Hormosira Research Articles

Epifaunal composition and fractal dimensions of marine plants in relation to emersion

Three macroalgae were studied: Enteromorpha sp. (Chlorophyceae), Hormosira banksii (Turner) Descaisne (Phaeophyceae), Corallina sp. (Rhodophyceae). Fractal dimensions (D) for the outlines of the three species were 1.24, 1.07 and 1.35 respectively in the step range 0.5–5.0 mm. All three species showed loss of epifauna on the falling tide; loss was greatest in Enteromorpha, least in Corallina. In Enteromorpha and Hormosira, most loss of epifauna was in the form of harpacticoid copepods; in Corallina loss was spread more evenly across the taxa. Epifaunal biomass and retention was much greater in Corallina than in the other two species, partially because of better water-retention properties. Enteromorpha and Hormosira both showed marked decreases in epifaunal diversity during emersion; Corallina did not.

Effects of trampling on a rocky intertidal algal assemblage in southern New Zealand

The effects of human trampling on a mid-intertidal assemblage dominated by the fucalean alga Hormosira banksii were tested experimentally on two rocky intertidal platforms on the east coast of the South Island of New Zealand. The major factors were Trampling intensity, Platforms and Timing of trampling. Seven trampling intensities (0, 10, 25, 50, 100, 150 and 200 passages per area) were used in 2-m long transects (0.6 m 2) during single tides in Spring and Autumn on each platform. H. banksii initially had >96% canopy cover in all treatments. As few as 10 tramples reduced this cover by up to 25% after a single tide. Progressively greater reductions occurred at higher trampling intensities, with >90% of the H. banksii canopy removed at 200 tramples. There was recruitment into the Spring transects during the following summer months, and by five months after trampling all treatments had at least 50% cover of H. banksii. Treatments initiated in Autumn had similar reductions in H. banksii cover as Spring treatments, but the recovery was delayed by seven months until recruitment occurred during the following summer. Fifty percent recovery of the canopy took at least a year in most Autumn treatments. After 21 months the Spring treatments had recovered to control levels (>97% cover), while after 16 months the Autumn treatments were still recovering. Understory encrusting and turfing coralline algae were reduced in cover after trampling, with the greatest effects at the higher trampling intensities. The reduction of corallines was mostly due to burn-off after the H. banksii canopy was removed. By the end of the experiment, corallines had returned to control levels in both the Spring and Autumn treatments. Bare primary space increased significantly with up to 60% bare rock at the higher trampling intensities one year after trampling. By the end of the experiment, bare space was reduced to <10% in the Spring treatments but averaged as high as 24% in the higher trampling intensities of the Autumn treatments. There was an interaction between demographic processes, particularly recruitment, and coralline algae in the recovery of H. banksii. Up to 70% of cover at the 200-trample intensity was from new recruits, while most recovery in the 10 and 25 trampling intensities was from re-growth of damaged fronds. However, at one platform, composed of soft siltstone, recruitment of H. banksii occurred almost exclusively on the damaged encrusting and turfing coralline algae. Overall, this experiment showed that trampling intensity had variable effects and that the interaction of season, location, indirect effects of reduction in coralline algae, and facilitative processes in recruitment of H. banksii all contribute to recovery after disturbance.

Physical disturbances and their direct effect on an indirect effect: responses of an intertidal assemblage to a severe storm

Indirect interactions are increasingly viewed as important ecological processes and have been catalogued as two types (interactive chain and modifying interaction). Such interactions on a rocky shore in New South Wales were analysed experimentally to test hypotheses derived from models to explain changes in assemblages following a severe storm. The storm removed canopies of algae ( Hormosira banksii); this was followed by recruitment of barnacles ( Chamaesipho tasmanica) into areas under former canopies, from which they had previously been absent. Controlled, replicated manipulations were done to test hypotheses that barnacles had been influenced by the algae themselves, by predatory whelks ( Morula marginalba) sheltering under the H. banksii, or by encrusting algae found in shade under the canopy. The primary cause of patterns in the cover of barnacles and changes caused by the storms was predation by whelks. Encrusting algae had a minor negative influence on barnacles. A canopy of H. banksii had no direct effect on the barnacles, but canopies indirectly influenced barnacles by providing shelter, therefore increasing the effectiveness (but not the numbers) of whelks. The conclusion is that indirect interactions are important, but cannot always be categorized as one or other of the two types. H. banksii is part of a chain, by providing the habitat necessary for whelks to act. They are also a modifier of the interaction because whelks forage differently under canopies of different sizes. Finally, predictions about interactions are difficult if they are dependent on recovery from unpredictable influences, such as large storms.

