Effect of epiphytism on reproductive and vegetative lateral formation in the brown, intertidal seaweed Ascophyllum nodosum (Phaeophyceae)

In the brown alga Ascophyllum nodosum (L) Le Jolis, a common species on sheltered Northern temperate rocky shores, gametes are produced in receptacles that emerge from small depressions (lateral pits) along the branched frond. These lateral pits are also the preferred settling site for the obligate epiphyte Polysiphonia lanosa (L) Tandy. Therefore, epiphytism can be expected to interfere with host reproductive output. The present study investigated the potential impact of the epiphyte on A. nodosum in two series of laboratory experiments that measured: (i) the direct shading of the host plant underneath an epiphyte canopy; and (ii) the development of receptacles in clean and epiphytised A. nodosum segments (excised from individual fronds) over a 6 month period. These experiments showed that light reaching emerged fronds underneath a dense epiphyte cover was reduced by 40%, and this was independent of the degree of desiccation the epiphyte experienced. Concurrently, in the growth study with epiphytised A. nodosum segments (segments with one clean and one epiphytised lateral pit) total receptacle biomass per epiphytised fragment was significantly reduced compared with clean segments (0.52 g and 1.25 g per gram of frond segment, respectively), although this effect was only significant in A. nodosum from sheltered shores. However, expressed as biomass per lateral pit, receptacle biomass in the remaining clean lateral pits in epiphytised segments was significantly increased in segments from both shores, demonstrating that A. nodosum can at least partially compensate for the loss of production resulting from epiphytism.     

THE DISTRIBUTION OF PHOTOSYNTHATE IN ASCOPHYLLUM NODOSUM AS IT RELATES TO EPIPHYTIC POLYSIPHONIA LANOSA12

The brown alga Ascophyllum nodosum is not a major source of organic carbon for its epiphytic red alga Polysiphonia lanosa. Plants pulse-labeled for 24–25 hr with NaH¹⁴CO₃ were examined for exudation and translocation. The maximum amount of radioactive carbon compounds lost from A. nodosum during this experimental period was less than 0.3% of the total ¹⁴C fixed by the alga, and of this amount, only 5% could, have moved through the frond. The remaining fraction of the ¹⁴C lost from the thallus was released into the water. The total exudate from A. nodosum was collected for 1 week in a series of flasks of filtered seawater changed at 12-hr intervals corresponding with the beginning of the light and dark periods, respectively. During 7 days at 15 C only 1.5% of the total ¹⁴C originally fixed had been released as radioactive organic carbon, whereas at 5 C, 0.6% of the total ¹⁴C fixed was found in the medium. No significant difference in the rate of exudation of organic ¹⁴C was observed in light or darkness. After fractionation of the exudate it was found that only 10% of the radioactivity in these exudates was composed of organic acids or amino acids. P. lanosa, on the other hand, is perfectly capable of fixing its own carbon. The photosynthetic rates measured by H¹⁴CO₃ uptake confirm the observations of Bidwell: 3.96 mg CO₂/g/hr (0.09 m mole/g/hr).     

Research note: Field evaluation of epiphyte recruitment (Vertebrata lanosa,Rhodophyta) in different microsite types on host fronds (Ascophyllum nodosum,Phaeophyceae)

The seaweed Ascophyllum nodosum (Phaeophyceae, Fucales) often forms extensive beds in wave‐sheltered, rocky intertidal habitats on northern Atlantic shores. Since this alga is an ecosystem engineer that influences benthic biodiversity, it is important to understand the factors that regulate its performance. Epiphytism is known to affect the performance of macroalgal hosts. In this study, we investigated the effects of surface irregularities on A. nodosum fronds (wounds, branch axils, and lateral pits resulting from receptacle shedding) on the recruitment rate of its obligate epiphyte Vertebrata lanosa (=Polysiphonia lanosa, Rhodophyta, Ceramiales). For this purpose, we performed a field experiment in Nova Scotia, Canada. In June–July 2007, we created wounds on the surface of host fronds that mimicked the wounds that result from invertebrate grazing. At that time, we also mapped the position of epiphyte‐free lateral pits and branch axils on host fronds. In October 2007, after the reproductive season for V. lanosa, the percentage of microsites colonized by this epiphyte was statistically similar for wounds and lateral pits, but significantly lower for branch axils, although by a small difference (mean recruitment rates ranged between 37 and 50%). Since V. lanosa is known not to colonize smooth frond surfaces, our study suggests that the degree of epiphyte load on A. nodosum beds should largely be affected by the overall amount of surface irregularities, with little influence of the relative availability of each microsite type.     

