Light and temperature requirements for growth and reproduction in gametophytes of Ecklonia maxima (Alariaceae: Laminariales)

The morphological and reproductive development of gametophytes of Ecklonia maxima (Osbeck) Papenf. has been studied in vitro under a wide range of light and temperature conditions, and the results related to the natural environment over the range of the distribution of the species. Initial vegetative growth was light saturated at 20 E m^-2 s^-1, and maximal at 17.5° and 20°C. Most rapid egg production corresponded to low cell number of female gametophytes, and this process was light saturated at 60 E m^-2 s^-1, and optimised at 15° and 17.5°C. Cell number was also low at lower temperatures, with reduced fertility rates. Sub-saturating irradiances and supraoptimal temperatures caused females to become filamentous, producing many more cells, and reducing reproductive rates. The final egg production per female was, however, greater in these sub-optimal conditions, and this phenomenon is interpreted as an ecological adaptation which improves survival prospects in conditions prevailing at the fringes of the depth and geographical distribution of the species. The optimal, and maximum (22.5°C) temperatures for reproduction are far higher than those of northern hemisphere Laminarians. E. maxima is very much a warm temperate organism, and this could have implications for marine phytogeographical studies on the west coast of southern Africa.     

Response of Ecklonia radiata (Laminariales) to light at 15°C with reference to the field light budget at Goat Island Bay,New Zealand

Gametophytes of Ecklonia radiata (C.Ag.)J.Ag. grew in culture at 15°C under daily quantum doses ranging from 0.86 to 360 cE m^-2. Growth rates increased with quantum doses up to 40 cE m^-2 d^-1, then reproduction began and the relative growth constant declined while ovum release came earlier with increasing light up to about 100 cE m^-2 d^-1. Above 100 cE m^-2 d^-1 there were no consistent trends with increasing light, except that at the higher quantum doses, fertile female plants had fewer and larger cells and therefore fewer potential ova. Reproduction varied with daily quantum dose rather than with daylength. Given the same daily dose, plants grew fastest in low photon flux density, long daylength conditions. Gametophytes grown in the field developed at similar rates to those in culture. Gametophytes survived seven months of darkness at 10°C but died after one week of darkness at 20° to 23°C. Sunlight of 1 000 E m^-2 s^-1 was fatal to gametophytes and to sporophytes under 2 mm long after 10 to 15 min. Light budgets were prepared for plants growing at 7-and 15-m depths from 1976 to May 1980 in Goat Island Bay, New Zealand (Lat.36° 16S, Long. 174° 48E). Underwater light was measured under various environmental conditions. Relationships between transmission of light through the sea, data from diving visibility records and continuous surface meteorological records were studied. Approximations were made of the average percentage of surface light transmitted to 7 and 15 m over half-monthly periods. By applying these average transmittance values to the records of surface incident light, the average daily quantum doses were calculated. Light on open bottom in Goat Island Bay may sometimes be limiting for gametophyte reproduction in winter at 15-m depth. At depths less than 7 m, summer photon flux densities may reach damaging levels.     

Temperature tolerances of two southern African Ecklonia species (Alariaceae: Laminariales) and of hybrids between them

The temperature tolerances in culture of Ecklonia maxima (Osbeck) Papenf., the dominant kelp in the Benguela upwelling region on the west coast of southern Africa, and the smaller E. biruncinata (Bory) Papenf., growing on the warmer south coast, have been investigated. Vegetative growth and reproduction of gametophytes show very similar patterns in the two species, although temperature optima in E. biruncinata are consistently 2 ° to 3 °C higher than those of E. maxima. Reciprocal crosses between clonal female and male gametophytes of the two species produced healthy juvenile sporophytes, indistinguishable from the parent crosses. All parents and hybrids grew well over a wide range of temperatures (8 ° to 22°C), with E. biruncinata sporophytes again having slightly higher optima than E. maxima. Both reciprocal crosses exhibited optima intermediate between the parent crosses. The results are discussed with respect to the origins and evolution of Ecklonia species in the region.     