SECRETION OF PHENOLIC SUBSTANCES INTO THE ZYGOTE WALL AND CELL PLATE IN EMBRYOS OF HORMOSIRA AND ACROCARPIA (FUCALES, PHAEOPHYCEAE)

We have used light and electron microscopy to study the secretion of phenolic substances into the primary walls and cross walls of zygotes and embryos of the brown algae Hormosira banksii (Turner) Decaisne (Hormosiraceae) and Acrocarpia paniculata (Turner) Areschoug (Cystoseiraceae). Phenolic compounds packaged within physodes are a major cytoplasmic component of brown algae. Physodes accumulate at the zygote periphery early in development and are secreted into the primary zygote wall. At germination, physodes accumulate at the rhizoid tip. The first sign of impending cytokinesis is the lining up of these phenolic vesicles in the plane of cell division. This precedes the arrival of other wall constituents. Physodes, together with other wall components, contribute to the development of the cell plate. We conclude that phenolic compounds play an important role in cell‐wall construction in these species.

Grazing and disturbance: an experimental analysis of patchiness in recovery from a severe storm by the intertidal alga Hormosira banksii on rocky shores in New South Wales

An extremely large storm in 1974 provided an opportunity to examine recovery from disturbance to the canopy of the alga Hormosira banksii. Cover had been measured prior to the storm, so its effects could be measured, not assumed. Rate of recovery varied. Some patches recovered quickly, others more slowly. Of various possibilities, two mechanisms could be most likely to explain this – the amount of damage sustained may have varied or grazers may have slowed recovery in some places. Algae were cut to remove fronds or scraped away to remove holdfasts and fronds to test the hypothesis that recovery would be faster in the former, where damage was less. Grazing molluscs were excluded from or let into experimental plots to test the hypothesis that grazing controlled recovery. Canopy quickly recovered where only fronds were removed. Grazing caused short-term reductions in rates of growth. Where holdfasts were also removed, recovery was slow and grazing also caused great reductions in rate of development of algae. The amount of damage was the primary control of recovery; canopies eventually developed even where grazers were active. To understand and eventually to predict the consequences of sudden or large disturbances needs a mix of long-term quantitative sampling and shorter-term controlled experiments.

A quantitative study of the patterns of morphological variation within Hormosira banksii (Turner) Decaisne (Fucales: Phaeophyta) in south-eastern Australia

Hormosira banksii shows a considerable degree of morphological variability throughout its range in south-eastern Australia, apparently in relation to the local habitat, and there have been several previous qualitative attempts to categorize this variation by recognizing ecoforms. From our quantitative morphometric analyses of plants from 21 sites covering 300 km of coastline in south-eastern Australia, using multiple discriminant function analysis based on seven vesicle characteristics (measuring size and shape), there is very little evidence of intergrading forms. The morphological variation is not multivariately continuous, as has been previously suggested, although each individual attribute does show more-or-less continuous variation, and the morphological variation is not a simple reflection of habitat but reflects more complex microhabitat relationships. The morphological forms that we recognize are multivariate, and thus all of the attributes need to be considered. In particular, volume (or surface area:volume ratio) is usually a very good discriminator between groups, indicating that both size and shape are important for defining the groups. We recognize two main phenotypically distinct groups, comprising plants from sheltered estuarine situations and those from exposed marine rock platforms. The vesicles of plants from the estuarine habitats are more-or-less spherical (length≈diameter), with a volume approximately 3–10 times that of vesicles from the marine plants; it is thus probable that the variation in the vesicle dimensions of these morphs can be linked to desiccation resistance. The estuarine and marine habitats are likely to be ecologically isolated from each other, and there is therefore unlikely to be a great deal of gene flow between these plants; if they are treated as separate species, then they would be H. banksii (Turner) Decaisne and H. sieberi (Bory) Decaisne, respectively. Three relatively distinct morphometric forms were also recognizable within the marine group, including plants from the bottom of rock pools; from rock pool edges and sublittoral regions; and from the surface of rock pools and exposed parts of the platforms. Two less distinctive morphometric forms were recognizable within the estuarine group, including plants from tidal flats and those from mangrove forests. The taxonomic status of these microhabitat forms remains uncertain.

