Seasonal Light and Temperature Interaction Effects on Development of Laminaria Saccharina (Phaeophyta) Gametophytes and Juvenile Sporophytes

Abstract

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

Environmental Influences on Kelp Performance across the Reproductive Period: An Ecological Trade-Off between Gametophyte Survival and Growth?

“…Seasonal variation in juvenile performance was assumed to be dependent on the intrinsic characteristics of the zoospores [29]. Tala et al [29] speculated that zoospores and gametophytes obtained in different seasons of the year may have different light and temperature requirements for growth and development [29], [30] and suggested that their study fell short of fully evaluating possible seasonal patterns, because this required special manipulation of the culture conditions to simulate environmental variation [29]. Despite the broad understanding of these seasonal patterns, very little is known about temporal variation in gametophyte growth and survival over smaller temporal scales, such as weeks and months across the reproductive period of a seasonally limited species.…”

The Effects of Variable Settlement and Early Competition on Patterns of Kelp Recruitment

“…The recruitment of these two kelps is usually greatest following disturbance from winter storms (Dayton and Tegner 1984, Harris et al 1984, Reed and Foster 1984 when rocky reefs on which the kelps attach are often fractured or scoured bare (Cowen et al 1982, Ebeling et al 1985. To date, much of the variation in the density of kelp recruitment has been attributed to variation in abiotic factors that affect the reproductive success of the microscopic gametophyte generation (Dayton 1985, Deysher and Dean 1986, Lee and Brinkhuis 1988. 1).…”

Long Island Sound

“…Optimal growth temperatures for gametophytes shift from 10-15 °C in March to 15-20 °C in July, exhibiting patterns of seasonal T acclimation. Optimal growth of young sporophytes for the species is 10-15 °C all year, but sporophytes from LIS have been found to survive up to 20 °C for all months except January (Egan et al 1989Lee and Brinkhuis 1988). The survival of plants in LIS at higher temperatures is attributed to the ability to accumulate and store higher levels of N in their tissues.…”

“…Temperature, light, and day length are primary factors controlling both distribution and productivity of seaweeds in LIS (Lee and Brinkhuis 1988;Brinkhuis et al 1983;Yarish et al 1984Yarish et al , 1986Yarish et al , 1987. Light intensity and wavelength are important for growth and reproduction.…”