Hildenbrandia Rubra Research Articles

The Marine Benthic Algae Diversity of Gabon: Case of the Rocky Foreshore of Cap Estérias

This study has allowed to classify the marine macroalgae from the intertidal zone on the Atlantic side of Cap Estérias (Gabon). This area has a rich biodiversity but very few studies in the knowledge of benthic macroalgae have been done. The first study on the knowledge of the algae of the Gabonese coast was made in February 1974 by John and Lawson. This article has been revised to transcribe books and our study would aim to update the existing collection. The algae census is spread over a year from August 2020 to August 2021 and is the first detailed study carried out over a year, with regard to this part of the Gabonese coast. This study has allowed to know the specific diversity, to determine the structure of the flora and its spread out over time. The results show a significant algal diversity of thirty five (35) identified species. Three classes of macroalgae were determined and the percentage of species in the class (%EC): Floridaophyceae at 50% EC, Phaeophyceae at 30% EC and Ulvophyceae at 20% EC. The red algae are the most common in the area with sixteen (16) species determined against twelve (12) species of brown algae and seven (7) species of green algae. The Phaeophyceae class presents the Dictyotaceae family which is the most diverse with 7 species found. Some species seen appear in the collection of John et al., but others are new species encountered in Gabon such as Caulerpa sertularioides, Bryopsis plumosa (two Ulvophytes), Padina arborescens which is a Pheophyte and Galaxaura filamentosa, Digenea simplex,Hildenbrandia rubra, Asparagopsis armata and Caulacanthus ustulatus which are Rhodophytes. Some species are permanently present, they are found in all seasons but with significant abundance from July to September.

Fucus vesiculosus adapted to a life in the Baltic Sea: impacts on recruitment, growth, re-establishment and restoration

Abstract Fucus vesiculosus is common both on the tidal coasts of the North Atlantic and in the Baltic Sea, where it has adapted to low salinity and nontidal conditions over the last 7000 years. During the late 1970s and early 1980s, extensive declines of F. vesiculosus populations were reported in the Baltic Proper, mainly attributed to high nutrient loads. During the past 30–40 years, considerable efforts have been made to reduce nutrient runoff to coastal areas but few successful initiatives to restore F. vesiculosus populations have been performed. In this paper, we present how substratum manipulation, i.e. clean rocky surfaces, brushing rocks, Hildenbrandia rubra cover and different filamentous algae, as well as different algal exudates, affect the recruitment and survival of juvenile F. vesiculosus. Further, we show through a 5-year field experiment that it will take at least 4–5 years to reach reproductive age for F. vesiculosus in the Baltic Sea. We also present transplantation studies from two different areas, showing that epiphytic load, light, grazing and type of substratum are some of the factors that need to be taken into consideration in order to achieve successful restoration of F. vesiculosus.

한국 동해안 중부의 저서 해조류 군집

Benthic marine algal flora and community structure at Chuksan on the mid-east coast of Korea were investigated seasonally from July 2007 to May 2009. Ninety-eight seaweed species were identified, including 13 green, 23 brown and 62 red algal species. The number of species found ranged between 33 and 63 among seasons. Two green (Ulva australis and Codium arabicum), three brown (Dictyota dichotoma, Sargassum fusiforme and Sargassum yezoense), and eleven red algae (Corallina pilulifera, Lithophyllum okamurae, Pachymeniopsis elliptica, Grateloupia filicina, G. cornea, Hildenbrandia rubra, Chondrus ocellatus, Acrosorium polyneurum, Chondria crassicaulis, Polysiphonia morrowii and Symphyocladia latiuscula) were observed throughout the survey period. Average marine algal biomass was and it ranged seasonally from 119.30 to . The vertical distribution of marine algae was characterized by Corallina pilulifera and Sargassum spp. in the intertidal zone; Sargassum spp. at 1 m depth; Sargassum spp. and melobesioidean algae at 5 m depth; and melobesioidean algae at 10 m depth.