EFFECTS OF PERIODIC DISTURBANCES FROM TRAMPLING ONROCKY INTERTIDAL ALGAL BEDS

We investigated the ability of an assemblage of animals and plants on rocky shores in southeastern Australia to resist and/or recover from repeated pulse disturbances in the form of trampling. Disturbances of four different intensities were applied experimentally over six summers, with no human access at other times of the year. The dominant intertidal plant, the brown alga Hormosira banksii, was affected by trampling, but the effects were heterogeneous between sites. At two sites, a series of pulse disturbances produced a series of pulse responses, although the effect of a given pulse varied among years, possibly related to the severity of summer desiccating conditions each year. At the third site, pulse disturbances produced a press response; at high levels of trampling, Hormosira was almost eliminated within 2 yr, and at two intermediate levels of trampling, cover was reduced from >90 to 60–70%, where it remained for 4 yr. Effects of trampling showed little small-scale spatial variation. Untrampled areas did fluctuate through time, often as a result of summer burnoff of algae. Natural disturbances occurred irregularly through the study, and their effects varied on very small spatial scales (among plots <30 m apart). Trampling enhanced the densities of a range of herbivorous mollusks, especially limpets, and reduced the abundance of articulated coralline algae, which were abundant in the understory of Hormosira mats. These effects varied among sites but showed much less variation on smaller spatial scales. The reductions in coralline algae may be a direct effect of trampling, but increases in mollusk abundance occurred some time after changes to Hormosira cover, and those changes may be an indirect effect of trampling. We compared the effects of trampling on areas of the shore that had been trampled for two and four summers, to test whether a past history of disturbance influenced the effect of a new disturbance. No significant effects were found on algae or mobile animals, although a mild summer may have made our test of history relatively weak. Hormosira banksii fits the definition of a keystone species or engineer and, as such, is an appropriate focus for management and as an indicator. Spatially heterogeneous effects of a constant physical perturbation, however, mean that management of these rocky shores requires more complex models and indicate that caution should be used in adopting this species as a uniform indicator of environmental change.

Arsenic compounds in a marine food chain

A three-organism food chain within a rock pool at Rosedale, NSW, Australia, was investigated with respect to arsenic compounds by high performance liquid chromatography – hydraulic high pressure nebulization – inductively coupled plasma mass spectrometry (HPLC-HHPN-ICP-MS). Total arsenic concentration was determined in the seaweed Hormosira banksii (27.2 μg/g dry mass), in the gastropod Austrocochlea constricta (74.4 μg/g dry mass), which consumes the seaweed, and in the gastropod Morula marginalba (233 μg/g dry mass), which eats Austrocochlea constricta. The major arsenic compounds in the seaweed were (2′R)-dimethyl[1-O-(2′,3′-dihydroxypropyl)-5-deoxy-β-d-ribofuranos-5-yl]arsine oxide and an unidentified compound. The herbivorous gastropod Austrocochlea constricta transformed most of the arsenic taken up with the seaweed to arsenobetaine. Traces of arsenite, arsenate, dimethylarsinic acid, arsenocholine, the tetramethylarsonium cation, and several unknown arsenic compounds were detected. Arsenobetaine accounted for 95% of the arsenic in the carnivorous gastropod Morula marginalba. In Morula marginalba the concentration of arsenocholine was higher, and the concentrations of the minor arsenic compounds lower than in the herbivorous gastropod Austrocochlea constricta.

