Attachment strength differs amongst life‐history stages of an intertidal,isomorphic red alga

Complex haploid‐diploid life cycles amongst marine organisms may be maintained by ecological differences in life‐history phases. For red algal species within the Gigartinaceae, such differences may be driven, in part, by different cell wall composition and resultant biomechanical strengths of haploid and diploid phases. A field experiment tested the attachment strengths of gametophytes and tetrasporophytes of the isomorphic red alga, Chondrus verrucosus (with comparisons of fertile and vegetative fronds, with and without natural tissue damage across three wave‐exposed sites). Seventy‐nine percent of all fronds broke at the stipe‐holdfast junction. There were significant differences in attachment strength (break force and break stress), but not gross morphology (frond length, number of branch axes, wet weight and cross‐sectional area of fronds that dislodged at the stipe‐holdfast junction) of life‐history phases, with tetrasporophytes exhibiting weaker tissue strength and attachment, and therefore greater susceptibility to dislodgement by waves. However, fertility and tissue damage did not consistently influence dislodgement in pull‐to‐break tests simulating the effects of single waves. The ecological and evolutionary consequences of greater susceptibility to dislodgement of tetrasporophytes (relative to gametophytes) warrant further investigation.     

Iridescence: a useful criterion to sort gametophytes from sporophytes in the red algaChondrus crispus

Carrageenan analyses ofChondrus crispus Stackhouse from Brittany, France, showed that the iridescent fronds always were kappa-carrageenan dominant and that the non-iridescent ones were lambda-carrageenan dominant, whatever their sizes and their vegetative or reproductive stages. Evidence is presented that the blue iridescence is independent of both the morphology of the fronds and their ecological situation (shelter, exposure). It is suggested that iridescence might be used to sort rapidly the kappa-carrageenan containingChondrus crispus (gametophytes) from the lambda-carrageenan containing ones (tetrasporophytes).     

IS THERE AN ECOPHYSIOLOGICAL EXPLANATION FOR THE GAMETOPHYTE–TETRASPOROPHYTE RATIO IN GELIDIUM SESQUIPEDALE (RHODOPHYTA)?1

In the fall, when 61% of the fronds of the Gelidium sesquipedale (Clem.) Born. et Thur. population located in Albufeira (southern Portugal) were reproductive, about 90% of these fronds were tetrasporophytes, whereas an equal percentage of female and male gametophytes was found (5%). The comparison of physiological performances of the reproductive phases (males, females and tetrasporophytes) did not reveal a physiological advantage of tetrasporic fronds. There were no significant differences either in the photosynthesis, nitrogen uptake, nitrate reductase activity, or biochemical composition of adult fronds. On the other hand, vegetative recruitment and spore production in the laboratory were significantly different. The re‐attachment to calcareous substrate and the subsequent rhizoidal growth were faster in tetrasporophytes. Particular levels of temperature, rather than irradiance, had an important effect on the phase differences in the spore release, attachment, and germination rates. Significant results were the higher release of carpospores at all irradiances at 17°C, and the higher attachment percentage of carpospores at 13°C versus tetraspores. Under higher temperatures (21°C), tetraspores showed higher attachment rates while carpospores germinated more. G. sesquipedale cystocarps released carpospores for 2 months, while tetrasporangia stopped shedding tetraspores after 1 month, resulting in a 3‐fold higher production of carpospores than tetraspores. Results showed that vegetative and spore recruitment may explain the low gametophyte–tetrasporophyte ratio of the studied population of G. sesquipedale as opposed to the physiological performance of phases.     

