The aim of the current investigation was to test the general convention that the Dasyaceae, Delesseriaceae and Rhodomelaceae are all monophyletic families of the red algal order Ceramiales. Phylogenetic relationships among 45 ceramialean taxa were determined, including eight ceramiacean, 18 dasyacean, nine delesseriacean and eight rhodomelacean species, plus two of uncertain ceramialean affinities, based on 34 anatomical characters and nuclear small subunit (SSU) rDNA sequences. Results from our ‘total-evidence’ approach were consistent with the notion that the Dasyaceae, Delesseriaceae and Rhodomelaceae have evolved from a common ancestor within a paraphyletic Ceramiaceae. Our data indicate, however, that the Rhodomelaceae alone is monophyletic at the family level, with both the Dasyaceae and Delesseriaceae polyphyletic. In particular we resolved two independent and well-supported lineages for the included Dasyaceae, viz., a Dasya group and a Heterosiphonia group, which were as distinct from one another as they were from the Rhodomelaceae and the various lineages of Delesseriaceae. The molecular data alone were equivocal on the issue of monophyly of the Dasyaceae. We therefore advocate conservative taxonomic revisions as an interim step towards eventual resolution of familial-level taxonomy in the Ceramiales. Based on our results, the Heterosiphonioideae H.-G. Choi, Kraft, I.K. Lee et G.W. Saunders subfam. nov. is proposed for Heterosiphonia and five closely related genera, and the Dasyoideae Schmitz et Falkenberg is emended for the remaining taxa. Although the Dasyoideae is a natural group, it is in need of a thorough systematic reinvestigation at the generic level. Our analyses indicate that the genus Dasya is polyphyletic or paraphyletic in excluding Dasysiphonia, Eupogodon and Rhodoptilum and that Heterosiphonia japonica also has affinities to this group, taxonomic issues that will be addressed in detail elsewhere.

An undescribed marine Pyramimonas, P. australis Andreoli et Moro, sp. nov., forming a bloom in a hole of Terra Nova Bay (Ross Sea, Antarctica) sea ice, was collected, but could not be cultured. Consequently, the description of this new species is based on light and electron microscope observations on samples that were fixed or stored at −80 °C, and its phylogenetic position inferred from nuclear-encoded small-subunit ribosomal DNA (SSU rDNA) and chloroplast-encoded rbcL gene sequences. This is the third Antarctic species described for this genus. The ultrastructure of the cell is consistent with species of the subgenus Trichocystis McFadden, but differs in that it has unique body and cyst scales, and a different encystment procedure. The outermost layer of body scales is formed by flat box scales with peripheral perforations oriented parallel to the four edges and with a further eight central perforations oriented perpendicular to the peripheral ones. Crown scales, which in many other species of the genus form the outermost layer over the entire cell body, were observed in this species in the flagellar pit over the box scales. The flagella are covered by a pentagonal underlayer of scales and by limuloid scales with two subsidiary spines, in addition to the central one. Encystment begins in the flagellate form resulting in a cyst with an irregular wall bearing spine scales. Ultrastructural and molecular data confirm that P. australis belongs to the subgenus Trichocystis.

In the red alga Bostrychia moritziana, release of spermatia is triggered by slight osmotic shock; they emerge under pressure apparently generated by swelling of the mucilaginous sheath. Spermatia adhere tenaciously to trichogynes of the carpogonium. Adhesion triggers spermatial mitosis, which is complete in about 30–45 min; there is no cytokinesis and the binucleate spermatium becomes vacuolated. The delicate, dynamic trichogyne cytoplasm contains complex membranous components and vacuoles. At the contact zone, the trichogyne and spermatial wall erode, forming a pore, and cytoplasmic continuity (plasmogamy) is achieved after about 50–70 min. Many trichogynes rupture during these events because of inadequate structural connection with the spermatia. Normally, both spermatial nuclei enter the trichogyne in sequence; rarely, both nuclei enter together. Entrance is rapid, and the nuclei often become thin and greatly elongated as each squeezes through the narrow pore into the trichogyne. Once inside, each nucleus resumes its normal shape as it starts to move steadily along the trichogyne, often with irregular pauses. One nucleus of each pair (not necessarily the first out of the spermatium) migrates along the trichogyne towards the carpogonium base to fertilize the female nucleus; the other moves in the opposite direction, away from the entry site, and it often ends up near the tip of the trichogyne. This same scenario was observed for each of several spermatia contributing nuclei to one trichogyne. Thus, our observations indicate that the two nuclei in each spermatium are differentiated so that only one is capable of fertilization, differentiation being visibly expressed in the direction that the nucleus moves as it enters the trichogyne.