How Does Immigration Influence Local Adaptation? A Reexamination of a Familiar Paradigm

How Does Immigration Influence Local Adaptation? A Reexamination of a Familiar Paradigm

Effects of secondarily treated sewage effluent on intertidal macroalgal recruitment processes

Effluent is discharged below the low-water mark at Boags Rocks, Victoria, Australia, at an average rate of 437 × 106 L day–1. Three study sites following a gradient of pollution from high (at Boags Rocks) to intermediate (Cape Schanck) to unpolluted (Cheviot Beach) were chosen for the main experiments. Surveys of the algal assemblages were conducted in spring and summer and showed the absence of the pre-discharge dominant Hormosira banksii at Boags Rocks and an abundance of turf-forming and ephemeral species at the two polluted sites. There was no evidence that the treated sewage detrimentally affected either the availability of propagules (asexual spores, gametes, zygotes or fragments) or macroalgal recruitment to artificial or natural substrata. Opportunistic genera such as UIva and Enteromorpha showed very high recruitment and propagule densities in the water column at polluted sites, apparently benefiting from the increased nutrient loads. Investigation of the number of H. banksii zygotes in water samples from various habitats showed very limited dispersibility for this species. The small dispersal shadow of H. banksii, combined with the environmental pressures placed on establishing zygotes, would severely limit the re-establishment of this species at polluted sites, even if given suitable conditions.

Using Developing Embryos of Hormosira banskii (Phaeophyta) as a Marine Bioassay System

Developing embryos of Hormosira banksii provide a very consistent, predictable, and flexible bioassay system. Fertile specimens can be collected throughout the year, and gamete release, high rates of fertilization and successful development of the early life stages of this alga are all easily obtained under laboratory conditions. As the early stages of embryo development are largely synchronous, this bioassay is based on the quantitative assessment of key morphogenetic characteristics at certain time intervals during the first 14 d. The characteristics measured are: fertilization (%) at 1 h, cell wall formation (day 1); rhizoid germination (day 2); cell division (day 3); more than four cell divisions (day 7); and evidence of meristematic activity (day 14). There are few inherent sources of variation in this bioassay system, the most notable being natural mortality rates and retarded development in some apparently healthy individuals. These are easily accounted for in properly designed experiments.

Inorganic carbon acquisition by Xiphophora chondrophylla (Phaeophyta, Fucales)

Abstract Measurements of parameters related to photosynthesis, with particular reference to the mechanism of inorganic C acquisition, were made on Xiphophora chondrophylla (R. Brown ex Turner) Montagne ex Harvey, an Australasian fucoid living in the upper subtidal and in low intertidal rock pools. Photosynthesis as a function of incident photon flux density and external inorganic C concentration, capacity to use HCO3−, diel changes in titratable acidity of cell contents (‘CAM-like’ behaviour), rates of dark inorganic 14C fixation and the δ13C values of plant organic C were similar to values previously found for emersed and submersed specimens of the sympatric Hormosira banksii (Turner) Decaisne. This is consistent with the proposed close relationship of the genera Hormosira and Xiphophora and with earlier work showing the phyletic, as well as ecologically adaptive, importance of certain characteristics of inorganic C acquisition in the Fucaceae and related fucoids. The N content of Xiphophora chondrophyll...

Effect of sewage effluents on germination of three marine brown algal macrophytes

Inhibition of germination of zygotes of the fucoid macroalgae Hormosira banksii and Phyllospora comosa and zoospores of the laminarian Macrocystis angustifolia was used as an end-point to assess the toxicity of three sewage effluents of differing quality. For each species, between-assay variation was low and results of tests with the reference toxicant 2,4-dichlorophenoxyacetic acid suggested that results are reproducible, especially in R. comosa. Each species showed a greater sensitivity to primary-treated effluent than to secondary-treated effluent, and higher variability in response to the primary effluent. High variation in response for each species when exposed to the primary effluent (compared with that for the secondary effluent) is presumably indicative of variation in quality of the primary effluent. The capacity to reproduce these assays, the sensitivity of species employed, and the ecological relevance of germination as a toxicological end-point suggest that germination tests of this nature may be useful in biological testing of effluent quality at discharge sites in south-eastern Australia.