New additions to the benthic marine flora of Kongsfjorden, western Svalbard, and comparison between 1996/1998 and 2012/2013

Abstract We did a survey on macroalgal diversity along a transect off Hansneset (78°39′N, 11°57′E), Kongsfjorden, western Svalbard, between 0- and >15-m depths in 2012/2013. One major intention was to compare our data to a similar study performed in 1996/1998 at the same site and to document possible changes. We identified 58 species of macroalgae, 12 Chlorophyta, 31 Phaeophyceae, and 15 Rhodophyta. One species (Sphacelorbus nanus) is a new record for Svalbard. Fourteen species are new records for the Kongsfjorden area. Fertile tetrasporophytes of Turnerella pennyi (Cruoria phase) and the microscopic Chlorochytrium stage of Spongomorpha aeruginosa are also recorded for the first time from Svalbard. An increase from 20 to 45 species in the littoral in 2012/2013 compared with 1996/1998 was recorded. This study increases the total macroalgal species diversity of Kongsfjorden to 76. While 62 species were found in 1996/1998 and 58 in 2012/2013, only 42 were common to both investigations. We have made some taxonomic annotations to 20 species/genera. Strikingly, we did not find again some red algae, such as Hildenbrandia rubra, Palmaria palmata, Polysiphonia spp., or Scagelia pylaisaei, that had been recorded in 1996/1998. Possible reasons for the changes based on recent knowledge from Kongsfjorden are discussed.

한국 남서해안 흑산도와 홍도의 조간대 해조류 생물량과 군집구조의 계절적 변동

Seasonal variation in marine macroalgal community structure was examined at the intertidal zones of Heuksando and Hongdo, Shinan, Korea, from July 2008 to May 2009. In total, 86 macroalgal species were identified, including 12 green, 19 brown, and 55 red algae; 67 species at Heuksando and 70 species at Hongdo, were observed. Annual seaweed biomass was 252.44 g dry <TEX>$wt/m^2$</TEX> at Heuksando and 217.67 g dry <TEX>$wt/m^2$</TEX> at Hongdo. The dominant seaweed in importance value (IV > 15) differed between the sites: Sargassum thunbergii at Heuksando and Corallina pilulifera at Hongdo. The vertical distribution pattern of seaweeds from the upper to lower intertidal zones at Heuksando was Gloiopeltis spp., Ulva spp. - S. thunbergii, S. fusiforme, Hildenbrandia rubra - S. thunbergii, C. pilulifera. On the rocky shore of Hongdo, seaweed zonation was distinct: Porphyra yezoensis, Gloiopeltis spp., Ulva spp. - C. pilulifera, S. fusiforme, Myelophycus simplex - Chondrus ocellatus, C. pilulifera, and Carpopeltis affinis. Annual seaweed coverage, richness index (R), evenness index (J'), and diversity index (H') values were greater at Hongdo (41.35%, 12.82, 0.59, and 2.50 respectively) than at Heuksando (31.54%, 11.93, 0.44, and 1.87 respectively), which may indicate that the seaweed community at Hongdo is more stable relative to the one at Heuksando.

납작돌잎(Lithophyllum yessoense)과 진분홍딱지(Hildenbrandia rubra)의 포자방출 및 생장에 미치는 수온의 영향

The effects of temperature on spore release, growth and photosynthetic efficiency of Lithophyllum yessoense and Hildenbrandia rubra were examined. L. yessoense was collected at Galnam and H. rubra was collected at Gyeokpo, Korea. The experimental temperatures were different for spore release (10, 15, <TEX>$20^{\circ}C$</TEX>), sporeling growth (10, 15, 20, 25, <TEX>$30^{\circ}C$</TEX>) and photosynthetic efficiency (10, 15, 20, <TEX>$25^{\circ}C$</TEX>). All other culture conditions were the same: 34 psu, 12:12 LD and <TEX>$50{\mu}mol$</TEX> photon <TEX>$m^{-2}s^{-1}$</TEX>. Spore liberation was maximal at <TEX>$10^{\circ}C$</TEX> for L. yessoense and at <TEX>$20^{\circ}C$</TEX> for H. rubra. After 14 days, the surface area of L. yessoense was 0.031 <TEX>$mm^2$</TEX> at <TEX>$25^{\circ}C$</TEX> and for H. rubra was 0.032 <TEX>$mm^2$</TEX> at <TEX>$20^{\circ}C$</TEX>. Sporelings of L. yessoense were a dark-red color and grew in a round shape. In contrast, H. rubra was bright pink and changed from a round shape in the early growth stage to later become flabelliform. Photosynthetic efficiency was highest between <TEX>$20-25^{\circ}C$</TEX> in both species. In conclusion, L. yessoense and H. rubra display different physiological features based on the optimal temperatures for spore release and sporling growth.

