Foliose Red Algae Research Articles

Video survey of deep benthic macroalgae and macroalgal detritus along a glacial Arctic fjord: Kongsfjorden (Spitsbergen)

In Kongsfjorden (Spitsbergen), we quantified the zonation of visually dominant macroalgal taxa and of detached macroalgae from underwater videos taken in summer 2009 at six transects between 2 and 138 m water depth. For the first time, we provide information on the occurrence of deep water red algae below the kelp forest and of detached macroalgae at water depth > 30 m. The presence and depth distribution of visually dominant red algae were especially pronounced at the outer fjord, decreased with proximity to the glacial front and they were absent at the innermost locations. Deepest crustose coralline red algae and foliose red algae were observed at 72 and 68 m, respectively. Brown algae were distributed along the entire fjord axis at 2–32 m. Green algae were only present at the middle to inner fjord and at areas influenced by physical disturbance at water depths of 2–26 m. With proximity to the inner fjord the depth distribution of all macroalgae became shallower and only extended to 18 m depth at the innermost location. Major recipients of detached macroalgae were sites at the shallower inner fjord and at the middle fjord below the photic zone at depths to 138 m. They may either fuel deep water secondary production, decompose or support carbon sequestration. Univariate and community analyses of macroalgal classes including detached macroalgae across transects and over depths reveal a considerable difference in community structure between the outermost sites, the central part and the inner fjord areas, reflecting the strong environmental gradients along glacial fjords.

Slow Community Development Enhances Abiotic Limitation of Benthic Community Structure in a High Arctic Kelp Bed

We examined the patterns of propagule recruitment to assess the timescale and trajectory of succession and the possible roles of physical factors in controlling benthic community structure in a shallow High Arctic kelp bed in the Beaufort Sea, Alaska. Spatial differences in established epilithic assemblages were evaluated against static habitat attributes (depth, distance from river inputs) and environmental factors (temperature, salinity, current speed, underwater light) collected continuously over 2–6 years. Our measurements revealed that bottom waters remained below freezing (mean winter temperatures ∼−1.8°C) and saline (33–36) with negligible light levels for 8–9 months. In contrast, the summer open water period was characterized by variable salinities (22–36), higher temperatures (up to 8–9°C) and measurable irradiance (1–8 mol photons m–2 day–1). An inshore, near-river site experienced strong, acute, springtime drops in salinity to nearly 0 in some years. The epilithic community was dominated by foliose red algae (47–79%), prostrate kelps (2–19%), and crustose coralline algae (0–19%). Strong spatial distinctions among sites included a positive correlation between cover by crustose coralline algae and distance to river inputs, but we found no significant relationships between multi-year means of physical factors and functional groups. Low rates of colonization and the very slow growth rates of recruits are the main factors that contribute to prolonged community development, which augments the influence of low-frequency physical events over local community structure. Mortality during early succession largely determines crustose coralline algal and invertebrate prevalence in the established community, while kelp seem to be recruitment-limited. On scales > 1 m, community structure varies with bathymetry and exposure to freshwater intrusion, which regulate frequency of primary and physiological disturbance. Colonization rates (means of 3.3–69.9 ind. 100 cm–1 year–1 site–1) were much lower than studies in other Arctic kelp habitats, and likely reflect the nature of a truly High Arctic environment. Our results suggest that community development in the nearshore Beaufort Sea occurs over decades, and is affected by combinations of recruitment limitation, primary disturbance, and abiotic stressors. While seasonality exerts strong influence on Arctic systems, static habitat characteristics largely determine benthic ecosystem structure by integrating seasonal and interannual variability over timescales longer than most ecological studies.

