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Sargassum polyceratium is widely distributed around the island of Curaçao (Netherlands Antilles) where it inhabits strongly contrasting habitats. Changes in population structure have been followed in three bays with increasing levels of wave exposure at two depths: shallow (0?m) and deep (18?m). The effects of increasing wave exposure were investigated by studying three deep-water populations; and the effects of depth by studying shallow- and deep-water populations in the two calmer bays. Total density and stage density (reproductive thalli, juvenile thalli) were determined and total and individual thallus biomass was estimated non-destructively. In the most wave-exposed deep-water population thalli were twice as long with more than twice the biomass than in the calmest deep-water population. Total density and juvenile density were highest in the bay with intermediate wave exposure. Depth was an important factor at both the individual and population level. Shallow-water thalli had basal holdfast areas that were four times larger than those from deep water, and thallus biomass was positively correlated with holdfast area. Shallow-water juveniles invested more in the development of a holdfast and lateral growth than deep-water juveniles. Total biomass per quadrat was up to 10-fold higher in shallow- than in deep-water populations. In shallow-water populations reproductive thalli were present throughout the year whereas in deep-water populations they were present only during autumn and winter. We conclude that both wave exposure and depth affect population structure. Thalli were generally bigger and total biomass higher in the more exposed bay(s) and in shallower water, contradicting the general pattern in macroalgae of reduced size and biomass with increasing wave exposure. [ABSTRACT FROM AUTHOR]

Investigates geographic variation in temperature responses (survival and growth) in two red algae: Digenea simplex C. Agardh and Champia parvula Harvey. Tropical to warm temperate distribution of the D. simplex; Extension of the C. parvula from the tropics into the cold temperate zone; Relation of ecoclinal variation to the amount of present and glacial selection pressure along the climate gradient.

Temperature and daylength responses were determined in culture for isolates of the red alga Cystoclonium purpureum (Hudson) Batters from Nova Scotia (NS, Canada), Helgoland (HE, Germany), and Roscoff (RO, France). Most isolates survived temperatures of -1.5% -2° to 23° C, whereas 25° C was lethal. Only the RO-gametophytes died at 23°C. Optimal growth conditions were 10°-20°C in both long and short days for the NS isolates and 8°-15° C and 8°-18%degC at daylengths of > 12 h for the RO and HE isolates, respectively. Tetrasporophytes and gametophytes of the NS isolate reproduced at 10°-20°C in long and short days within 5 months. At lower temperatures reproduction was limited or slow. The European isolates formed tetrasporangia at 10°-20°C (HE) or 5°-18°C (RO), spermatangia at 5°-15%degC (HE) or 5°-20°C (RO), and carpospores at 5°-15°C (HE) or 10°-15°C (RO). Short days either blocked or delayed reproduction of the European isolates. The phenology of C. purpureum was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. In early spring, growth was rapid and plants started to from reproductive structures. In summer, tetra- and carpospores were shed followed by degeneration of the upright axes while branched holdfasts persisted. New upright axes and juvenile plants were formed in autumn, but these remained small during the winter months. Published data indicate that the seasonal pattern at Nova Scotia is similar, although the onset of growth and reproduction is delayed until the end of spring. These observation correspond well with the results of the experiments. The life history of C. purpureum is regulated by temperature and daylength. In the eastern Atlantic, the limiting effects of short days confines growth and reproduction to spring and summer. In the western Atlantic, low winter temperatures alone bring about the same seasonal pattern. After plants have reproduced, uprights degenerate in spite of continuing favorable conditions. [ABSTRACT FROM AUTHOR]

