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.     

Temporal dynamics of inducible anti‐herbivory defenses in the brown seaweed Ascophyllum nodosum (Phaeophyceae)1

Anti‐herbivory defenses support persistence of seaweeds. Little is known, however, about temporal dynamics in the induction of grazer‐deterrent seaweed traits. In two induction experiments, consumption rates of the periwinkle Littorina obtusata (L.) on the brown seaweed Ascophyllum nodosum (L.) Le Jolis were measured in 3‐d intervals. Changes in palatability of directly grazed A. nodosum were tested every 3 d with feeding assays using fresh and reconstituted seaweed pieces. Likewise, assays with fresh A. nodosum assessed changes in seaweed palatability in response to water‐borne cues from nearby grazed conspecifics. Consumption rates of L. obtusata varied significantly during the 27‐d induction phase of each experiment. Direct grazing by L. obtusata lowered palatability of fresh and reconstituted A. nodosum pieces to conspecific grazers after 15 d as well as after 6 and 12 d, respectively. After 12, 18, and 24 d, fresh A. nodosum located downstream of L. obtusata‐grazed conspecifics was significantly less palatable than A. nodosum located downstream of ungrazed conspecifics. Changes in L. obtusata consumption rates and A. nodosum palatability during both induction experiments suggest temporal variation of grazer‐deterrent responses, which may complicate experimental detection of inducible anti‐herbivory defenses.     

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.

     

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.     

Effect of seaweed concentrate on hydroponically grown spring barley

Spring barley (Hordeum vulgare cv. Triumph) was grown hydroponically over a 6-week period. Two treatments were incorporated either into the hydroponic solution or sprayed onto the plants at rates of 1 ml per 3 litres. The treatments applied were: (i) a seaweed concentrate prepared fromAscophyllum nodosum (L.) Le Jolis (marketed as Maxicrop Triple), (ii) a ‘Trace element’ treatment incorporating the micro and macro nutrients added to the seaweed extract base to produce the formulated product Maxicrop Triple and (iii) a control treatment. Irrespective of the mode of application, plants treated with Maxicrop Triple grew faster than plants under either of the two other treatments. Elevated growth rates were also found for the ‘Trace element’ treated plants when incorporated into the hydroponic solution. At the final harvest, plants with Maxicrop Triple incorporated into the hydroponic solution showed increases from 56–63% over the control treatment for the growth characteristics measured. ‘Trace element’-treated plants produced increases of between 25–45%. When the treatments were sprayed the effect was less pronounced. Maxicrop Triple increased growth characters by 35–38% and the ‘trace element’ treatment gave increases in the range of 2–13%.     

Enhanced leaf chlorophyll levels in plants treated with seaweed extract

Application to the soil of an aqueous alkaline extract ofAscophyllum nodosum resulted in higher concentrations of chlorophyll in the leaves of treated plants in comparison to control plants treated with an equivalent volume of water. Positive results were obtained with all species tested (tomato, dwarf French bean, wheat, barley, maize). When the seaweed extract was applied as a foliar spray, similar effects on leaf chlorophyll contents were obtained, except in the case of dwarf French bean plants, for which no significant difference was recorded between test and control plants. When the betaines present in the seaweed extract were applied as a mixture in the same concentrations as those in the diluted seaweed extract (-aminobutyric acid betaine 0.96 mg L^–1, -aminovaleric acid betaine 0.43 mg L^–1, glycinebetaine 0.34 mg L^–1), very similar leaf chlorophyll levels were recorded for the seaweed extract and betaine treated plants. This suggests strongly that the enhanced leaf chlorophyll content of plants treated with seaweed extract is dependent on the betaines present.     

