Regeneration and reproduction of Mazzaella cornucopiae (Rhodophyta, Gigartinaceae) after frond harvesting

The effects that different intensities of frond harvesting have on frond regeneration and subsequent production of reproductive structures were investigated for the red intertidal alga Mazzaella cornucopiae (Postels & Ruprecht) Hommersand from British Columbia, Canada. Harvesting was done by pruning fronds in the late spring (when stand biomass is highest) of 1993 at two intensities: total and partial collection of fronds, in this second case leaving all frond biomass less than 1 cm high in place. Holdfasts were not damaged. Total percent cover of thalli, frond density, mean frond length, and stand biomass for these experimental quadrats were statistically similar to values for control quadrats in the spring of 1994. These results suggest that one total harvest of fronds per year, done in late spring without damaging holdfasts, may give the highest sustainable yield of biomass. The effects of harvesting intensity on reproduction were variable and difficult to explain. Neither the appearance nor the abundance of cystocarpic fronds were affected by frond pruning, compared with control areas, but pruning did affect the appearance and the abundance of tetrasporic fronds. Partial pruning resulted in a longer presence of tetrasporic fronds, whereas total pruning was associated with their complete absence. Results are compared with those for the few other species of the Gigartinaceae for which experimental harvesting has been done. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interannual variation of the abundance of Mazzaella cornucopiae (Rhodophyta, Gigartinales) from Pacific Canada in relation to changes in abiotic variables

The seaweed Mazzaella cornucopiae (Postels & Ruprecht)Hommersand is common in rocky intertidal areas from Pacific Canada andis a potential economic resource. In both 1993 and 1994, the abundanceof M. cornucopiae from Prasiola Point, southern Barkley Sound, washigh in spring and summer and low in fall and winter. In 1995, however,the abundance in summer was unexpectedly low, and this trend deepenedin 1996. Correlations between the temporal changes of abundance and ofsome abiotic variables were done as a first approach to explaining thesechanges of abundance. The abiotic variables used were air temperature,sea surface temperature, wave height, all three measured on an oceanicbuoy close to Prasiola Point, and seawater salinity, determined for coastalwaters from northern Barkley Sound. These were the closest sites toPrasiola Point for which reliable abiotic data existed. None of thecorrelations were significant. Field observations done at Prasiola Pointsuggest that air temperatures reached higher values there than at theoceanic buoy. Together with irradiance, in situ air temperature may havehad an important role in the interannual differences of abundance througha higher physical stress on thalli, resulting in the high proportion ofbleached tissues observed in summer 1996. Future studies on thepopulation dynamics of M. cornucopiae should benefit fromquantifying these variables in situ.     

Summer biomass of a population of Iridaea cordata (Gigartinaceae,Rhodophyta) from Antarctica

Results of a seasonal study on biomass in an infralittoral population of Iridaea cordata from Terra Nova Bay (Ross Sea, Antarctica) are reported. Thalli were collected during the IX Italian Antarctic Expedition (austral summer 1993–94). The population studied is that living at depths of 4 to 6 m, where the highest density of plants occurred. The highest value of biomass (wet weight 3440 g m^–2) was found at the beginning of summer. In that period 72.5% of biomass was from 128 specimens belonging to weight classes 8 (>16 to 32 g) to 10 (>64 g), corresponding to 13.4% of the population in numbers. Small (<1 g) and medium (1 to 8 g) specimens provided the remaining biomass of 5% and 22.5%, respectively. During the month of January, the number of heavy specimens decreased. At the end of that month biomass reached a minimum of 2225 g m^–2. In February the biomass increased to 3169 g m ^–2, 72% of which was from 120 specimens belonging to weight classes 7 (>8 to 16 g) to 9 (>32 to 64 g), which numerically represented 18.5% of the population. Data showed that biomass depended mainly on the presence of large heavy specimens, even though they were always few in number. Moreover, the occurrence of such large thalli at the beginning of summer suggests that Iridaea cordata continues to grow during the long antarctic winter.     

A discrete-time logistic model of frond dynamics for Mazzaella parksii (Rhodophyta, Gigartinales)

Mathematical modelling is useful in population ecology and resource management. Logistic models have traditionally been applied to unitary organisms, but it is unclear whether they could be used at the frond (ramet) level for clonal seaweeds. This study shows that frond dynamics for the clonal seaweed Mazzaella parksii (=M. cornucopiae) can be described by a discrete-time logistic model. The model is realistic in that it includes density-dependence, which was previously demonstrated experimentally for this species, and only necessitates data on frond density measured at discrete time intervals. This may constitute a useful tool for the management of clonal seaweeds of economic importance that occur in dense stands. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phenology of Gigartina skottsbergii (Gigartinaceae,Rhodophyta) in Ancud Bay,southern Chile

This study reports the variations in biomass and reproductive phenology in a natural bed of Gigartina skottsbergii over a period of a year and correlates these variations with the abiotic factors solar radiation, number of daylight hours, water temperature and salinity. The results obtained show an annual production cycle with maximum biomass values in spring-summer, correlated with high solar radiation and to a lesser extent with salinity. Sexual reproduction was maximum in autumn-winter, correlated with low temperature and short-day conditions. The population showed a large gametophytic dominance according to size and biomass, which suggests that there is not ecological equivalence between the life history phases of the species. Finally, based on the results, a restriction of harvesting to spring-summer is suggested.     