Responses to temperature and daylength were determined in laboratory culture for isolates of the red alga Phylophora pseudoceranoides (Gmelin) Newroth el A.R.A. Taylor from Nova Scotia, Iceland, Roscoff (France), and Helgoland (Germany). All isolates grew from 3° to 25° C and survived from -2° Or 0° C to 27° C but not 30° C. Reproductive requirements differed between life history phases and isolates. Isolates from Helgoland and Roscoff formed sporangial sori at 3°-20°C, tetraspore at 3°-12° C, and procarps at 10°-20° C, irrespective of daylength. Spermatangia developed at 10°-23° C but only in long days. As the other European isolates, the isolate from Iceland formed tetrasporangia at 3°-12° C, but it had an additional requirement for short days. The Nova Scotian isolate formed sori at 10°-20°C and sporulated at 10°-18°C. when grown plants were transferred form noninductive to inductive conditions, sori were formed after 4 months and tetraspores developed and were shed (1-)3 months later. Procarps formed 1(-3) months after transfer. The phenology of P. pseudoceranoides was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. Plants were perennial, forming new blades from October to June, which degenerated between August, and February. In June, reproductive structures (sori, spermatangia, and procarps) started to appear on the new blades. From October to April, mature cystocarps were found. Mature tetrasporangia were observed only in February. The life history of P. pseudocernoides is regulated by temperature and daylength. Differential effects on the different life history phase all serve to confine the production of spores (both carpospores and tetraspores) to the winter season. Difference in response between isolates from different geography regions bring about the same effect: spores are shed only in winter. The nature of the geographic boundaries of P. pseudoceranoides id discussed. [ABSTRACT FROM AUTHOR]

The red alga Acrosymphyton purpuriferum (J. Ag.) Sjböt. (Dumontiaceae) is a short day plant in the formation of its tetrasporangia. Tetrasporogenesis was not inhibited by I h night-breaks when given at any time during the long (16 h) dark period (tested at 2 h intervals). However, tetrasporogenesis was inhibited when short (8 h) main photoperiods were extended beyond the critical daylength with supplementary light periods (8 h) at an irradiance below photosynthetic compensation. The threshold irradi. ance for inhibition of tetrasporogenesis was far lower when supplementary light periods preceded the main photoperiod than when they followed it (<0.05 μmol . m[SUP-2] ˙ s[SUP-1] vs. 3 μmol.m[SUP-2].s[SUP-1]. The threshold level also depended on the irradiance given during the main photoperiod and was higher after a main photoperiod in bright tight than after one in dim light (threshold at 3 &mumol˙m[SUP-2]˙s[SUP-1] after a main photoperiod at ca. 65 μmol.m[SUP-2]˙s[SUP-1] vs. threshold at <0.5 μmol.m[SUP-2]˙s[SUP-1] aider a main photoperiod at ca. 35 μmol.m[SUP-2]˙s[SUP-1]. The spectral dependence of the response was investigated in day-extensions (supplementary light period (8 h) after main photoperiod (8 h) at 48 μmol. m[SUP-2]˙s[SUP-1] with narrow band coloured light. Blue light CA 420 nm) was most effective, with 50% inhibition at a quantum-dose of 2.3 mmol.m[SUP-2]. However, yellow &lamda; = 563 nm) and red light (&lamda; = 600 nm; &lamda; = 670 nm) also caused some inhibition, with ca. 30% of the effectiveness of blue tight. Only far-red tight (&lamda; = 710 nm; &lamda; = 730 nm) was relatively ineffective with no significant inhibition of tetrasporogenesis at quantum-doses of up to 20 mmol˙m[SUP-2]. [ABSTRACT FROM AUTHOR]

Genetic differentiation among geographic isolates of the pantropical to warm-temperate red alga Digenea simplex (Wulfen) C. Agardh was investigated using random amplified polymorphic DNA (RAPD) markers, crossing studies, and temperature tolerances experiments. Eleven isolates representing populations from the Caribbean, eastern Atlantic, and Indo-West Pacific were compared. RAPD analysis clearly revealed an Indo-West pacific group, a Caribbean/Cape Verde Islands group, and a Canary Islands group. Crossing studies showed different levels of interfertility. In most crosses between Western Australian and Atlantic and Atlantic isolates, no hybrid tetrasporophytes were formed. In crosses between Caribbean and Cape Verde Islands isolates, tetrasporophytes developed, but the viability of tetraspores was reduced. Full sexual compatibility was observed among Cape Verde Islands isolates and among isolates from Bonaire. Temperature tolerance studies indicate that Pacific isolates have a broader temperature survival range than Atlantic isolates, which may be correlated to local temperature extremes. Despite the reduced level of sexual compatibility between Caribbean and Cape Verde Islands isolates, their shared position in the RAPD analysis and similar temperature responses suggest trans-Atlantic dispersal in the near geological past. In addition to their discrete position in the RAPD distance analysis, the Canary Islands isolates were significantly more cold-tolerant than the other Atlantic isolates. This finding is consistent with the hypothesis that the Canary Islands were recolonized from cold-adapted eastern Mediterranean populations after the last Pleistocene glaciation. [ABSTRACT FROM AUTHOR]