The demography of fronds of Chondrus crispus Stackhouse

A demographic analysis was done of an intertidal stand of Chondrus crispus Stackhouse at Pubnico Point, Nova Scotia. The distribution of gametophytic and tetrasporophytic fronds was assessed. Fronds were placed in one of four size-classes. Size-specific measurements for fronds are presented. Gametophytic fronds dominated the stand. Fronds in Size-Class 2 exhibited high survivorship. Survivorship fell sharply when fronds entered Size-Class 3 and Size-Class 4. Fronds became fertile and highly branched when in the third and fourth size-classes. It is suggested that these two factors contribute to the higher mortality rates of such individuals.Monthly spore release rates·m^?2 for gametophytes and tetrasporophytes were measured. The annual release rate of carpospores exceeded the annual release rate of tetraspores by a ratio of 4.7:1. Rates did not fall below 10⁶ spores released·m^?2·month^?1 for either phase.     

Differential ecological responses to environmental stress in the life history phases of the isomorphic red alga Gracilaria chilensis (Rhodophyta)

In order to better understand the alternation of generations that characterizes haploid–diploid life cycles, we assessed the existence of ecological differences between the two phases (haploid gametophyte and diploid tetrasporophyte) in Gracilaria chilensis, a rhodophyte with a typical Polysiphonia-type life cycle. We investigated the effect of light intensity and salinity on viability and growth of both phases at different ontogenetic stages: juveniles and adults. In our study, the survival of juvenile gametophytes (n) was higher than the survival of juvenile tetrasporophytes (2n) despite culture conditions; however, low salinity had greater effect on carpospores (2n) than on tetraspores (n). On the other hand, a complex interaction between salinity and light intensity within each life history phase generated observed differences between juvenile growth rates. Low light was shown to trigger early onset of alteration of the holdfast growing pattern. In addition, adult tetrasporophytes showed, despite the conditions, a faster vegetative growth than female and male gametophytes. These differences between phases could have led to the complete dominance of tetrasporophyte fragments of fronds observed in G. chilensis farms. We hypothesize that Chilean fishers could have unknowingly selected for tetrasporophyte thalli during domestication of the species, thus enhancing the natural trend of tetrasporophytes dominance already present in estuarine natural populations of free-floating plants.     

A simulation model for an Iridaea splendens (Gigartinales,Rhodophyta) population in Vancouver,Canada

Populations of Iridaea splendens at Brockton Point, Stanley Park, Vancouver, Canada were observed to alternate in dominance between the gametophytic phase in summer and tetrasporophytic phase in winter. The mechanism regulating this alternation is not clear. Using a matrix projection model to simulate population growth, we show that this alternation is possible if there are differential survival and recruitment rates of the two phases in summer and winter. Sensitivity and elasticity analyses indicate the relative importance of perennation vs. recruitment. Recruitment from tetrasporophytes and from gametophytes both contribute about 25% to the population growth. Perennation among gametophytes is more important than among tetrasporophytes. The implication of this is that if this population is to be harvested, more tetrasporophytes can be harvested than gametophytes without resulting in the depletion of the resource. This is simulated in the matrix model by comparing the relative effects on population growth of increasing the mortality rate of the perennation phase of tetrasporophyte and gametophyte by 50 to 75%, and increasing recruitment rate in either phase, from summer to winter or from winter to summer.Dedicated to Dr T. Bisalputra of the University of British Columbia on the occasion of his retirement.     

GENETICS OF GRACILARIA TIKVAHIAE (RHODOPHYCEAE). X. STUDIES ON A BISEXUAL CLONE12

A male done of the red alga Gracilaria tikvahiae McLachlan spontaneously produced a bisexual frond which remained bisexual in subsequent subcultures. Both male and female components of bisexual fronds were functional; however, some unusual results were obtained in crosses. When bisexual fronds were crossed with a normal haploid male, the resulting carpospores all developed into diploid male gametophytes. When bisexual plants were self fertilized, all the carpospores yielded diploid bisexual gametophytes. Only when bisexual plants were crossed to normal haploid females, did carpospores develop into diploid tetrasporophytes as they normally do. The F₁ gametophyte generation obtained from these tetrasporophytes, however, included not only females and males but also bisexual plants, in a 2:1:1 ratio. These results are consistent with the interpretation that bisexual plants have a recessive mutation of a gene other than the primary sex determining locus, and that this mutation is expressed only in male plants. It is suggested that the altered gene may ordinarily have a regulatory function in the maintenance of the dioecious condition.     