A microalga was isolated from the pack-ice of Wood Bay (Antarctica) during austral summer 1993–4. By comparison with an authentic strain obtained from Sammlung von Algenkulturen at the University of Göttingen (SAG 860–3), its ultrastructural details and pigment composition were very similar to those of Pleurochloris meiringensis. However, sequence analysis of the entire 18S rRNA gene revealed substantial genetic divergence (57 nucleotide substitutions and 19 insertions/deletions) between SAG 860–3 and the Antarctic isolate. Phylogenetic analysis of complete 18S rRNA gene sequences from 18 microalgal species, including the two strains studied, rejected the hypothesis that the Antarctic isolate is the sister species to Pleurochloris meiringensis. Molecular evidence indicates that the Antarctic isolate is the sister group of a clade that comprises two other representatives of the Xanthophyceae (synonym Tribophyceae): Pleurochloris meiringensis and Botrydiopsis intercedens. This leads us to conclude that this microalga is a new species belonging to a new genus and the name Pseudopleurochloris antarctica is proposed.

Cells of the potentially toxic dinoflagellate Alexandrium catenella have a complement of features typical of dinoflagellates, including dinokaryon, pusule and amphiesma. No endosymbiotic bacteria were found in the Californian strain examined, which is weakly toxic. The chloroplast consists of a central pyrenoid complex with radiating chloroplast lobes, an arrangement found also in certain other gonyaulacoid dinoflagellates. Cells are often arranged in few-celled chains and a cytoplasmic connection interconnects adjoining cells. Striated fibres line the attachment canal and also subtend the apical pore, making up an ‘apical fibrous complex’. The flagellar apparatus basically resembles that of other gonyaulacoids. However, Alexandrium catenella, Gonyaulax spinifera and Protoceratium reticulatum share the presence of two striated collar connectives and a single-stranded microtubular root associated with the longitudinal basal body, in addition to the multi-stranded root characteristic of dinoflagellates in general. Ultrastructural features indicate that these three species are closely related while Ceratium furcoides, another gonyaulacoid dinoflagellate, apparently lacks these features.

The green alga Chlamydomonas reinhardtii can use the ureides allantoin and allantoate as sole nitrogen sources. Once the uptake systems for allantoin and allantoate were induced, the uptake and growth rates were identical for the two ureides. However, the enzymatic activities involved in the degradation of the two ureides (allantoinase and allantoicase) were regulated differently. Allantoinase seems to be constitutive, since it was detected in all the nitrogen sources studied, while allantoicase behaved as an inducible enzyme, since it was present only in cells cultured in ureides or any metabolic precursor of these compounds. Neither allantoinase nor allantoicase activities were repressed by ammonium in the presence of ureides. Allantoicase activity was not induced under nitrogen starvation conditions, while it was induced in cells that had been cultured with allantoin or allantoate in the dark. Allantoin uptake showed a pattern similar to that of allantoate under all nutritional and environmental conditions tested. Inhibition of allantoin and allantoate uptake by N-ethylmaleimide suggests that thiol (SH–) groups are involved in both uptake systems. The use of both allantoin and allantoate was similarly inhibited by the metabolic poisons tested (cyanide, azide, 2,4-dinitrophenol and 3′-(3,4-dichlorophenyl)-1′,1′-dimethyl urea) but only at very high concentrations. The possibility that uptake of allantoin and allantoate might take place through two independent systems is discussed.