Fluorescence responses of photosynthesis to extremes of hyposalinity, freezing and desiccation in the intertidal crust Hildenbrandia rubra (Hildenbrandiales, Rhodophyta)

K.Y. Kim and D.J. Garbary. 2006. Fluorescence responses of photosynthesis to extremes of hyposalinity, freezing and desiccation in the intertidal crust Hildenbrandia rubra (Hildenbrandiales, Rhodophyta). Phycologia 45: 680–686. DOI: 10.2216/05-43.1A winter collection of the intertidal, red algal crust, Hildenbrandia rubra (Sommerfelt) Meneghini, was examined for tolerance of photosynthesis to extremes of temperature, salinity and desiccation. Pulse amplitude modulation fluorometry of chlorophyll a fluorescence was used to determine various photosynthetic parameters including effective quantum yield (ΦPSII) and relative electron transport rate (rETR). Thalli from the same collection were successively exposed to freezing, desiccation, hyposalinity and high temperature. Thus thalli over 13 days experienced temperature fluctuations from −17 to 27°C, from fully hydrated to extremely desiccated, from full seawater to 4 psu and back, all without any apparent long-term effects to the photosynthetic apparatus. There was no significant difference in ΦPSII between thalli at the beginning and end of the experiments. Algae showed a significant acclimation to low light in that immediately after collection thalli had optimum light intensity, Ik, in terms of rETR at 50 μmol photons m−2 s−1, whereas 24 h later maximal rETR was at about 20 μmol photons m−2 s−1. Hildenbrandia rubra is the most physiologically tolerant of any tested seaweed, and this helps explain its wide geographic and ecological range.

Why overgrowth of intertidal encrusting algae does not always cause competitive exclusion

Encrusting algae are well-known to be able, for long periods, to withstand shading and overgrowth by other organisms. How this is achieved remains a mystery. It had been proposed that connections with unshaded (non-overgrown) parts of the thallus may allow transfer of nutrients to the shaded part. From this model, I proposed and tested the hypothesis that shaded patches of the intertidal red alga, Hildenbrandia rubra, would survive overgrowth longer, or better, when connected to unshaded thallus than when experimentally separated from surrounding alga. Experimental treatments were shading (black or transparent 80 mm perspex discs or no cover) and scraping (scraped around the disc to remove contacts, a control for effects of scraping, no treatment). The 9 orthogonal combinations of cover and scraping were applied to 3 independent, random replicates (i.e. 27 plots) in each of four randomly chosen sites. In all 4 sites, over 13 months, shaded H. rubra survived in greater abundance (as % cover) where in contact with surrounding thallus. In one site, there was no effect of shading unless the thallus was isolated. In two sites, shading reduced cover, but was more deleterious where the thallus was isolated. In the fourth site, there were artefacts due to a perspex cover, but still less cover of alga where it was isolated. This encrusting alga can withstand a long period of complete shading, provided there is connection to unshaded thallus. Interpreting or predicting overgrowth interactions in terms of competitive outcomes is therefore dependent on consideration of whether the overgrown species is actually being affected. It also depends on the duration of overgrowth and, as shown here, the extent to which connectivity with unshaded thallus is effective at preventing or reducing any consequences. Observations and experiments that do not ascertain these are difficult to interpret.