Size structure and dynamics of an invasive population of lineage 2 of Asparagopsis taxiformis (Florideophyceae) in the Alboran Sea

In this study, we present basic population data of the red macroalga Asparagopsis taxiformis, widely recognized as invasive in the Mediterranean Sea. A 13‐month field study was carried out on a population located in southern Spain, addressing its phenology, population dynamics and demography. We further tested whether biomass variations were related to environmental variables at the study site. Gametophytes were present year‐round while tetrasporophytes were only found in spring and summer. Recruitment capacity and vegetative growth of the gametophytes are discussed as important modulators for the population structure and enhancers of its persistence. Thallus size‐time histograms revealed a high prevalence of small shoots that showed high mortality that was not related to self‐thinning. Biomass of A. taxiformis was higher from March to July. Vegetative growth was the main way the gametophyte population was maintained, although the presence of tetrasporophytes and fertile gametophytes in the field confirms that sexual reproduction also occurs. Its continuous and high recruitment, in terms of the number of smallest shoots, makes this southern population of A. taxiformis a source of future invasive populations due to the intensive maritime traffic in the region.     

FOURIER TRANSFORM INFRARED MICROSPECTROSCOPY AS A TOOL TO IDENTIFY MACROALGAL PROPAGULES1

Understanding of macroalgal dispersal has been hindered by the difficulty in identifying propagules. Different carrageenans typically occur in gametophytes and tetrasporophytes of the red algal family Gigartinaceae, and we may expect that carpospores and tetraspores also differ in composition of carrageenans. Using Fourier transform infrared (FT‐IR) microspectroscopy, we tested the model that differences in carrageenans and other cellular constituents between nuclear phases should allow us to discriminate carpospores and tetraspores of Chondrus verrucosus Mikami. Spectral data suggest that carposporophytes isolated from the pericarp and female gametophytes contained κ‐carrageenan, whereas tetrasporophytes contained λ‐carrageenan. However, both carpospores and tetraspores exhibited absorbances in wave bands characteristic of κ‐, ι‐, and λ‐carrageenans. Carpospores contained more proteins and may be more photosynthetically active than tetraspores, which contained more lipid reserves. We draw analogies to planktotrophic and lecithotrophic larvae. These differences in cellular chemistry allowed reliable discrimination of spores, but pretreatment of spectral data affected the accuracy of classification. The best classification of spores was achieved with extended multiplicative signal correction (EMSC) pretreatment using partial least squares discrimination analysis, with correct classification of 86% of carpospores and 83% of tetraspores. Classification may be further improved by using synchrotron FT‐IR microspectroscopy because of its inherently higher signal‐to‐noise ratio compared with microspectroscopy using conventional sources of IR. This study demonstrates that FT‐IR microspectroscopy and bioinformatics are useful tools to advance our understanding of algal dispersal ecology through discrimination of morphologically similar propagules both within and potentially between species.     

Population modelling of Gelidium sesquipedale (Rhodophyta, Gelidiales)

A matrix population model of Gelidium sesquipedale, a commercial agarophyte from the Northeast Atlantic, was developed based on demographic data obtained during two years in a commercial stand of Cape Espichel, Portugal. G. sesquipedale individuals were classified into categories such as life cycle phase, spores, juveniles and adult frond size, because the species vital rates, fecundity, fertility, survival, growth and breakage depend on them. We also exemplify the use of a user-friendly modelling software, Stella, to develop a structured-population model. This is the first time this software has been used to model the demography of seaweed populations. The Stella model developed here behaved very similarly to the matrix model, because of its particular construction, which causes the forcing functions to be discrete rather than continuous. The relative importance of spore recruitment and vegetative growth of new fronds in both population growth and population structure was investigated. Elasticity analysis suggests that vegetative recruitment is the most important demographic parameter controlling population growth together with survival and transitions between juveniles (1–6 cm fronds) and class 1 fronds (6–9 cm fronds). On the other hand, sexual reproduction may, by itself, efficiently control the relative proportion of gametophytes and tetrasporophytes in the population, even though its contribution to recruitment is extremely small. A 40% difference in the growth rates of gametophyte and tetrasporophyte submatrices resulted from natural differences in spore recruitment rates. This revised version was published online in June 2006 with corrections to the Cover Date.     

