BIOTIC

BIOTIC Species Information for Saccharina latissima

Researched by

Nicola White and Charlotte Marshall

Data supplied by

MarLIN

Refereed by

Dr Joanna Jones

Reproduction/Life History

Reproductive type

Alternation of generations

Developmental mechanism

Spores (sexual / asexual)

Reproductive Season

Possibly all year - see additional information.

Reproductive Location

Reproductive frequency

Annual episodic

Regeneration potential

Life span

3-5 years

Age at reproductive maturity

1-2 years

Generation time

1-2 years

Fecundity

Insufficient information

Egg/propagule size

Insufficient information

Fertilization type

External

Larvae/Juveniles
Larval/Juvenile dispersal potential	Insufficient information	Larval settlement period	Insufficient information
Duration of larval stage	Insufficient information

Reproduction Preferences 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