A revision of the check-list of the red (Rhodophyta), green (Chlorophyta) and brown (Ochrophyta, Phaeophyceae) seaweeds of Britain has been compiled and revealed 644 taxa, mostly at species level but including infraspecific taxa: 348 reds, 110 greens and 186 browns. There were 30 additions to the list, notably five newly described species and five new non-native additions. In addition to the check-list, an updated list of non-native species was compiled based on a stringent review of the available evidence. We have listed 31 non-native species (~5% of the flora), although the numbers may be considerably higher and probably include species that are effectively naturalized and perceived to be part of the indigenous flora. The check-list is discussed in relation to the impact of molecular techniques on the identification, taxonomy and phylogeny of species, and points to the need for a comprehensive, in-depth study on the identity and relationships of the seaweeds of Britain.

A total of 34 marine algae are reported for the first time based on historical herbarium collections from the marine shores of Tonga in the central South Pacific Ocean: eight Rhodophyta and 26 Chlorophyta. One species of Rhodophyta, i.e. Trichogloea requienii, and four species of Chlorophyta, i.e. Caulerpa plumulifera, Codium extricatum, Udotea glaucescens and Valoniopsis pachynema, represent the first records from central Polynesia. The red alga Titanophora pikeana has only been previously reported in this region from the adjacent western Melanesian islands of Fiji and the isolated Hawaiian Islands to the north. The other 28 algal species are widely distributed marine species around tropical and subtropical islands in the Pacific Ocean.

Seaweed farming is often depicted as a sustainable form of aquaculture, contributing to poverty reduction and financial revenues in producer countries. However, farms may negatively affect seagrasses and associated organisms (e.g. invertebrate macrofauna) with possible effects on the flow of ecosystem goods and services to coastal societies. The present study investigates the influence of a seaweed farm, and the farmed seaweed Eucheuma denticulatum in particular, on fishery catches using a traditional fishing method (“madema” basket traps) in Chwaka bay (Zanzibar, Tanzania). The results suggest that a seaweed farm, compared to a seagrass bed, had no influence on catch per unit effort (no. of individuals per catch, or catch weight) or no. of species per catch, but significantly affected catch composition (i.e. how much that was caught of which species). The two species contributing most to differences between the sites were two economically important species; the herbivorous seagrass rabbit fish Siganus sutor, which was more common in the seaweed site and is known to graze on the farmed algae; and the benthic invertebrate feeder chloral wrasse Cheilinus chlorourus, more common in the seagrass site. Compared to vegetation-free bottoms, however, the catches were 3−7 times higher, and consisted of a different set of species (ANOSIM global R > 0.4). As traps placed close to the seaweeds fished three times more fish than traps placed on sand patches within the seaweed farm, the overall pattern is attributed to the presence of submerged vegetation, whether seagrass or seaweed, probably as shelter and/or food for fish. However, qualitative differences in terms of spatial and temporal dynamics between seagrass beds with and without seaweed farms, in combination with other factors such as institutional arrangements, indicate that seaweed farms cannot substitute seagrass beds as fishing grounds.

For the first time, photosynthesis of Myriogramme mangini (Gain) Skottsberg, one of the dominant red macroalgae in the sublittoral of Signy Island (South Orkney Islands), was studied in situ under natural irradiance levels in specially developed incubation chambers. M. mangini is adapted to low irradiance levels. Water transparency varied over the year. A maximum attenuation coefficient (kd) of 0.328 m−1 was reached in January, and the water was clearest in September with a kd value of 0.079 m−1. Classification of the water type on a Jerlov scale, gave water type 4 in January and II in May and June. The mean kd value over the year was 0.158 m−1 and the water was classified as Jerlov's water type 1. The euphotic depths (Zeu) for 1%, 0.1% and 0.01% surface irradiance levels were 29.1 m, 43.7 m and 58.3 m, respectively. Photosynthetic characteristics were determined, with the oxygen production rates and irradiance levels measured in situ, using P-I curves. The initial saturation irradiance (Ik) varied significantly from 18.0 ± 1.5 μmol m−2 s−1 in autumn to 10.5 ± 1.8 μmol m−2 s−1 in early spring. Mean photosynthetic capacity (Pg max) ranged from 57.2 ± 1.3 μmol O2 g−1DW h−1 to 63.1 ± 1.6 μmol O2 g−1DW h−1. The photosynthetic efficiency (α) was 3.2 ± 0.2 μmol O2 g−1DW h−1 (μmol m−2 s−1)−1 in autumn and 6.0 ± 1.0 μmol O2 g−1DW h−1 (μmol m−2 s−1)−1 in early spring. Compensation irradiance (Ic) was low and ranged from 2.5 to 2.8 μmol m−2 s−1. Estimates of annual net production rates were 128.1 and 0.6 mmol O2 g−1DW y−1 at 5 m depth and 20 m depth, respectively. A maximum depth of occurrence of M. mangini was predicted at 22.9 m (2.7% of the surface irradiance).