Spatial and temporal variations of Chondrus crispus (Gigartinaceae, Rhodophyta) carrageenan content in natural populations from Galicia (NW Spain)

Qualitative and quantitative differences in carrageenan composition of gametophytes and tetrasporophytes of Chondrus crispus were observed in this study. Carrageenans in gametophytes belong to the kappa family (κ-, ι-, ν- and μ-carrageenan). The dominant fractions were κ- and ι-carrageenan (more than 50% of the total carrageenans). In tetrasporophytes, the presence of λ-carrageenan was confirmed. Carrageenan content in gametophytes (37.4?±?1.68% DW) was higher than in tetrasporophytes (29.13?±?0.76% DW). Spatial and temporal variation in carrageenan content in both life cycle phases appears to be related mainly to seawater and air temperatures, insolation, water movement and desiccation. The highest values of carrageenan content were recorded in those localities where higher values of precipitation, wind speed or water movement occurred. A bimodal temporal pattern on carrageenan content was observed. Fronds showed a high carrageenan content in spring and autumn. During these seasons, the content was over 40% in gametophytes and 30% in the tetrasporophytes. In summer and winter, these values down in both life cycle phases below 30%. In general the highest carrageenan contents were related to highest seawater temperatures. On the contrary, high air temperature and high insolation appeared to be unfavourable for carrageenan production. GLM models were obtained to predict carrageenan production from natural C. crispus populations, along Galician coast.     

Evidence of reproductive cost in the triphasic life history of the red alga Gracilaria chilensis (Gracilariales,Rhodophyta)

The extent of changes in basic physiological and demographic traits associated with reproduction was investigated in the highly cultivated haploid–diploid red alga, Gracilaria chilensis. Sixty individuals bearing vegetative and reproductive fronds collected in the natural population of Niebla (39°52′?S, 73°23′?W), in Chile, were cultivated under controlled culture conditions. Our results demonstrated that vegetative fronds have a higher survival rate and a better growth rate than reproductive ones irrespective of the type of individual analyzed (male gametophyte, female gametophyte, and tetrasporophyte). Moreover, the reproductive fronds clearly showed a decrease in photosynthetic activity compared to non-reproductive ones. In males and tetrasporophytes, the photosynthetic reduction in reproductive individuals could be explained by a physical effect of reproductive structure development as well as spores release, disrupting the continuity of the photosynthetic cortical tissues. Translocation of photoassimilates from nearby vegetative tissue or the previous accumulation of photosynthetic products seems to be a prerequisite for reproductive structure development in this species. Altogether, these results document for the first time in G. chilensis that reproduction has a strong physiological effect on male, female, and tetrasporophyte fronds. This trade-off between reproduction, growth, and survival suggest the existence of reproductive costs in the life history of G. chilensis.     