Effect of solar ultra-violet radiation on the kelp Ecklonia radiata

During spring and summer, 1982–1986, experiments were carried out near Marmion Reef, Western Australia. In summer, nearly 30% of the surface solar ultraviolet radiation (280 to 400 nm) penetrates offshore waters to 5 m depth. Experimental removal of the mature Ecklonia radiata kelp canopy in summer results in tissue damage, photopigment destruction, reduced growth, and low survivorship of subcanopy kelp sporophytes. These effects do not occur with canopy removal in winter. Laboratory experiments revealed that the UV component of radiation, rather than intense photosynthetically active radiation, was responsible for the inhibition of growth and photodamage. UV radiation probably affects survival of the settlement stages of E. radiata sporophytes, thus excluding them from otherwise suitable substrata in shallow waters. UV radiation is implicated in the reduction of canopy productivity in summer.     

In situ exudation of phlorotannins by the sublittoral kelp Ecklonia radiata

Exudation of phlorotannins (polyphenolics) was measured in situ from the sublittoral kelp Ecklonia radiata at two locations near Sydney, New South Wales, Australia during 1992–1993. Minimally disruptive techniques were used in which individual plants were enclosed within clear plastic bags in order to concentrate exudates. Rates of exudation from E. radiata were low relative to most previous studies, with a mean rate (averaged across four seasons and two sites) of 5.5 g g (dry wt)^-1 h^-1. Exudation was greatest in summer and least in winter at one site, but there were no seasonal differences at a second, more protected site. There was no measurable diurnal variation in exudation rates. Exudation after a period of heavy storms was not significantly different from exudation during calm weather, but severe physical damage to the kelp did increase exudation. Our results suggest that exudation of phlorotannins in temperate Australian waters may be less ecologically important than has been suggested for coastal systems in the Northern Hemisphere.     

Growth of juvenile Macrocystis pyrifera (Laminariales) in relation to environmental factors

Instantaneous relative growth rates, (d^-1), were measured for juveniles of the giant kelp Macrocystis pyrifera transplanted to study sites in Southern California kelp forests between 1978 and 1982. Growth rates ranged from negative values (indicating loss of tissue) to 0.03 (doubling of total frond length every 19 d). Multiple regression analysis of growth versus irradiation, temperature, nitrogen concentration and amount of fouling revealed that all these factors had significant effects, together accounting for about 50% of the total variance. Elevated irradiation and nitrogen levels had strongly stimulatory effects (tissue nitrogen may have been more critical than ambient nitrogen for growth), while high temperature and fouling had strongly inhibitory effects. Irradiation was the most important factor influencing growth in 6 of the 8 transplant experiments. During these 6 experiments, the compensating irradiation level (below which there was no growth) was between 0.4 and 0.7 E m^-2 d^-1, and saturating irradiation was between 2 and 3 E m^-2 d^-1. During two of the experiments, growth was apparently limited by extremely high temperatures or low nitrogen levels. Quantum irradiation levels in the kelp forest were generally between the compensation and saturation levels. However, irradiation levels occasionally dropped below the compensation point for several months. Irradiation was occasionally low enough to limit the distribution of juvenile kelp by inhibiting growth, especially in the deeper portions of the kelp forest and under dense canopies formed by adult plants.     

Growth of the kelp Ecklonia radiata near the northern limit of its range in Western Australia

The length, growth and survivorship of mature sporophytes of Ecklonia radiata (C.Ag.) J. Agardh were measured on two patch reefs within the lagoon of a high-latitude, coralreef atoll (Easter Group, Houtman Abrolhos; 28° to 29° S; 113°35 to 114°03E) for 1 yr (1982–1983). The sites differed in their proximity to the perimeter reef, but had similar regimes of temperature, light, nutrient concentration and water movement. Kelp length, growth rate and survivorship differed significantly between sites, although plant density was similar (less than l m^-2). At the site near the lagoon perimeter, the central lamina averaged 381 mm in length, grew at an annual mean rate of 1.28 mm d^-1, and 56% of tagged individuals had died after one year. The corresponding values for the site near the centre of the lagoon were: 257 mm, 0.75 mm d^-1 and 92%. Three other sites on the coastal limestone reefs near Perth (400 km to the south) were studied for various intervals over a 5 yr period (April 1979 to August 1984). The kelp from the low-latitude sites were smaller, grew more slowly, and suffered similar or greater mortality than their southern counterparts. Latitudinal comparisons were confounded by differences in kelp density between sites, but there is no evidence for density-dependent effects on the measured parameters across the range of natural densities observed. Growth rates at all sites were negatively correlated with ambient sea temperatures when these were above 20°C. There was no evidence of adaptation to the higher sea temperatures experienced at the Abrolhos, and temperature cannot be dismissed as a factor controlling the growth of the species near the northern limit of its distribution on the Western Australian coast. Other factors however must be involved in determining the latitudinal position of that limit.     