The phenology of six Antarctic red macroalgae, Delesseria salicifolia Reinsch, Gymnogongrus antarcticus Skottsberg, Gymnogongrus turquetii Hariot, Hymenocladiopsis crustigena Moe, Kallymenia antarctica Hariot and Phyllophora ahnfeltioides Skottsberg, was investigated in a two-year culture study under fluctuating daylengths imitating the conditions of King George Island, South Shetland Islands. The algae were cultured at 0°C in filtered, nutrient enriched seawater under photon fluence rates of 3, 10, 25, 50 μmol photons m−2 s−1. All species are classified as season anticipators, starting growth in late winter–spring and stopping growth before the summer solstice. Formation of new blades was observed from January/February onwards in most of the species. Carpospore formation was observed in K. antarctica in early summer. Growth was light saturated at photon fluence rates of 3 μmol photons m−2 s−1 in D. salicifolia and at 10 μmol photons m−2 s−1 in the other species, corresponding to an annual light dose of 31.4 and 157 mol photons m−2. The results show that this type of life strategy is typical for species from the Antarctic and give further evidence on the high degree of shade adaptation of Antarctic algae and predict a lower distribution limit for these species at 37 ± 15 m and 23 ± 10 m, respectively.

This study investigated major pigment patterns of 8 cyanoprokaryota, 2 rhodophytes and 2 cryptomonads isolated from freshwater ecosystems. Analysis was done by means of HPLC. The method, historically adapted to marine phytoplankton, was modified to accommodate limnic algae. Quantitative results obtained in this study can be used for phytoplankton quantification techniques based on pigment patterns. Compared to marine strains, the studied freshwater cyanoprokaryote strains reveal a more complex pigment pattern, including myxoxanthophyll, canthaxanthin and echinenone. Cryptophyta possess the two acetylenic class-specific marker compounds allo- and monadoxanthin, crocoxanthin was not detectable. Rhodophytes show a simple pigment pattern similar to marine species. Previous reports as to the existence of chlorophyll-d could not be confirmed (historical reports probably refer to an artefact of preparation). Besides methodological considerations, the phenomenon of complementary chromatic adaptation is discussed briefly.

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.

Grateloupia doryphora (Montagne) Howe, originally described from Peru, has repeatedly been reported as an invasive species in Atlantic and Mediterranean waters. Various attempts to explain this species’ route of introduction have been unsatisfactory. New evidence from comparative rbcL sequence analysis and morphology suggests that this adventive species in the NE and NW Atlantic corresponds with G. turuturu Yamada, originally described from Japan. This provenance follows a well-recognized trend of invasive marine organisms that have colonized the Atlantic Ocean and Mediterranean Sea from Pacific NE Asia.

The apex of the tetrasporangial branches of Osmundea spectabilis var. spectabilis (= Laurencia spectabilis var. spectabilis) exhibits cavities in which tufts of multicellular trichoblasts occur. Trichoblast development in Osmundea spectabilis var. spectabilis begins with the differentiation of an epidermal cell within the crypt. This cell differentiates into a trichoblast mother cell (TMC). The TMC divides to form a two-celled incipient trichoblast. Successive periclinal divisions of the apical cell of the young trichoblast result in the formation of a multicellular developing trichoblast. With the exception of the apical cell all trichoblast cells are at the same developmental stage. They possess a large nucleus, abundant plastids with peripheral and some internal thylakoids and dictyosomes. Daughter chloroplasts result from one constriction or multiple fission of a single chloroplast. Dictyosomal cisternae and mucilage sacs contribute material to wall formation. Each differentiating trichoblast cell is surrounded by a bi-layered wall. The outer wall layer represents the trichoblast mother cell wall and the inner wall layer is the trichoblast cell wall. Mature trichoblast cells have thin walls, probably as a consequence of mucilage extrusion, the most likely function of trichoblasts in Osmundea.