PHOTOSYNTHETIC RESPONSES TO LIGHT AND TEMPERATURE OF THE HETEROMORPHIC MARINE ALGA MASTOCARPUS PAPILLATUS (RHODOPHYTA)1

Physiological differentiation of the heteromorphic life-history phases of the red alga Mastocarpus papillatus (C. Agardh) Kützing was assessed. Photosynthetic responses to light and temperature of the erect, foliose gametophyte were compared to those of the crustose tetrasporophyte. Plants of both phases were collected from four locations on the Pacific coast of Baja California, Mexico, and California, USA, between 32–4l° N latitude. Within each location, the chlorophyll-specific, light-saturated photosynthetic rates of gametophytes were generally five times greater than those of tetrasporophytes. Initial slopes of photosynthesis: irradiance curves were greater for gametophytes than for tetrasporophytes. The crust and the blade from each location were similar with respect to dark respiration rates. For tetrasporophytes from all locations, the photosynthetic temperature optima were between 12–15° C. The photosynthetic temperature optima for gametophytes ranged from 15–17° C for plants from Trinidad Head (41° N) to 22–25° C for plants from Punta Descanso (32° N). Both gametophytes and tetrasporophytes from the northernmost location had significantly higher photosynthetic rates than the same phase from the other three locations. The photosynthetic responses to light support models for the life history in which life history phases have different ecological roles. The gametophyte, thought to be specialized for rapid growth and competition, may allocate more resources to photosynthetic machinery, hence the higher maximum photosynthetic rates. The tetrasporophyte, thought to be specialized for resistance to herbivores, may allocate more resources to structural or chemical defenses in preference to photosynthetic machinery. Consequently, the tetrasporophyte has lower photosynthetic capacity.     

MORPHOLOGY AND REPRODUCTION OF THE RED ALGA ACROCHAETIUM PECTINATUM IN CULTURE12

The life history of the marine red alga Acrochaetium pectinatum (Kylin) Hamel was studied in unialgal culture using supplemented natural seawater media. The tetrasporophytes are larger than the gametophytes, have a compact filamentous basal system, and produce monosporangia and tetrasporangia. Mono-spores give rise to tetrasporophytes. Tetraspores develop into small gametophytes with unicellular bases. The gametophytes are heterothallic when small (usually less than 500 μ) but as some females become larger (2-3 mm) they produce spermatangia as well as carpogonia. Gametophytes may bear mono-sporangia in addition to carpogonia or spermatangia. These monospores give rise to gametophytes. Fertilization of the carpogonia has not been observed. The tetrasporophytes produce only monosporangia in day-lengths of 12-16 hr, but both tetrasporangia and monosporangia are formed in daylengths of 6–10 hr. Tetrasporangial production is reduced at 15 C compared with 10 C. Light intensity in the range of 5-200 ft-c (cool white fluorescent lighting) has no apparent influence on induction of tetrasporangia. Induction of tetrasporangia is not a photoperiodic response because their development is not inhibited by a brief light break in the middle of the dark period in short daylengths. Plastid morphology, origin, and frequency of sporangia and vegetative branching are variable during the ontogeny, and consequently are somewhat unreliable as taxonomic criteria. Differences in basal systems between gametophytes and tetrasporophytes also indicate that this feature, which is used to distinguish major subgeneric groupings in Acrochaetium, may not be as useful as previously thought.     

Seasonal variation of carrageenan yield,gel strength and viscosity in Sarcopeltis (ex Gigartina) skottsbergii from Southern Chile

Chile is one of the top carrageenan producers worldwide, and Sarcopeltis (ex Gigartina) skottsbergii one of the topmost exploited carrageenophytes from the wild in the world. Total yield, gel strength and viscosity from two contrasting environments Calbuco and Ancud (Inner and Outer Sea, Chile) were estimated monthly in approximately 2 years for this species. While carrageenan yields did not show differences between localities, gametophytes in spring–summer had 15% higher, compared to tetrasporophytes. Sizes (frond surface) normally did not affect carrageenan yields. Gametophytes showed clear differences in gel strength between seasons, but not between localities, with maximum peaks during winter–spring months in Calbuco and autumn-winter months in Ancud. Seasonal variations in viscosity were also significant. While gametophyte viscosity did not exceed 120 cPs, tetrasporophytes reached 1400 cPs in Calbuco and 1000 cPs in Ancud. More remarkably, a positive correlation between viscosity and gel strength was found in S. skottsbergii gametophytes, which is significantly different between both localities. These results suggest that selective harvesting in spring–summer should be preferred to optimize cost–benefit of harvesting activities and subsequent carrageenan productivity.     