Improved methods of analysis for betaines in <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis> and its commercial seaweed extracts

Beneficial effects of seaweeds and their extracts on crop performance have been attributed to a variety of compounds, including the betaines which are quaternary ammonium betaines. Methods of analysis of betaines published thus far suffer from low sensitivity, lack of baseline separation of individual betaines and from interference from other sample constituents. A rapid cleanup protocol and a sensitive LC-MS/MS method of analysis were developed to afford baseline separation of four betaines in the brown alga Ascophyllum nodosum and its commercial seaweed extract. Using this method, the presence of glycine betaine, δ-aminovaleric acid betaine, γ-aminobutyric acid betaine and laminine in A. nodosum, and commercial extracts derived from A. nodosum, were confirmed and quantified. The major betaine present was γ-aminobutyric acid betaine accounting for 0.008–0.014% of the dry weight of the seaweed and 0.014–0.027% of the dry weight of the commercial extracts. Seasonal variation in betaine content was observed. Differences in the total betaine content were observed between A. nodosum of the yellow (0.011–0.017% dry weight) and the olive green (0.017–0.021% dry weight) coloured morphologies.     

Long-term changes in heavy metal loadings of Ascophyllum nodosum from the Firth of Clyde,UK

The aim of this work is to describe changes in heavy metal concentrations in Ascophyllum nodosum from 1964 to 1994. Samples were collected from three sites in the Firth of Clyde and analysed for zinc, manganese, iron, copper, lead and nickel. The results were analysed using the multivariate technique Principal Components Analysis (PCA). At the Wemyss Bay site there was a trend towards increasing lead and nickel over the study period, which could not be accounted for by local industrial activity. At the Hunterston site, two groups were well separated by the PCA ordination, based on manganese and zinc concentrations, which corresponded to land reclamation activities in the area. The separation of samples at the Ardneil Bay site correlated well with copper concentration and this corresponded to the termination of industrial effluent with heavy copper loadings. Other changes in industrial effluent were also reflected in the Hunterston and Ardneil Bay site ordinations. The PCA technique highlighted the interplay between metals. The work demonstrated the potential for using multivariate analysis of seaweed metal concentrations in monitoring a posteriori the environmental impact of industrial change.     

PHOSPHOENOLPYRUVATE CARBOXYKINASE ACTIVITY IN ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE)1

PEP-dependent⁴ CO₂-fixation by extracts of Ascophyllum nodosum (L.) Le Jol. is reported. The carboxylation of PEP is Mn²⁺ dependent and ATP is shown to be a product. IDP was found to be less efficient as a phosphate acceptor than ADP and 3-mercaptopicolinic acid inhibited the carboxylation reaction. Extracts decarboxylated OAA only in the presence of ATP and had high activities of MDH and GOT. This evidence, together with the probable absence of PEPC, PEPCTrP, and PC in A. nodosum extracts, favors the view that PEPCK is responsible for the light-independent CO₂-fixation observed in this alga.     

Reduction of nitrate leaching from soil treated with an Ascophyllum nodosum based soil conditioning agent

A commercially available soil conditioning agent prepared from a brown marine alga, Ascophyllum nodosum, was tested for its ability to effect leaching rates of nitrate from two soil types. The use of the material led to a significant (p < 0.05) reduction of nitrate leaching from a soil composed of sand and compost (50:50). This revised version was published online in August 2006 with corrections to the Cover Date.     

Adaptations by macroalgae to low carbon availability. I. A buffer system in Ascophyllum nodosum, associated with photosynthesis

Abstract The exchange of CO₂, H⁺ and O₂ between seawater and the intertidal brown macroalga Ascophyllum nodosum (L.) Le Jolis were measured in a flowthrough system. While the algae were kept in darkness, seawater with artificially increased alkalinity and pH at 9.85, was alternated with ‘normal’ seawater at pH 8.0. A proton buffering system, with capacity to release and reabsorb about 20 μmol protons per gram alga (fresh weight) was revealed. As the algae were returned to the ‘normal’ seawater, the kinetics of proton reabsorbtion indicated that a proton uptake was gradually induced. This proton uptake, which was not connected to ion exchange in the cell wall, reached its maximum after 12 h. If subjected to high alkalinity seawater in the light, A. Nodosum for a certain period of time was capable of carrying out O, evolution in excess of the import of inorganic carbon. This ‘photosynthetic buffering capacity’ amounted to about 17 μmol O; per gram alga. Besides depending on a buffer of photorcducible substances, this ‘photosynthetic buffering capacity’ appeared to be functionally connected with the proton buffer. The time course for the discharge of the ‘photosynthetic buffer system’ and for the reabsorbtion of protons into the proton buffer (about 6h for 90× of the capacity at a temperature of 6°C) suggests that the ‘photosynthetic buffer system’ has a functional importance in the adaptation of A. nodosum to intertidal regions. The function of the buffer system is discussed in relation to the crassulacean acid metabolism (CAM)-like characteristics recently shown for the intertidal brown algal family Fucaceae.     

