Host Seaweeds Research Articles

Epiphytic microbiome associated with intertidal seaweeds in the Mediterranean Sea: comparative analysis of bacterial communities across seaweed phyla

The complex interactions between epiphytic bacteria and marine macroalgae are still poorly understood, with limited knowledge about their community structure, interactions, and functions. This study focuses on comparing epiphytic prokaryotes community structure between three seaweed phyla; Chlorophyta, Rhodophyta, and Heterokontophyta in an easternmost rocky intertidal site of the Mediterranean Sea. By taking a snapshot approach and simultaneously collecting seaweed samples from the same habitat, we minimize environmental variations that could affect epiphytic bacterial assembly, thereby emphasizing host specificity. Through 16S rRNA gene amplicon sequencing, we identified that the microbial community composition was more similar within the same seaweed phylum host compared to seaweed host from other phyla. Furthermore, exclusive Amplicon Sequence Variants (ASVs) were identified for each algal phyla despite sharing higher taxonomic classifications across the other phyla. Analysis of niche breadth indices uncovers distinctive affinities and potential specialization among seaweed host phyla, with 39% of all ASVs identified as phylum specialists and 13% as generalists. Using taxonomy function prediction, we observed that the taxonomic variability does not significantly impact functional redundancy, suggesting resilience to disturbance. The study concludes that epiphytic bacteria composition is connected to host taxonomy, possibly influenced by shared morphological and chemical traits among genetically related hosts, implying a potential coevolutionary relationship between specific bacteria and their host seaweeds.

Spatio-temporal variability and association of diatom-dinoflagellate assemblages of Acanthophora, Hypnea and Gracilaria (Rhodophyta)

ABSTRACT Epiphytic microalgae can significantly affect the host seaweed either by complementing, or competing for, resources. Here, epiphytic diatom and dinoflagellate species assemblages on the macroalgae Acanthophora spicifera, Hypnea pannosa and Gracilaria salicornia collected during the north-east (February), inter- (April) and south-west (June) monsoons in 2015 along the coast of Lucero, Pangasinan, North-western Philippines were examined and characterized. Results showed that diatom–dinoflagellate assemblages strongly clustered by season rather than by geographic location. Within season, a minor clustering by macroalgal forms, rather than host species identity, was also observed, which could be associated with the differences in the complexity and texture of the upright and prostrate seaweeds. Examination of the ‘thallisphere’ using confocal laser scanning microscopy further revealed the close proximity of some of the ‘resident’ epiphytic species to the cortical cells of the host, causing deformities and implying more complex interactions. Our results suggest that epiphytic community assemblages were influenced by both the environmental conditions associated with seasonal variation and the microhabitats in the surface of the different algal forms.

Detection of a chemical cue from the host seaweed Laurencia dendroidea by the associated mollusc Aplysia brasiliana.

Chemical cues from sessile hosts can attract mobile and associated organisms and they are also impotant to maintain associations and overall biodiversity, but the identity and molecular structures of these chemicals have been little explored in the marine environment. Secondary metabolites are recognized as possible chemical mediators in the association between species of Laurencia and Aplysia, but the identity of the compounds has not been established. Here, for the first time, we experimentally verify that the sesquiterpene (+)-elatol, a compound produced by the red seaweed Laurencia dendroidea, is a chemical cue attracting the associated sea hare Aplysia brasiliana. In addition to revealing the nature of the chemical mediation between these two species, we provide evidence of a chemical cue that allows young individuals of A. brasiliana to live in association with L. dendroidea. This study highlights the importance of chemical cues in Laurencia-Aplysia association.

Epiphytic Microalgal Species Composition and Dynamics on Host Green Seaweeds (Ulvaphyceae) on the Northern Coast of Jeddah, Saudi Arabia