CUTICLES FROM CHONDRUS CRISPUS (RHODOPHYTA)1

A simple, nondestructive physical process was developed for routinely isolating the outermost layers from female, male, and sporophyte fronds of Chondrus crispus Stack-house. Yields of pure cuticles from apical segments ranged from 0.74 to 2.35% on a dry weight basis after 5–7 d of culture. These undegraded cuticles were examined by electron microscopy (scanning and transmission electron microscopy), spectroscopy (infrared and X-ray), and chemical means. Cuticles isolated from female or male fronds were characterized by parallel arrays of electron-dense lamellae (typically 6–14) alternating with more electron-transparent regions. The thickness and uniformity of these lamellae provide the physical basis for the iridescence characteristic of C. crispus fronds. Sporophyte fronds are not iridescent. This phenomenon may be explained by the fewer electron-dense cuticular lamellae (usually three to seven) and the fact that these lamellae anastomose freely to form a thin cuticle with a highly irregular substructure. Elements detected by X-ray analysis, in addition to carbon and oxygen, included Mg, Br, S, and Ca in both gametophyte and sporophyte cuticles. Major features of FTIR spectra of all cuticles were absorbances due to proteins. A strong band, indicative of sulfate ester, occurred near 1250 cm^?1 in all cuticle preparations. Gametophyte, but not sporophyte, cuticles absorbed at 935, 846, and 800 cm^?1 consistent with the presence of kappa and/or iota carrageenan. Amino acid analyses showed that sporophyte and gametophyte cuticles were generally similar in gross composition. All contained proline as the principal residue together with significant amounts of cysteine, methionine, and lysine. Protein contents calculated from these analyses ranged from 37.6 to 44.4% on a dry weight basis as compared to 51.5–56.7% calculated from total nitrogen values. Up to 75% of the cuticle mass was solubilized by sodium dodecyl sulfate-β-mercaptoethanol. Three similar migrating bands were seen in female and male cuticle extracts on sodium dodecyl sulfate–polyacrylamide gel electrophoresis; however, none of the three weaker bands from sporophyte cuticles comigrated with those from gametophytes. Chloroform-methanol extraction removed < 3.3% of the cuticle mass, suggesting that lipids were minor components.     

TWO MORPHOLOGICALLY SIMILAR BIOLOGICAL SPECIES: CHONDRUS PINNULATUS AND C. ARMATUS (GIGARTINACEAE,RHODOPHYTA)1

The nature of the relationship between Chondrus pinnulatus (Harvey) Okamura f. pinnulatus and C. pinnulatus f. armatus (Harvey) Yamada et Mikami (Gigartinaceae, Rhodophyta) was investigated by comparative analysis of their biogeography, phenologies, life histories, gross and vegetative morphology, crossability, and upper thermal tolerance. The forma pinnulatus has a more northerly distribution in Japan and adjacent waters, exhibiting adaptation to the cooler regions, whereas the forma armatus has a more southerly range. The latter may be the result of a higher thermal tolerance. Both formae have a Polysiphonia-type life history and are similar in their internal vegetative morphology. They can, however, be distinguished by gross morphology: forma pinnulatus has wide, flattened axes, compressed to flattened ultimate segments and proliferations, while forma armatus has narrow, compressed to subterete axes and subterete to terete ultimate segments and proliferations. These differences persist in laboratory culture. All intraformae crosses were positive, with carpospores from the cross developing into fertile F₁ tetrasporophytes releasing tetraspores that developed into dioecious F₁ gametophytes, the female gametophytes of which formed normal cystocarps. This suggests that members of populations of each forma freely interbreed. Among interformae crosses, only some offspring derived from geographically distant strains bore normal cystocarps in the F₁ female gametophytes. Other crosses showed that interbreeding between populations of these two formae was blocked by various isolating mechanisms: incompatibility, hybrid inviability, and hybrid sterility. Reproductive isolation between f. pinnulatus and f. armatus is virtually complete in wild populations, because hybrid populations have not been found in the wild. In addition, these two entities can be considered biological species that are also referred to the taxonomic species, C. armatus and C. pinnulatus, because they do not overlap with regard to the morphology of the ultimate segments and proliferations. Subtle (but significant) gross morphological differences, partial interfertility between the two species, and deleterious hybridization in the area in which they occur sympatrically suggest that their evolutionary divergence was relatively recent.     

