Algae 1

Algae Introduction

  • Introduction to Algae

    • Transitioning from microbes to algae, building on lab experiences with macroalgae and seagrasses.

    • Will cover both microalgae and macroalgae, including their roles in ecosystems and human applications.

    • Differentiating eukaryotic algae from cyanobacteria (blue-green algae), focusing solely on eukaryotic algae in this lecture.

Lecture Objectives

  • Defining Algae

    • Defining the term "algae" is complex due to its informal and non-taxonomic nature.

    • Understanding the common understanding of the term.

  • Marine Algae Groups and Habitats

    • Identifying major groups of marine algae and their primary habitats.

  • Basic Principles and Characteristics

    • Understanding basic characteristics (functions and importance) of algae groups.

  • Ecological Roles

    • Describing ecological roles (e.g., planktonic, benthic, biomass production).

What Are Algae?

  • General Characteristics

    • Algae are generally aquatic and photosynthetic organisms.

    • They are oxygenic autotrophs, performing photosynthesis and producing oxygen.

    • Typically smaller and less structurally complex than land plants, distinguishing them from seagrasses.

  • Exclusions

    • Seagrasses are excluded due to their complexity as flowering plants adapted to marine environments.

    • Cyanobacteria are excluded because they are bacteria, not eukaryotic algae.

  • Photosynthesis in Algae

    • Algae use light to fix carbon dioxide and produce oxygen, similar to cyanobacteria.

  • Informal Grouping

    • The term “algae” is informal and lacks true scientific or evolutionary meaning.

Significance of Algae

  • Ecological Importance

    • Algae are very evident in many environments and produce significant biomass, especially in shallow coastal waters.

    • Rapid growth and reproduction allows them to quickly produce a lot of biomass.

  • Simple Structure

    • Their simple structure allows for rapid growth, without complex roots or vascular systems.

  • Food Webs

    • The Algae are important food source for other organisms.

  • Global Primary Production

    • Algae contribute over 50% of global primary production in marine environments.

Why Study Algae?

  • Ecological Role

    • They form the foundation of most marine food webs, with hydrothermal vents being a notable exception.

  • Economic Value

    • Some algae like nori (Porphyria) are highly valuable in cuisine.

  • Toxicity

    • Some algae can be toxic, leading to severe poisonings like ciguatera poisoning through the food chain.

  • Environmental Impact

    • Algal blooms can become environmental weeds, especially in polluted coastal waters, causing fish kills.

  • Diversity and Beauty

    • Algae are diverse, with unique life histories and patterns, and are often beautiful.

  • Aquaculture

    • Increasingly important in aquaculture due to growing understanding and commercial applications.

Eukaryotic Algae

  • Classification

    • Focus on eukaryotic plants, distinguished from bacteria and archaea by cell membranes and a nucleus.

  • Phylogenetics

    • Algae are classified within the plant kingdom, including red algae (Rhodophyta) and chlorophytes (green algae), along with land plants.

Serial Endosymbiosis

  • Process Description

    • Serial endosymbiosis explains the evolution of complex organisms, starting with a bacterial cell (cyanophyte).

  • Primary Endosymbiosis

    • A eukaryotic cell consumes a cyanophyte, which becomes a chloroplast capable of photosynthesis.

    • This process changes cellular processes, enabling photosynthesis within the eukaryotic cell.

  • Evolutionary Stages

    • Multiple stages of endosymbiosis have led to diverse algal groups and other organisms.

  • Products of Endosymbiosis

    • Primary endosymbiosis gave rise to green algae, red algae, and glaucophytes.

    • Lectures will detail differences among these major algal groups.

  • Schematic Overview

    • Illustrates primary endosymbiosis leading to glaucophytes, red algae, and green algae.

    • Subsequent endosymbiotic processes resulted in brown algae and other phytoplankton groups.

    • Green algae also underwent endosymbiosis and eventually evolved into land plants.

Red Algae (Rhodophyta)

  • Essential Characteristics

    • Defined by photosynthetic pigments: chlorophyll a, phycoerythrin (red), and phycocyanin (blue).

  • Pigment Significance

    • The red algae show close relation to cyanobacteria due to sharing phycoerythrin and phycocyanin pigments.

  • Storage and Movement

    • Store photosynthetic products as Floridian starch.

    • Lack flagella, so they cannot move.

  • Morphology

    • Mainly multicellular with a filamentous architecture, based on chains of cells dividing lengthwise and sideways.

  • Plastid Characteristics

    • Plastids have single thylakoid lamellae, similar to cyanobacteria, where photosynthetic pigments are located.