Epiphytic microalgae on seaweeds are sessile microscopic plants grown with attached or associated to seaweeds hosts and seaweeds are multicellular and macroscopic macro-algae, which are abundant in intertidal zones of coastal environments. Study on epiphytic microalgae is rare at Jeddah coast of the Red Sea. Thus, an investigation on epiphytic microalgae species composition and dynamics on seaweeds of Ulvaphyceae was carried out at northern coast of Jeddah, the Red Sea. The Red Sea is narrow oceanic basin which is lying between the African and the Asian continental shelves. During the study, 3 species of seaweeds were recorded in Ulvaphyceae which were Chaetomorpha linum, Enteromorpha intestinalis and Ulva lactuca. A total of 70 epiphytic microalgae were identified, including 63 belong to Bacillariophyceae, 5 belong to Cyanophyceae and 2 belong to Dinophyceae. Among the identified epiphytic microalgae of the host seaweeds of Ulvaphyceae, the percent contribution of epiphytic Bacillariophyceae, Cyanophyceae and Dinophyceae were 91.53, 6.55 and 2.61%, respectively. The cell abundance of epiphytes on host seaweeds of Ulvaphyceae varied from 8.00 to 93.00 cells/ cells/100 g of Ulvaphyceae seaweeds. The highest cell abundance was in spring and the lowest was in summer. On host seaweeds of Ulvaphyceae, the epiphytes of Licmophora abbreviata, Gyrosigma fasciola, Leptocylindrus danicus, Navicula distans, Navicula transitans, Pleurosigma angulatum and Pleurosigma normanii, Thalassionema frauenfeldii and Nitzschia hungarica were above 10% among epiphytic microalgae though Amphora spp., and Cocconeis spp., were found throughout the year. This finding could be the important source for future explanation of marine epiphytes and their host seaweed eco-biogeographical phenomena in the Red Sea.

Epiphytic Microalgal Dynamics and Species Composition on Brown Seaweeds (Phaeophyceae) on the Northern Coast of Jeddah, Saudi Arabia

Epiphytic microalgae grow on host seaweeds. Seaweeds are multicellular macro-algae, which are abundant in intertidal zones of coastal environments. The report on epiphytic microalgae is rare in the Red Sea. Thus, an investigation on epiphytic microalgae was carried on northern coast of Jeddah, the Red Sea, Saudi Arabia. The Red Sea is narrow oceanic basin which is lying between the African and the Asian continental shelves. During the study, 4 species of seaweeds were recorded in Phaeophyceae which were Laminaria sp., Padina fraseri, Sargassum muticum and Turbinaria ornata. A total of 83 epiphytic microalgae were identified, including 76 belong to Bacillariophyceae, 5 belong to Cyanophyceae, 1 belongs to Chlorophyceae and 1 belongs to Dinophyceae. On seaweeds of Laminaria sp., the dominant epiphytes were Leptocylindrus danicus, Licmophora flabellata and Navicula ramosissma. On seaweeds Padina fraseri, the dominant epiphytes were Cylindrotheca closterium, Navicula sp., Nitzschia sp. and Prorocentrum lima and Cocconeis lineatus. On seaweeds of Sargassum muticum, the dominant epiphytes were Navicula distans, Nitzschia socialis and Navicula vanhoeffeni. On seaweeds Turbinaria ornata, the dominant epiphytes were Leptocylindrus minimus, Bacillaria paxillifer, Leptocylindrus danicus, Nitzschia hungarica and Thalassionema frauenfeldii. The host seaweeds influenced the associated diatoms mainly through its morphology and surface texture and roughness to provide a point of attachment and shelter for host-adapted species. Most of the dominant epiphytes were in smaller cell size diatoms, except Cylindrotheca closterium. The findings of the study focused on individual species of benthic marine diatoms associated with specific seaweeds species even in different regions of the Red Sea in different seasons of Saudi Arabia. These findings could be the important source for future explanation of marine eco-biogeographical phenomena in the Red Sea.

O-heterocyclic derivatives with antibacterial properties from marine bacterium Bacillus subtilis associated with seaweed, Sargassum myriocystum.