Life-cycle of <Emphasis Type="Italic">Scinaia interrupta</Emphasis> (Nemaliales,Rhodophyta)

The life-cycle of Scinaia interrupta (A.P. de Candolle) M. J. Wynne was investigated in vitro using four irradiance regimes: 4, 8, 12 and 16 μmol photons m⁻² s⁻¹. A triphasic heteromorphic life-cycle was observed. Carpospores released by cystocarps of gametophytes collected in the field developed into filamentous tetrasporophytes, which produced tetrahedral tetrasporangia. Tetrasporangial development was accelerated under higher irradiance levels. Tetraspores germinated into filamentous protonemal gametophytes, initially identical to the tetrasporophyte. Filamentous gametophytes developed apical utricles and gave rise directly to the fleshy gametophyte. Further development of the fleshy gametophyte was not observed at the lowest irradiance regime (4 μmol photons m⁻² s⁻¹). The present study reports for the first time the influence of the irradiance regime on the initial tetrasporangial development and in the development of the fleshy gametophyte, and reinforces the importance of light intensity on Scinaia life-cycle. Production of apical utricles by the filamentous gametophyte is newly reported for the genus.     

Intergametophytic selfing and microgeographic genetic structure shape populations of the intertidal red seaweed Chondrus crispus

Understanding how abiotic factors influence the spatial distribution of genetic variation provides insight into microevolutionary processes. The intertidal seascape is characterized by highly heterogeneous habitats which probably influence the partitioning of genetic variation at very small scales. The effects of tidal height on genetic variation in both the haploid (gametophytes) and diploid (tetrasporophytes) stages of the red alga Chondrus crispus were studied. Fronds were sampled every 25 cm within a 5 m × 5 m grid and along a 90-m transect at two shore heights (high and low) in one intertidal site in France. The multilocus genotype of 799 fronds was determined (N_haploid = 586; N_diploid = 213) using eight microsatellite loci to test the following hypotheses: (i) high and low shore fronds belong to genetically differentiated populations, (ii) gene flow is restricted within the high shore habitat due to tidal-influenced isolation and (iii) significant F_IS values are driven by life history characteristics. Pairwise F_ST estimates between high and low shore levels supported the hypothesis that high and low shore fronds were genetically differentiated. The high shore was characterized by the occurrence of within-shore genetic differentiation, reduced genetic diversity and increased levels of intergametophytic selfing, suggesting it is a marginal environment. These results suggest at fine scales within the intertidal seascape the same mechanisms as those over the species’ distributional range are at work with core and marginal population dynamics.     

SPORELING COALESCENCE IN CHONDRUS CRISPUS (RHODOPHYCEAE)1

Coalescence of developing sporelings of Chondrus crispus Stackhouse was observed. Juvenile tetra-sporophytes showed a higher proportion of coalescence than developing gametophytes. Stages of complete coalescence between different sporelings are illustrated. Coalesced sporelings exhibit vertical and horizontal alignment of cells, as well as “cuticular” continuity and secondary pit connections between adjacent, coalesced sporelings. Ultimately the cells in the center of the coalesced sporelings produce upright, multiaxial fronds that grow more rapidly than fronds of non-coalesced sporelings. Other red algae, such as Gracilaria verrucosa (Hudson) Papenfuss and Gigartina stellata (Stackhouse) Batters also show a similar sequence of sporeling coalescence and enhanced growth. The ecological significance of sporeling coalescence is discussed.