Marine Algae, Seagrasses, and Salt Marsh Ecosystems: Key Concepts and Structures

Seaweeds

Organisms collectively referred to as macroalgae, including green, red, and brown algae.

Marine primary production

Most marine primary production comes from phytoplankton.

Three major groups of marine macroalgae

Chlorophyta (green algae), Rhodophyta (red algae), Phaeophyta (brown algae).

Fouling community

A community of organisms that settle on submerged surfaces; Compensation depth is the depth at which photosynthesis equals respiration.

Thallus

The complete body of a seaweed, including all its parts.

Holdfast

The structure that anchors seaweeds to the substrate.

Stipe

The stalk-like structure that supports the thallus in some seaweeds.

Characteristics of flowering plants not found in seaweeds

Flowering plants have true roots, stems, and leaves, while seaweeds do not.

Photosynthetic pigments in seaweeds

Chlorophyll a, chlorophyll b, carotenoids in green algae; phycoerythrin and phycocyanin in red algae; fucoxanthin in brown algae.

Function of accessory pigments

They capture light energy for photosynthesis, especially in low-light conditions.

Carbohydrate in cell walls of seaweeds

Cellulose is found in the cell walls of seaweeds and higher plants.

Mucilage

A gelatinous substance in macroalgae that aids in buoyancy and protection.

Primary methods for reproduction in seaweeds

Reproduction occurs through asexual (fragmentation, spores) and sexual methods (gametes).

Sporophyte

The diploid phase in the life cycle of seaweeds that produces spores.

Sporangium

A structure in which spores are produced.

Haploid vs. diploid sporophytes

Sporophytes are diploid (2N), while spores are haploid (1N).

Gametophyte

The haploid phase in the life cycle of seaweeds that produces gametes.

Gametangia

Structures that produce gametes in gametophytes.

Haploid vs. diploid gametophytes

Gametophytes are haploid (1N), while gametes are also haploid.

Alternation of generations

The life cycle of organisms that alternates between haploid and diploid phases.

Mitosis vs. meiosis in sporophytes

Sporophytes use meiosis to form spores.

Mitosis vs. meiosis in gametophytes

Gametophytes use mitosis to form gametes.

General characteristics of Chlorophyta

Green algae that are primarily freshwater, but some are marine; they have chlorophyll a and b.

Coenocytic thallus

A type of thallus that is multinucleate and lacks septa.

Strategies of green algae against herbivory

Production of secondary metabolites and tough cell walls.

Characteristics of Rhodophyta

Red algae that contain phycoerythrin; often found in deeper waters.

Unique features of red algae life cycles

Include the carposporophyte and tetrasporophyte stages.

Epiphyte

An organism that grows on another organism but is not parasitic.

Epizoic

An organism that lives on the surface of an animal.

Importance of coralline algae

They contribute to reef building and provide habitat for marine organisms.

Characteristics of Phaeophyta

Brown algae that contain fucoxanthin; typically found in colder waters.

Familiar examples of brown algae

Kelp, sargassum, and fucus.

Trumpet cells

Specialized cells in brown algae that facilitate gas exchange.

Perennial vs. annual in brown algae

Many brown algae are perennial as sporophytes and annual as gametophytes.

Rhizoids

Root-like structures that anchor algae but do not absorb nutrients.

Examples of halophytes

Salt-tolerant plants like mangroves and salt marsh grasses.

General characteristics of halophytes

Plants adapted to high salinity environments.

Phloem

The vascular tissue responsible for transporting nutrients in plants.

Xylem

The vascular tissue responsible for transporting water in plants.

Hydrophytes

Plants that thrive in water; not all are halophytes.

Major structures in seagrasses

Roots, rhizomes, leaves, and flowers.

Nodes and internodes

Nodes are points of leaf attachment; internodes are the segments between nodes.

Functions of roots

Anchoring the plant and absorbing nutrients and water.

Aerenchyme

A tissue with air spaces that helps with buoyancy and gas exchange.

Lacunae

Air-filled spaces in aquatic plants that aid in buoyancy.

Tannins

Chemical compounds that provide protection against herbivory.