The presence of intracellular bacteria in the dinoflagellate Gyrodinium instriatum Freudenthal & Lee has previously been described but the bacterial flora associated with this species has not been characterized. In this study, new results of transmission electron microscopy (TEM) and in situ hybridization using several bacterial group-specific oligonucleotide probes are presented. The long-term association of endocytoplasmic and endonuclear bacteria with G. instriatum has been confirmed. All endonuclear and most of the endocytoplasmic bacteria labelled were identified as belonging to the betaproteobacteria. Large clusters of Cytophaga-Flavobacterium-Bacteroides (CFB) were labelled and observed in the cytoplasm of the dinoflagellate cells, but were absent from the nucleus. Gammaproteobacteria were only observed outside the dinoflagellates. No alphaproteobacteria were detected either free-living or intracellular. Empirical observation of intracellular CFB reflected a degradation process of moribund dinoflagellate cells, whereas the systematic colonization of dinoflagellate nucleoplasm by betaproteobacteria suggested a true symbiotic relationship. Natural colonization may have occurred, perpetuated by vertical transmission of intracellular bacteria to the dinoflagellate daughter cells, via a pool of bacteria sequestered within the nucleus. Dividing bacteria were observed in the nucleus and equilibrium may be maintained by release of endonuclear bacteria to the cytoplasm through nuclear envelope constrictions.

Three sand-dwelling species of the marine dinoflagellate genus Sinophysis were examined from intertidal and subtidal North German Wadden Sea sand and are illustrated by light and scanning electron microscopy. Two are described as new: S. stenosoma sp. nov. and S. grandis sp. nov. Sinophysis stenosoma sp. nov. is compressed laterally with a cell size of 37–56 μm long and 21–33 μm wide, a length/width ratio of 1·43–1·89, an epitheca width (dorsoventrally) of 5·5–8·0 μm, and a sulcus length of about half the cell length. Sinophysis grandis sp. nov. is compressed laterally with a cell size of 50–59 μm long and 35·0–41·5 μm wide, a length/width ratio of 1·29–1·61, an epitheca width (dorsoventrally) of 12–17 μm, and a sulcus length of about three-quarters the cell length. The third species, Sinophysis ebriolum (Herdman) Balech, is the most common species in the Wadden Sea. All species occur throughout the year and are all sand-dwelling, non-photosynthetic, with a smooth theca. They can be distinguished by size, length/width ratio, epitheca size, relative sulcal length and thecal pore pattern. A key to the five known Sinophysis species is provided.

The composition (% relative abundance) of the benthic diatom community was studied in the littoral zone (0–5 m) of the NW and E coasts of the brackish, non-tidal Gulf of Riga, in the Baltic Sea. The samples were collected concomitantly with measurements of sediment primary productivity and chlorophyll a during three cruises, representing three seasons (autumn, spring, summer). At all depths, the living diatom community was dominated by epipsammic species, the most abundant taxa being Martyana atomus, a species of Fragilariaceae and Achnanthes delicatula. The community was characterized by a stable composition and a high species diversity throughout the study period (Shannon–Weaver, mean H′ = 4·4). Principal Component Analyses (PCA), together with Redundancy Analysis (RDA) based on 129 taxa, revealed both spatial (site and depth) and seasonal differences in the diatom communities. However, these differences were mainly caused by the varying proportions of taxa common in both sampling areas in all three seasons, rather than by actual major taxonomic changes in the species present in communities. The distribution of the typical epipsammic species along the depth gradient was not uni-directional. The dominance of attached life forms, and the absence of a well-developed epipelic community, reflects the physically dynamic substratum, particularly in the eastern part of the Gulf. As a result, primary productivity is kept rather low, decreasing rapidly with depth due to frequent turbidity of the water column.

Cyanobacteria are often the dominant phototrophs in high-latitude lakes and streams where they must experience continuously low temperature and extreme variations in daylength. The present study examined the interaction between these two variables for the growth and physiology of an Arctic isolate of the mat-forming species Schizothrix calcicola (Agardh) Gomont. Growth rates (μ), photosynthesis (P), respiration (R), pigment composition and in vivo absorption characteristics were measured under 15 combinations of daylengths (8[ratio ]16, 12[ratio ]12, 16[ratio ]8, 20[ratio ]4 and 24[ratio ]0 L/D) and temperatures (5, 15 and 25 °C). μ increased with increasing temperature (μmax at 5 °C = 0·12 d−1, μmax at 25 °C = 0·28 d−1) and a similar trend was observed in photosynthetic capacity (average PBmax at 5 °C = 4·42 mg C (mg Chl a)−1 h−1, average PBmax at 25 °C = 5·74 mg C (mg Chl a)−1 h−1), pigment content and absorbance. Daylength had a positive effect on μ and pigment absorption, but not pigment content. The shape of the μ–daylength curve varied with temperature: μ was a linear function of daylength at 5 °C, but at 15 and 25 °C the relationship resembled a rectangular hyperbola and μ saturated at 16[ratio ]8 and 12[ratio ]12 L/D, respectively. The non-linear relationship between μ and daylength at high temperature was related to a reduction in net photosynthesis under extended daylength; at 25 °C, net P under 24[ratio ]0 L/D was 0·82±0·37 mg O2 (mg Chl a)-1 h−1, while under 8[ratio ]16 L/D, it was 6·54±0·69 mg O2 (mg Chl a)−1 h−1. The constant increase in growth with increasing daylength at low temperature may reflect an adaptive tolerance to the combination of cold temperature and continuous daylight during the Arctic summer.