Functionality of HELCOM HUB classification in describing variation in rocky shore communities of the northern Baltic Sea

Habitat classification schemes provide tools for harmonized mapping, monitoring and assessment of habitats across regions. They also offer ways to simplify large biodiversity datasets to reveal main environmental and biological characteristics of a region, which might be sufficient level of detail for example in regional planning processes. Since 2013, HELCOM underwater biotope and habitat classification system (HELCOM HUB) has provided a framework to classify the marine underwater nature of the Baltic Sea, but so far, its functionality in describing the variation in Baltic Sea biological communities has only rarely been tested. We tested the functionality of HELCOM HUB in describing variation in rocky shore communities on a large scale, across the Finnish marine area. We found the classification tool very useful in simplifying complex biodiversity data and in creating quantitative presentations on community variation. The results show how the proportional occurrences of different rocky shore communities change in relation to each other along the environmental gradients of the northern Baltic Sea: along the coast in different salinity regimes, from sheltered archipelagos to the open sea and when going from shallow sublittoral to deeper waters. Although the importance of regional habitat classification schemes is recognized, we found also some weaknesses in HELCOM HUB. The red algal communities that are generally recognized as key components of northern Baltic Sea rocky shores were clearly “lost in classification”, although they were shown to be both common and to occur in relatively high coverages, especially in the southwestern part of the study area. This was mainly due to division of red algae into many “sub-groups” at levels 5 and 6 in the classification (e.g. perennial foliose red algae and perennial non-filamentous corticated red algae) that led to their “fragmentation” within the classification. This further resulted in low coverages of red algae within the sub-groups, and finally, in their classification to other classes such as blue mussels or other algal groups. The result highlights the need to consider the restrictions of any classification system when classified data is used in management contexts. When taxa are “lost in classification”, we might not just ignore species or communities, but also key ecosystem functions.

Foliose species of New Zealand red algae: diversity in the genus Tsengia (Tsengiaceae, Halymeniales), including T. northlandica sp. nov.

ABSTRACT Identification of foliose red algae is particularly problematic as many of the characters used, such as general overall habit, colour, and texture, are often dependent on environmental or developmental characteristics of the specimen in question. One foliose red algal genus that has received little attention and is quite common in parts of New Zealand is Tsengia. Collections of multiple foliose specimens of Tsengia from various locations and habitats in New Zealand have highlighted the wide morphological variation that exists within single species. Our molecular data clearly show three foliose species of Tsengia, two of which are associated with previous names (T. laingii, Nemastoma laciniatum) common in southern New Zealand, and one species described from this study, T. northlandica sp. nov., from northern New Zealand. The discovery of another foliose species of Tsengia in Stewart Island suggests greater diversity in this group that will only increase the difficulty in determining species from field collections. While these foliose species are distinct using various molecular species delimitation techniques, morphologically they are extremely diverse (plastic) with overlapping habits.

Plant Part Age and Size Affect Sessile Macrobenthic Assemblages Associated with a Foliose Red Algae Phycodrys rubens in the White Sea

Facilitation by foundation species commonly structures terrestrial and marine communities. Intraspecific variation in individual properties of these strong facilitators can affect the whole suite of the dependent taxa. Marine macroalgae often act as ecosystem engineers, providing shelter and substrate for numerous associated organisms. Epibiosis of foliose red algae, however, remains underexplored, especially in the high latitudes. Here we studied sessile macrobenthic assemblages associated with a foliose red algae Phycodrys rubens in the White Sea (66° N) shallow subtidal, and the effect of individual plant properties on their structure. The blades of P. rubens develop annually, and it is possible to tell the young (usually larger) plant parts from the old ones. We hypothesized that epibenthic community structure depends on plant part age and size. We examined epibiosis on 110 plants at two sites, and the results generally supported our hypotheses. Old plant parts were several times smaller, and had higher total cover than young parts. Sponges strongly dominated the epibiosis on old parts, and young parts were dominated by polychaetes and bryozoans. Plant part surface area negatively correlated with total cover on young parts, while on old parts the relatioship was location-specific. On young parts the relative abundance of a polychaete Circeis armoricana increased with surface area, and the proportion of sponges decreased. The patterns indicate that epibenthic community structure is linked to the demography of an ecosystem engineer.

Increased sediment load during a large-scale dam removal changes nearshore subtidal communities.