Systematics of the red algal order Acrochaetiales and related taxa was investigated using combined small- and large-subunit nuclear ribosomal DNA (SSU and LSU rDNA, respectively) sequence data. These data were subjected to distance, parsimony and maximum likelihood analyses. The resulting phylogenies were congruent with previously published SSU results in that all included orders (Balbianiales, Batrachospermales, Nemaliales, Palmariales and Thoreales) were resolved as monophyletic except the Acrochaetiales, which consisted of two lineages (Acrochaetiales I and II). The Batrachospermales and Thoreales occupied equivocal positions as early diverging lineages, while the Balbianiales generally resolved as sister to an Acrochaetiales–Nemaliales–Palmariales (ANP) complex. Relationships among the four lineages of the ANP complex were not completely resolved, but detailed analyses weakly positioned Acrochaetiales II as sister to the Nemaliales, whereas Acrochaetiales I displayed a moderate to strong affiliation with the Palmariales. Acrochaetiales I included representatives of the genera Acrochaetium,Audouinella and Rhodochorton, whereas Acrochaetiales II had a number of acrochaetioid species including a representative of the genus Colaconema. Compared with published SSU phylogenies, bootstrap values within the two Acrochaetiales lineages increased substantially in combined SSU/LSU analyses. Based on these results, emended generic descriptions are provided for Acrochaetium, Audouinella, Colaconema and Rhodochorton, and a new family of acrochaetioid algae is described, the Colaconemataceae J. T. Harper et G. W. Saunders. The Acrochaetiaceae now includes the genera Acrochaetium, Audouinella and Rhodochorton, while the Colaconemataceae is considered monogeneric at this time. It is quite likely that additional genera will be recognized within the Colaconemataceae pending further investigation. Acrochaetiaceae is retained as the sole family of the Acrochaetiales, although the tenuous recognition of the Palmariales as distinct from this order is discussed, whereas Colaconemataceae is transferred to the new order Colaconematales J. T. Harper et G. W. Saunders.

We examined three species of diminutive Porphyra,Porphyra suborbiculata Kjellman from the North Pacific, Porphyra lilliputiana W. A. Nelson, G. A. Knight et M. W. Hawkes from the South Pacific, and Porphyra carolinensis Coll et J. Cox from the western North Atlantic. These taxa were compared in terms of morphology, habitat data and sequence haplotypes of nuclear small subunit rDNA (SSU) and internal transcribed spacers of the nuclear rDNA cistron (ITS). These three species have similar morphologies and growth habits, and share very similar type descriptions and habitat records. Haplotype variation was found within the 11 samples of P. lilliputiana we examined and within P. suborbiculata samples from two locations, but the single P. carolinensis haplotype (from collections from two separate locations) was identical to one found in several widespread P. lilliputiana samples. Unrooted phylogenetic trees based on sequence data do not support any of the three species as being a monophyletic group. We conclude that these three taxa represent a single species with the oldest name P. suborbiculata having nomenclatural priority. It is likely that P. suborbiculata has recently been introduced to the western Atlantic from the Pacific region.

A minute parasite of Neosiphonia poko (Hollenberg) Abbott from a shallow lagoon on the central-Pacific Johnston Atoll is described as Neotenophycus ichthyosteus Kraft et Abbott, gen. et sp. nov. The infective parasite cell first connects to a central-axial cell of the host, then emerges from between host pericentral cells at a node before dividing into a three- or four-celled primary axis. Epibasal cells of the parasite divide to form three pericentral cells whose derivatives produce a globular head on the basal cell and on which reproductive structures differentiate almost immediately. Trichoblasts on any life-history stage are completely lacking. Spermatangia are borne on mother cells across the whole thallus surface. Procarps consist of four pericentral cells that encircle a subapical fertile-axial cell in an ampullar configuration, one of the pericentral cells serving as the supporting cell and bearing a four-celled carpogonial branch and a single sterile cell. Diploidization results in a longitudinal/concave division of the auxiliary cell and formation of an arching linear series of inner gonimoblast cells, each dividing toward the thallus surface into gonimoblast filaments of very narrow, horizontally aligned cells terminated by initially monopodial, later by sympodial, carposporangia, the whole of the mature female gametophyte consisting of an amalgam of several cystocarps within a lax jacket of sterile gametophytic tissue. Tetrasporophytes are composed of lobes of pericentral-cell-derived filaments, each axial cell of which is ringed by three pericentral cells producing tetrahedral tetrasporangia enclosed by two pre-sporangial cover cells. Affinities of the new genus are discussed and comparison is made particularly to the enigmatic parasite Episporium centroceratis Möbius. It is concluded that relationships with any previously described tribe are so remote or obscure that the new tribe Neotenophyceae should be proposed for it.