Effects of small-scale disturbances of canopy and grazing on intertidal assemblages on the Swedish west coast

The effects of small-scale disturbances (80×30-cm plots) of canopy and grazers on intertidal assemblages were investigated in this 4-year experiment on sheltered rocky shores on the Swedish west coast. Canopy disturbances due to ice scouring were mimicked by removal of adult plants of the seaweed Ascophyllum nodosum (L.) Le Joli. Density of the main epilithic grazing gastropods, Littorina spp., was lowered by exclosure and handpicking. Based on earlier experiments in other areas, the general hypothesis was that canopy removal and grazer exclosure, alone or in combination, should increase the recruitment of A. nodosum or other fucoid juveniles, and change the structure of the understorey assemblage. There was an effect of canopy removal on the development of this assemblage, lasting for more than 31 months. Both increased and decreased abundances of species were found as short-term effects, but there was also a longer-term effect with increased abundance. Grazer exclosure was only effective in combination with canopy removal, causing a short-term increase in ephemeral green algae. Short-term effects of canopy removal were also the increase in recruitment of Semibalanus balanoides (Linnaeus) and the decrease of the red alga Hildenbrandia rubra (Sommerfelt) Meneghini. Fast recruitment and growth of fucoid species ( Fucus serratus L. and F. vesiculosus L.) restored the canopy and conditions of the understorey within 18 months. Thus, the canopy removal changed the physical conditions for the understorey, making it possible for other species to coexist in this community. Surprisingly, no effect of canopy removal or grazer exclusion was found on the recruitment of juvenile A. nodosum, neither by canopy removal nor grazer exclosure. The lack of such effects might be due to the early mortality caused by other grazers (small, mobile crustaceans), or to the low density of periwinkles on these shores. However, despite the patchy and generally low recruitment of A. nodosum juveniles, observations suggested that the cover of A. nodosum in manipulated patches would return to initial levels, either by recruitment or regrowth of small holdfasts and from growth of edge plants.

Taxonomic Notes on Marine Algae from Malaysia. II. Seven Species of Rhodophyceae

Six species of marine algae are reported from Malaysia for the first time and their characteristic features are described: Hildenbrandia rubra (Sommerfelt) Meneghini (Hildenbrandiales, Hildenbrandiaceae); Grateloupia filicina (Lamouroux) C. Agardh (Cryptonemiales, Halymeniaceae); Taenioma perpusillum (J. Agardh) J. Agardh, Taenioma dotyi Hollenberg and Zellera tawallina Martens (Ceramiales, Delesseriaceae), and Amansia rhodantha (Harvey) J. Agardh (Ceramiales, Rhodomelaceae). The occurrence of Taenioma dotyi in Malaysian waters is the first report outside the Hawaiian Islands. Amansia rhodantha is newly recorded for the Pacific Ocean. The presence of Gelidiella pannosa (Feldmann) Feldmann et G. Hamel (Gelidiales, Gelidiaceae) in Malaysia is confirmed.

Spatial and temporal variation of cyanobacteria-dominated epilithic communities on a tropical shore in Hong Kong

Species abundance (percentage surface cover) and overall biomass (chlorophyll a) of cyanobacteria-dominated epilithic communities were assessed for 19 months on a semiexposed. rocky shore in Hong Kong. Thirty-three cyanobacterial species, as well as diatoms and macroalgae, were recorded. Cyanobacteria were found at all levels below the supralittoral zone, which was bare owing to the small splash zone. The upper eulittoral zone was dominated by coccoid species, especially a brown band of Gloeocapsa pleurocapsoides. A black band of Kyrtuthrix maculans dominated the lower part of the upper eulittoral. A variety of filamentous and coccoid cyanobacteria were recorded in the mid eulittoral, and a thin film of the encrusting red alga Hildenbrandia rubra dominated the lower eulittoral. Chlorophyll a levels peaked in the mid eulittoral and were lowest in the supralittoral. Broad zonation patterns were consistent throughout the year, but there was a clear seasonal variation in species abundance. In winter, macroalgae and diatoms dominated the shore, although the species composition varied year to year. Species richness of cyanobacteria was highest in winter, and nonheterocystous filamentous species (Lyngbya spp., Oscillatoria spp.) dominated. With increasing air temperatures, macroalgae, diatoms, and some cyanobacterial species died; however, species such as Kyrtuthrix and Gloeocapsa appeared to be high-temperature tolerant and increased in summer. Toward the end of summer, heterocystous cyanobacteria (e.g. Calothrix spp.) proliferated. Chlorophyll a levels were highest in winter in the mid and low eulittoral, and they greatly decreased in summer, especially in the high supralittoral. On Hong Kong shores, temporal variation in species richness, abundance, and biomass of cyanobacteria is strongly influenced by seasonal changes in environmental conditions.