Gametophyte-sporophyte coalescence in populations of the intertidal carrageenophyte <Emphasis Type="Italic">Mazzaella laminarioides</Emphasis> (Rhodophyta)

Mazzaella laminarioides has consistently been reported as a typical coalescent/clump species with a triphasic life history of the Polysiphonia-type in which the haploid gametophyte is the predominant phase with respect to the diploid sporophyte. Preliminary observations of intertidal populations revealed that, in some instances, cystocarpic and tetrasporic fronds emerged from the same clump (G-T clumps), implying a coalescent process of haploid and diploid thalli by fusion of their corresponding adjacent basal holdfasts. Population surveys at three sites in Coliumo Bay, central Chile, were carried out to characterize frond demography as well as to asses the frequency of gametophyte-tetrasporophyte (G-T) coalescence. Visual and resorcinol methods were employed to determine the phases of the fronds collected over central transects of 15 randomly sampled clumps. Coalescence of G-T clumps was infrequent, with gametophytes dominating over tetrasporophyte thalli.     

Population studies and carrageenan properties of Chondracanthus teedei var. lusitanicus (Gigartinaceae, Rhodophyta)

Features of an intertidal population of Chondracanthus teedei var. lusitanicus, which occurs in sandy basins on rocky shores of part of the Portuguese coast (Buarcos, Figueira da Foz), were studied over one year. Biomass and plant size showed a small increase in early spring (April), a marked increase in early summer (June/July) and were at a minimum in late summer. There was generally more tetrasporophytes (4–32.5%) than female gametophytes (3–29%), which contrasts with other geographical regions where C. teedei populations have been studied, such as Brazil and France. However, non-fructified thalli predominated throughout the year. Phycocolloid extracts were compared for the various stages using spectroscopic methods (FTIR, FT-Raman, ¹H- and ¹³C-NMR). These showed a hybrid carrageenan belonging to the lambda family in the tetrasporophyte and a hybrid kappa-iota-mu-nu carrageenan in the female gametophyte and non-fructified thalli. The average phycocolloid content was 34.9% dry weight, with a maximum of 43.6% in July. The combination of high available biomass and phycocolloid content makes this species a potentially important source of kappa/iota hybrid carrageenan in Portugal additional to the traditionally harvested carrageenophytes.     

Population studies on a South African carrageenophyte: Iridaea capensis (Gigartinaceae,Rhodophyta)

An intertidal population of Iridaea capensis in the south-western Cape Province of South Africa has been studied in detail for a year. The species is generally restricted to sand-inundated rocky shores, which appears not to be the case for Iridaea species in the Pacific. In early winter (June) biomass, plant density and plant size were at a minimum. A small increase in these parameters occurred in August, but there was a massive increase in plant numbers and biomass in October. The largest plants were recorded in summer (February). The population was over 70% sporophytes in April, but switched to almost 80% gametophytes following heavy recruitment between August and October, and remained significantly gametophyte-dominated through April of the following year. Carrageenan levels were high (ca 42% of dry weight) in late winter-spring, and lowest (ca 30–35%) in summer-autumn. Strong offshore wind conditions in early summer caused a reduction in biomass, and it is hypothesized that the associated upwelling of nutrient rich water may be implicated in the lower carrageenan levels at this time.     

Reliability of the resorcinol method for identifying isomorphic phases in the Gigartinaceae (Rhodophyta)

The Gigartinaceae are economically important because the carrageenans in this family are used for a variety of purposes including food stabilizers, food substitutes, pharmaceutical applications and cosmetics. The resorcinol method takes advantage of the different carrageenans found in life history phases in this family to identify nonreproductive phases, and consequently, a better understanding of the biology of this economically important family is possible. This study investigates sources of variability that could affect the accuracy of the resorcinol method in identifying phases within the Gigartinaceae. Vegetative disks of Iridaea splendens from different areas of the blade and disks containing reproductive structures all reacted consistently to the resorcinol reagent. The minimum size and testing conditions required to reliably identify phases at the germling stage of I. splendens were determined. Phases of I. splendens cannot be identified if blades are stored in 3% formaldehyde in seawater. Phases of I. splendens, I. lineare, I. heterocarpa, Rhodoglossum californicum and R. affine can be identified reliably at different times of the year. Manipulations of the resorcinol method improved its accuracy in identifying phases of Iridaea cornucopiae and Gigartina exasperata but the high percent of G. exasperata misidentified demonstrates that it cannot be assumed that the current resorcinol method works for all taxa in the Gigartinaceae.     