Physiological Characteristics of Mycosphaerella ascophylli, a Fungal Endophyte of the Marine Brown Alga Ascophyllum nodosum

Mycosphaerella ascophylli Cotton, a fungal endosymbiont in the thallus of the marine brown alga, Ascophyllum nodosum (L.) Le Jol., was brought into axenic culture. Most of its nutritional requirements proved to be similar to those characteristic of marine saprophytic fungi: growth optimum at pH 7 to 8, good growth only with a high concentration of NaCl, ability to utilize nitrate as a nitrogen source and glucose, galactose and mannose as carbon sources. The fungus was more specifically characterized by a low temperature optimum (20°C, or lower), a requirement for both thiamin and biotin, and inability to metabolize xylose and fructose.     

Formaldehyde,as its dimedone adduct,fromAscophyllum nodosum

Formaldehyde, as its dimedone adduct (formaldemethone), has been isolated fromAscophyllum nodosum and characterised by thin-layer and overpressured layer chromatography, and from proton nuclear magnetic resonance spectroscopic and electron impact mass spectrometric data. Formaldemethone was detected in extracts of both fresh and dry alga. It is postulated that during dynamic methylation and demethylation processes in the cells, hydroxymethyl groups may be formed, which dependent on pH, are in equilibrium with either free formaldehyde or ions such as iminium, oxonium and thionium; these species will react with dimedone to form formaldemethone. The amount of formaldehyde captured by the dimedone reagent increases as the concentration of dimedone is increased, until a maximum is reached.     

BENTHIC METABOLISM ON A SHELTERED ROCKY SHORE: ROLE OF THE CANOPY IN THE CARBON BUDGET1

While the importance of canopy‐forming algae in structuring ecosystems is recognized, their role in the carbon budget is still not well understood. To our knowledge, no measurements of rocky shores primary production and respiration under emersion periods have been carried out in situ. A benthic chamber coupled to a CO₂‐infrared gas analyzer was used to measure gross primary production and respiration on the Ascophyllum nodosum (L.) Le Jol. zone of a sheltered rocky shore in Brittany, France. Over a year of monthly measurements on the zone with and without the A. nodosum canopy showed fairly high production and respiration values for the global community as well as carbon fluxes due to the canopy that largely dominated the benthic metabolism of the zone. The strong canopy respiration relative to the primary production also suggested a high metabolic activity by microscopic heterotrophs on the surface of the alga. Both the canopy and the understory annual primary production and respiration were under the control of light and temperature seasonal variations. Finally, the range of the amount of carbon produced on the A. nodosum zone during diurnal emersions was estimated. Additional measures accounting for the day–night cycles and seasonal light variations over an entire tidal cycle are, however, necessary to establish an annual carbon budget. Such measures using the benthic chamber together with complementary techniques would allow a better understanding of the functioning of sheltered rocky shores.     

149 Distribution and Invasion of Bangia Atropurpurea (Rhodophyta) in the Laurentian Great Lakes

Müller et al. (1998) noted that freshwater collections of the genus Bangia formed a distinct group separate from marine entities in gene sequence analyses. Recently, the species epithet B. atropurpurea has been resurrected to represent this freshwater lineage. This taxon is one of many invasive species within the Laurentian Great Lakes. B. atropurpurea was first observed in Lake Erie in 1964 and by 1982 was observed in all of the Great lakes except Lake Superior. The present study was initiated to examine the further spread of B. atropurpurea and determine the origin of these populations. Hence, a survey of all the Great Lakes was conducted in 1995 (86 sites) and again in 2002 (104 sites). Bangia was observed at 43 sites in 1995 and 39 sites in 2002. For the first time, this alga has been observed to be present in the St. Lawrence River (1995), Georgian Bay on Lake Huron (2002) and Lake Simcoe (eastern shore, 2002) and hence this alga appears to be spreading into new locations. Cluster analyses of morphological data reveal three distinct groupings that do not separate according to location or lake basin. Preliminary analyses of ITS 1 and 2 sequences show differences among samples within Lake Ontario and among all Lakes; however, collections from Lake Simcoe are very similar in sequence. We are continuing to examine the relationship of Great Lakes populations with freshwater collections from Europe.     

