An assessment of the influence of host species, age, and thallus part on kelp-associated diatoms

Diatom community composition and abundances on different thallus parts of adult and juvenile specimens of Ecklonia maxima and Laminaria pallida were examined in False Bay, South Africa, using light and scanning electron microscopy. Altogether, 288 thallus portions were analysed. Diatom abundances ranged from 0 to 404 cells mm−2 and were generally higher on E. maxima and juvenile thalli than L. pallida and adult specimens. Moreover, diatom abundances differed between the various thallus parts, being highest on the upper blade and lowest on the primary blade. A total of 48 diatom taxa belonging to 28 genera were found. Gomphoseptatum Medlin, Nagumoea Witkowski and Kociolek, Cocconeis Ehrenberg, and Navicula Bory were the most frequently occurring genera, being present in 84%, 65%, 62.5%, and 45% of the analysed samples, respectively. Among these, Cocconeis and Gomphoseptatum were the most abundant, contributing 50% and 27% of total diatom cells counted collectively across all samples

Epiphytic diatom assemblages associated with South African kelps: Ecklonia maxima and Laminaria pallida

Magister Scientiae (Biodiversity and Conservation Biology)Kelp forests are dynamic and productive ecosystems which host large biodiversity of sessile fauna and flora, including diatoms. These microalgae occur at the base of coastal marine food webs and contribute substantially to the productivity of marine ecosystems. Diatoms constitute one of the most common and species-rich groups of both phytoplankton and phytobenthos. Possessing a unique silica cell wall, diatoms play a key role in the global carbon and silicon cycles. As the changes in species composition of diatom communities are a direct reaction to the combination of environmental factors prevailing in their ecosystems, diatom analysis is widely and successfully used in biomonitoring of various environmental conditions and paleoecological reconstructions

The effects of stress on benthic algal communities

The effects of stress on both microalgal and macroalgal communities are considered. On one hand the contrasting approaches of studies of these two communities reflect intrinsic differences in plant size, longevity and ease of handling. On the other hand they reveal that biological monitoring of the potentially deleterious effects of man's activities has focused largely on freshwater environments in which macroalgae only occasionally dominate. Large conspicuous plants can be readily investigated as individuals, whereas it is virtually impossible to trace effects of stress on an individual cell of a vegetatively-reproducing microalga; a population approach is almost inevitably necessary. However, rapid turnover rates, a spectrum of ecological characteristics distributed between many taxa, and the potential for statistical analysis, have facilitated the use of microalgae in environmental impact studies. Failure to extend such investigations into marine systems rests as much on man's ability to ignore environmental deterioration until it affects his quality of life as on the visual dominance of seaweeds around our coasts. However, large gaps remain in our knowledge of both large and small algae; some reported community changes over time are suspect, and the causes of even blatant changes are not always apparent

Seasonally fluctuating fouling control of Fucus vesiculosus and Fucus serratus from the Baltic Sea: Is fouling control linked to abiotic and biotic variables?

In this doctoral project, I investigated the putative seasonal fluctuating chemical fouling control of the perennial macroalgae Fucus vesiculosus and Fucus serratus from the Baltic Sea under in situ conditions as well as potential links between the chemical fouling control and different abiotic and biotic factors. My thesis highlights the seasonal dynamics of the chemical micro- and macrofouling control of F. vesiculosus and F. serratus from the Baltic Sea tested under in situ conditions as well as the impact of environmental variables on the fouling control strength. Further, this work demonstrates that both Fucus species exhibit pro- and antifouling properties during summer when fouling pressure is highest indicating a complex regulation of biofouling control. The study thus provides new insides into the complex algae-environment-fouler interactions and their seasonal dynamics

Seasonally fluctuating fouling control of Fucus vesiculosus and Fucus serratus from the Baltic Sea : is fouling control linked to abiotic and biotic variables?

In this doctoral project, I investigated the putative seasonal fluctuating chemical fouling control of the perennial macroalgae Fucus vesiculosus and Fucus serratus from the Baltic Sea under in situ conditions as well as potential links between the chemical fouling control and different abiotic and biotic factors. My thesis highlights the seasonal dynamics of the chemical micro- and macrofouling control of F. vesiculosus and F. serratus from the Baltic Sea tested under in situ conditions as well as the impact of environmental variables on the fouling control strength. Further, this work demonstrates that both Fucus species exhibit pro- and antifouling properties during summer when fouling pressure is highest indicating a complex regulation of biofouling control. The study thus provides new insides into the complex algae-environment-fouler interactions and their seasonal dynamics.In dieser Doktorarbeit wurde die vermeintlich saisonal fluktuierende chemische Fouling-Kontrolle der mehrjährigen Makroalgen Fucus vesiculosus und Fucus serratus aus der Ostsee unter in situ Bedingungen sowie mögliche Zusammenhänge zwischen der chemischen Foulingkontrolle und verschiedenen abiotischen und biotischen Faktoren untersucht. Meine Doktorarbeit verdeutlicht die jahreszeitliche Dynamik der chemischen Mikro- und Makrofouling-Kontrolle von F. vesiculosus und F. serratus aus der Ostsee unter in situ Bedingungen sowie den Einfluss von Umweltvariablen auf die Fouling Kontrollstärke. Zusätzlich zeigt diese Arbeit, dass beide Fucus Arten pro- und antifouling Eigenschaften im Sommer aufweisen, wenn der Fouling-Druck am höchsten ist, was eine komplexe Regulierung der Biofouling-Kontrolle andeutet. Diese Studie liefert somit neue Einsichten in die komplexe Algen-Umwelt-Fouler Interaktion und ihre jahreszeitliche Dynamik