MOLECULAR SYSTEMATIC ANALYSES INDICATE THAT THE ENIGMATIC APOPHLAEA IS A MEMBER OF THE HILDENBRANDIALES (RHODOPHYTA, FLORIDEOPHYCIDAE)

Nuclear small‐subunit (SSU) ribosomal DNA sequences were determined for Apophlaea lyallii Hooker f. et Harvey from New Zealand and an isolate of Hildenbrandia rubra (Sommerfelt) Meneghini from France. These data, in addition to SSU sequences representative of all the major florideophyte lineages, were used in molecular systematic investigations to confirm inclusion of Apophlaea in the Hildenbrandiales. Anatomical features that serve to unite Apophlaea and Hildenbrandia are discussed to buttress this result. Furthermore, our analyses support recognition of the Hildenbrandiales as sister to all other extant florideophyte lineages studied to date. An anomalous result positioning the SSU sequence generated herein for Hildenbrandia rubra closer to Apophlaea lyallii than to a previously published sequence for Hildenbrandia rubra requires further investigation.

Feeding effects of postlarval red abalone, Haliotis rufescens (Mollusca: Gastropoda) on encrusting coralline algae

Detailed examinations of an algal-microherbivore symbiosis have revealed mutualistic components of such herbivore-plant interactions. High-resolution photomicroscopy and experimental analyses in the field and laboratory were used to evaluate effects of foraging by Haliotis rufescens (red abalone) postlarvae ˜ 200 μm in length, on their encrusting red algal hosts, Lithothamnion (=Lithothamnium) californicum, Lithophyllum lichenare, and Hildenbrandia rubra (=H. prototypus). We have quantified the microscopic food availability, postlarval foraging behaviour, changes in stomach and faecal contents, growth, and mutualistic effects of grazing. Host algae were found to benefit both from a reduction in coverage by epiphytic algae, and from enhancement of vegetative growth.

Algal seasonality on an exposed rocky shore in Hong Kong and the dietary implications for the herbivorous crab Grapsus albolineatus

Patterns of algal seasonality, and their effect on the diet and feeding preferences of the herbivorous crab Grapsus albolineatus were investigated over an 18-mo period from March 1993 to August 1994 on an exposed tropical rocky shore (Hok Tsui Peninsula at Cape d' Aguilar, Hong Kong). Algal cover was greatest in the winter months, and lowest in the summer. Foliose algae such as Ulva fasciata, Porphyra suborbiculata, and Dermonema frappieri were dominant in the winter, but died off in the summer. During the hot summer months, perennial encrusting algae e.g., Ralfsia expansa, Hildenbrandia rubra, H. occidentalis, coralline crusts and the encrusting cyanobacteria Kyrtuthrix maculans, were the dominant algal species. Seasonal variation in algal abundance influenced the dietary selectivity of the herbivorous crab G. albolineatus. In the winter, the crab fed selectively on filamentous algae (e.g. Hincksia spp., Cladophora spp., Enteromorpha spp., and the cyanobacteria Lyngbya sp.). Foliose algae (e.g. U. fasciata, P. suborbiculata, Pterocladia tenuis) formed a small part of the diet, despite being the dominant species on the shore. Foliose and filamentous algae were virtually absent from the shore in the summer, and the crabs switched to feeding solely on encrusting algae. Electivity indices revealed preferences for green and brown turf species, and avoidance of foliose algae. Faecal analysis revealed that a greater proportion of the food is digested in the winter, suggesting that G. albolineatus is able to digest filamentous algae more efficiently than encrusting algae. Feeding preferences of G. albolineatus appear to be influenced by a number of factors, including the availability, digestibility and morphology of algae. The foraging behaviour and cheliped morphology of the crab also affect food choice. The monsoonal nature of Hong Kong's climate controls the diversity and abundance of intertidal algae and, therefore, indirectly influences the diet and subsequent growth and reproductive success of the herbivorous crab G. albolineatus.