Mesoherbivores reduce net growth and induce chemical resistance in natural seaweed populations

Herbivory on marine macroalgae (seaweeds) in temperate areas is often dominated by relatively small gastropods and crustaceans (mesoherbivores). The effects of these herbivores on the performance of adult seaweeds have so far been almost exclusively investigated under artificial laboratory conditions. Furthermore, several recent laboratory studies with mesoherbivores indicate that inducible chemical resistance may be as common in seaweeds as in vascular plants. However, in order to further explore and test the possible ecological significance of induced chemical resistance in temperate seaweeds, data are needed that address this issue in natural populations. We investigated the effect of grazing by littorinid herbivorous snails (Littorina spp.) on the individual net growth of the brown seaweed Ascophyllum nodosum in natural field populations. Furthermore, the capacity for induced resistance in the seaweeds was assessed by removing herbivores and assaying for relaxation of defences. We found that ambient densities of gastropod herbivores significantly reduced net growth by 45% in natural field populations of A. nodosum. Seaweeds previously exposed to grazing in the field were less consumed by gastropod herbivores in feeding bioassays. Furthermore, the concentration of phlorotannins (polyphenolics), which have been shown to deter gastropod herbivores, was higher in the seaweeds that were exposed to gastropod herbivores in the field. This field study corroborates earlier laboratory experiments and demonstrates that it is important to make sure that the lack of experimental field data on marine mesoherbivory does not lead to rash conclusions about the lack of significant effects of these herbivores on seaweed performance. The results strongly suggest that gastropods exert a significant selection pressure on the evolution of defensive traits in the seaweeds, and that brown seaweeds can respond to attacks by natural densities of these herbivores through increased chemical resistance to further grazing.     

SEASONALITY OF MICROBIAL FOULING ON ASCOPHYLLUM NODOSUM (L.) LEJOL., FUCUS VESICULOSUS L., POLYSIPHONIA LANOSA (L.) TANDY AND CHONDRUS CRISPUS STACKH1

The nature and seasonal extent of microbial fouling on Ascophyllum nodosum (L.) LeJol., Fucus vesiculosus L., Polysiphonia lanosa (L.) Tandy and Chondrus crispus Stackh. were observed by scanning electron microscopy. Bacterial filaments and smaller rod and coccoid forms dominated the fouling communities on all species, with pennate diatoms constituting a minor component in contrast to results with plastic substrates on which pennate diatoms dominated and preceded bacterial colonization. The total percent microbial coverage on the surfaces of all four seaweed species was determined by monthly stereological analyses of representative composite micrographs. These showed a simultaneous decline between April and May which could represent the die-off of the cold water bacterial flora when water temperature increased past the threshold for obligate psychrophiles. Microbial colonization patterns were directly correlated (P = 0.005) with maximum coverage in April and November–December and reduced levels from May to October. Significant inverse (P < 0.041) correlations between total percent coverage and water temperature indicate distinct seasonal cycles, however, the patterns of dominance by filamentous bacteria and rod and coccoid forms were markedly different. Total coverage patterns of both rhodophytes showed no apparent seasonal cycle and were not related to water temperature. Rod and coccoid bacteria were apparently suppressed year round on P. lanosa relative to the other species. These interspecific differences in seasonal fouling patterns are discussed in light of possible modes of regulation, especially algal antibiosis.     

A NEW RECORD AND ERADICATION OF THE NORTHERN ATLANTIC ALGA ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE) FROM SAN FRANCISCO BAY,CALIFORNIA, USA1

A new record of the Northern Atlantic fucoid Ascophyllum nodosum (L.) Le Jolis (Knotted wrack) was discovered on a shoreline in San Francisco Bay, California during a survey of intertidal habitats in 2001–2002. The alga showed no signs of deterioration 2.5 months after its initial detection. The healthy condition, presence of receptacles with developing oogonia, potential for asexual reproduction, and ability to withstand environmental conditions, both inside the Bay and on the outer Pacific coast, prompted a multiagency eradication effort. Given the relatively small area of shoreline inhabited by the alga, in combination with its absence in 125 other surveyed locations, we decided that manual removal of the seaweed would be the most environmentally sensitive yet effective eradication approach. No A. nodosum has been detected at the site since December 2002, and the species is thought to have been locally eradicated. The site continues to be monitored to assess the success of the eradication efforts.     