  • Cell Covering

    • Cellulose with sulfated polysaccharides (agar and carrageenan) used commercially as thickening agents.

  • Species and Habitat

    • Largest group of marine macroalgae with 5-6,000 species.

    • 95% marine, primarily benthic (attached to the bottom).

  • Subclasses

    • Bangioficidae: Simple, primitive, uninucleate, lack pit connections; reproduce asexually through fragmentation.

    • Floridia ficidae: Dominant group; focus of study due to prevalence; possess pit connections.

  • Electron Micrograph Example

    • Illustration of a red algal plant (Helipylon) fixing calcium carbonate in its cell walls.

    • Inside the cell: chloroplasts with thylakoid lamellae and Floridian starch granules.

    • Pit connections: unique connections between cells in Floridia ficidae.

  • Triphasic Life History

    • Unique to red algae, involving three stages: a gamete-producing phase, a spore-producing phase, and an extra diploid carposporophyte phase (parasitic on the female plant).

    • This adaptation compensates for the lack of flagella, providing more opportunities for spore dispersal.

  • Alternation of Generations

    • Explains the typical alternation between gametophyte and sporophyte stages found in most algae.

    • Details the additional parasitic carposporophyte stage in red algae.

  • Polycyphonia

    • Common example, shows filamentous architecture with cells dividing sideways.

  • Reproductive Structures

    • Male gametophytes produce spermatia, while female gametophytes produce capagonium (egg cell).

    • Illustrates fertilization and development of the carposporophyte on the female plant.

    • The tetrasporophyte stage releases tetraspores, completing the cycle.

  • Economic Importance

    • Used in cosmetics, ice creams, and toothpaste due to gelling capacity.

    • Important in food, such as nori and lava bread.

  • Gracilaria

    • Red algal farming for Gracilaria in Zanzibar, Tanzania, used as a cash crop.

  • Species Diversity

    • Examples include Gracilaria, Eucuma, Hypnia, and calcareous species like Jania and Corallina.

    • Hydrolython: encrusting red algae.

    • Jania: distinguished by calcareous feel; can be epiphytic on seagrass.

    • Long threads of Hypnia.

    • Laurentia and sarconema: can show fluorescence, masking red color.

Green Algae (Chlorophyta)

  • Phylogenetic Position

    • Sit alongside land plants in the kingdom Plantae.

  • Endosymbiosis

    • Product of primary endosymbiosis, simpler than land plants.

  • Land Plants

    • Gave rise to land plants and other groups through serial endosymbiosis. (e.g., euglenoids, chloroarachnophytes).

  • Pigments

    • Contain chlorophyll a and b, like land plants.

  • Accessory Pigments

    • Accessory pigments include beta carotene, lutein, and zeaxanthin.

  • Function of Pigments

    • These pigments capture extra light wavelengths and protect the chloroplast from excess light.

  • Storage Products

    • Store energy as starch, similar to land plants.

  • Plastids

    • Thylakoids are stacked (2-6 stacks).

  • Flagella

    • Motile cells have flagella (2 or more flagella).

  • Marine / Fresh Water

    • Some groups are clearly marine vs freshwater.

    • Will focus on Ulva, Cladophora, Bryopsidophisi, and Dasycladales.

  • Flagella structure is used to classify them.

Green Algae Groupings

  • Prasinophyceae:

    • Unicellular flagellates in plankton.

    • Cell covering: Organic scales.

    • Important genera include Tetracellmus, used in aquaculture.

  • Ulvophyceae:

    • Cell covering: Fibers made of mannan or xylan in a mucus matrix.

    • Benthic.

    • Morphology: Unicellular, multicellular, or siphonocladous.

    • Mostly benthic and marine.

    • Important genera include Ulva (sea lettuce).

  • Cladophorales:

    • Cell wall has a crystalline structure.

    • Filamentous growth, but contains multiple nulcei (siphonocleidase).

    • Benthic and intertidal.

    • Examples include, Cladophora, Ketomorpha, Streuvia, Vaulonia.

  • Bryopsidales:

    • Cell wall has fibers in a matrix.

    • Single multinucliate sell.

    • Macroscopic.

    • Mostly tropical.

    • Examples include, Bryopsis, Kallerpa, Halameda, Codium, Euditea, and Chlorodesma.

  • Dasycladales:

    • Cell walls are fibery

    • Siphonous

    • Often calcified

    • Example genera, Acetabularia (umbrella seaweed). A tiny parvocaulus and neomerus.