The coastal marine ecosystem near the Elwha River was altered by a massive sediment influx—over 10 million tonnes—during the staged three-year removal of two hydropower dams. We used time series of bathymetry, substrate grain size, remotely sensed turbidity, scuba dive surveys, and towed video observations collected before and during dam removal to assess responses of the nearshore subtidal community (3 m to 17 m depth). Biological changes were primarily driven by sediment deposition and elevated suspended sediment concentrations. Macroalgae, predominantly kelp and foliose red algae, were abundant before dam removal with combined cover levels greater than 50%. Where persistent sediment deposits formed, macroalgae decreased greatly or were eliminated. In areas lacking deposition, macroalgae cover decreased inversely to suspended sediment concentration, suggesting impacts from light reduction or scour. Densities of most invertebrate and fish taxa decreased in areas with persistent sediment deposition; however, bivalve densities increased where mud deposited over sand, and flatfish and Pacific sand lance densities increased where sand deposited over gravel. In areas without sediment deposition, most invertebrate and fish taxa were unaffected by increased suspended sediment or the loss of algae cover associated with it; however, densities of tubeworms and flatfish, and primary cover of sessile invertebrates increased suggesting benefits of increased particulate matter or relaxed competition with macroalgae for space. As dam removal neared completion, we saw evidence of macroalgal recovery that likely owed to water column clearing, indicating that long-term recovery from dam removal effects may be starting. Our results are relevant to future dam removal projects in coastal areas and more generally to understanding effects of increased sedimentation on nearshore subtidal benthic communities.

Molecular Assisted Identification Reveals Hidden Red Algae Diversity from the Burica Peninsula, Pacific Panama

The marine flora of Panama harbors a rich diversity of green, red and brown algae, and despite chronic understudy, it is reported as the second most diverse marine flora along the Pacific Central American coast, with 174 macroalgal species. Extensive new collections and molecular assisted identification (MAI) by an international team of researchers has revealed an even greater diversity for this country. Here, the intertidal and shallow subtidal marine flora of the remote Burica Peninsula is introduced. This area is characterized by an uplifted extensive intertidal flat composed of firm, sedimentary benthos known as mudrock, on which abundant algal communities thrive, even during extended periods of exposure. A collection of nearly 200 brown, green and red macroalgae specimens representing the first marine floristic inventory of this region was made in January 2011, and results of analyses of 45 foliose red algae specimens are presented. DNA sequence data for several loci (rbcL-3P; COI-5P; UPA) have been generated for molecular assisted identification and to guide morphological assessments. Twenty-six species were identified among the specimens including 21 new Pacific Panama records, as well as previously unrealized transisthmian distributions, and two new species, Neorubra parvolacertoides sp. nov. and Grateloupia irregularis sp. nov.

Amalthea and Galene, two new genera of Halymeniaceae (Rhodophyta) from New Zealand

Abstract New Zealand foliose red algae belonging to the family Halymeniaceae were examined with a focus on species that have been placed in the genera Halymenia and Cryptonemia. Phylogenetic analyses of plastid-encoded rbcL and morphological observations were undertaken. Samples from northern New Zealand, referred to as Halymenia latifolia, were compared genetically with H. latifolia from its type locality in France. The New Zealand material was clearly separate from the genus Halymenia and from H. latifolia, and was found to be closely related to Halymenia abyssicola from Mexico. The new genus Amalthea is described to accommodate the New Zealand taxon. Samples referred to Cryptonemia sp. from New Zealand formed a well-supported clade with Cryptonemia rotunda from Korea and Japan. This clade was distinct from the clade containing the generitype Cryptonemia lomation from France and other species of Cryptonemia. We propose a new genus Galene to include three species from New Zealand, two of which are described as new here and transfer Cryptonemia rotunda to this new genus.

First record of Schizymenia apoda (Schizymeniaceae, Rhodophyta) in New Zealand

The foliose red alga Schizymenia apoda (Schizymeniaceae) is reported for the first time in New Zealand waters. Its identity was confirmed by rbcL sequence data and morphological observations. This alga has been reported from both the Atlantic and the North Pacific and, although it is very variable in colour and habit, it is easily distinguished morphologically by the presence of refractive gland cells (visible in surface view), large cystocarps with a pronounced ostiole, and the lack of tetrasporophyte blades. Although not reported as an introduced species elsewhere, in New Zealand S. apoda was collected at the ferry terminal and on pontoons and pilings in the marinas of Wellington Harbour. It was also discovered in Otago Harbour. The examination of herbarium specimens and recent collections from areas outside the harbour has resulted in only a few samples that could be referred to this species, leading us to consider this a new introduction.