Cryptomonas sp. Φ is an undescribed cryptomonad used for many studies into the endosymbiotic origin of plastids. Cryptomonas sp. Φ was characterized using electron microscopy, DNA sequencing and karyotyping. DNA sequence data show that Cryptomonas sp. Φ has been confused with the related cryptomonad, Guillardia theta, which is the organism actually used in most published studies on cryptomonad endosymbiosis to date. It is proposed that the strain Cryptomonas sp. Φ be recognized as a distinct species under the name Hanusia phi. Although Hanusia phi shares molecular and karyotypic features with G. theta, it cannot be assigned to Guillardia because it does not fit the morphological description of this genus. H. phi differs from G. theta in periplast structure, configuration of the furrow-gullet system, and cell size. Morphologically, however, H. phi is very similar to Teleaulax acuta, Teleaulax merimbula and the diplomorph of Proteomonas sulcata.

Caulerpa (Chlorophyta, Ulvophyceae) is a common marine tropical-subtropical genus of about 70 species, inhabiting the eulittoral zone on rocks and corals as well as mangroves. The genus is particularly diverse and abundant along southern Australian coasts, where it is thought to have originated. Here, we compare sequences from the nuclear ribosomal cistron among five species of Caulerpa, including nine populations of Caulerpa filiformis from two biogeographic regions: five from Australia and four from South Africa. Species relationships were well resolved by internal transcribed spacer (ITS) sequences and supported by high bootstrap values as follows: (C. geminata (C. simpliciuscula (C. trifaria (C. scalpelliformis (C. filiformis – Australia, C. filiformis – South Africa))))). Nucleotide divergence within C. filiformis was low with four and five nucleotide differences present in ITS1 and ITS2 respectively. Unexpectedly, the 5.8S rRNA gene showed eight nucleotide differences between the Australian and South African populations and may indicate cryptic species. The Australian C. filiformis is probably not a South African introduction. These sequences provide an independent means for assessment of species relationships and appear, in so far as limited taxon sampling permits, to follow chloroplast ultrastructural groupings proposed 20 years ago.

Inorganic carbon acquisition under emerged conditions was studied in the red macroalga Bostrychia scorpioides by investigating the effects of changes in the pH of the water film surrounding the thalli when emerged and of inhibitors of carbonic anhydrase (CA; EC 4.2.1.1). The CO2 uptake rate increased by approximately 150% when the pH of the water film was changed from 8·1 to 10·5. Acetazolamide (AZ), an inhibitor of the external CA, inhibited CO2 uptake by 50% at pH values higher than 8·7. The effect of ethoxyzolamide (EZ), an inhibitor of both external and internal CA, was more pronounced than that of AZ, inhibiting the CO2 uptake rates by 80% at all the pH values assayed. At pH 10·5, CO2 flux into the cells exceeded by several orders of magnitude the flux supported by the spontaneous dehydration of HCO3− to CO2 in the water film. From these results it was concluded that the main source of inorganic carbon was atmospheric CO2. The driving force for the flux of atmospheric CO2 into the cell must be the CO2 concentration gradient. Therefore, low internal CO2 concentration might be necessary to account for the CO2 fluxes measured. The function of the internal CA could be to speed up the transformation of CO2 into HCO3− inside the cell. The function of the external CA could not be fully described from the experiments although it was demonstrated that the external enzyme enhanced the CO2 flux from air to cell surface.