Ecological studies ofSargassum thunbergii (Mertens) O. Kuntze in Maizuru Bay,Japan Sea

Sargassum thunbergii growing on the sheltered coast of Maizuru Bay, which faces the Japan Sea, has been ecologically studied. The alga is perennial, its basal part (holdfast and stem) persisting even after its primary laterals have decayed. The alga forms a conspicuous zone especially in the summer. In the winter the plant is small and its growth is very slow. After that, with the rising of both temperature and tidal levels the alga grows progressively both in length and weight, and also forms numerous lateral branches. In summer (July to August) when the tidal levels are high (+21 cm to +43 cm), the alga is always submerged. At this time, the water temperature reaches the highest in the year (27–29 C), and the alga attains its maximum length and weight. Simultaneously, maturation occurs, and soon afterwards its primary laterals rapidly decay away, while young primary laterals beging to grow. Formae ofSargassum thunbergii (f.typicum, f.latifolia, f.nipponicum and f.swartzianum), which were established by Yendo (1907) and by Okamura (1923) are also discussed in terms of their ecology.     

Extracts of the Brown Seaweed <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis> Induce Gibberellic Acid (GA<Subscript>3</Subscript>)-independent Amylase Activity in Barley

Extracts of the brown seaweed Ascophyllum nodosum have been used as a biostimulant to promote growth and productivity in a number of agricultural production systems. Although the extracts have been shown to improve seedling emergence and vigor in a variety of plants, including barley, the mechanism(s) of this growth-promoting effect is(are) largely unknown. In our study, A. nodosum extract induced amylase activity in barley seed-halves; a significant difference in amylase activity was observed in seeds without an embryo. The addition of activated charcoal to the treatment media negated the bioactivity of the extracts suggesting the organic nature of bioactive compounds in A. nodosum extracts. The extracts induced amylase activity in a gibberellic acid (GA)-deficient barley mutant (grd2). LC-MS-MS analysis failed to detect the presence of GA₃ in the extracts. ABA supplementation of the medium caused a significant reduction of amylase activity in GA-treated seeds compared with those treated with the A. nodosum extract. Taken together, our results suggest that the organic components of A. nodosum extract induce amylase activity independent of GA₃ and might act in concert with GA-dependent amylase production leading to enhanced germination and seedling vigor in barley. Being derived from a renewable resource, the bioactive compounds from A. nodosum could be used to improve crop productivity in sustainable agricultural systems.     

PROPERTIES OF PHOSPHOENOLPYRUVATE CARBOXYKINASE FROM ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE)1

Phosphoenolpyruvate carboxykinase was purified to electrophoretic homogeneity from the brown alga. Ascophyllum nodosum (L.) le Jol. Its molecular mass was 60 kDa as determined by gel filtration. The pH optimum of the carboxylating reaction was 7.9 and the apparent K_m for PEP⁴, ADP and HCO₃^- were 0.036, 0.0116 and 50 mol · m^-3, respectively. Rates of light and dark carbon fixation are also reported for A. nodosum apices and it is shown that rates of in vitro PEPCK activity would account for the observed rate of dark fixation. The physiological role of PEPCK is discussed in relation to light-independent carbon fixation.     

Microbial herbivory on the brown tide alga, Aureococcus anophagefferens: results from natural ecosystems, mesocosms and laboratory experiments