Development and phenology of Ecklonia radiata at two depths in Goat Island Bay,New Zealand

Ecklonia radiata (C. Ag.) J. Ag. growing in Goat Island Bay, New Zealand produced up to 6 kg dry weight of tissue m^-2 yr^-1 in dense populations at 7-m depth. Half this tissue and an unknown amount of exudates were sloughed or torn off. Tissue production at 15 m was 0.3 to 0.5 kg m^-2 yr^-1. At this depth the plants grew only half as fast as in shallow water and the population density was decreased. Approximately 20% by weight of tissue produced at 7 m and 10% of that at 15 m was reproductive tissue. At both depths the elongation rate and percentage of water in stipes varied with stipe size. Initial sorus formation was related to plant size and not to age. Seasonal fluctuations in growth rate, haptera formation, frond size and sporulation were delayed in plants in deeper water.     

Parthenogenesis,apogamy and apospory in Alaria crassifolia (Laminariales)

In cultures of Alaria crassifolia Kjellman, unfertilized eggs developed normally into haploid sporophytes which differentiated into a holdfast, stipe and blade with a midrib. The terminal cells of a male gametophyte grew apogamously into haploid sporophytes with narrow blades which lack the midrib. Further, diploid gametophytes were formed by apospory from vegetative cells of a diploid sporophyte. They were monoecious and their fertilized eggs developed into tetraploid sporophytes. Nuclear phases of the sporophytes and gametophytes concerned were confirmed by cytological observations.This work was supported by Grant No. 38803 from the Ministry of Education of Japan.     

Nitrogen uptake kinetics in three year-classes of Laminaria groenlandica (Laminariales: Phaeophyta)

Nitrate and ammonium uptake rates were measured for three year-classes of the perennial macrophyte Laminaria groenlandica Rosenvinge, collected from nitrogen-depleted waters in Barkley Sound, British Columbia, Canada, in summer 1981. A time course of uptake rate revealed that ammonium uptake was high during the first hour and then decreased for all three year-classes; the opposite pattern was exhibited for the time course of nitrate uptake rate. Nitrate uptake rate increased linearly with nitrate concentration up to the highest level tested (60 M). The nitrate uptake rate of first-year plants was three times higher than second- and third-year plants; ammonium uptake rates showed similar patterns to those for nitrate. The interaction between nitrate and ammonium was examined for first-year plants. Nitrate and ammonium were taken up simultaneously and uptake rates were identical and equal to uptake rates when only nitrate or ammonium was present in the medium. Therefore, first-year plants are able to take up twice as much inorganic nitrogen per unit time when both nitrate and ammonium are present. First-year plants showed significant diel periodicity in ammonium uptake rates, whereas second- and third-year plants showed no periodicity in nitrate or ammonium uptake rates.     

Reproduction,growth and photosynthesis of gametophytes of Laminaria saccharina grown in blue and red light

The induction of reproductive activity by blue light in female gametophytes of the brown alga Lamnaria saccharina has been investigated and related to other effects of red and blue light on these plants. Although germination of zoo-spores is slightly delayed in red light, female gametophytes grow at similar rates in blue and red light of the same quantum irradiance up to an age of 8 to 10 days, when plants in blue light begin to form eggs. The percentage of plants forming eggs is proportional to the total quanta of blue wavelengths received up to a saturating value of about 400 μE·cm^-2; a 50% response is induced by 200 μE·cm^-2. The action spectrum for the induction of fertility has a main peak at 430 to 450 nm, with two subsidiary peaks in the blue and one in the near-ultraviolet light, but the action spectrum for photosynthesis is quite different, with peaks in the red, green and blue regions. These results indicate that egg formation in female gametophytes occurs as a specific morphogenetic response to blue light, which is independent of photosynthesis and growth, and trial experiments with male gametophytes of L. saccharina and gametophytes of other species of Laminariales indicate that these plants react similarly.     