Dormancy of<Emphasis Type="Italic"> Arabidopsis</Emphasis> seeds and barley grains can be broken by nitric oxide

Seeds of Arabidopsis thaliana (L.) Heynh. and grains of barley (Hordeum vulgare L.) were used to characterize the affects of nitric oxide (NO) on seed dormancy. Seeds of the C24 and Col-1 ecotypes of Arabidopsis are almost completely dormant when freshly harvested, but dormancy was broken by stratification for 3 days at 4°C or by imbibition of seeds with the NO donor sodium nitroprusside (SNP). This effect of SNP on dormancy of Arabidopsis seeds was concentration dependent. SNP concentrations as low as 25 M reduced dormancy and stimulated germination, but SNP at 250 M or more impaired seedling development, including root growth, and inhibited germination. Dormancy was also reduced when Arabidopsis seeds were exposed to gasses that are generated by solutions of SNP. Nitrate and nitrite, two other oxides of nitrogen, reduced the dormancy of Arabidopsis seeds, but much higher concentrations of these were required compared to SNP. Furthermore, the kinetics of germination were slower for seeds imbibed with either nitrate or nitrite than for seeds imbibed with SNP. Although seeds imbibed with SNP had reduced dormancy, seeds imbibed with SNP and abscisic acid (ABA) remained strongly dormant. This may indicate that the effects of ABA action on germination are downstream of NO action. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide (cPTIO) strengthened dormancy of unstratified and briefly stratified Arabidopsis seeds. Dormancy of three cultivars of barley was also reduced by SNP. Furthermore, dormancy in barley grain was strengthened by imbibition of grain with cPTIO. The data presented here support the conclusion that NO is a potent dormancy breaking agent for seeds and grains. Experiments with the NO scavenger suggest that NO is an endogenous regulator of seed dormancy.Abbreviations ABA Abscisic acid - cPTIO 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide - GA Gibberellin - SNP Sodium nitroprusside - NO_x Gaseous oxides of nitrogen     

The phylogeographic architecture of the fucoid seaweed Ascophyllum nodosum: an intertidal ‘marine tree’ and survivor of more than one glacial–interglacial cycle

Aim Ascophyllum nodosum (L.) Le Jolis is a dominant fucoid seaweed occurring along sheltered, rocky shores throughout the North Atlantic (but not in the Pacific), where it is a foundational species of the intertidal community. Its large size and vulnerability to ice‐scour have led to the hypothesis that contemporary populations in the north‐west Atlantic may be the result of de novo recolonization from the north‐east Atlantic since the Last Glacial Maximum (LGM) (c. 20 ka). We tested this hypothesis. Location Temperate North Atlantic rocky intertidal between c. 42 and 65° N latitude. Methods More than 1300 individuals from 28 populations were sampled from across the entire range of A. nodosum and genotyped for six microsatellite loci, and > 500 individuals were genotyped for two mitochondrial loci, an intergenic spacer (IGS) and the tRNA (W) gene (trnW). Population structure and historical demography were analysed in a standard population genetics and coalescence framework. Results Based on the presence of private alleles and haplotypes, we found that A. nodosum has survived on both sides of the Atlantic (since before the LGM, dating back to at least the penultimate Eemian interglacial) with similar effective population sizes and divergence times (1.2 and 0.8 Ma). Dispersal has been predominantly from Europe to North America, and there is very weak present‐day population differentiation across the North Atlantic. Diversity measures provided additional support for determining the location of refugia. Main conclusions Ascophyllum nodosum was apparently little affected by the LGM, although contemporary climate change is likely to have major effects on its latitudinal distribution on both sides of the North Atlantic. It is a very long‐lived species, analogous in virtually all demographic aspects to a tree – resistant to extinction but vulnerable to catastrophic events. The Brittany peninsula is a hotspot of genetic diversity worthy of conservation.     

Induced resistance in intertidal macroalgae modifies feeding behaviour of herbivorous snails

Herbivory in terrestrial and marine systems can induce changes in plant chemistry affecting the foraging behaviour of herbivores. A model based on terrestrial plant-herbivore interactions predicts herbivory-induced changes in leaf chemistry to be manifested in (1) increased herbivore mobility, (2) increased feeding dispersal and (3) reduced tissue consumption by herbivores. This study is the first to demonstrate that herbivory-induced changes in the tissue chemistry of the brown seaweed Ascophyllum nodosum elicit the same response in the feeding behaviour of the gastropod Littorina obtusata as predicted for herbivorous insects, providing good evidence for the models validity across different ecosystems. The potential benefit of increased feeding dispersal to terrestrial plants as suggested by the model is the prevention of concentrated damage to apical tissues thereby preserving the plants ability to compete for light; A. nodosum does not conform to these predictions. Increased dispersal of feeding damage on A. nodosum away from primary frond tissues would reduce the likelihood of frond breakage implying a fitness benefit of induced resistance.     