The brown seaweed, Sargassum myriocystum associated with heterotrophic bacterium, Bacillus subtilis MTCC 10407 (JF834075) exhibited broad-spectra of potent antibacterial activities against pathogenic bacteria Aeromonas hydrophila, Vibrio vulnificus, and Vibrio parahaemolyticus. B. subtilis MTCC 10407 was found to be positive for polyketide synthetase (pks) gene, and therefore, was considered to characterize secondary metabolites bearing polyketide backbone. Using bioassay-guided fractionation, two new antibacterial O-heterocyclic compounds belonging to pyranyl benzoate analogs of polyketide origin, with activity against pathogenic bacteria, have been isolated from the ethyl acetate extract of B. subtilis MTCC 10407. In the present study, the secondary metabolites of B. subtilis MTCC 10407 with potent antibacterial action against bacterial pathogens was recognized to represent the platform of pks-1 gene-encoded products. Two homologous compounds 3 (3-(methoxycarbonyl)-4-(5-(2-ethylbutyl)-5,6-dihydro-3-methyl-2H-pyran-2-yl)-butyl benzoate) and 4 [2-(8-butyl-3-ethyl-3,4,4a,5,6,8a-hexahydro-2H-chromen-6-yl)-ethyl benzoate] also have been isolated from the ethyl acetate extract of host seaweed S. myriocystum. The two compounds isolated from ethyl acetate extract of S. myriocystum with lesser antibacterial properties shared similar structures with the compounds purified from B. subtilis that suggested the ecological and metabolic relationship between these compounds in seaweed-bacterial relationship. Tetrahydropyran-2-one moiety of the tetrahydropyrano-[3,2b]-pyran-2(3H)-one system of 1 might be cleaved by the metabolic pool of seaweeds to afford methyl 3-(dihydro-3-methyl-2H-pyranyl)-propanoate moiety of 3, which was found to have no significant antibacterial activity. It is therefore imperative that the presence of dihydro-methyl-2H-pyran-2-yl propanoate system is essentially required to impart the greater activity. The direct involvement of polarisability (Pl) with the target bioactivity in 2 implied that inductive (field/polar) rather than the steric effect (parachor) appears to be the key factor influencing the induction of antibacterial activity. The present work may have a footprint on the use of novel O-heterocyclic polyketide products from seaweed-associated bacterium for biotechnological, food, and pharmaceutical applications mainly as novel antimicrobial secondary metabolites.

Predation constrains host choice for a marine mesograzer

For small sedentary herbivores that inhabit seaweeds, choosing a host that provides adequate nutrition and refuge should be favored by natural selection. Yet, the relative importance of seaweed nutritional value versus habitat quality in driving mesograzer host choice remains poorly understood for most herbivores. Previous work in coastal North Carolina, USA, and 2 tropical locations suggests that amphipods often utilize host seaweeds that offer superior refuge from both omni vorous and carnivorous consumers. Our study was conducted in New Zealand, where carnivores alone are the major consumers of seaweed-dwelling amphipods. We show that the herbivorous amphipod Aora typica preferentially utilizes the dictyotalean seaweed Dictyota kunthii over a dominant canopy-forming kelp, Ecklonia radiata, and that this preferred seaweed host provides a superior refuge from predators in both laboratory and field experiments. There was no difference in A. typica feeding preference between D. kunthii and E. radiata, but A. typica grew faster when reared on E. radiata. These results suggest that seaweed refuge quality, not nutritional quality, drives A. typica host preference and distribution in this system.

Trophic cascade in a seaweed-epifauna-fish food chain

Trophic cascades have been described in many ecosystems where predation on a herbi- vore affects biomass or productivity of primary producers. While trophic cascades can be particularly strong on rocky reefs, the majority of studies are restricted to sea urchin herbivores despite the pres- ence of numerous other grazers. The present study examines the potential for predation by small fishes on New Zealand rocky reefs to suppress small invertebrate grazers (epifauna) living on brown seaweeds, with cascading effects on host seaweeds and their epiphytic algae. A trophic cascade was identified in experiments run in outdoor mesocosms. When epifaunal densities were reduced either artificially or by fish predation, seaweeds were more fouled, but less damaged, than where epifaunal populations flourished. These experimental findings were not fully consistent with patterns observed at field sites with varying fish densities. Variation in epifaunal taxonomic structure and seaweed palatability potentially dampened the cascading effect of fish predation on epifauna. Trophic cas- cades with non-urchin herbivores warrant further study, with a combination of laboratory and field work necessary to understand systems in which herbivores are difficult to manipulate.

