Saccharina latissima

Researched ByNicola White and Charlotte MarshallData Supplied ByMarLIN
Refereed byDr Joanna Jones
Taxonomy
Scientific nameSaccharina latissimaCommon nameSugar kelp
MCS CodeZR354Recent SynonymsNone
PhylumChromophycotaSubphylum
SuperclassClassPhaeophyceae
SubclassOrderLaminariales
SuborderFamilyLaminariaceae
GenusSaccharinaSpecieslatissima
Subspecies  
Additional InformationAlso known as sugar kelp and sea-belt. The name sugar kelp refers to a whitish, sweet-tasting powder which forms on the dried frond.
Taxonomy References
General Biology
Growth formFoliose, ForestFeeding methodPhotoautotroph
Mobility/MovementSee additional information, Permanent attachmentEnvironmental positionEpilithic, Epifloral, See additional information
Typical food typesNo text enteredHabitSee additional information
BioturbatorNot relevantFlexibilityHigh (>45 degrees)
FragilityIntermediateSizeLarge(>50cm)
HeightGrowth Rate1.1 cm/day
Adult dispersal potentialNot relevantDependencyIndependent
SociabilitySolitary
Toxic/Poisonous?No
Additional InformationGrowth
Laminaria saccharina grows fastest from late winter to spring at a rate of about 1.1 cm/day although growth rates of up to 4.87 cm/day have been recorded. Growth then declines from June onwards and may cease in late summer. The reduction in summer growth rate is thought to be due to nitrate limitation (Sjøtun, 1993). The length:width ratio of newly grown lamina tissue varies throughout the year and is highest during the periods of fast growth, that is, December to June (Sjøtun, 1993). By shifting effort towards growth in width in late summer, it is possible that the plant can maximize the lamina area for autumn and winter and therefore increase the amount of stored carbon available for plants at this time (Sjøtun, 1993).

The seasonal growth pattern results in annual growth rings or lines in the stipe, which can be used to age the plant. The species may occur as an annual opportunist.

Morphology
The shape of the frond can vary with environmental conditions. Gerard (1987) found that plants subjected to constant longitudinal tension (as would be expected in higher water flow rates) may become morphologically enhanced to a more streamlined shape. In laboratory simulations, he found that plants subjected to longitudinal stress had significantly narrower blades and a significantly higher rate of cell elongation at the end of the six week experiment, compared to those plants that had not experienced the same stress. Laminaria saccharina plants from wave exposed sites have short, solid stipes and short, narrow and thick tissued fronds with closely wrinkled blades (Lüning, 1990). In contrast, plants from sheltered sites have a broad thin blade with an undulate surface (Lüning, 1990).

Mobility
The majority of Laminaria saccharina plants are permanently attached to the substratum. This may include bedrock and large boulders down to pebbles. Even sand grains can provide an attachment sufficient enough to allow the young sporophytes to segment and develop into new plants (Burrows, 1958). However, Burrows (1958) also described large populations of 'loose lying' Laminaria saccharina in Port Erin Bay, Isle of Man, which showed no signs of ever having been attached. She concluded that, apart from at the earliest stages of sporophyte development, an attachment to the substratum is not essential for the growth of the plant.