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.     

Changes in composition of rockweed (Ascophyllum nodosum) beds due to possible recent increase in sea temperature in Eastern Canada

Ascophyllum nodosum (rockweed) is the main economic resource of the seaweed industry in the Atlantic Provinces of Canada. The annual harvest steadily increased since 1995, reaching a historic peak of 37,000 tonnes in 2007. Due to a high demand for fertilizers and animal feed supplements derived from rockweed, this trend seems likely to continue. The current management plan for the sustainable harvest of the A. nodosum resource is considered conservative. The resource has been managed with a precautionary approach since 1995 to protect the integrity of the habitat. Acadian Seaplants Limited (ASL) has been granted approximately 90% of the government-issued licenses to harvest A. nodosum resources in the Maritimes. The Canadian approach is based on an annual harvest from a given bed and not strip-and-return after several years. Since 1995, ASL has proactively undertaken extensive annual surveys and research on biomass productivity of this renewable resource to establish acceptable annual exploitation rates. Historically, the rockweed beds of southwestern Nova Scotia (NS) have been almost 99% pure A. nodosum, with a minor component of Fucus vesiculosus. However, since 2004, a steady increase in F. vesiculosus, with a peak of 4.6% of the total biomass in 2008, was recorded. This coincided with one of the mildest winters on record for the Maritimes. This increase in temperature seemed to be also responsible for an unusual recruitment of the blue mussel Mytilus edulis in rockweed beds in some areas of southern New Brunswick (NB) in 2006, causing the detachment of up to 30% of the seaweed biomass in some harvesting sectors. Another phenomenon observed in southwestern NS during 2003 and 2004 was extensive ice damage on rockweed beds produced by an early melting of the ice, with losses of up to 90% of the rockweed biomass in some areas.     

Bait worm packaging as a potential vector of invasive species

Invasive species have become an increasingly greater concern for the ecological health of coastal ecosystems, yet vectors of these introductions often are unclear. This project evaluated the potential for the brown seaweed Ascophyllum nodosum ecad scorpiodes (Hauck) Reinke, packaged with bait worms (Nereis virens) harvested from the coast of Maine (USA), as a vector of invasive marine fauna and flora. Often, the seaweed and contents of the bait boxes are discarded into the water by recreational fishermen after using the bait worms, and any included non-native species may then be introduced. Bait boxes were purchased from several commercial vendors in Connecticut and New York over a two-year period. Subsamples of the seaweed were placed in laboratory culture and the growth of associated macro- and microalgae was monitored. Marine invertebrate species present in the samples were also identified and quantified. Results indicated 13 species of macroalgae and 23 species of invertebrates were associated with baitboxes. Among the highly diverse microbial assemblage detected, two species of potentially toxic marine microalgae, Alexandrium fundyense Balech and Pseudonitzschia multiseries (Hasle) Hasle, were found both prior to and after incubation at various temperatures, indicating these harmful algae are brought to and can survive in receiving waters. These findings highlight the need to consider alternative choices of bait box packaging materials or appropriate disposal methods of the seaweed in order to minimize the transport of species which are not native to the receiving coastal waters.     

ROLE OF SURFACE WOUNDS AND BROWN ALGAL EPIPHYTES IN THE COLONIZATION OF ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE) FRONDS BY VERTEBRATA LANOSA (RHODOPHYTA)1