Seasonal variation in total and soluble tissue nitrogen of Pleurophycus gardneri (Phaeophyceae: Laminariales) in relation to environmental nitrate

Seasonal variations in tissue nitrogen (ethanol soluble nitrate and ninhydrin positive substances, as well as total nitrogen) of different thallus parts of Pleurophycus gardneri Setchell and Saunders were monitored simultaneously with ambient seawater nitrate from 1982 until 1984 in Bamfield, Vancouver Island, British Columbia, Canada. A trend of low, nearly zero levels in ambient nitrate typical for the area in late spring and early summer normally contrasts with average nitrate concentrations of 10 mol NO₃ ^- l^-1 in late fall and winter. Total nitrogen content was greater in the perennial thallus parts, stipe and holdfast than in the annual blade and peaked in fall and early winter. The longitudinal thallus distribution of nitrate revealed a distinct and significant concentration of nitrate in the haptera reaching at maximum 8% nitrate-N of the internal total nitrogen. Internal nitrate concentration ranged from 20 to 5 000 times the ambient nitrate concentration in the midrib, and from 40 to 3 100 times in the wing, while the range was greatest with 400 to 14 000 times in the haptera. P. gardneri contained at most about 7 mol NO₃ ^- g fresh wt^-1 in the blade, which corresponds to about 6% of total tissue nitrogen. Ninhydrin positive substances comprised the major portion of the soluble N pool in P. gardneri and showed a pronounced seasonality. Concentrations of ninhydrin positive substances ranged from 20 to 800 g N g fresh wt^-1 in the midrib and in the wing. In the stipe, ninhydrin positive substances varied from 180 to 2 200 g N g fresh wt^-1, and from 250 to 1 200 g N g fresh wt^-1 in the haptera. Evidence is given that (1) the perennial parts, stipe and haptera of P. gardneri contain the majority of nitrogen products independent of season and ontogenetic stage; (2) ninhydrin positive substances are the most abundant internal nitrogen constituents; (3) the low N values in the blade in summer suggest a nitrogen limited growth; and (4) nitrate may not be the predominant external nitrogen source.     

Response to light by trochophore larvae of Spirobranchus giganteus

Trochophore larvae of Spirobranchus giganteus (Pallas) respond positively to white light at levels of illumination from 1 to 2 168×10¹⁴ quanta cm^-2 s^-1. In this range the strength of the response is not correlated with irradiance level. The response is increased by dark adaptation. At low levels of irradiance (0.1-2.0×10¹⁴ quanta cm^-2 s^-1) larvae respond positively to blue (360-510 nm, max. 430 nm) and green (475–620 nm, max. 530 nm) light but not to wavelengths of 590 nm or over. The light response develops gradually during the 12 h following the appearance of the eyespot and is maintained throughout the remainder of the planktonic phase.     

Alleviation of nickel stress by halophilic bacteria in mungbean(Vigna radiata)

Mungbean is an important, short-duration legume crop with high nutritive value for poor families, where protein and micronutrient scarcity are most pervasive. In developing countries, like Pakistan, where mungbean is one of the greatest sources of protein for underprivileged people, salinity and metal stresses are drastically limiting its yield. Therefore, it is necessary to explore the ways for promoting the growth of mungbean under stressed conditions. This study provides the basis for the use of two previously isolated halophilic and nickel-resistant bacteria [Bacillus subtilis and Halomonas aquamarina(1)] in promoting the growth of mungbean plant under nickel-stressed environments. These bacterial strains were previously found to improve the growth of plants under salinity because of their good biofilm-forming abilities. We hypothesized that these two halophilic and nickel-resistant biofilm-forming bacteria can help the plants to grow under nickel-stressed environments by promoting soil aggregation as they were previously reported to resist salinity and nickel stress, as well as were found to promote plant growth under saline environments. The results revealed that under nickel stress, both bacteria promote plant growth by facilitating the formation of soil aggregates through an increase in their extra polymeric substance(EPS) production.     