Distribution and symptoms of epiphyte infection in major carrageenophyte-producing farms

High density commercial farming of carrageenophyte Kappaphycus alvarezii is often plagued with “ice-ice” disease and epiphyte infection, which eventually leads to reduced production and in some cases collapse of crop. Epiphyte outbreak has been occurring regularly in major carrageenophyte farms in the Philippines, Indonesia, Malaysia and Tanzania. Infected materials from these countries were studied to establish baseline information on the epiphyte’s identity, density, symptoms and secondary infection on the host seaweed. The causative organism was identified as Neosiphonia apiculata (Hollenberg) Masuda et Kogame, based on its morphological features. Epiphyte density on host seaweed materials decreased in the following order: the Philippines (88.5 epi cm−2), Tanzania (69.0 epi cm−2), Indonesia (56.5 epi cm−2) and Malaysia (42.0 epi cm−2). Initial symptoms were the presence of tiny black spots, indicating the embedded tetrasporeling in seaweed cortex layer. Vegetative form emerged after 2 weeks measuring less than 0.5 mm in length with a density of less than 25.0 epi cm−2. Upon maturation, infected seaweed takes on a “hairy” appearance with “goose-bumps” like cortical swellings. The epiphyte appears as a solitary plant with multiple secondary rhizoids or as multiple epiphytes appearing from a single cortical opening. At the end of infection, the epiphytes left dark pits on the cortical swelling, and the carrageenophytes are infected by opportunistic bacteria. Bacterial enumeration of healthy and infected seaweed materials showed an increase of more than 300% in total bacterial count on infected materials dominated by Alteromonas sp., Flavobacterium sp. and Vibrio sp.

Herbivory in the gammarid amphipod Aora typica: relationships between consumption rates, performance and abundance across ten seaweed species

This paper reveals a substantial capacity for herbivory of seaweeds in the gammarid amphipod Aora typica, adults eating seven of ten taxonomically and morphologically diverse seaweed species offered to them in a no-choice assay. The green algae Ulva spathulata and Enteromorpha intestinalis were consumed at the highest rates in both no-choice (2.3–2.5 mg blotted weight individual−1 day−1) and multiple-choice assays (0.5–1.3 mg blotted weight individual−1 day−1). Adult A. typica collected from two different species of brown seaweeds had very similar feeding preferences to each other. Juvenile A. typica grew to reproductive maturity on the green algae E. intestinalis and U. spathulata, and the brown algae Carpophyllum maschalocarpum and Ecklonia radiata. In common with previous studies on members of other amphipod families, survivorship of juvenile amphipods was positively correlated with feeding preferences of adults across seaweed species (r2=0.43, P=0.04). However, densities of A. typica on seaweeds in the field (excluding the intertidal E. intestinalis and U. spathulata) were not significantly correlated with feeding preferences of adults (r2=0.07, P=0.5) or survivorship of juveniles (r2=0.17, P=0.31). This suggests that either host seaweeds are not a major dietary component of these amphipods in nature, or that the host’s value as a food source is overridden by other properties such as the degree of shelter it affords from larger consumers. This study provides the first demonstration that a member of the cosmopolitan amphipod family Aoridae is capable of consuming a diverse range of seaweeds.

HOST USE BY AUSTRALASIAN SEAWEED MESOGRAZERS IN RELATION TO FEEDING PREFERENCES OF LARGER GRAZERS

Marine mesograzers use individual seaweeds as both habitat and food. Previous studies by M. E. Hay, J. E. Duffy, and others have shown that mesograzers can acquire enemy-free space by inhabiting and consuming seaweeds that are chemically defended against larger, more mobile consumers. However, their studies, carried out in North Carolina and two tropical regions, consider only a small number of mesograzer species and focus primarily on fishes, even though some other large consumers can destroy mesograzers' host seaweeds. We asked whether the previous findings could be generalized to (1) mesograzers at the community level, (2) large consumers other than fishes, and (3) a different ecosystem in another region, namely, diverse temperate rocky reef communities in Australia and New Zealand. Results from both Australasian regions were similar. In multiple-choice feeding assays larger grazers (three fishes, four gastropods, and three sea urchins) varied in breadth of preferences, but most often preferred to eat green algae of the family Ulvales and the red alga Pterocladiella capillacea, all of which were restricted to the intertidal zone. Most of the mesograzers surveyed (seven amphipods, three isopods, a gastropod, and a sea urchin) preferred to eat the seaweed species from which they were collected, many of which were either inaccessible or less palatable to many larger grazers. This difference in mesograzer vs. larger grazer feeding preferences was consistent with the findings of Hay and Duffy et al. However, community-level patterns of mesograzer distribution and abundance were not consistent with the extensions of the theory developed here. Seaweeds that were less palatable to the larger grazers did not tend to support more mesograzer individuals, mesograzer species, or specialist mesograzers (for either the entire mesograzer assemblage or just for sedentary mesograzers), but the evenness of entire mesograzer assemblages was significantly higher on seaweeds that were less palatable to larger grazers. We argue that spatial refuges on Australasian rocky reefs and differences in the biology of both the seaweed and animal species in Australasia vs. previously studied locations enable palatable seaweeds to persist in the face of herbivory by larger grazers, which reduces the selective pressure on mesograzers to inhabit unpalatable species.