Biology References
Distribution and Habitat
Distribution in Britain & IrelandAll coasts of Britain & Ireland.
Global distributionRecorded from the Atlantic coasts of Europe as far north as Novaya Zemlya and south to northern Portugal and around Iceland. Also found in Greenland, Eastern coast of America down to New Jersey, Pacific coast of America, Bering Straits and Japan.
Biogeographic rangeNot researchedDepth rangeSublittoral fringe to 30 m
MigratoryNon-migratory / Resident
Distribution Additional InformationLaminaria saccharina is often found on unstable substrata such as rocks and boulders. The species is adapted to growing on these by having a flexible stipe which reduces leverage on any boulder to which it is attached, reducing the chance of its being turned over by wave movement. The species can even grow unattached and extensive populations can develop on loose-lying sand in calm conditions. In wave-exposed conditions the species may extend into the lower eulittoral.
Substratum preferencesBedrock, Large to very large boulders, Small boulders, Cobbles, PebblesPhysiographic preferencesOpen coast, Strait / sound, Sealoch, Ria / Voe, Estuary
Biological zoneSublittoral Fringe, Upper InfralittoralWave exposureSheltered, Very Sheltered
Tidal stream strength/Water flowStrong (3-6 kn), Moderately Strong (1-3 kn), Weak (<1 kn), Very Weak (negligible)SalinityFull (30-40 psu), Low (<18 psu), Reduced (18-30 psu), Variable (18-40 psu)
Habitat Additional Information
Distribution References
Reproduction/Life History
Reproductive typeAlternation of generations Developmental mechanismSpores (sexual / asexual)
Reproductive SeasonPossibly all year - see additional information.Reproductive Location
Reproductive frequencyAnnual episodic Regeneration potentialNo
Life span3-5 yearsAge at reproductive maturity1-2 years
Generation time1-2 yearsFecundityInsufficient information
Egg/propagule sizeInsufficient informationFertilization typeExternal
Larvae/Juveniles
Larval/Juvenile dispersal potentialInsufficient informationLarval settlement periodInsufficient information
Duration of larval stageInsufficient information  
Additional Information
Overview of life history
Laminaria saccharina has a typical laminarian life history, in which a macroscopic and structurally complex diploid sporophyte phase alternates with a microscopic haploid gametophyte. The species is a short-lived perennial. Sporophytes (clearly visible adult plants) typically have a life span of 2 to 4 years, although plants may occur as annuals. Specimens over four years old have been recorded from a fjord in Greenland (Borum et al., 2002).
Timing of reproduction
Laminaria saccharina plants usually takes 8 to 15 months to reach fertility at which point the central portion of the blade is covered in unilocular sporangia, that produce zoospores by meiosis. Lüning (1988) reported that sorus (a group of sporangia) formation in Laminaria saccharina from Helgoland, in the Southern North Sea, was restricted to autumn conditions whilst Kain (1979) and Parke (1948) reported that, in the British Isles, sorus formation was most frequent in both autumn and winter. It has been suggested that, in the Arctic, Laminaria saccharina sporophytes may carry sori throughout the year and can therefore produce gametophytes in all seasons (Makarov & Schoschina, 1998, cited in Sjøtun & Schoschina, 2002). Similarly, Parke (1948) reported that in sheltered habitats on the south Devon coast, reproductive tissue was present in all months, although October to April was the most frequent period of spore production in the British Isles for this species.
Reproduction
  • Each sporangium contains 32 zoospores that develop into microscopic dioecious haploid gametophytes.
  • The gametophyte goes through a 'dumbbell' stage before enlargement (female) or division (male). This stage is characterized by swelling at the distal end of the germination tube, which is separated by a cell wall from the original spore case from which the tube initially arose (Kain, 1979).
  • Lüning (1990) recognized three stages in the development of gametophyte:
    (1) germination of the embryospore to form the gametophyte;
    (2) vegetative growth of the gametophyte to form either a larger single celled female gametophyte or, in the case of male gametophytes, a few small cells, and
    (3) the reproductive phase. If environmental factors do not induce fertility in the gametophyte (see factors affecting reproduction below), filamentous growth occurs.
  • The filaments of female gametophytes are, on average, approximately 10 µm in diameter and those of males are usually half of that (Kain, 1979). Male gametophytes are more branched than the females and have more numerous, smaller and paler cells.
  • If the gametophytes become fertile, male gametophytes develop antheridia that produce sperm. The females develop oogonia in which the egg develops (Birkett et al., 1998). This egg is subsequently discharged. After the egg has emerged, the cell wall closes behind it and forms a cushion on which the egg is seated (Bisalputra et al., 1971).
  • The external egg is fertilized by the motile sperm and the resultant zygote eventually develops into the new sporophyte.
  • After fertilization, a thick cell wall is formed around the zygote and when the zygote reaches 10-16 µm in diameter, it starts to elongate rapidly (Bisalputra et al., 1971).
  • Sporophytes first become attached by filamentous rhizoids but later by large branched haptera (Burrows, 1971).
  • After rhizoid attachment, an attachment disc is formed from the swollen base of the stipe (Kain, 1979).
  • Cell division in the young sporophyte gives rise to a broad flat thallus but eventually a meristem gives rise to a flat blade above it and a cylindrical stipe below (Burrows, 1971). By this stage the plant has taken on the recognizable 'kelp shape'.


Factors controlling reproduction
Light regime
Experimental work using various red and blue light regimes suggest that the onset of fertility in female gametophytes is controlled specifically by blue light above a certain irradiance (Lüning & Dring, 1975). In their experiments, female gametophytes grown in red light for ten days continued to grow vegetatively with no egg production. In contrast, nearly 100% of gametophytes grown in blue light (1.5 nE cm-2 sec-1 (total irradiation per second)) over the same period became fertile. Equally, plants that had been grown in red light for two weeks became fertile after being irradiated with blue light (1-4 nE cm-2 sec-1) for a period of time. After 96 hours of irradiance almost 100% of gametophytes had become fertile. Lüning (1990) also concluded that only blue light induces fertility.
Lüning (1988) cultivated adult sporophytes near Helgoland in the Southern North Sea and cultivated them under various light regimes. Sori were only formed in the 'short day' regime (8:16 hours light:dark respectively). No sori were formed in the 'long day' (16:8) or 'night break' (8:7.5:1:7.5) regimes.
Lüning (1990) found that at 10 °C, the gametophyte could survive at least five months in total darkness.
Temperature
Lee & Brinkhuis (1988) studied the effects of seasonal light and temperature interactions on the development of Laminaria saccharina gametophytes and juvenile sporophytes in Long Island Sound and found that, in general:
  • germination of zoospores was inhibited at 20 °C;
  • gametophyte growth improved with increasing temperature between 4-17 °C;
  • fecundity was totally inhibited at 20 °C;
  • sporophyte growth was inhibited at 17 and 20 °C, and
  • temperature for optimal growth depended on the time of year.
These authors also found that sex ratio was significantly affected by temperature and between 17-20 °C male gametophytes were more prevalent.
Sjøtun & Schoschina (2002) reported 100 % germination of embyospores at 0 °C in this species suggesting a good adaptation to Arctic conditions.
See 'sensitivity' (adult) section on temperature for further information.
Reproduction References