Light and temperature demands for growth and reproduction of laminarian gametophytes in southern and central California

The gametophytes of 9 laminarian species (4 from southern California, and 5 from central California, USA) became fertile in the unicellular stage (female gametophytes) or in a few-celled stage (male gametophytes), when appropriate temperatures and a sufficiently high quantum irradiance in the blue part of the spectrum were supplied. Vegetative growth, leading to the formation of filamentous gametophytes was light-saturated at relatively low irradiances (4 W m^-2; equivalent to about 2 nE cm^-2 sec^-1 or an illuminance of 1000 lux), whereas 2 to 3 times this irradiance in continuous fluorescent cool white light was needed to induce the majority of the gametophytes to become fertile. An illuminance of 8300 lux did not inhibit the development of the gametophytes from southern Californian species. Egregia menziesii exhibited an exceptionally low quantum demand for induction of fertility. Gametophytes of species from central and southern California differed in regard to their temperature optimum for growth (12°C in the former, 17°C in the latter) and their upper temperature limit for reproduction (17°C in the former, 20°C in the latter).     

Autecology and clonal variability of the marine centric diatom Thalassiosira rotula (Bacillariophyceae) in response to light,temperature and salinity

The influence of 49 combinations of salinity (10–40 S, at 5 S intervals) and temperature (0°–30°C, at 5C° intervals) on the maximum daily division rate (K) and 18 combinations of light intensity (six levels) and temperature (5°, 15°, and 25°C) on photosynthesis, cell division, and chlorophyll a was examined using two clones of Thalassiosira rotula Meunier isolated from the upwelling area of Baja California (clone C8) and from Narragansett Bay, Rhode Islands (clone A8). Physiological differences appear to characterize these to clones with regard to their temperature tolerance (C8 5°–30°C, A8 0°–25°C), maximum growth rate (C8 K=2.9, A8 K=2.4), chlorophyll a content, and in the rates of growth and photosynthesis in response to light intensity and temperature. Optimum salinity for both clones (25–30 S) was generally independent of temperature, while chlorophyll a content decreased with temperature. T. rotula is a cosmopolitan paractic species; experimental studies indicate that it is eurythermal and moderately euryhaline. Comparison of five additional Narragansett Bay isolates of T. rotula reveal minimal spacial or temporal variability in genetically determined physiological characteristics within this local population.     

Interactions between light and temperature on the physiological ecology ofGracilaria tikvahiae (Gigartinales: Rhodophyta)

The biology and ecology of the Antarctic scallop Adamussium colbecki has been investigated on the west side of McMurdo Sound, Antarctica, principally at Explorers Cove, during the austral summer of 1981–1982. This conspicuous benthic invertebrate exhibits highest densities, 85 individuals m^-2, in shallow (4 to 6 m) water. Densities decrease to 20 m^-2 at 30 m. Biomass levels are highest in shallow water, 1 600 g wet wt m^-2. Provisional growth information suggests that 8 cm individuals are about 12 yr old. Mortality is apparently caused chiefly by a hyposaline lens of seawater, which forms under the sea ice during the summer melt; predators do not appear to be important. High biomass levels and a short generation time suggest that A. colbecki is an important species in a very productive community on the west side of McMurdo Sound. The shallow benthos of Explorers Cove is an important exception to the generalization that Antarctic ecosystems are dominated by indigestible filter-feeders.     