Temperature and community consequences of the loss of foundation species: Surfgrass ( Phyllospadix spp., Hooker) in tidepools

By ameliorating environmental conditions, mediating species interactions and regulating resource availability in ecosystems, habitat-forming, foundation species underlie the structure and function of many ecological communities. Current and predicted human-induced changes to ecosystems require a mechanistic understanding of how foundation species enable the persistence of diverse, functioning ecological communities. By manipulating the abundance of a putative foundation species of rocky intertidal tidepool communities, the seagrass Phyllospadix spp. (surfgrass), this study assesses how surfgrass affects the thermal environment and structure of tidepool communities over a period of two years. Surfgrass removal pools experienced temperatures up to 10 °C higher than control pools during low tide. Changes in community composition of sessile organism accompanied this change in thermal regime. Over two years, removal pools saw a significant decline in the abundance of coralline crusts and bare space and an increase in the abundance of foliose red algae while control pool communities remained stable. At the level of functional groups, community similarity metrics showed pool communities became more variable in space in response to surfgrass removal, demonstrating that pool communities diverge dramatically in the absence of surfgrass. In removal pools, recovery of surfgrass was limited with less than 25% of pre-removal abundance after two years. However, removal pool communities shifted toward species compositions that favor surfgrass recruitment and suggest a mechanism by which surfgrass recovery may be enhanced over the long-term. Surfgrass clearly play a foundational role in tidepools by reducing pool temperatures and act to stabilize tidepool communities.

Scale-dependent relationships between benthic habitat characteristics and abundances of blacklip abalone, Haliotis rubra (Leach)

Habitat characteristics can influence marine herbivore densities at a range of spatial scales. We examined the relationship between benthic habitat characteristics and adult blacklip abalone (Haliotis rubra) densities across local scales (0.0625–16 m2), at 2 depths, 4 sites and 2 locations, in Tasmania, Australia. Biotic characteristics that were highly correlated with abalone densities included cover of non-calcareous encrusting red algae (NERA), non-geniculate coralline algae (NCA), a matrix of filamentous algae and sediment, sessile invertebrates, and foliose red algae. The precision of relationships varied with spatial scale. At smaller scales (0.0625–0.25 m2), there was a positive relationship between NERA and ERA, and negative relationships between sediment matrix, sessile invertebrates and abalone densities. At the largest scale (16 m2), there was a positive relationship between NERA and abalone densities. Thus, for some biotic characteristics, the relationship between NERA and abalone densities may be scalable. There was very little variability between depths and sites; however, the optimal spatial scale differed between locations. Our results suggest a dynamic interplay between the behavioural responses of H. rubra to microhabitat and/or to abalone maintaining NERA free of algae, sediment, and sessile invertebrates. This approach could be used to describe the relationship between habitat characteristics and species densities at the optimal spatial scales.

Western rock lobsters ( Panulirus cygnus) in Western Australian deep coastal ecosystems (35–60 m) are more carnivorous than those in shallow coastal ecosystems

The western rock lobster ( Panurilus cygnus George.) is a conspicuous consumer in the coastal ecosystems of temperate Western Australia. We used stable isotope analysis and gut content analysis to determine the diet and trophic position of western rock lobsters from mid-shelf coastal ecosystems (35–60 m depth) at three locations. Lobsters were primarily carnivorous, and no consistent differences in diet were detected with varying lobster size, sex or among locations. The main components of the diet were bait (from the fishery) and small crustaceans – crabs and amphipods/isopods. Foliose red algae, bivalves/gastropods and sponges were minor contributors to diet. The diet of lobsters in deep coastal ecosystems differed from the results of previous studies of diets of lobsters from shallow coastal ecosystems. In particular, coralline algae and molluscs – important prey in studies of lobsters from shallow coastal ecosystems – were minor components of the diet. These differences are likely to reflect differences in food availability between these systems and potentially, differences in choice of prey by lobsters that inhabit deeper water. Given the high contribution of bait to lobster diet, bait is likely to be subsidizing lobster production in deep coastal ecosystems during the fishing season.

