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Seasonal variation in density, thallus length and biomass, population size structure, and allometric length-biomass relationships was investigated in populations of Sargassum ilicifolium (Turner) C. Agardh, Sargassum subrepandum (Forssk.) C. Agardh, and Turbinaria triquetra (J. Agardh) Kütz. (Phaeophyceae) on shallow reef flats in the southern Red Sea. Thallus length and biomass varied strongly with season, with the highest values occurring in the cooler months. Thallus densities showed no significant temporal variation. Log-total biomass versus log-density relationships were positive throughout the growth season without any decrease in the slope of the relationship. In two populations, biomass-density combinations approached the interspecific biomass-density line, but the massive annual shedding of modules occurred before self-thinning would set in. Allometric length-biomass relationships varied with season in all populations and were associated with seasonal module initiation, growth, and shedding. Evidence of a strong asymmetric competition was found in two high-density populations. These populations showed a predominance of small thalli during peak development, asymmetrical Lorenz curves, increasing Gini coefficients, and increasing thallus length relative to biomass during the main growth phase. In two other less crowded populations, small thalli were absent during peak development, Lorenz curves were symmetrical, and Gini coefficients decreased during the main growth phase. In these populations, size equalization appears to be due to responses at the modular level rather than size-dependent mortality. We conclude that changes in size structure in this highly seasonal environment are determined by module dynamics, modified by asymmetric competition in some populations, with a minor role of recruitment and no regulatory effect of self-thinning. [ABSTRACT FROM AUTHOR]

Module dynamics in the fucoid alga Turbinaria triquetra (J. Agardh) Kützing were studied on a shallow reef flat in the southern Red Sea. Seasonal patterns in thallus density and size were determined, and the initiation, growth, reproduction, and shedding of modules were studied using a tagging approach. The effects of module density and module/thallus size on module initiation, growth, reproduction, and shedding were analyzed, and the occurrence of intraspecific competition among modules was examined. Seasonal variation occurred mainly at the modular level. There was a restricted period of new module formation in the cooler season, followed by fast growth and reproduction, massive shedding of modules from the end of the cooler season onward, and strongly reduced biomass in summer. There was no evidence of suppressed growth in small modules due to intraspecific competition. Module density and thallus/module size had opposite effects on elongation rates. High module densities enhanced maximum elongation rates (fastest-growing module per thallus), resulting in longer thalli. On the other hand, elongation rates decreased and tissue loss increased with increasing module length. Reproduction had no clear effect on elongation rates, indicating that there was no direct trade-off between reproduction and growth. The apparent size-dependence of reproduction was due to delayed fertility in young modules. Module initiation and shedding were independent of module density. Shedding was also independent of module size and reproductive status. We conclude that seasonal changes in the environment affect module initiation, growth, reproduction, and shedding, whereas density and size-dependent processes mainly affect growth rates. [ABSTRACT FROM AUTHOR]

The potential to acclimate photosynthesis to sub- and supra-optimal temperatures was investigated in seven isolates of Valonia utricularis (Roth) C. Agardh, a green macrophyte with a tropical to warm-temperate distribution. Photosynthesis-light response curves were obtained by measuring chlorophyll a fluorescence characteristics of algae grown at optimal (25°C), sub- and supra-optimal temperatures. Suboptimal temperatures were chosen to support 30% of the maximum relative growth rate in each isolate. Thermal acclimation was investigated by comparing short-term and long-term temperature effects on the initial rate of increase of the relative electron transport rate (rETR) and the maximum rETR under light-saturating conditions. Isolates from the northeast Atlantic and the Mediterranean all showed a strong potential to acclimate maximum rETR to suboptimal growth temperatures, i.e. short-term temperature effects were diminished after acclimation. However, photoinhibition, measured as a decrease of the maximal quantum yield (Fv/Fm), was found when plants were grown at 30°C. The isolates reduced light harvesting at 30°C by decreasing total chlorophyll content and by increasing the chlorophyll a/b ratio. Up-regulation of photoprotective processes by the xanthophyll cycle pigments was not observed. In contrast, isolates from the Indo-west Pacific were unable to acclimate photosynthesis to suboptimal growth temperatures and these temperatures were strongly photoinhibiting, even though adjustments on the pigment level were observed. All Indo-west Pacific isolates reached comparable maximum rETR values at 30° and 25°C. Thus, the Atlantic/Mediterranean isolates had a stronger potential to acclimate photosynthetic rates at suboptimal growth temperatures compared to the Indo-west Pacific isolates, which was accompanied by losses at 30°C. The results are discussed in a biogeographical context. [ABSTRACT FROM AUTHOR]