On the finestructure of flagellar hairs in the brown algae (Phaeophyceae)

The fine structure of the tripartite tubular flagellar hairs in male gametes of the brown algae Ectocarpus siliculosus (Dillwyn) Lyngbye, Laminaria digitata (Hudson) Lamouroux, Fucus serratus Linnaeus, Hormosira banksii (Turner) Decaisne and Durvillaea potatorum (Labillardière) Areschoug has been investigated by negative staining. In all these species three terminal filaments are present, with a long central filament and two thinner, shorter and equal filaments inserted laterally to the central one. The distribution of this feature is discussed in relation to the phylogenetic position of the Phaeophyceae.

The phylogenetic affinities of Notheia anomala (Fucales, Phaeophyceae) as determined from partial small-subunit rRNA gene sequences

Abstract Partial nucleotide sequences of the nuclear small-subunit ribosomal RNA genes (SSU), as inferred from polymerase chain reaction (PCR)-amplified products, have been determined for Caulocystis cephalornithos (Labillardiere) Areschoug (Cystoseiraceae), Hormosira banksii (Turner) Decaisne (Hormosiraceae), Sargassum vestitum (R. Brown ex Turner) C. Agardh (Sargassaceae) and Notheia anomala Harvey et Bailey (Notheiaceae). These taxa are referred to three of the six families currently placed in the order Fucales, plus the monotypic Notheiaceae, which has variously been placed in the Chordariales, the Fucales or the Notheiales. Our investigations indicate that the SSU gene provides suitable divergence for assessing relationships among the fucalean families. Phylogenetic analyses of the partial SSU gene sequences ally the Notheiaceae with the Fucales, although not closely with its virtually obligate host, Hormosira banksii of the monotypic Hormosiraceae. The data are equivocal as to the positioning of the...

Inorganic carbon acquisition by Hormosira banksii (Phaeophyta: Fucales) and its epiphyte Notheia anomala (Phaeophyta: Fucales)

Abstract Measurements of parameters related to photosynthesis, with particular reference to the mechanism of inorganic C acquisition, were made on the obligate epiphyte Notheia anomala Harvey et Bailey (Phaeophyta: Fucales) and on its most usual basiphyte, Hormosira banksii (Turner) Decaisne (Phaeophyta: Fucales). The work on Hormosira banksii included a comparison of specimens which are normally emersed at low tide on rock platforms with specimens which are normally submersed in rockpools at low tide; the rockpool specimens are those which most commonly bear Notheia anomala. No significant differences were detected for any of the characteristics tested, i.e. photosynthetic rate as a function of incident photon flux density, external inorganic C concentration and plant N content; capacity to use HCO3−; diel changes in titratable acidity of cell contents (‘CAM-like’ behaviour); rates of dark 14C-inorganic C fixation; δ13C values of plant organic C. These data are consistent with there being no significant ...

Effects of secondarily-treated sewage effluent on the early life-history stages of two species of brown macroalgae: Hormosira banksii and Durvillaea potatorum

Sewage effluent has a deleterious effect on the early life-history stages of Hormosira banksii (Turner) Decaisne and Durvillaea potatorum (Labillardiere) Areschoug. High concentrations of sewage effluent (28 and 40% in seawater) inhibit zygote germination by 55 to 95%, retard embryo growth (80 to 100%) and cause severe embryo mortality, with less than 60 and 5% surviving after 14 d, respectively. It is probable that such adverse effects would significantly reduce levels of recruitment of these species in sewage-affected localities, and that sewage effluent has played an important role in the decline of these species from several rock platforms in south-east Victoria, Australia. Zygote germination, embryo growth and embryo mortality were inhibited ≅40% more strongly in sewage effluent than diluted seawater, showing that the effect of sewage effluent is not simply one of seawater dilution. However, this effect was only observed at high concentrations (28 and 40%). The absence of any difference between the low concentrations of sewage effluent (4 and 12% in seawater) and diluted seawater suggests that the dilution of waste water is important in mitigating its more harmful effects. The sensitivity of H. banksii and D. potatorum embryos to the composition of the medium in which they grow and the ease with which they can be manipulated in culture suggest that they may be utilised as biological indicators of water quality.