In situ quantification of a natural settlement cue and recruitment of the Australian sea urchin Holopneustes purpurascens

In the first study of its kind, the recruitment of the Australian sea urchin Holopneustes purpurascens is compared to quantitative in situ measurements of a nat- urally occurring settlement cue, histamine. More than 90% of new recruits were found on either the foliose red alga Delisea pulchra or on coralline turf algae while 8% of recruits were found on the brown alga Homeostrichus olsenii. These algae induced the settlement (and meta- morphosis) of almost all larvae in laboratory assays after 24 h. No new recruits were found on Ecklonia radiata or Sargassum vestitum and unfouled E. radiata induced low levels of settlement in laboratory assays. Thus, the algae on which we found the most recruits in the field induced the highest rate of settlement in laboratory assays. D. pul- chra contained far higher levels of histamine than all other algae and the coralline algae lacked measurable histamine. Seawater collected in situ adjacent to D. pul- chra induced low levels of settlement of aged larvae in laboratory assays and contained the highest concentra- tion of histamine (~5 nM). With the exception of coralline algae, variation in settlement and recruitment was consis- tent with the variation among species histamine contents. Antibacterial treatment of Amphiroa anceps greatly reduced the number of larvae settling in response to the alga. Biofilms of 2 bacterial strains isolated from the sur- face of coralline algae induced settlement of 20 to 43% larvae in laboratory assays after 96 h and media in which these strains were cultured contained more histamine. These initial results support a biofilm derived settlement cue for larval H. purpurascens from coralline algae.

TEN YEARS OF INDUCED OCEAN WARMING CAUSES COMPREHENSIVE CHANGES IN MARINE BENTHIC COMMUNITIES

One of the most commonly predicted effects of global ocean warming on marine communities is a poleward shift in the distributional boundaries of species with an associated replacement of cold-water species by warm-water species. However, these types of predictions are imprecise and based largely on broad correlations in uncontrolled studies that examine changes in the distribution or abundances of species in relation to seawater temperature. Our study used an 18-year sampling program in intertidal and subtidal habitats and before-after, control-impact analyses. We show that a 3.58C rise in seawater temper- ature, induced by the thermal outfall of a power-generating station, over 10 years along 2 km of rocky coastline in California resulted in significant community-wide changes in 150 species of algae and invertebrates relative to adjacent control areas experiencing natural temperatures. Contrary to predictions based on current biogeographic models, there was no trend toward warmer-water species with southern geographic affinities replacing colder- water species with northern affinities. Instead, the communities were greatly altered in apparently cascading responses to changes in abundance of several key taxa, particularly habitat-forming subtidal kelps and intertidal foliose red algae. Many temperature-sensitive algae decreased greatly in abundance, whereas many invertebrate grazers increased. The responses of these benthic communities to ocean warming were mostly unpredicted and strongly coupled to direct effects of temperature on key taxa and indirect effects operating through ecological interactions.

Seasonal changes in an intertidal annual algal assemblage in northern Japan: The role of pre‐emption and grazing on algal replacement

The pattern and process of seasonal changes in an intertidal annual algal assemblage were examined at Hiura, northern Japan. Short‐term field experiments (<2 months’ duration) were set up to quantify the effects of both grazing and pre‐emption on species replacement in the assemblage in three different seasons. An 8‐month field experiment was set up to quantify long‐term effects, including the indirect effects of both grazing and competitive dominance on the community structure. Results suggested that seasonal change in the algal assemblage resulted from the interaction of abiotic environmental change, competition and grazing. The relative contribution of these factors varied within a short period, presumably as a result of seasonal changes in physical environmental stress, free space availability and grazing pressure. From February to March, when grazer density was low and there was much free space available for algae, the dominant species shifted from foliose green alga Monostroma angicava to filamentous red alga Bangia atropurpurea, because B. atropurpurea grew faster than M. angicava. This species replacement was not influenced strongly by biological interaction but by temporal changes in abiotic environmental conditions. From April to mid May, when there was less free space available for algae in the natural community, the dominant B. atropurpurea decreased with increasing foliose red alga Porphyra yezoensis, because only P. yezoensis was able to invade an area pre‐empted by algae. Grazing did not affect this species replacement. After mid May, the two dominant species, P. yezoensis and B. atropurpurea, decreased. Their decline was mainly caused by desiccation stress and was partially affected by grazing.

