Biogeography of Macroalgae R&D

Aquatic Botany BR25820 Biogeography of Macroalgae Reproduction and Dispersal

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  • Title: Aquatic Botany BR25820 Biogeography of Macroalgae Reproduction and Dispersal

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Key Concepts

  • Biogeography of Macroalgae

    • Discusses the reproduction and dispersal mechanisms of macroalgae.

  • Reproductive Methods

    • Asexual reproduction

    • Sexual reproduction

    • Alternation of generations

  • Spore Production and Dispersal Factors

    • Factors include:

      • Water motion

      • Parent plant

      • Spore clouds

      • Drifting plants

  • Specific Species Dispersal

    • Dispersal mechanisms observed in Laminaria digitata and Saccharina latissima.

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Saccharina longicruris

  • Recognized as a synonym of S. latissima.

  • Geographic Location: Northeastern Atlantic (Newfoundland coast).

  • Sporophyte Characteristics

    • Releases approx. 9 x 10^9 spores per year.

    • About 9 x 10^6 spores recruit to the gametophyte stage.

    • Typically, only one sporophyte matures to reproductive size.

Asexual Reproduction

  • Common among seaweeds and kelps.

  • Economic Investment in Resources

    • Formation of small multicellular or unicellular propagules in large quantities.

  • Stoloniferous Growth

    • Example: Caulerpa sertularioides.

  • Spores produced by mitosis in sporangia.

  • Genetic Implications

    • Asexually produced offspring are clones; limited diversity can be concerning but mitigated in suitable habitats.

Alternation of Generations

  • Algae exhibit alternation of generations, predominant in most chlorophytes, phaeophytes, and rhodophytes.

  • Cycles between haploid (gametophyte) and diploid (sporophyte) stages.

  • Example: Rhodophyta involves a triphasic life cycle with carposporophyte stage.

  • Meiosis introduces genetic variability.

Spore Production

  • No specific ontogenetic pattern (e.g., Laminaria: days; Macrocystis: 9-12 months; Fucus: 2 years).

  • No clear relationship between spore size and survival rates.

  • Mostly random but Factors Affecting Spore Production:

    • Seasonality: Varied by species and latitudinal resource availability.

    • Abiotic Factors: Light, temperature, nutrients impact spore viability.

Dispersal in Macroalgae

  • Sessile species so need dispersal.

  • Biogeographical significance of propagules:

    • Essential for colonizing new habitats and community stability.

    • Sessile organisms risk extinction without efficient dispersal strategies.

  • Dispersal Agents:

    • Motile animals, invertebrate shells, fecal pellets, and various water masses.

    • floating substrata- man made or epiphytic.

    • Wind-driven currents: These can transport macroalgae spores and fragments across vast distances, facilitating colonization in new habitats.

Dispersal: Water Motion

  • Relies on small propagules (spores, zygotes) for dispersal.

  • External water forces overshadow internal locomotion:

    • Small cells swim at 80-300 µm/s, while wave flows can reach 1-10 m/s.

  • Propagule fate is largely water flow-dependent, varying in depth and proximity to the shore:

  • unidirectional in deeper waters.

  • more chaotic near the shore/substratum.

  • timing of release.

Dispersal: Parent Plant

  • Water velocity decreases at the substratum level, affecting propagule release height.

  • The positioning of reproductive organs influences dispersal efficiency:

    • Smaller plants release spores near the substratum, while larger fronds potentially utilize surface flow but may not always do so effectively.

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Dispersal: Spore Clouds

  • Propagule clouds drift unless extreme turbulence occurs.

  • Simultaneous Release Importance:

    • Groups dispersing are more efficient than individuals.

    • sequence of smaller releases (patchy)

    • Release patterns and currents influence dispersion scales.

    • timed to storms or tides - as a group release at the same time to maximise dispersal - synchronic

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Dispersal: Drifting Plants

  • Dislodgement or fragmentation can promote extensive travel.

  • fragments remain fertile

  • Examples of species mobility:

    • Ascophyllum nodosum: travels up to 5,500 km.

    • Sargassum spp.: 600-900 km.

  • Monecious species benefit from self-fertilization—supporting rapid establishment in new environments.

  • Baker’s law - rapid spread

Measuring Dispersal

  • Employing population genetics and hydrodynamic models to study dispersal patterns.

  • Investigating migrations reveals gene flow dynamics.

Dispersal in Laminaria digitata

  • Alternation between haploid (gametophyte) and diploid (sporophyte) phases is evident.

  • Sporophytes develop sori at the ends of their thalli with dispersal ranges of up to 2 km.

  • Limited spore longevity (around 72 hours) restricts dispersal ability.

degree of gene flow between populations in different areas, but after comparing different populations they conform to a model of isolation by distance

Field Study Overview

  • Notable site: Strangford Lough, County Down, NI (150 km²).

  • Sampling conducted from 16 sites to analyze current influence on dispersal.

  • Utilized 3 microsatellite markers for genetic analysis.

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Genetic Similarity Findings

  • Proximity correlating with genetic similarity.

  • Utilized MIKE21 hydrodynamic modeling to assess dispersal potential.

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Data Representation (Graph/Table)

  • Visual representation of total spore release dynamics.

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Summary of Findings: Dispersal in Laminaria digitata

  • High gene flow observed, influenced by geographic proximity.

  • Occasional long-distance dispersal potential exists, though most spores settle nearby.

  • The hydrodynamic environment at Strangford Lough complicates understanding of dispersion.

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Dispersal in Saccharina latissima

  • Reproductive biology mirrors that of Laminaria digitata.

  • A notable biofuel crop, featuring biphasic reproduction influences.

  • Short-distance fertilization crucial for gamete proximity.

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Genetic Homogeneity Study

  • Investigated potential gene flow barriers due to large water expanses near Strangford Lough.

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Impact of Geographic Range on Genetics

  • Results show variance in conformance to isolation by distance models.

  • Genetic homogeneity noted across broader surveyed populations.

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Genetic Analysis Deduction

  • Four distinct populations identified across 14 sites.

  • BAPS analysis

  • Freshwater influences, such as Belfast Lough, may disrupt typical genetic isolation patterns.

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Summary Conclusions

  • Reproduction: Algae reproduce asexually and sexually through alternating generations.

  • Dispersal Mechanisms: Involves spores and fragments transported by water, animals, etc.

  • Laminaria digitata shows isolation by distance within certain populations, while Saccharina latissima displays non-isolation influenced by hydrodynamic factors.