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]

Seasonal patterns in thallus length, biomass, reproduction, total biomass m -2 and size structure were monitored in populations of Dictyota cervicornis and Stoechospermum polypodioides on a shallow reef flat in the southern Red Sea. These tropical reef flats are exposed to extreme temperatures of about 34°C in summer and to temperatures of about 25°C in winter. Both species showed peaks in length, biomass and reproduction in winter; macrothalli were absent in summer. Thallus length, biomass and the proportion of reproductive thalli showed a strong negative correlation with seawater temperature. Young thalli first appeared in November, following a drop in seawater temperature from about 33 to 31°C. Macroscopic thalli had disappeared in May, when temperatures had reached the same values as those at the start of the growth season (33°C). When reef substrata collected in summer were kept at sub-ambient temperatures (29-31°C), macroscopic thalli of D. cervicornis developed. Size structure varied over time, probably because of non-synchronous development and tissue loss among thalli. Reproduction was size-dependent. We conclude that D. cervicornis and S. polypodioides have highly seasonal patterns of growth and reproduction related to the seasonal variation in the environment, especially temperature. [ABSTRACT FROM AUTHOR]

Because tropical marine macrophytes experience high ultraviolet-B radiation (UVBR: 280–320 nm) it is assumed that they have high UV tolerance. This was investigated by examining the relative UV sensitivity of five Caribbean red macrophytes. Furthermore, the possibility of temperature dependence of UV effects was examined over a tropical temperature range. Algal fragments of intertidally occurring Gelidiopsis planicaulis (Taylor) Taylor, Wurdemannia miniata (Duby) Feldman and Hamel, and Hypnea spinella (Agardh) Kützing, and the subtidal species Bryothamnion triquetrum (Gmelin) Howe and Heterosiphonia gibbesii (Harvey) Falkenberg were repeatedly subjected to artificial UVBR and ultraviolet-A radiation (UVAR: 320–400 nm) at 22, 26 and 30°C, whereas exposure to photosynthetically active radiation (PAR) served as control. Growth rates, optimal quantum yield of PSII and accumulation of DNA damage were monitored for 10 days, whereas the relative abundance of the D1 reaction centre binding protein and the presence of UV absorbing compounds were investigated in some samples. UVAR and UVBR significantly depressed growth rates of all species. UVBR exposure caused accumulation of DNA damage and resulted in stronger growth reduction than UVAR. UVBR and UVAR caused a depression of optimal quantum yield and a lower D1 abundance. However, the former recovered fast and acclimated to the UV treatments. Some species produced UV absorbing compounds in response to UVAR. UV exposure caused less pronounced effects in intertidally occurring species than in subtidal species. UV effects on growth, the accumulation of DNA damage and UV induced depression of optimal quantum yield were independent of temperature in most species. We conclude that high UVBR in tropical regions may depress in situ growth rates of these intertidal and subtidal red macrophytes. [ABSTRACT FROM AUTHOR]