148 Life History and Feeding Preferences of Gallery‐Forming Harpacticoids in Dictyotalean Seaweeds

The harpacticoid copepod Dactylopusioides macrolabris has been reported to make galleries beneath the cuticle of cortical cells of Dictyota dichotoma (Dictyotales, Phaeophyceae; Green 1958). Besides this species, we have found several more harpacticoids from Japanese coasts that have similar habits, infesting various dictyotalean species. In laboratory culture experiments growing the harpacticoids for several generations and recording their behaviors by interval video recoding, we have found that these harpacticoids spend most of the lives in the galleries, feeding only on the algal tissues. Different species showed different feeding preferences even among morphologically very close species: one species fed most of the dictyotalean species examined, whereas another species could digest only one species. In order to discuss the evolutionary interactions between the harpacticoids and host seaweeds, comparative molecular phylogenetic analyses of the harpacticoids and host seaweeds were studied using rDNA ITS2 (harpacticoids) and rbcL (Dictyotales) DNA sequences.

Excretory products of mobile epifauna as a nitrogen source for seaweeds

The potential for excretory product of mobile epifauna to be source of nitrogen for seaweeds was investegated for the fucalean alga Carpophyllum plumosum var. capillifolium at Matheson Bay, northeastern New Zealand.The epifauna excreted an average of 1.5–2.1 times as much nitrogen as the plants were using. A comparison of rates at which the plants took up ammonium with turnover rates of water in the bed indicated that the plants could derive, on average, up to 79% of the nitrogen they required for growth from ammonium excreted by epifauna. This value was estimated under the assumption that ammonium excreted was instantaneously diluted into the water mass surrounding the entire bed. In nature, the availability of ammonium to the individual host seaweed should be greater owing to hydrological processes that restrict water flow around the plant.

Associational resistance and shared doom: effects of epibiosis on herbivory.

The potential for spatial associations between palatable and unpalatable plant species to reduce herbivore pressure on the palatable species has been described as associational resistance, associational refuge or associational defense for numerous terrestrial and marine communities. One of the closest associations between species-epibiosis-has not been thoroughly investigated in this regard. In this study we evaluated how different associations between host seaweeds and epibiotic plants and animals influenced the movement of an omnivorous sea urchin (Arbacia punctulata) to the host and subsequent feeding on the host. A. punctulata showed clear preferences when given pairwise choices between 12 prey species (3 animals, 9 algae). These preferences were consistent and allowed us to rank the six epibiont species and six host species linearly from least to most preferred by A. punculata. Most host-epibiont associations dramatically changed urchin preference, increasing or decreasing urchin grazing on fouled hosts as compared to clean conspecifics. Herbivory on the host increased when the epibiont was more preferred, and decreased when it was less preferred than the unfouled host alga. Taking the host species as a point of reference, we classified epibiosis-caused decrease in herbivory as associational resistance, while epibiont-caused increases in herbivory were defined as shared doom. These epibiont-host-herbivore interactions could select for hosts that facilitate the growth of certain low preference epibionts on their surfaces in situations where the resulting decreases in herbivory would offset the various negative effects of being fouled. In contrast, in situations where herbivores are common, the negative effects of being fouled by palatable epibionts may be much greater than is generally assumed. In our assays, unpalatable hosts fouled by palatable epibionts became much more attractive to urchins and rose several ranks on the urchins' preference hierarchy.