50 Can the effects of ocean warming on temperate reef communities be accurately predicted? lessons from a large scale, long term field experiment in central California

One of the most commonly predicted effects of global ocean warming on marine communities is a poleward shift in the distribution of species with an associated replacement of cold‐water species by warm‐water species. Such predictions are imprecise and based largely on broad correlations in uncontrolled studies that examine changes in species composition and abundance relative to seawater temperature. Before‐After‐Control‐Impact (BACI) analyses of the effects of a large thermal discharge shows that an induced 3.4 deg. C rise in seawater temperature over 10 years along 2 km of rocky coastline resulted in significant community‐wide changes in 150 species of algae and invertebrates relative to controls. Contrary to predictions from biogeographic models, there was no trend towards warm‐water species with southern geographic affinities replacing cold‐species with northern affinities. Instead, communities were greatly altered in apparently cascading responses to changes in abundance of several habitat‐forming taxa, particularly subtidal kelps (e.g. Pterygophora californica) and intertidal foliose red algae (e.g. Mazzaella flaccida). Many temperature sensitive algae decreased greatly in abundance, whereas many invertebrate grazers increased. The results indicate that the responses of temperate reef communities to ocean warming can be strongly coupled to direct effects on habitat‐forming taxa and indirect effects operating through ecological interactions. Given our understanding of temperate reef ecology and its local variability, the results also suggest that accurate predictions of the effects of global ocean warming will be difficult to make.

Rhodolith bed diversity in the Gulf of California: the importance of rhodolith structure and consequences of disturbance

Rhodolith beds, unattached coralline reefs, support a high diversity and abundance of marine species from both hard and soft benthos. We used surveys in multiple shallow (3-20 m) beds in the Gulf of California to (1) examine seasonal patterns in associated floral and faunal diversity and abundance, (2) compare differences in faunal associations between rhodolith beds and adjacent sedimentary habitats, (3) examine the importance of complexity of rhodolith structure to community structure, and (4) estimate the impact of anthropogenic disturbance on rhodoliths and associated species. 2. Macroalgal richness was seasonal, and beds supported higher richness in winter (to 36 species) than summer (6-7 species), primarily due to foliose red algae. Strong seasonal variation in the abundance of dominant cover organisms was due to a shift from macroalgae and mat-forming colonial invertebrate species to microalgae. 3. The community in a rhodolith bed of high-density thalli (El Coyote average 11000 thalli/ m 2 ) had higher richness (52 versus 30 species) and abundance of epibenthic and crypto- and in- faunal species compared with an adjacent sand community. Species diversity and abundance was particularly high for unique cryptofaunal organisms associated with rhodolith interstices. Cryptofauna reached average densities of 14.4 organisms/ cm 3 rhodolith, the majority of which were crustaceans, polychaetes and cnidarians along with rhodolith-specific chitons. 4. Results from sampling across a range of rhodolith morphs in the El Requeson bed (with lower average cryptofaunal densities of 2.3 organisms/ cm 3 ) revealed that the total organisms supported by a rhodolith significantly increased with both complexity (branching density) and space available (thallus volume). These data suggest that reducing the population size structure, structural complexity and cover of living rhodoliths could decrease species richness and abundance. 5. While disturbance is a natural feature of these free-living beds, increased anthropogenic disturbance from trawling, anchoring and changes in water quality can directly impact the bed community through substrate alteration. Commercial fishing threatens rhodolith beds in the Gulf of California by decreasing rhodolith size and increasing sedimentation and burial rates. In addition to

Use of Cell‐Specific PAM‐Fluorometry to Characterize Host Shading in the Epiphytic Dinoflagellate Gambierdiscus toxicus

