I n prezious studies, Laminaria saccharina L. (Lamour.) sporophytes were found to exhibit two major peaks of sporogenesis and a n annual life cjcle i n Long Island Sound, ,Vew York. Youngsporophjtes were observed shortly after the sporogenesis peaks i n early autumn and spring, but most of the mature sporophjtes decajed during summer. A new study was conducted to determine if the spring sporogenesis actitritj contributed to the recruitment observed i n autumn through oversummering of gametophytic and jutlenile sporophjtic stages, as prezliouslj suggested. Reproductzon and growth i n gametophjtes and growth i n j u t w i l e sporophytes were studied under crossed gradients of light and temperature. Periodic outplantings of substrata seeded with gametophjtic and sporophytic stages to the jield were conducted to assess actual survitlal.The optzmum temperature and light conditions f o r gametophjte development, growth and reproductzon varied with the time of jear meiospores were obtained. Most of this variation was attributable to temperature. A seasonal adaptation to temperature i n most detdopmental stages was obsenled. Higher temperatures resulted i n greater numbers of male gametophytes. Gametophjtic stages could deuelop at all times, suggesting that oversummering i n this stage u a s possible. Juvenile sporophjtes had a narrower optimum temperature range and again photon Jluence rate contributed little to observed tlariances. Outplanting of sporophjtic stages at varzous tzmes durzng the year indicated onlj sporophjtes prepared f r o m autumn and wznter could survive summer conditions. The thalli of these plants grew rapidly i n spring and eroded back to the meristematic region i n summer. Most of these plants then quicklj became reproductive, resultzng i n another autumn sporogenesis peak. Gametophjtic and sporophytic outplantings prepared from spring meiospores did not survive the summer. Thus, the recruitment obserued i n autumn can onlj be the result of the previous autumn's sporogenesis activitj. The sporogenous activities of spring and earlj summer appear to be unimportant, despite the fact that all reproductive indices are superior at those tzmes.Distributional ranges of seaweed species are generally governed by survival of adult plants and their

Laminaria saccharina (L) Lamour. Sporophytes were monitored monthly from October 1982 to September 1983 to investigate reproduction phenology and relationshiops to growth paatterns aaat its southern limit of distribution in the northwest Atlantic Ocean (Long Island Soundd). Plants exhibited an annual growth pattern. Growth raate, bladelehgth, maximum width, area, stiipe lehgth an wet weight swhoed the same seasonal pattern and reached maximum values between May and June. Only blade thickness continued to increase tthrooughout the ovservation period. Blade dissintegration occurred dduring August and September. Reproductive sporophytes occurred throughout the observation period; the greatest frequency of appearance occurred in October (43.8%) and June (37.8%). The blade area covered by sori ranged from 2.4% (Janaury) to 6.1% (August). Meiospore release under laboratory conditions was maximum in May and minimum in July. No meio‐spores were released in August Sporulation was not correlated with meristematic growth of nitrogen content How ever, reproductive plants were generally larger and thicker throughout the sporulation period, and had a greater carbort content is spring than nonreproductive plants. Fecundity and reproductive success of female gametophytes were maximum in spring and minimum in winter. The growth of early sporophyte stages in the laboratory was greatest in early spring; however, juvenile macroscopic stages were hardly observed in the field during summer months due to warm water temperatures. “Over‐summering” of gamelophytes and / or microscopic sporophytes may account for the annual cycle of Laminaria at its southern limit of distribution.

No abstract

No abstract