A new member of Delesseriaceae (Ceramiales, Rhodophyta) is described from Southern Taiwan and the Philippines. On the basis of comparative vegetative and reproductive morphology, and phylogenetic analysis inferred from nuclear-encoded large-subunit ribosomal DNA sequences (LSU rDNA), we conclude that it belongs in the genus Drachiella, tribe Schizoserideae, subfamily Phycodryoideae. The new taxon shares with other Drachiella species the absence of macro- and microscopic veins; diffuse growth by marginal and intercalary meristematic cells; a polystromatic, lobed thallus; abundance of rhizoidal marginal proliferations used for attachment; convoluted plastids in surface cells; abundant secondary pit connections among adjacent vegetative cells; large intercellular spaces between surface cells; procarps confined to the upper side of the thallus, circular in outline, consisting of a supporting cell bearing a strongly curved carpogonial branch and two sterile groups that remain undivided; vertical division of gonimoblast initial from auxiliary cell, and unilateral, monopodial branching of gonimoblasts; and mature cystocarps with a massive candelabrum-like fusion cell of fused gonimoblasts bearing carposporangia in branched chains. It is distinguished from the other members of the genus by thalli that consist of extensive tangled mats of prostrate and overlapping decumbent blades, procarps confined to the upper side of the thallus, and the lack of basal stalks or stipes. Whereas the Schizoserideae is predominantly a Southern Ocean tribe, one of the tribe's four genera, Drachiella, was known only from the eastern Atlantic and Mediterranean. We herein report the first record of the genus for the Indo-Pacific Ocean, and describe Drachiella liaoii, sp. nov., as a fourth species in the genus.

Laurencia Lamouroux (Rhodophyta) was recently separated into three genera – Laurencia, Chondrophycus (Tokida et Saito) Garbary et Harper and Osmundea Stackhouse – each of which was newly defined based on vegetative and reproductive structures. In this study, the previously unknown vegetative and reproductive morphology of two Australian endemic species of Laurencia, L. clavata Sonder and L. elata (C. Agardh) Harvey, was studied, particularly in the context of the revised generic delineation. These species exhibit vegetative axes with four pericentral cells and trichoblast-type spermatangial development. Tetrasporangia are abaxially produced from the existing third and fourth pericentral cells. L. clavata has terete thalli with distinctive verticillate branching and is similar to Chondria C. Agardh, rather than to Laurencia, in having an unusually marked constriction at the base of the branches and starch accumulation in subcortical and medullary cells. Compared to Laurencia, apical cells of this species exhibit a less oblique division; the resulting recognizable axial cell rows extend somewhat below the branches, and particularly at a young stage they are also clear throughout branchlets. However, other vegetative and spermatangial structures show that L. clavata is more closely allied to Laurencia than to Chondria, and it is placed in Laurencia. By contrast, L. elata exhibits morphology typical of Laurencia and is characterized by large, robust, compressed thalli with fastigiately distichous branching and an extensive secondary cortex. Furthermore, it appears to be distinct from similar species in sometimes having a parasitic species of Janczewskia Solms-Laubach (Rhodophyta). Taxonomy of Laurencia is discussed on the basis of these and previous studies.

The reproductive structures in Actinotrichia fragilis (Forsskål) Børgesen are described, including the first report of the structure and development of the carpogonial branch and cystocarp for the genus. Tetrasporangia usually arise in a terminal position on assimilatory filaments; occasionally they are formed laterally and in a secund manner. In male thalli, conceptacles are initiated from the apical pit of a thallus branch. Filaments bearing spermatangia issue from the inner face of the conceptacle wall. In female thalli, a carpogonial branch consists of a carpogonium, hypogynous cell and basal cell. Carpogonial branches may arise in two ways, either replacing a vegetative branch or rarely as a third branch between vegetative dichotomous branches. Before fertilization, the hypogynous cell divides to produce four cells. Subsequently, the basal cell produces branched filaments that eventually form the pericarp, which envelops the carpogonial branch and developing gonimoblast. After fertilization, the carpogonium divides transversely into two cells. The upper progeny cell retains its cytoplasmic connection to the trichogyne. The lower cell produces a lateral gonimoblast initial. Primary gonimoblast filaments form a compact pseudoparenchymatous mass at the base of the carposporophyte. Carposporangia are produced singly from the tips of the secondary gonimoblast filaments, which develop from the primary gonimoblast mass. Many simple or little-branched sterile paraphyses issue from the inner face of the pericarp and grow into the cavity. A comparison of the reproductive structures of Actinotrichia with those of the other genera of the Galaxauraceae suggests that the genus is closely related to Tricleocarpa Huisman et Borowitzka and Galaxaura Lamouroux.

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.

