(1980) showed that two morphological strains of Chondrus crispus had different temperature/growth optima in cul- ture. It is, however, apparent from the present ...
MARINE BIOLOGY
Marine Biology 66, 89-94 (1982)
9 Springer-Verlag 1982
Optimal Growth and Maximal Survival Temperatures of Atlantic Laminaria Species (Phaeophyta) in Culture J. J. Bolton and K. Ltining Biologische Anstalt Heigoland (Meeresstation); 2192 Helgoland, Germany (FRG)
Abstract
The effects of temperature on growth rate of rapidlygrowing cultured macrosporophytes of 9 isolates of Atlantic Laminaria comprising 4 species have been investigated. No significant population variation was observed within species despite wide variations in temperature between the original collecting sites. L. saccharina showed a broad temperature optimum in the 10~ ~ range, whereas L. longicruris had a sharp optimum at 10 ~ L. digitata and L. hyperborea grew more slowly, with only slightly sub-optimal growth over a wide temperature range, but with peaks at 10 ~ (L. digitata) and 15 ~ (L. hyperborea). The maximum survival temperatures of individual male and female vegetatively-growing gametophytes were ascertained for these species plus the Arctic L. solidungula, and were as follows: L. saccharina and L. longicruris, 23 ~ L. digitata (male), 23 ~ L. digitata (female), 22 ~ L. hyperborea, 21 ~ L. solidungula, 18 ~ The lack of within-species differences demonstrates that the success of the genus in areas with different temperature regimes is brought about by phenotypic plasticity of individuals rather than the selection of temperature races or ecotypes.
Introduction
Kain (1979) in her recent review of the genus Laminaria was of the opinion that "the effect of temperature on the growth rate has received little critical attention". Owing to the logistical problems of culturing large plants in the laboratory, most previous investigations have been carried out on microsporophytes up to a few mm in length (Kain, 1965, 1969; Perez, 1971; Cosson, 1973). Despite the large variation in temperature regimes over the distribution range of Laminaria species, no attempt has previously been made to ascertain whether genetic differences exist
between populations with respect to growth in various temperatures. The present study investigates the growth rates in unialgal culture of rapidly-growing macrosporophytes (initially 5 to 8 cm blade length) of nine isolates of Atlantic Laminaria spp. over a range of temperatures. For comparison, the maximum survival temperatures of individual male and female gametophytes were also examined.
Materials and Methods
Sporophyte Growth The cultures used and their original sites of collection are listed in Table 1. Fertility could not be induced in gametophytes of Laminaria solidungula, and thus only gametophyte survival experiments were carried out on this species. Sporophyte cultures were initiated from previously isolated unialgal male and female gametophyte cultures. These consisted entirely of vegetative filaments, having been cultured in red fluorescent light at an irradiance of 10#tool m -1 s -1 at 10~ (Ltining and Dring, 1972, 1975). The culture medium was heat-sterilized enriched sea water (ES enrichment, Provasoli, 1968) throughout. The parent male and female gametophytes were gently ground in a mortar to produce fragments 1 to 10 cells in length and poured into a plastic vessel ( 1 6 x l 0 x 6 c m ) containing 500 ml of medium, the bottom of which was covered with 50 to 60 PVC plates (2 x 1 x0.5 cm). These were placed in white fluorescent light (Osram 65W/19; 60 #tool m -1 s -~) for a 2-wk fertilisation period, following which the irradiance was reduced to 40~mol m -~ s-*. Aeration was provided and the medium renewed weekly. After a period of 8 to 10 wk the plates with small attached sporophytes were placed in large, aerated, Plexiglas-covered tanks ( 1 5 0 x 5 0 x l 0 c m ) containing 401 of medium, for a further 2 to 4 wk until the plants were 5 to 8 cm long and ready for experimentation. 0025-3162/82/0066/0089/$ 01.20
J. J. Bolton and K. Lfining: Effect of Temperature on Atlantic Laminaria Spp. in Culture
90 Table 1. Origins of parent sporophytes
Species
Code
Collection site
Latitude Longitude
L. L. L. L.
S. HEL D. HEL H. HEL S. BRI
Helgoland, Germany Helgoland, Germany Helgoland, Germany Brest, Brittany, France
54~
L. saccharina
S. IOM
Port Erin, Isle of Man, United Kingdom
L. L. L. L. L.
S. ESP L. HFX D. HFX L.IGL -
Espegrend, Norway St. Margarets Bay, Nova Scotia, Canada St. Margarets Bay, Nova Scotia, Canada Igloolik, North West Territories, Canada Igloolik, North West Territories, Canada
saccharina (L.) Lamour. digitata (Huds.) Lamour. hyperborea (Gunn.) Fosl. saccharina saccharina longicruris la Pyl. digitata longicruris solidungula J. Ag.