Group I introns found in nuclear small subunit ribosomal RNA genes of the ballistoconidiogenous anamorphic yeast Bensingtonia ciliata and Bensingtonia yamatoana.

Four group I introns were found in the nuclear small subunit ribosomal RNA genes (SSU rDNA) of the ballistoconidiogenous anamorphic yeast genus Bensingtonia. Two of them were found in B. ciliata, type species of the genus, with the length of 335 nt and 341 nt. The remaining two were found in B. yamatoana with lengths of 454 nt and 457 nt, respectively. The four introns were located at two different sites within the SSU rDNA. The first insertion site was the same position as group I introns found in the SSU rDNA of Dunaliella parva-5', Dunaliella salina, Protomyces inouyei-5' and Ustilago maydis. The second insertion site was shared among group I introns found in the SSU rDNA of Chlorella ellipsoidea, Hildenbrandia rubra, Pneumocystis carinii and Protomyces inouyei-3'. The putative secondary structures of the introns resembled those of subgroup IC1. Principal coordinate analysis of core regions of 15 group I introns found in SSU rDNA of eukaryotes showed that the sequence of B. ciliata-5' intron resembled that of the B. yamatoana-5' intron, and the sequence of the B. yamatoana-3' intron resembled that of the Protomyces inouyei-5' intron. Bensingtonia ciliata-3' intron had relatively different sequences compared to other group I introns examined. Group I introns in the nuclear SSU rDNA of red and green algae, ascomycetes and basidiomycetes, examined in this study, were scattered on the principal coordinate analysis.

The ecology of intertidal algal crusts: variation within a functional group

Encrusting marine algae are found at all depths in the photic zone from polar to tropical seas worldwide, yet little is known about their ecology. Crusts (including red, brown, and green algae as well as lichens and Cyanobacteria) tend to predominate in areas of high disturbance (e.g. from herbivores or sand scour) or high stress ( = low potential productivity, e.g. high on the shore). Patterns of crust and herbivore distribution and abundance were quantified in the intertidal zone in Washington state, and then the two environmental parameters predicted to be critical to among-crust variation in survival were manipulated: disturbance potential by varying abundances of herbivores, or by eliminating herbivores and artificially disturbing crusts with nylon and steel brushes; productivity potential by transplanting crusts along an environmental gradient from the high to the low intertidal zone and onto a submerged raft. Within-functional-group variation among crusts was studied by transplanting eight species (varying in calcification, thickness, tightness of construction, and other characters), and measuring their survival and growth over 2–3 yr in the different environments. Crusts varied widely in their responses to both disturbance and productivity potential. In general, thick, calcified, or very tightly constructed crusts withstood being steel-brushed at regular intervals. Nylon brushing sometimes actually benefitted these crusts relative to the controls (unbrushed but cleaned monthly), probably because of the reduction in fouling. In contrast, thinner or more loosely-constructed species showed poor survival when steel-brushed and often suffered significant losses even when nylon-brushed. Most crusts tended to do best in habitats having higher productivity potential (lower intertidal zone), showing mortality or reduced growth when transplanted into more stressful areas, although two species were healthiest under “stressful” conditions, i.e. desiccated or submerged in high pools. Experiments in the laboratory with herbivores (littorinid snails, limpets, and a chiton) demonstrated that they did not always consume the species that are mechanically easiest to remove (as indicated by the steel brushing experiments). Three species were avoided, including a brown known to contain high concentrations of phenolics, a blue-green crust, and a lichen with a blue-green phycobiont. All crusts grew very slowly, even in their optimal habitats; the fastest species grew laterally at < 20 mm/yr, and the slowest measurable at < 0.5 mm/yr. Some species showed no lateral growth over 2 yr. This low ability to sequester space, and their two-dimensional growth form, means that crusts often rely on grazers or other disturbance to keep from being overgrown. In other cases, they grow in areas where desiccation or low light levels apparently eliminate other algal forms. Crusts survive disturbance by either resisting it (through calcification or toughness), tolerating it (by being thick or regenerating rapidly), or avoiding it (by having an opportunistic life history, living in refugia such as crevices or high tidepools, or being unpalatable). Their life histories are highly variable, allowing them to exploit habitats in different ways. For example, in the mid intertidal zone in Washington the three dominant crust species include: (1) a fast-growing, frequently-recruiting brown ( Ralfsia pacifica Hollenberg) that senesces after several years and sloughs away; (2) a fast-growing but rarely-recruiting red (“Petrocelis”) that lives for decades; and (3) a very slow-growing and rarely-recruiting red [ Hildenbrandia rubra (Sommerfelt) Meneghini] that persists even when overgrown, and regenerates following disturbance. These diverse morphologies and life history strategies help make this morphology an ecological success.