18S rDNA gene metabarcoding of microeukaryotes and epi-endophytes in the holobiome of seven species of large brown algae

Brown algae (Phaeophyceae) are habitat-forming species in coastal ecosystems and include kelp forests and seaweed beds that support a wide diversity of marine life. Host-associated microbial communities are an integral part of phaeophyte biology, and whereas the bacterial microbial partners have received considerable attention, the microbial eukaryotes associated with brown algae have hardly been studied. Here, we used broadly targeted “pan-eukaryotic” primers (metabarcoding) to investigate brown algal-associated eukaryotes (the eukaryome). Using this approach, we aimed to investigate the eukaryome of seven large brown algae that are important and common species in coastal ecosystems. We also aimed to assess whether these macroalgae harbor novel eukaryotic diversity and to ascribe putative functional roles to the host-associated eukaryome based on taxonomic affiliation and phylogenetic placement. We detected a significant diversity of microeukaryotic and algal lineages associated with the brown algal species investigated. The operational taxonomic units (OTUs) were taxonomically assigned to 10 of the eukaryotic major supergroups, including taxonomic groups known to be associated with seaweeds as epibionts, endobionts, parasites, and commensals. Additionally, we revealed previously unrecorded sequence types, including novel phaeophyte OTUs, particularly in the Fucus spp. samples, that may represent fucoid genomic variants, sequencing artifacts, or undescribed epi-/endophytes. Our results provide baseline data and technical insights that will be useful for more comprehensive seaweed eukaryome studies investigating the evidently lineage-rich and functionally diverse symbionts of brown algae.publishedVersio

Molecular support for temporal dynamics of induced anti-herbivory defenses in the brown seaweed Fucus Vesiculosus

Grazing by the isopod Idotea baltica induces chemical defenses in the brown seaweed Fucus vesiculosus. A combination of a 33 day induction experiment, feeding choice assays and functional genomic analyses was used to investigate temporal defense patterns and to correlate changes in palatability to changes in gene expression. Despite permanent grazing, seaweed palatability varied over time. Controls were significantly more consumed than grazed pieces only after 18 and 27 days of grazing. Relative to controls, 562/402 genes were up-/down-regulated in seaweed pieces that were grazed for 18 days, i.e. when defense induction was detected. Reprogramming of the regulative expression orchestra (translation, transcription), up-regulation of genes involved in lipid and carbohydrate metabolism, intracellular trafficking, defense and stress response, as well as downregulation of photosynthesis was found in grazed seaweed. These findings indicate short-term temporal variation in defenses and that modified gene expression patterns arise at the same time when grazed seaweed pieces show reduced palatability. Several genes with putative defensive functions and cellular processes potentially involved in defence, such as reallocation of resources from primary to secondary metabolism, were reveale

Successful invaders are better defended: The example of Gracilaria vermiculophylla

To evaluate the importance of anti-herbivore resistance for algal invasion success we compared resistance traits among specimens of the red macroalga Gracilaria vermiculophylla from six native populations in Korea and China and eight invasive populations in Europe and Mexico that were maintained under identical conditions in the laboratory. Herbivorous snails both from the native range (Littorina brevicula) and from the invaded range (Littorina littorea) consumed significantly less of seaweed specimens originating from non-native populations. Metabolome profiling revealed that this preference was correlated with an increased woundactivated production of deterring prostaglandins and hydroxyeicosatetraenoic acids. Thus, invasive populations of G. vermiculophylla are more strongly defended against challenge by herbivores and other biological enemies that cause local tissue or cell disruption and activate oxylipin production. Anthropogenic distribution of genotypes adapted to resist elevated feeding pressure probably contributed to the invasion success of this species

Temporal and spatial distribution of grazers and kelp phlorotannins in Kachemak Bay, Alaska

Thesis (M.S.) University of Alaska Fairbanks, 2006The potential influence of grazers on the density and distribution of kelp thalli is substantial and may be mediated by kelp phlorotannins serving in a defensive role. The purpose of this study was to determine how temporal and spatial phlorotannin patterns in four kelp species in Kachemak Bay, Alaska, are influenced by density and distribution of the gastropod grazer Lacuna vincta and environmental variables. Temporal phlorotannin patterns from June 2004 through December 2005 were mainly explained by the life history of particular kelp species as well as strong correlations with light attenuation and nitrate concentration. The Optimal Defense Theory of resource allocation to differentiated tissues was supported by observations of higher proportional allocation to attachment structures and meristematic tissue in all kelp species. Lacuna vincta distribution was not clearly related to phlorotannin content and therefore, grazer habitat and food choices may be influenced by the combination of high phlorotannin content, tissue toughness and/or nutritional content. Strong physical disturbances such as currents and wave action may supersede these factors and drive grazer distribution. An understanding of the biological and physical factors affecting phlorotannin content and distribution in kelp thalli may suggest reasons for temporal and spatial kelp bed variability.1. General introduction -- 2. Seasonal variation in kelp phlorotannins in relation to grazer, light and nutrient dynamics in the Alaskan sublittoral zone -- 3. Within-thallus phlorotannin allocation and induction in Northeastern Pacific kelps -- 4. General conclusions

Ecology of microbes associated with a macroalgal host: effects of environmental conditions on the composition of epibacterial communities and repellant effects of microbial epibionts on barnacle larvae

Dissertation on the effects of environmental conditions on the epibacterial communities associated with macrolaga