The experimental apparatus consisted of a similar tank with aeration, continuous water agitation by a rotary pump (Eheim, West Germany; type 1036) and cool white fluorescent light (50ktmol m -~ s-~; 16:8 LD regime). Six experimental tanks were run concurrently with water temperatures of 0 ~ 5 ~ 10 ~ 15 ~ 20 ~ and 23 ~ (0 ~ with a range of +_2 C ~ all others +_1 C~ Experimental plants were cut back to 2 cm blade length and a 1.5 m m diameter hole was punched in the blade 1 cm from the transition zone and hole (see Markham et al., 1980). Ten plants of each isolate were measured after 7 d and the specific growth rate (SGR) calculated as % increase d -~ using the formula SGR =
loge (L~/L1) T '
where L~ = initial length ( = stipe/blade transition zone to punched hole), L1 = length on day T.
Gametophyte Survival The maximum survival temperature of individual male and female gametophytes was ascertained by placing a small amount of vegetative filamentous material in 10 ml of Provasoli ES medium in a test tube. These were positioned in a rack submerged in a controlled-temperature water bath (using a Colora cryostat; Colora Messtechnik, Lorch, F R G ) in continuous dim light (10ktmoI m -1 s-l). The water baths were maintained at 18 ~ 20 ~ 21 ~ 22 ~ 23 ~ and 24 ~ (all +- 0.1 C~ After 14 d, the material was placed in a Petri dish containing 30 ml of fresh medium at 10 ~ in red light (20ktmol m -1 s-~; emmission spectrum as specified by Ltining and Dring, 1972) for 2 to 3 wk. Survival was recorded as ability for vegetative regrowth of the filamentous gametophyte. For comparison, fertile fronds of Helgoland Laminaria saccharina were induced to release spores, and roughened glass slides with newly settled zoospores were incubated in test tubes alongside the cultured gametophytes, followed by a similar period in fresh medium at 10 ~
7~
48~ 4O30'W 54O5'N, 4O30'W 60o10'N, 5O30'E 44~ 69~
63o55'W 82o30'W
Results
The growth rates over a range of experimental temperatures ofLarninaria saccharina sporophytes from four sites are represented in Figs. 1 and 2. The curves show optimal growth (15 to 18% d -1) in the 10~ ~ range, either with no significant difference between 10 ~ and 15 ~ (Espegrend and Isle of Man) or with a slight peak at 10 ~ (Helgoland and Brittany). All plants disintegrated after 7 d at 23 ~ Growth was reduced at 20 ~ to 50-70% of the optimum in all isolates; the Espegrend plants were extremely fragile and lost pigment from the tip of the blade at this temperature. Growth was similarly reduced at 5 ~ (60-70% of optimal) and all isolates grew at much slower rates (20-40% of optimal) at 0 ~ Both isolates ofLaminaria longicruris (Fig. 3) showed a marked peak of growth (19% d -1) at 10 ~ Plants from both Igloolik and Halifax showed reduced growth at 5 ~ (60 to 70% of optimal) and extremely reduced growth at 0 ~ (30 to 35% of optimal). At 15 ~ the Igloolik isolate grew less well than the Halifax isolate (55% and 80% of optimal respectively). Growth was further reduced to 40-50% of optimal at 20 ~ and all plants disintegrated at 23 ~ Laminaria digitata from Helgoland and Halifax (Fig. 4) showed similar patterns of growth at the various temperatures, although the Halifax isolate grew slightly, though significantly, more slowly at all experimental temperatures. Both isolates grew considerably more slowly than L. saccharina and L. longicruris, with significant optima at 10 ~ of 7 and 9% d -1 respectively. Growth was reduced to a similar extent at 5 ~ and 15 ~ (ca 75% of optimal for the Halifax isolate and ca 83% of optimal for the Helgoland isolate). L. digitata grew well at 0 ~ (60 and 70% of optimal respectively), more slowly at 20 ~ (43 and 60% of optimal) and all plants disintegrated at 23 ~ The Helgoland Laminaria hyperborea (Fig. 5) grew more slowly under the experimental conditions than the other species, with a peak of 6,4% d -1 at 15 ~ A broad peak is apparent, with growth at 5 ~ and 10 ~ of 71 and 76% of that at 15 ~ Growth was much reduced at 20 ~ (51%) and at 0 ~ (31% of optimal).
J. J. Bolton and K. Limning: Effect of Temperature on Atlantic Laminaria Spp. in Culture
91
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