Eighteen collections of red-coloured Audouinella from Central Mexico and southeastern Brazil detected three species. The most common species, A. eugenea, is characterized by macroscopic thalli, the erect system consisting of filaments with cylindrical cells, undifferentiated into proximal and distal parts, and relatively large monosporangia ([ges ] 12·0 μm long). Spermatangia and possible propagules were observed in some Mexican populations. This is the third Audouinella species observed to have gametangia and the first member of the Acrochaetiales with putative propagules. The second species, from Central Mexico, was characterized by the following features: macroscopic thalli, the erect system differentiated into proximal parts with cylindrical cells, unbranched or rarely branched, and distal parts with barrel-shaped cells, abundantly branched to form dense fascicles, with alternate or dichotomous branching, some at right-angles to the axis, and relatively large monosporangia ([ges ] 12·0 μm long). The morphologically distinct proximal and distal portions of the erect system, the latter forming dense fascicles, was a consistent character so far unknown in Audouinella; thus, we propose a new species, A. huastecana sp. nov. The third species is a microscopic epiphyte, A. meiospora, with a well-developed prostrate system composed of creeping and loosely aggregated filaments, and a short homogeneous erect system ([les ] 15 cells) of filaments with cylindrical or barrel-shaped cells and small monosporangia ([les ] 13·0 μm long). A. eugenea and A. meiospora are characterized for the first time from the Southern and Northern Hemispheres, respectively, both occurring mostly in areas of tropical or subtropical rainforests. A. meiospora is reported from new macroalgal hosts. A. eugenea and A. huastecana tended to occur in warm, alkaline waters with a high ion content that were moderate to fast flowing, whereas A. meiospora was not associated with particular habitats.

The only eukaryotes found in highly acidic environments (pH 0·5–3) with elevated temperatures (up to 56 °C) are three species of unicellular red algae: Cyanidioschyzon merolae, Cyanidium caldarium and Galdieria sulphuraria. These habitats are scattered all over the world and are usually very small. Because all three species are strictly acidophilic and will not tolerate desiccation, distribution by wind or water seems very unlikely. The populations in the various habitats might have been isolated for very long times, providing a unique opportunity to observe a significant degree of independent evolution under strong selective pressure. We investigated the biogeography of 18 isolates of these red algae by comparison of partial sequences of the 18S rRNA. A gene tree based on 18S rRNA assigns 15 strains to one branch with high bootstrap values. These isolates share the feature of facultative heterotrophy, whether or not they were originally placed in the genus Galdieria. The remaining three strains – Galdieria maxima, C. merolae and C. caldarium – form a sister clade to this group. The exact position of these two groups in relation to other red algae remains unresolved. The evolutionary distance between individual Galdieria strains is high, indicating that within this genus several races have developed significantly altered 18S sequences. Our comparison of 18S sequences from thermo-acidophilic red algae indicates that even within a seemingly homogeneous group of eukaryotic organisms the limits of phylogenetic analysis may be reached.

The red algae generally are considered to have no motile stages. We have confirmed sporadic reports of motile spores in a few red algae by recording freshly released live spores with time-lapse videomicroscopy. Of the 25+ species investigated, only a few had spores that appeared to be immobile. Cells of unicellular species often displayed active movement although were otherwise indistinguishable from nearby immobile cells, and these may be equivalent to the motile spores released after differentiation in more complex multicellular species. There was considerable variation among members of the Bangiophycidae. Cells of Porphyridium often moved at around 0·66 μm s-1 and had conspicuous mucilage tails. Flintiella and Rhodospora showed no cellular movement. Rhodosorus sometimes moved a little and all four strains displayed continuous cytoplasmic rotation within the wall. Glaucosphaera was inert but displayed formation and transport of vesicles from the perinuclear region to the surface where they were discharged. Spores (whether monospores, tetraspores or carpospores) of almost all other species or strains available displayed various forms of motility. Some (e.g. Batrachospermum-Chantransia monospores) showed smooth, directional and continuous gliding (c. 2·2 μm s-1) for shorter or longer distances, clearly detectable to the naked eye through the microscope. In others, movement could be almost as fast or slower, non-continuous and undirectional. Certain spores (e.g. monospores of the filamentous Audouinella sp.) were amoeboid, and in some cases (e.g. Sahlingia) cells actively squeezed through the irregular interstices of a crustose colony. The mechanism of movement is unknown; polysaccharide secretion may be involved in some cases. These forms of motility may be significant as dispersal mechanisms, by moving spores out of the stagnant boundary layer, and in settling processes, by allowing spores limited ability to optimize their site of germination.