda filum and C. tomentosa (Phaeophyta, Laminariales) from Nova Scotia

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Abstract
The occurrence of sporophytes of Chorda tomentosa and C. filum in the southern Gulf of St. Lawrence was correlated with the field temperature regime. Temperature tolerances of gametophytes and young sporophytes of both species were tested in culture, using isolates from both the gulf and the outer Atlantic coast of Nova Scotia. Chorda tomentosa sporophytes appeared in late winter when the water surface was frozen, were fertile from April to June, and died when water temperature approached 20.degree. C. In culture, sporophytes tolerated-1 to 15 but became moribund at 20.degree. C. Gametophytes in constant temperature reproduced readily at 5.degree. C, occasionally at 0 and 10.degree. C, but not at higher temperatures; they survived to 24.degree. C. After 6 months in dim light at 10.degree. C some gametophytes also released gametes at 15.degree. C. Sporophytes of C. filum appeared in the field in spring after the water temperature had risen above 1.degree. C and persisted through the warm months. New sporophytes appeared in the autumn after the water temperature dropped below 15.degree. C but did not survive the winter. In culture, sporophytes died at -1 and 28.degree. C and survived between 0 and 24.degree. C. Gametophytes reproduced readily from 5 to 12, rarely at 0 and 15.degree. C, and not at higher temperatures. Gametophytes of both species survived 5 months in 0 .+-. 2.degree. C, .ltoreq. 1 .mu.E m-2 s-1.