Abstract. Cell‐specific fluorescence characteristics were used to characterize the light tolerance of the toxic benthic dinoflagellate Gambierdiscus toxicus. The fluorescence parameter Fv : Fm was measured using pulse amplitude modulation (PAM) fluorometry on individual cells collected from foliose red algae growing in the sub‐tidal margin of South Water Cay, Belize. Samples were collected over several days during sunny and cloudy conditions and compared to samples incubated in situ. The data from individual cells were used to generate both Fv : Fm frequency histograms and averages. Maximum individual cell values of Fv : Fm reached 0.81 in pre‐dawn samples, a value near the theoretical maximum for PAM fluorometry. In field samples from macroalgal hosts, average Fv : Fm values declined only slightly during the day, but cells incubated in bottles under 47 % incident sunlight showed a significant mid‐day depression. In freshly collected samples, near‐maximum Fv : Fm values could be found in individual cells during the entire day; however, the frequency histograms indicated a greater range in Fv : Fm values during the afternoon than in the morning. In contrast, cultures of G. toxicus showed a tight distribution around a mean. Field samples showed a rapid recovery to near‐maximum Fv : Fm within 2 min when assayed using a standardized actinic light series. Similar results were obtained in laboratory cultures of G. toxicus grown at 73 µmol photons · m‐2 · s‐1, but not at 383 µmol photons · m‐2 · s‐1. These data provide empirical support for suggestions that G. toxicus exploits the three‐dimensional structure of the algal host thallus to minimize light exposure. This strategy permits G. toxicus, a high‐light intolerant species in culture, to thrive in shallow, well‐lit tropical seas. It may also partially explain the observed preference of G. toxicus for complex, foliose macroalgae as hosts.

Host specificity of the endophytic sporophyte phase of Acrosiphonia (Codiolales, Chlorophyta) in southern British Columbia, Canada

We investigated the host specificity of Acrosiphonia’s (Codiolales, Chlorophyta) endophytic sporophyte phase, previously identified as Chlorochytrium inclusum and Codiolum petrocelidis. In southern British Columbia, Canada, ‘Chlorochytrium inclusum’ is abundant in the foliose red alga, Mazzaella splendens, whereas ‘Codiolum petrocelidis’ densely colonizes the red algal crust, Petrocelis franciscana. Examination of foliose and crustose algae revealed a wide range of alternate hosts for Acrosiphonia sporophytes. Three foliose red algae, M. heterocarpa, M. sanguinea and Sparlingia pertusa, and two crustose algae, Raifsia pacifica and Hildenbrandia occidentalis, are newly reported hosts for ‘Chlorochytrium’ and ‘Codiolum’. This is the first study to report ‘Codiolum’ colonization of a brown alga (= Raifsia), and foliose brown and green algae have never been reported to be colonized by ‘Chlorochytrium’. ‘Codiolum’ demonstrated a greater affinity for Petrocelis than for other coexisting crustose algae, and ‘Chlorochytrium’ colonized some foliose red algal species more frequently than others. Endophyte density data suggest that variations in structural composition among host species (i.e. how closely appressed the filaments are in crusts, and the compactness in the cells of the cortex and medulla of foliose red algae) may be important in determining the ease of penetration by the endophyte. Host cell wall composition is suspected to play a role in preferential colonization by ‘Chlorochytrium’. Carrageenophytes and carragar-producing hosts were colonized by higher densities of ‘Chlorochytrium’ than were agarophytes. The hypothesis that host life history phases might be differentially susceptible to colonization by endophytes was not supported in our study; among host species with an alternation of generations neither the gametophytes nor the sporophytes seemed to be consistently more heavily colonized.

Life history of Acrosiphonia (Codiolales, Chlorophyta) in southwestern British Columbia, Canada

This study establishes the phenology of the alternate life history phases of the green alga Acrosiphonia in British Columbia, Canada. Free-living, filamentous plants are seasonal, March-July, with peak percent cover (10%) in April. Plants are fertile immediately after establishment. The unicells, previously identified as Chlorochytrium inclusum and Codiolum petrocelidis, are the sporophyte phase of Acrosiphonia. 'Chlorochytrium,' spherical and 160-280 μm in diameter, colonizes the foliose red alga Mazzaella splendens 1 mo after filamentous Acrosiphonia plants appear. Maximum density (53 'Chlorochytrium' cells/cm(2) of blade) was recorded in May. 'Codiolum,' on the other hand, is stalked (the vesicle measures 150 × 50 μm) and colonizes the red algal crust Petrocelis. Peak density (22 400 'Codiolum' cells/cm(2) of crust) was recorded 2 mo after 'Chlorochytrium' density peaked. The endophytes survive high summer temperatures, which correlate with death of the free-living plants, and overwinter in their hosts. Zoospore release in late winter corresponds to decreased host abundance, suggesting the endophytes have evolved a strategy whereby duration in the host is synchronized with host seasonality. A bet-hedging strategy is proposed for Acrosiphonia's life history: two morphologically different phases have adapted to a seasonally variable environment, with the sporophyte phase capable of colonizing two different hosts.