The sublittoral red alga Delesseria sanguinea was pre-cultivated in the laboratory in a predominantly green light field at 10 μmol m−2 s−1 (10 °C), with an approximately 0·5% daily increase in blade area. Such pre-cultivated blades were exposed horizontally in flow-through chambers for 5–6 days in April and May to solar radiation reduced to 19% and 11%, respectively, by neutral density screens. In all three experiments, the full solar spectrum (UVB+UVA+PAR) reduced growth rate significantly to 0–50% of values obtained in PAR alone, while this occurred with UVA+PAR in only one experiment. The growth rate of a Delesseria blade may thus be used as a sensitive and reliable biological indicator of UVB in natural solar radiation at a pre-chosen, neutral reduction level. Rapid measurements of growth rate of apical parts of Delesseria blades during and after UVB+UVA pulses of 2, 3 or 6 h duration were performed in the laboratory by measuring thallus area every 2 min by means of a CCD camera coupled to an on-line, computer-aided image analysis system. A single pulse of 2 or 3 h duration administered during the light phase caused a temporary drop in growth rate during and after the pulse, with recovery starting 2·5 h after the end of the pulse and completed by the end of the light phase. A single 6 h pulse at a biologically effective UVB dose (BEDDNA300 nm) of only 0·5 kJ m−2 reduced growth rate by 55% if administered around noon, but halted growth almost completely if supplied at night, when no photoreactivation was possible. The UVB-sensitive behaviour of Delesseria compares well with the highly sensitive phytoplankton alga Emiliania huxleyi whose growth was reported to be halted at a daily, weighted BEDDNA300 nm of 0·4 kJ m−2 administered during 4 days for 3 h in the middle of the light period.

Amphora angusta Gregory, Amphora ventricosa Gregory and Amphora macilenta Gregory have been misunderstood for the last 140 years. Gregory described these species from sublittoral sediments off the west coast of Scotland. Although the illustrations were excellent for their time (1857), it is impossible to be confident of identification using Gregory's paper, and subsequent authors have created such confusion that records of these taxa must be regarded as untrustworthy unless backed by photographic evidence. In this paper, the first to describe in detail the recently established genus Seminavis, we show that A. angusta is in fact a species of Amphora Ehrenberg, whereas A. ventricosa sensu Gregory represents two independent species of the genus Seminavis D. G. Mann, namely Seminavis ventricosa (Gregory) Garcia-Baptista (non S. ventricosa sensu Garcia-Baptista 1993) and Seminavis arranensis Danielidis & D. G. Mann, sp. nov. The form usually known as A. ventricosa is neither of these and requires a new name, Seminavis robusta Danielidis & D. G. Mann, sp. nov. The long forgotten and misclassified species A. macilenta Gregory is shown to be yet another Seminavis species, requiring a new combination as S. macilenta (Gregory) Danielidis & D. G. Mann, comb. nov.; contrary to previous claims, it is separate from A. ergadensis Gregory, which is a true Amphora. Valve and girdle ultrastructure, plastid arrangement and auxosporulation are described for Seminavis and resemble those in the Naviculaceae sensu stricto.

Exposure of Fucus spiralis germlings to precise copper concentrations (0 to 844 nM Cu2+) in chemically defined medium demonstrated a relationship between ultrastructural changes and growth retardation with increasing copper concentration. Electron-translucent vesicles, present in ova, which normally disappear after fertilization, accumulated in germlings exposed to Cu2+ above 10·6 nM, suggesting that copper may inhibit a metabolic pathway involved in cell wall formation which is initiated by fertilization. No membrane damage was observed during the exposure period. During a post-exposure period in copper-free medium, recovery occurred (rhizoid extension, apical hair formation) in germlings previously exposed to concentrations below 106 nM Cu2+ and electron-translucent vesicles became granular and disappeared. It is proposed that the electron-translucent vesicles contain a cell wall precursor and that copper inhibits its incorporation into the cell wall, preventing growth and development of the zygote.