Interactions between light and temperature on the physiological ecology ofGracilaria tikvahiae (Gigartinales: Rhodophyta)

Main effects and interactions of light and temperature on rates of growth (), net photosynthesis (P_s), and dark respiration (R) of the red seaweedGracilaria tikvahiae were investigated in outdoor, nutrient-replete continuous-flow seawater culture chambers. Below 15°C,G. tikvahiae did not grow and between 15° and 30°C, both main effects and interactions of light and temperature on and P_s were significant, which explains the occurrence of this alga as a summer annual in its northern range. Temperature interacted with light (I) through its influence on the vs I and P_s vs I curves. The initial slope of the vs I curve, , the light saturation intensity, I_s, and maximum growth rate, _max, were all significantly lowerat 15°C compared to 20°, 25°, or 30°C. Maximum values of _max, the P_s:R ratio and the net photosynthesis:gross photosynthesis ratio (P_s:P_g) all occurred at 25°C, suggesting that this is the best temperature for growth ofG. tikvahiae. Values for P_max increased up to 30°C, indicating that the temperature for maximum growth and net photosynthesis are not the same forG. tikvahiae. Significant photoinhibition of growth and photosynthesis at full incident sunlight (I₀) occurred at 15°C but not at 20°, 25°, or 30°C. Steele's equation fit the 15°C vs I data best, whereas the hyperbolic tangent function fit the 20°, 25°, and 30°C data best. Main effects and interactionof light intensity and temperature on rates of R were also significant (P<0.001). R was highly intercorrelated with and P_s (0.86r0.94), indicating that R inG. tikvahiae is primarily regulated by growth rate and not temperatureper se. Environmental factors that regulate growth, such as light intensity, exert a great influence on R inG. tikvahiae.     

Effect of acclimatization to low temperature and reduced light on the response of reef corals to elevated temperature

This study tested the effects of acclimatization on the response of corals to elevated temperature, using juvenile massive Porites spp. and branching P. irregularis from Moorea (W149°50′, S17°30′). During April and May 2006, corals were acclimatized for 15 days to cool (25.7°C) or ambient (27.7°C) temperature, under shaded (352 μmol photons m⁻² s⁻¹) or ambient (554 μmol photons m⁻² s⁻¹) natural light, and then incubated for 7 days at ambient or high temperature (31.1°C), under ambient light (659 μmol photons m⁻² s⁻¹). The response to acclimatization was assessed as biomass, maximum dark-adapted quantum yield of PSII (F _v/F _m), and growth, and the effect of the subsequent treatment was assessed as F _v/F _m and growth. Relative to the controls (i.e., ambient temperature/ambient light), massive Porites spp. responded to acclimatization through increases in biomass under ambient temperature/shade, and low temperature/ambient light, whereas P. irregularis responded through reduced growth under ambient temperature/shade, and low temperature/ambient light. Acclimatization affected the response to thermal stress for massive Porites spp. (but not P. irregularis), with an interaction between the acclimatization and subsequent treatments for growth. This interaction resulted from a lessening of the negative effects of high temperature after acclimatizing to ambient temperature/shade, but an accentuation of the effect after acclimatizing to low temperature/shade. It is possible that changes in biomass for massive Porites spp. are important in modulating the response to high temperature, with the taxonomic variation in this effect potentially resulting from differences in morphology. These results demonstrate that corals can acclimatize during short exposures to downward excursions in temperature and light, which subsequently affects their response to thermal stress. Moreover, even con-generic taxa differ in this capacity, which could affect coral community structure. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

In-situ measurements of nitrogenous nutrient uptake by kelp (Ecklonia maxima) and phytoplankton in a nitrate-rich upwelling environment

Nitrogen uptake by the kelp Ecklonia maxima Osbeck and phytoplankton was examined under different conditions of nutrient availability in a kelp bed off the Cape of Good Hope by measuring nutrient depletion in large plastic bags by the kelp and ¹⁵N uptake by phytoplankton. E. maxima took up nitrate and ammonia, but not urea, and showed only a weak preference for reduced nitrogen. Phytoplankton absorbed all three forms of nitrogen available, with a preference for ammonia and urea. Ambient nitrate concentration exhibited a marked and rapid decrease with northerly winds and an increase in response to offshore southerly winds. Nitrogen uptake by E. maxima was linearly related to ambient concentration and did not saturate even at nitrate concentrations >20g-at N l^-1, resulting in a significantly higher tissue nitrogen content under upwelling conditions. Nitrate imported by upwelling was the chief source of nitrogen utilised within the kelp bed. Locally regenerated nitrogen (ammonia and urea) was calculated to contribute only ca 4% of total nitrogen uptake during upwelling and 30% during the relaxation or downwelling phase.