Temperature tolerances and relative growth rates were determined for different isolates of the tropical to warm temperature seaweed species Cladophoropsis membranacea (C. Agardh) Boergesen (Siphonocladales, Chlorophyta) and some related taxa. Most isolates of C. membranacea survived undamaged at 18° C for at least 8 weeks. Lower temperature (5°-15° C) were tolerated for shorter periods of time but caused damage to cells. All isolates survived temperatures up to 34° C, whereas isolates from the eastern Mediterranean and Red Sea survived higher temperatures up to 36° C. Growth occurred between 18° and 22° C, but an isolate from the Red Sea had an extended growth range, reaching its maximum at 35° C. Struvea anastomosans (Harvey) Piccone & Grunow, Cladophoropsis sundanensis Reinbold, and an isolate of C. membranacea from Hawaii were slightly less cold-tolerant, with damage occurring at 18° C. Upper survival temperatures were between 32° and 36° C in these taxa. Temperature response data were mapped onto a phylogenetic tree. Tolerance for low temperatures appears to be a derived character state that supports the hypothesis that C. membranacea originated from a strictly tropical ancestor. Isolates from the Canary Islands, which is near the northern limit of distribution, are ill adapted to local temperature regimes. Isolates from the eastern Mediterranean and Red Sea show some adaptation in local temperature stress. They are isolated from those in the eastern Atlantic by a thermal barrier at the entrance of the Mediterranean. [ABSTRACT FROM AUTHOR]

Chilling induced inhibition of photosynthesis was studied in nine isolates of the marine tropical to warm-temperate green macrophyte Valonia utricularis (Roth) C. Agardh. According to their temperature requirements for growth and survival, the isolates belong to a cold-tolerant Atlantic/Mediterranean group and a cold-sensitive Indo-west Pacific group. After 5 hours exposure to 5 degrees C under moderate light, all isolates experienced similar substantial photoinhibition, which approached steady state levels after a decline in Fv/Fm to about 40% of the initial values. After return to optimal temperature and dim light conditions, Fv/Fm values increased with biphasic kinetics. A fast phase with half-life times of less than 30 minutes (dynamic photoinhibition) was followed by a slow phase lasting a few hours, indicating repair of photodamaged PSII reaction centres (chronic photoinhibition). In the Atlantic/Mediterranean isolates the fast phase accounted for more than 80 % of the recovery response, showing that these isolates were able to cope with the applied low temperature stress by down-regulating their PSII reaction centres. In contrast, the two isolates from the Seychelles were predominantly photodamaged. In a second experiment, three isolates (Corsica, Seychelles, Japan) were exposed to a similar relative amount of cold stress (0, 10, 15 degrees C, respectively). The Japanese isolate and the isolate from the Seychelles showed significantly less inhibition compared to 5 degrees C exposure, but no significant difference was found in the Corsican isolate. However, the degree of low temperature stress had no significant influence on the relative contributions of dynamic and chronic photoinhibition. Only two of the seven investigated isolates had a lower final inhibition level when grown at sub-optimal temperatures than at optimal temperatures. However, all sub-optimally grown Atlantic/Mediterranean isolates exhibited faster recovery kinetics from chilling-induced photoinhibition than optimally grown plants. This is related to a faster recovery from chronic photoinhibition than to a higher relative contribution of dynamic photoinhibition. A specific role of the photoprotective pigments of the xanthophyll cycle, leading to an acclimation response in the Atlantic/Mediterranean isolates may be involved. We conclude that ecotypic differentiation in V. utricularis is mirrored in different degrees of susceptibility to low temperature stress.