The genus Polysiphonia Greville, nom. cons., has had a long and confused nomenclatural history. At present, Polysiphonia has a wide circumscription, including at least 200 species, but it is heterogeneous in many vegetative and reproductive developmental features. Central to any re-evaluation of the genus is a detailed examination of the type species of Polysiphonia, P. urceolata (Lightfoot ex Dillwyn) Greville, which is conspecific with P. stricta (Dillwyn) Greville. We here report on the vegetative and reproductive morphology of P. stricta, including P. urceolata, based on type and other material from the British Isles. Thalli consist of prostrate and erect ecorticate axes with four pericentral cells, attached by unicellular rhizoids remaining in open connection with pericentral cells. Prostrate axes lack vegetative trichoblasts; trichoblasts occur seasonally on erect axes. Branch initials are cut off from the subapical cell at intervals of four or five segments in dichotomous and alternating pairs rather than being formed from each axial cell in the spiral pattern typical of most species of Polysiphonia. Spermatangial branch initials, which are trichoblast homologues, are produced directly from each axial cell at the tips of erect branches, not subtended by trichoblasts, and have two- to five-celled sterile tips when mature. The mature carpogonial branch is four-celled with a two-celled first sterile group and a one-celled second sterile group. Following presumed fertilization, direct fusion apparently takes place between carpogonium and auxiliary cell; mature cystocarps are usually urceolate. Tetrasporangia are formed from the third pericentral cell, in straight series, and have two pre-sporangial cover cells. Previous accounts of a third, post-sporangial cover cell could not be substantiated. P. stricta and a small group of other Polysiphonia species differ in several important respects from most members of the genus, which have rhizoids cut off from pericentral cells by a cell division, abundant trichoblasts, spirally arranged tetrasporangia and a post-sporangial cover cell. The branching pattern of P. stricta highlights the difficulties of distinguishing between the tribes Polysiphonieae and Pterosiphonieae.

This paper continues a series of studies of the allogamous raphid diatom Achnanthes longipes, which has a complex reproductive system combining unisexual, bisexual and monoecious behaviour. Following earlier work on the effects of inbreeding in the progeny of crosses between two unisexual clones, we studied the progeny of clones that are capable of a high degree of selfing in monoclonal culture (‘monoecious clones’). Three generations of selfed progeny were examined. In addition, we investigated the F1 generation obtained after crossing two different monoecious clones. Monoecious clones produced monoecious or, more rarely, bisexual progeny, but did not give rise to unisexual progeny. As in inbred lineages made by crossing closely related unisexual clones, inbreeding in monoecious lineages leads to a reduction in the number of gametes formed by the gametangia, from two to one. Inbred clones exhibit marked inbreeding depression and only three inbred generations were possible in monoecious lineages. In the third, final inbred generation, monoecious sexual reproduction was initiated in monoclonal cultures but gametes rarely fused and none of the auxospores and initial cells that were formed were viable; this also occurred when the inbred clones were crossed with any of the other clones available. The significance of inbreeding and other aspects of the breeding system in A. longipes is discussed.

Phylogenetic analyses of the Dasyaceae based on sequence analysis of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) and 42 morphological characters are presented. Comparative sequence analysis confirms the general view of the Ceramiaceae as a primitive, paraphyletic group giving rise to the Rhodomelaceae, Delesseriaceae and Dasyaceae within the monophyletic Ceramiales. On the basis of both data sets, the Heterosiphonia-like genera (Heterosiphonia, Colacodasya and Dasyella) are the most primitive members of the Dasyaceae, whereas the Dasya-like genera (Dasya, Pogonophorella, Eupogodon and Rhodoptilum) and Thuretia and Dictyurus are of more recent origin. On the basis of morphological data only, Thuretia and Dictyurus form a sister group to Heterosiphonia, and Eupogodon is monophyletic whereas Dasya and Heterosiphonia are not. Primary radial symmetry has arisen once in the Dasya clade but is secondarily obscured in some species by heavy, asymmetrical cortication that gives the appearance of bilateral symmetry. This is illustrated by species of Eupogodon and Rhodoptilum.

Use of isozymes (including allozymes) in studies of population genetics and systematics of seaweeds has increased sufficiently in the last decade to allow some generalization. Only a single locus has been observed for about half the enzymes analysed in seaweeds, compared with 29% in vascular plants. Compared with higher plants, macroalgal species generally have low amounts of electrophoretically detectable genetic variation; the lowest levels of genetic variation found in natural populations are those reported for seaweeds. Nonetheless, seaweeds show an association between levels of genetic diversity as revealed by isozymes and species-specific attributes, such as mating system and predominance of asexual versus sexual reproduction. In systematic studies, isozymes have revealed cryptic species and identified pairs of sibling taxa. The quaternary structure of enzymes appears to be conserved at the phylum level. With the current availability of improved techniques for enzyme electrophoresis and for data interpretation, we expect future studies utilizing isozyme electrophoresis to provide further insight into population and evolutionary processes in seaweeds.