The sensitivity to UV-B radiation (UVBR: 280–315 nm) was tested for littoral (Palmaria palmata [L.] O. Kuntze, Chondrus crispus Stackhouse) and sublittoral (Phyllophora pseudoceranoides S. G. Gmelin, Rhodymenia pseudopalmata [Lamouroux] Silva, Phycodrys rubens [L.] Batt, Polyneura hilliae [Greville] Kylin) red macrophytes from Brittany, France. Algal fragments were subjected to daily repeated exposures of artificial UVBR that were realistic for springtime solar UVBR at the water surface in Brittany. Growth, DNA damage, photoinhibition, and UV-absorbing compounds were monitored during 2 weeks of PAR + UV-A radiation (UVAR) + UVBR, whereas PAR + UVAR and PAR treatments were used as controls. The littoral species showed a higher UV tolerance than the sublittoral species. After 2 weeks, growth of P. palmata and C. crispus was not significantly affected by UVBR, and DNA damage, measured as the number of cyclobutane-pyrimidine dimers per 106 nucleotides, was negligible. Photoinhibition, determined as the decline in optimal quantum yield, was low and decreased during the course of the experiment, coinciding with the production of UV-absorbing compounds in these species. In contrast, no UV-absorbing compounds were induced in the sublittoral species. Growth rates of P. pseudoceranoides and R. pseudopalmata were reduced by 40% compared with the PAR treatment. Additionally, constant levels of DNA damage and pronounced photoinhibition were observed after the UVBR treatments. Growth was completely halted for Phycodrys rubens and Polyneura hilliae, whereas DNA damage accumulated in the course of the experiment. Because Phycodrys rubens and Polyneura hilliae showed the same degree of photoinhibition as the other sublittoral species, it appears that the accumulation of DNA damage may have been responsible for the complete inhibition of growth. The results suggest an important role of DNA repair pathways in determining the UV sensitivity in red macrophytes. [ABSTRACT FROM AUTHOR]

The accumulation of DNA damage (thymine dimers and 6-4 photoproducts) induced by ultraviolet-B radiation was studied in Palmaria palmata (L.) O. Kuntze under different light and temperature conditions, using specific monoclonal antibodies and subsequent chemiluminescent detection. Both types of damage were repaired much faster under ultraviolet-A radiation (UVAR) plus photosynthetically active radiation (PAR) than in darkness, which indicates photoreactivating activity. At 12° C, all thymine dimers were repaired after 2 h irradiation with UVAR plus PAR, whereas 6-4 photoproducts were almost completely repaired after 4 h. After 19 h of darkness, almost complete repair of 6-4 photoproducts was found, and 67% of the thymine dimers were repaired. In a second set of experiments, repair of DNA damage under UVAR plus PAR was compared at three different temperatures (0, 12, and 25° C). Again, thymine dimers were repaired faster than 6-4 photoproducts at all three temperatures. At 0° C, significant repair of thymine dimers was found but not of 6-4 photoproducts. Significant repair of both thymine dimers and 6-4 photoproducts occurred at 12 and 25° C. Optimal repair efficiency was found at 25° C for thymine dimers but at 12° C for 6-4 photoproducts, which suggests that the two photorepair processes have different temperature characteristics. [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]

We examined the temperature tolerance of microscopic phases from geographically disjunct isolates of eight species or closely related, putatively conspecific taxa of temperature brown algae with disjunct distributions. Maximum within-taxon differences were small and ranged from 1.6° to 4.3°C. Desmarestia aculeate and Sphaerotrichia divaricata, both with northern hemisphere amphioceanic distributions, showed little or no significant intraspecific variation between the mean upper survival limits (USL) of Atlantic and Pacific strains (δUSL ≤ 1.4°C), which would agree with a relatively recent separation of the respective populations. Among the plants with bipolar distributions, there was likewise very little difference (δUSL 0-1.1°C) between northern and southern hemisphere strains in Striaria attenuata and in the species pair Desmarestia viridis/D. Wilii. In desmarestia ligulata, and in the species pairs Desmarestia firma/D. munda, Dictyosiphon foeniculaceus/D. hirsutus, and Scytothamnus australis/Scytothamnus sp., significant differences occurred, which indicate longer divergence times. δUSL in these cases ranged from 1.7° to 2.7°C, without overlap between strains from the northern and southern hemispheres. All species that passed the equator during cooler epochs had a USL of 26-27°C, at least in some geographical isolates. The NE Asian kelp Undaria pinnatifida, which passed the equator in recent times, had a USL of 29.6°C. We hypothesize that the mechanism of spreading in the amphipolar species studied was migration of vegetative microthalli. The more unlikely alternative hypothesis of continuous populations through the tropics during a cooler epoch would imply a drop in seawater temperatures to approximately 20°C in summer and 15°C in winter, which is not supported by paleoclimatic evidence. [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]