Rhizome

A horizontal underground stem that can produce new shoots.

Ecological roles of seagrasses

They provide habitat, stabilize sediments, and improve water quality.

Adaptation of seagrasses vs. salt marsh plants

Seagrasses are more adapted to marine life than salt marsh plants.

Location of salt marshes

Coastal areas where saltwater and freshwater mix.

Characteristics of salt marsh plants

Salt-tolerant, often have specialized structures for salt excretion.

Facultative halophyte

A plant that can grow in both saline and non-saline environments.

Ecological roles of salt marsh plants

They stabilize shorelines and provide habitat for wildlife.

Location of mangroves

Tropical and subtropical coastal areas.

Mangal

A coastal ecosystem dominated by mangrove trees.

Lenticels

Small openings in the bark of mangroves for gas exchange.

Stilt roots

Roots that provide support and stability in mangroves.

Prop roots

Roots that grow down from branches to provide additional support.

Drop roots

Roots that extend from the trunk to the ground for stability.

Cable roots

Roots that spread horizontally to anchor mangroves.

Anchor roots

Roots that secure mangroves to the substrate.

Pneumatophores

Air-filled roots that protrude above the soil for gas exchange.

Ecological roles of mangroves

They protect coastlines, provide habitat, and improve water quality.

General characteristics of animals

Multicellular, eukaryotic organisms that are heterotrophic.

Phylum Porifera

Includes sponges; characterized by a porous body and lack of true tissues.

Ostium

Small openings in sponges that allow water to enter.

Spongocoel

The central cavity of a sponge.

Osculum

The large opening at the top of a sponge through which water exits.

Collar cell

Cells in sponges that help filter food from water.

Pinacocyte

Flat cells that form the outer layer of a sponge.

Archaeocyte

Totipotent cells in sponges that can differentiate into other cell types.

Spicule

Structural elements in sponges that provide support.

Spongin

A fibrous protein that makes up the skeleton of some sponges.

Three sponge body forms

Asconoid, syconoid, and leuconoid, each differing in complexity.

Nutrition in sponges

Sponges filter feed by drawing in water and trapping food particles.

Reproduction in sponges

Sponges reproduce asexually through budding and fragmentation, and sexually as hermaphrodites.

Amphiblastula

A type of larva produced by sponges during reproduction.

Phylum Cnidaria

Includes jellyfish, corals, and sea anemones; characterized by cnidocytes.

Cnidarian characteristics

Radial symmetry, a gastrovascular cavity, and specialized stinging cells.

Cnidarian polyp

The sessile, cylindrical form of a cnidarian.

Cnidarian medusa

The free-swimming, umbrella-shaped form of a cnidarian.

Cnidocyte

Specialized cells in cnidarians that contain nematocysts.

Cnida

The stinging structure within a cnidocyte.

Cnidocil

The trigger structure on a cnidocyte that activates the nematocyst.

Nematocyst

A type of cnida that can inject toxins into prey.

Characteristics of Hydrozoa

Typically have both polyp and medusa stages; often colonial.

Class Anthozoa

Includes corals and sea anemones; only exist in polyp form.

Importance of scleractinian corals

They build reefs that provide habitat for diverse marine life.

Class Scyphozoa

Includes true jellyfish, characterized by a dominant medusa stage.

Class Cubozoa

Includes box jellyfish, known for their potent venom.

Planula larvae

The free-swimming larval stage of cnidarians.

Asexual reproduction in anthozoans

Includes budding and fission.

Symbiotic relationships in cnidarians

Examples include clownfish with sea anemones and zooxanthellae with corals.

Characteristics of Ctenophora

Comb jellies with eight rows of cilia for locomotion.

Ctenes

The comb-like structures used for movement in ctenophores.

Bilateral symmetry

A body plan that can be divided into two mirror-image halves.

Importance of bilateral symmetry

It allows for more complex body structures and movement.

Cephalization

The concentration of sensory organs and nervous tissue at the anterior end.

Phylum Platyhelminthes

Includes flatworms such as planarians, flukes, and tapeworms.

Class Turbellaria

Includes free-living flatworms, characterized by a soft body and ciliated epidermis.