Experiments were conducted with natural plankton assemblages from two areas in Great South Bay (GSB) and the Peconic Bays Estuary System, NY, to compare the rates of growth and pelagic grazing mortality of Aureococcus anophagefferens with co-occurring phytoplankton. We hypothesized that A. anophagefferens would experience low mortality rates by microbial herbivores (relative to feeding pressure on other algae) thus providing it with a competitive advantage within the phytoplankton community. In fact, substantial rates of mortality were observed in nearly every experiment in our study. However, mortality rates of A. anophagefferens were less than intrinsic growth rates of the alga during late spring and early summer in Great South Bay, resulting in positive net growth rates for the alga during that period. This timing coincided with the development of a brown tide in this estuary. Similarly, growth rates of the alga also exceeded mortality rates during bloom development in natural plankton assemblages from the Peconic Bays Estuary System held in mesocosms. In contrast to the situation for A. anophagefferens, growth rates of the total phytoplankton assemblage, and another common picoplanktonic phytoplankter (Synechococcus spp.), were frequently less than their respective mortality rates. Mortality rates of A. anophagefferens in both systems were similar to growth rates of the alga during later stages of the bloom. Laboratory studies confirmed that species of phagotrophic protists that consume A. anophagefferens (at least in culture) are present during brown tides but preference for or against the alga appears to be species-specific among phagotrophic protists. We conclude that two scenarios may explain our results: (1) protistan species capable of consuming the brown tide alga were present at low abundances during bloom initiation and thus not able to respond rapidly to increases in the intrinsic growth rate of the alga, or (2) the brown tide alga produced substance(s) that inhibited or retarded protistan grazing activities during the period of bloom initiation. The latter scenario seems less likely given that significant mortality of A. anophagefferens was measured during our field study and mesocosm experiment. However, even a minor reduction in mortality rate due to feeding selectivity among herbivores might result in a mismatch between growth and grazing of A. anophagefferens that could give rise to significant net population growth of this HAB species. Either scenario infers an important role for trophic interactions within the plankton as a factor explaining the development of brown tides in natural ecosystems.     

Distribution, biomass and primary production of an Ahnfeltia tobuchiensis (Ahnfeltiales, Rhodophyta) population in the Bay of Izmena, Kunashir Island

Regularities of distribution and primary production of an Ahnfeltia tobuchiensis (Kanno et Matsubara) Mak. population, an agar-containing red alga, were studied in the Bay ot Izmena. Experiments were conducted in a flow-through system under conditions similar to algal habitats. The population of A. tobuchiensis unattached to the ground may be from a few centimeters to as much as 1 m thick. It has been shown that only the upper part of a stratum 15–20 cm thick receives a sufficient amount ot light to realize its production potential. While 15–20% of photosynthetically active radiation (PAR) of that falling on the water surface reaches the stratum surface, only 0.1% of PAR from that falling on the water surface penetrates through stratum 15 cm thick. It has been shown for A. tobuchiensis that its photosynthetic rate curve during the daytime mainly follows the PAR intensity curve. The highest values of photosynthetic rate have been measured in the afternoon when PAR reaches its maximum. It is noted that a stratum 15–20 cm thick has peak values ot net primary production (NPP) which averages 3.2 g C m^?2 day^?1. The total area of A. tobuchiensis population was 23.4 km², and its biomass was 125 000 tons in this area. On average, the NPP of the A. tobuchiensis population made up in summer and in autumn was 46.8 and 25.0% of its biomass, respectively.     

Long-term increase in Karenia brevis abundance along the Southwest Florida Coast

Data collected along the southwest coast of Florida between Tampa Bay and Sanibel Island on the abundance of the toxic dinoflagellate Karenia brevis from 1954 to 2002 were examined for spatial and temporal patterns. K. brevis was found to be approximately 20-fold more abundant within 5 km of the shoreline than 20–30 km offshore. Overall, K. brevis was approximately 13–18-fold more abundant in 1994–2002 than in 1954–1963. In 1954–1963, K. brevis occurred primarily in the fall months. In 1994–2002, it was more abundant not only in the fall, but also in the winter and spring months. It is hypothesized that greater nutrient availability in the ecosystem is the most likely cause of this increase in K. brevis biomass, and the large increase in the human population and its activities in South Florida over the past half century is a major factor.     

Biomass and height of Ascophyllum nodosum after two decades of continuous commercial harvesting in eastern Canada

With the increasing demand for seaweed resources worldwide, management must ensure that the harvest of wild seaweed stocks is sustainable. We evaluate the impact of over 25 years of commercial harvesting of Ascophyllum nodosum in eastern Canada by comparing the biomass and height of the seaweed in the late 1990s to the late 2010s over a broad spatial scale spanning the provinces of Nova Scotia and New Brunswick. There has been no significant decrease in the biomass of A. nodosum in either province, and biomass has increased in some regions of New Brunswick during that period. The average height of A. nodosum has decreased by 7.8 cm in Nova Scotia while it increased by 13.8 cm in New Brunswick. Biomass of A. nodosum in unharvested sectors was 7% higher than that in harvested sectors while height of A. nodosum in unharvested sectors in New Brunswick is similar to the values observed in harvested sectors. Over the same period, water temperature has increased in both provinces and, in recent years, has at times exceeded the optimal growing temperature for A. nodosum within bays in Nova Scotia. We conclude that the current management and harvest of A. nodosum in eastern Canada are sustainable and maintain the biomass and height of A. nodosum beds but that control sites are necessary to offer adequate comparisons as environmental conditions are changing.