The intertidal distribution of the grey mangrove (Avicennia marina) in southeastern Australia: The effects of physical conditions, interspecific competition, and predation on propagule establishment and survival

Abstract The upper and lower limits of the distribution of mature Avicennia marina lie between mean high water and mean sea level in open estuaries in southeastern Australia. Newly established seedlings are highly variable in abundance, but are rarely found in the saltmarsh or on mudflats. Their distribution is unlikely to be limited by dispersal because propagules disperse into the saltmarsh and to intertidal mudflats, but their establishment may be limited by physicochemical conditions, interspecific competition and predation.The model that physicochemical conditions control the intertidal limits of establishment of seedlings was accepted for propagules stranding in the saltmarsh but rejected for those stranding on mudflats. No seedlings established on saltmarsh sediments but similar numbers of seedlings established within light gaps in adult mangrove stands and on intertidal mudflats. The model that interspecific interaction with freeliving macroalgae (Hormosira banksii) reduces the establishment of seedlings on mudflats covered with macroalgae or in stands with a ground cover of macroalgae was accepted. Under controlled conditions five times as many propagules established on cleared ground compared with ground covered with macroalgae. Predators also reduce seedling establishment, but the model that they preferentially act on propagules stranding on the mudflat was rejected. The low number of seedlings found on mudflats without macroalgae appears to relate to wave and current effects on establishment and the effects of waterlogging or fouling on survival.

Quantitative Evaluation of Erotactin Secretion in Eggs of Hormosira banksii (Fucales, Phaeophyceae)

AbstractThe release of the C11‐hydrocarbon spermatozoid attractant hormosirene by eggs of the Australian fucoid Hormosira banksii has been determined quantitatively using a closed‐loop extraction technique. The eggs secrete erotactin for more than 2 weeks with an exponentially decreasing rate. The initial secretion rate was estimated to be 75 fmol h−1 egg−1 and the total amount of hormosirene produced per egg to be 2.35 pmol (0.35 ng). The results were used to calculate the threshold range for spermatozoid chemotaxis in the pheromone gradient around eggs.

Effects of Trampling on Plant and Animal Populations on Rocky Shores

We examined experimentally the effects of disturbances caused by pedestrian traffic on the animals and plants living on an intertidal rocky shore in south-eastern Australia. Individual footsteps damaged some animals, but the percentage of animals that was crushed was low. Molluscs, except large limpets, were more often dislodged than crushed, and some damage was sustained by barnacles and mussels. The survival of individuals of two gastropod species, Bembicium nanum and Austrocochlea constricta, was not affected by dislodgment, because they quickly righted themselves. The limpet Cellana tramoserica was not damaged by being kicked or stepped on. The dominant plant on these shores, the brown alga Hormosira banksii, was easily damaged, with ca. 20% of the biomass of individual plants being removed by a single footstep. The amount of tissue lost increased with the number of footsteps, with a maximum loss of approximately 75%. We investigated the effects of three levels of sustained trampling (33 d of trampling, spread over 4 mo) on the organisms in three habitats: Hormosira Mats, Coralline Algal Mats, and Bare Rock. The algal mats were most affected by trampling. Hormosira Mats were damaged severely by high- and low-intensity trampling. Upright coralline algae in the Coralline Algal Mat were damaged by high-intensity trampling. Numbers of the gastropod Turbo undulates in both of these habitats were reduced. The Bare Rock habitat was not affected significantly by trampling. Five months after the end of trampling, heavily trampled and control strips of coralline Algal Mats were not distinguishable, as all treatments underwent pronounced seasonal changes. Within the Hormosira Mats, the low-intensity treatments and controls were not different, but algal cover in the heavily-trampled areas remained 400 d of recovery, Hormosira cover was only 60%, three quarters of the value for control areas. The indirect effect of increased mollusc abundance was still apparent. Trampling by visitors could result in replacement of the Hormosira mat species assemblage with 'bare' rock and grazing molluscs, and trampling should be considered as a disturbance capable of directly and indirectly influencing intertidal populations on rocky shores.