Relationship between cover of Chondrus crispus (Gigartinales,Rhodophyta) and Phymatolithon (Corallinales,Rhodophyta) on friable rock substrata

Field observations in sublittoral Prince Edward Island, Canada, indicated that on a friable sandstone substratum Chondrus crispus was more commonly associated with Phymatolithon sp. than with bare rock. Thus, a substantial proportion of the population of Irish moss along the coast of Prince Edward Island occurs on this encrusting coralline. These observation may be explained on the basis of the relative stability of the substratum in contrast to other studies in which sloughing of epithallial cells by species of both Phymatolithon and Lithothamnium has been reported to limit epiphytism by fleshy macrophytes.Issued as NRCC 31426.     

Annual growth rate of the calcareous red alga Lithothamnion corallioides (Corallinales,Rhodophyta) in the Bay of Brest,France

Lithothamnion corallioides Crouan et Crouan (Rhodophyta, Corallinales) is the main constituent of the maerl beds of the Bay of Brest (Atlantic coast of western Brittany). Its growth rate was measured monthly in situ during one year. Growth rates were obtained by an adaptation of the buoyant weight technique. The highest daily growth rate was observed in July and reached 0.26 % d^–1 (S.D. = 0.06), when expressed as the increase of calcium carbonate weight. The average daily growth rate was 0.12% d^–1 (S.D. = 0.04) for a period of 275 days (summer and autumn 1988, winter 1989). Using this preliminary data, the calcium carbonate accretion rate can be estimated provisionally: 876 g m^–2 year^–1, a rate much lower than that of tropical reef coralline algae, but higher than that of Lithophyllum incrustans, the well known temperate European reef-builder.     

Demographic models to simulate the stable ratio between ecologically similar gametophytes and tetrasporophytes in populations of the Gigartinaceae (Rhodophyta)

In populations of the Gigartinaceae (Rhodophyta), gametophytes often predominate numerically over tetrasporophytes. Several hypotheses have been proposed to explain this dominance, based on the usually implicit assumption that the stable ratio between gametophytes and tetrasporophytes (G:T ratio) should be 1 if both reproductive phases are ecologically similar. We developed demographic models to test this assumption, for which we considered that both phases are ecologically similar. Defining ecologic similarity for most demographic rates is relatively straightforward, except for rates of spore output. The first set of models considered the same spore output per thallus of both phases as representing ecologic similarity. Model iterations led to stable G:T ratios of 1 for triennial and for perennial thalli, regardless of the initial G:T ratio, but not for annual thalli with initial G:T ratios different from 1. However, equal spore output may not represent ecologic similarity, due to size differences between carpospores and tetraspores. The second set of models considered the lowest possible spore output for each phase, according to the life history of this family: only one carposporangium, with one carpospore, is produced from every two gametophytes and only one tetrasporangium, with four tetraspores, is produced by every tetrasporophyte. Model iterations led to stable G:T ratios of 2.8 for most cases, a ratio of 1 being obtained only every 2 years for annual thalli with an initial G:T ratio of 1. Increasing absolute spore output, without altering the relative output between phases and incorporating density-independent mortality through a matrix model, given the same mortality rate for both phases, did not modify results. We suggest that the combination of both modeling and field research may uncover more rapidly than otherwise the most relevant ecologic differences between phases, if any, that underlie the G:T ratio observed for a given population.     

Seasonal variations in sterol composition of Delesseria sanguinea (Ceramiales,Rhodophyta)

On Normandy coasts, the red alga Delesseria sanguinea perennates by its stipe; fronds grow in January and disappear in June. Seasonal variations in sterol composition in relation to the biology of D. sanguinea are reported. Sterols in cellular membranes are free or conjugated by esterification with fatty acids, heterosides or lipid complexes like phospholipids. Both kinds of sterols were analyzed by GC-MS. The major sterol (80%) found in fronds was cholesterol whereas in stipes, cholesterol was also the major sterol in spring, but in September, an important reduction in cholesterol yield was noted with proportional increase in sitosterol content. It appears that cholesterol is synthesized in fronds in spring, then transferred to the stipe, which loses an important amount of cholesterol with loss of the blades.     