Ascophyllum nodosum (L.) Le Jol. forms extensive beds in wave‐sheltered, rocky intertidal habitats on the northwestern Atlantic coast. This fucoid seaweed is host to an obligate red algal epiphyte, Vertebrata lanosa (L.) T. A. Chr. [=Polysiphonia lanosa (L.) Tandy], and two facultative brown algal epiphytes, Elachista fucicola (Velley) Aresch. and Pylaiella littoralis (L.) Kjellm. Although V. lanosa can occur throughout most of the length of host fronds, it largely predominates in midfrond segments. The two brown algal epiphytes are restricted to distal segments. Through field experiments conducted in Nova Scotia, Canada, we tested the hypothesis that surface wounds are required for the colonization of distal segments of host fronds by V. lanosa. Distal tissues normally have a smooth surface because of their young age (A. nodosum fronds grow apically). By creating small wounds that mimicked grazing wounds distributed elsewhere on host fronds, we demonstrated that V. lanosa can colonize distal frond segments during the growth and reproductive season (summer and autumn). Approximately half of the artificial wounds were colonized by V. lanosa during this time. The experimental exclusion of both brown algal epiphytes from distal frond segments did not affect colonization by V. lanosa. Thus, we conclude that the absence of surface irregularities on distal segments of host fronds, specifically small wounds, is the main factor explaining the absence of V. lanosa there. We propose that further experimental work clarifying epiphyte distribution in host beds will enhance our ability to understand the functional role of epiphytes in intertidal ecosystems.     

Navicula endophytica Sp.Nov., A pennate diatom with an unusual mode of existence

The diatom Navicula endophytica sp. nov., first observed by Baardseth (1966) in the intercellular substance of receptacles of Ascophyllum nodosum, is described. The species has been encountered neither as an epiphyte on this seaweed nor as a planktonic form.     

THE ROLE OF ALLELOPATHIC SUBSTANCES IN THE “SMOTHER CROP” BARLEY

The high degree of success of barley as a “smother crop” generally has been attributed to physical competition for nutrients and water. However, it was found that even in the absence of such competition, barley still inhibits germination and growth. This occurred both in mixed cultures receiving adequate nutrients and water and in germination tests. Aqueous leachates of seeds and roots of barley caused similar inhibition of germination and growth, thereby indicating an inhibitory allelopathic substance. A specificity of reaction was found, with the greatest inhibition occurring with Stellaria media (L.) Cyr., less with Capsella bursa-pastoris (L.) Medic. and tobacco (Nicotiana tabacum L.), and no significant effect with wheat (Triticum aestivum L.). A concentration effect and possible periodic production of the inhibitor were indicated. Living plants and aqueous leachates of living roots were more inhibitory than dead ones, thereby supporting the hypothesis of an active metabolic secretion of the allelopathic substance. Preliminary attempts to identify the active inhibitory components demonstrated the presence of alkaloids, with a much greater concentration of substance in the living than in the dead root leachates. The alkaloid, gramine, known to occur in barley, was found to have an inhibitory effect on the growth of Stellaria media and it is suspected as an active component of the root leachates. These results suggest that factors other than the previously assumed physical competition are involved in the mechanism of the “smother crop” barley.     

Effect of Processing on the Microflora of Norwegian Seaweed Meal,with Observations on Sporendonema minutum (H?ye) Frank and Hess

Meal from the brown seaweed Ascophyllum nodosum (L.) Le Jol. is mainly used as an animal feed supplement. Since moist weed often develops a marked mold growth and since little was known about the microflora of seaweed meal, a cultural procedure was developed to enumerate the populations of bacteria, yeasts, and molds of seaweed meals manufactured by different drying processes. The microflora could be supported by a variety of media varying in levels of nutrition and in the source and concentration of salts. Fresh weed contained less than 10³ bacteria and less than 10² yeasts and molds per g (dry weight). The type and extent of microbial populations in seaweed meal appeared to be dependent upon the method of seaweed drying. Rotary drum-drying at temperatures decreasing from 800 to 80 C maintained or reduced the microbial populations to 10³ organisms per g (dry weight). Although meals with high nutritional quality can be obtained with warm air- or rock-dried weed, these conditions can also permit bacterial and mold development. Extended rock-drying in variable weather conditions and prolonged storage of moist weed, both of which decrease the nutritional quality, also lead to high bacterial numbers and to a marked development of the halophilic brown mold Sporendonema minutum which attained populations of 10⁸ viable spores per g of dried weed. A poultry diet containing 5% badly molded weed had no apparent toxic or growth-depressing effect when fed to chicks.