Effects of Grazing, Canopy Cover and Substratum Type on the Abundances of Common Species of Seaweeds Inhabiting Littoral Fringe Tide Pools

Experimental manipulations were used to differentiate the effects of grazing, Fucus distichus canopy cover and the presence of Hildenbrandia rubra on the recruitment density of F. distichus and the cover abundance of ephemeral algae

Cell sloughing and chloroplast inclusions inHildenbrandia rubra(Rhodophyta, Hildenbrandiales)

Light and electron microscope studies of a specimen of Hildenbrandia rubra revealed two unusual features not found in other collections. A large portion of the crust surface was necrotic. The depth of the affected areas varied, but in some places it was great enough to remove conceptacles. Beneath the zone of dead cells, regeneration was indicated by cytokinesis in the top layer of healthy cells. Severing of pit connections in response to cell mortality is described. Chloroplasts of both living and dead cells had conspicuous spherical inclusions, which were visible even with the light microscope. These inclusions generally had a homogeneously granular substructure. Rarely, a less dense, non-granular substance and phytoferritin were present within the inclusion. It is not known whether there is a causal connection between the presence of chloroplast inclusions and necrosis.

Snail grazing and the abundance of algal crusts on a sheltered New England rocky beach

The encrusting algae Ralfsia verrucosa (Areschoug) and Hildenbrandia rubra (Meneghini non Harvey) are the dominant primary space holders on protected rocky beaches in southern New England where the herbivorous snail Littorina littorea (Linnaeus) is found at extremely high densities. All erect algal species are excluded by heavy grazing pressure. We here examine the influence of snail grazing on the abundance of these two species in light of their relative physical and chemical antiherbivore defense mechanisms. Of the two, Hildenbrandia rubra is the more grazer resistant. Experimental removal of Littorina littorea from a penned area for 12 months resulted in increased Ralfsia verrucosa abundance relative to a control area, though there was marked seasonal variation in abundance in both control and snail removal areas. Hildenbrandia rubra abundance was not directly affected by the presence of Littorina littorea, and revealed very little growth and no detectable recruitment in either area. Increased Ralfsia verrucosa growth in snail removal areas, however, resulted in R. verrucosa overgrowing >95% of the Hildenbrandia rubra initially present, though this overgrowth was not lethal to Hildenbrandia rubra. At the high snail densities found on protected rocky beaches in southern New England, grazing pressure precludes the presence of all erect algae and limits overgrowth and substratum monopolization by encrusting algal species.