Chondrus crispus (Gigartinaceae,Rhodophyta) tank cultivation: optimizing carbon input by a fixed pH and use of a salt water well

The injection of exogenous carbon into intensively cultivated algal tanks is necessary to insure a maximum growth rate by stabilizing the dissolved inorganic carbon (DIC) pool, but represents the major part of the cultivation cost (ca. 73%). This study was conducted in paddle-wheel tanks ranging in size from 260 m² to 1000 m². Additional carbon was provided by carbon dioxide mixed into the incoming sea water through a tubular reactor. Production vs pH was analysed on 120 growth measurements covering two years of continuous cultivation. Whereas production peaked at pH 8.0–8.2, the economic optimum for pH regulation was in the range 8.4–8.5, where CO₂ injection was greatly reduced (–29%) for only a slight decrease in production (–4%). Expressed as a function of pH level, the specific carbon injection (g c gdw^–1 of Chondrus produced) showed an inverse exponential relationship, whereas gross photoconversion ratio (gdw mol photons^–1) varied according to a second degree equation with a low amplitude. The photoconversion ratio was not improved when the culture was maintained at a DIC concentration higher than the natural equilibrium (0.64 ± 0.11 gdw mol photons^–1 at 2.35 mM and 0.65 ± 0.15 gdw mol photons^–1 at 3.19 MM).A complementary source of carbon was found in underground salt water with a high and stable DIC concentration (10.15 ± 0.25 mmole Cl^–1). The mixing of the well water with natural sea water allowed another economy of CO₂ (–20% at pH 8.5) and nutrients (–12%), the total unitary cost of production being cut by about 17%.     

Chemotaxonomy of New Zealand red algae in the family Gigartinaceae (Rhodophyta) based on galactan structures from the tetrasporophyte life-stage

The identification of the polysaccharides from tetrasporophytic plants of nine endemic New Zealand species belonging to the Gigartinaceae, ‘Gigartina’ ancistroclada, ‘G.’ grandifida, Gigartina dilatata, G. divaricata, G. macrocarpa, G. marginifera, G. pachymenioides, G. sp. ‘Lindauer 164’ and Sarcothalia livida using infra-red spectroscopy in conjunction with constituent sugar and glycosyl linkage/substitution analysis is reported. All nine species contain galactans with structures consistent with λ-type carrageenans. Differences in the structures of the galactans in these and a further six previously studied species indicate chemotaxonomically distinct groupings that correspond to Sarcothalia, ‘Sarcothalia’ and Gigartina genera plus some outliers. These distinct, chemotaxonomic groupings are aligned to those determined by rbcL sequence analysis reported in the literature.     

Some effects of plant growth regulators on tissue cultures of the marine red alga Agardhiella subulata (Gigartinales,Rhodophyta)

We examined whether auxins and cytokinins, either singly or in combination, stimulate cell division in tissue cultures of a red seaweed. Our experimental model consisted of filamentous and callus-like growths that developed from cross-sectional discs cut from young branches of Agardhiella subulata. Plant growth regulators were added to the medium to give combinations of an auxin with a cytokinin over a range of concentrations (1 µg L^–1 –10 mg L^–1). Several mixtures of auxins and cytokinins, as well as some single auxins, cytokinins and phenolics, stimulated cell division and growth in the tissue cultures beyond that of controls. The treatments that were effective included: phenylacetic acid/zeatin; phenylacetic acid/6-benzylaminopurine; -naphthaleneacetic acid/zeatin; 2,4,5-trichlorophenoxyacetic acid/6-benzylaminopurine; and indoleacetic acid/kinetin. High concentrations of cytokinins (i.e. 10 mg L^–1) inhibited the regeneration of plants in some of the cell cultures. These results provide further evidence that growth regulators can be used for the tissue culture of seaweeds and for the study of developmental phenomena in these plants.     

The effect of localised eutrophication on competition between Ulva lactuca (Ulvaceae,Chlorophyta) and a commercial resource of Gracilaria verrucosa (Gracilariaceae,Rhodophyta)

In spring (August) 1993 a bloom of Ulva lactuca appeared for the first time in Saldanha Bay, South Africa, and persisted through summer. Ulva wash-ups contaminated the beach and part of the commercial Gracilaria beach-cast had to be discarded. The biomass and distribution of Gracilaria and Ulva are described in relation to the seasonal water chemistry of the bay. Gracilaria survives in deeper water in summer by the pulsing of nutrients on an approximately 6-day cycle of movement of the thermocline that separates nutrient-rich bottom water from warm oligotrophic surface water. Ammonium-rich fish-factory discharge into this surface layer in a sector of the bay provided localised conditions for Ulva to out-compete Gracilaria at depths of 2–5m, demonstrating the powerful disruptive effect of eutrophication in this strongly stratified system.