Marine Biology and Oceanography Study Notes

Marine Biology and Oceanography: Lecture 11 - Benthic Primary Producers

Overview of Marine Macroalgae

  • Marine macroalgae commonly referred to as seaweed.
    • Source for various algal species and their ecological significance.
  • Existence of symbiont microalgae.
    • Examples include:
    • Thalassia testudinum (a seagrass species)
    • Halodule wrightii
    • Halophila engelmannii

Definitions and Characteristics of Seaweed / Macroalgae

  • Algae: Photosynthetic organisms that exist in various environments including:
    • Marine and freshwater settings.
    • Desert sands, hot boiling springs, snow, and ice.
    • Usually classified under the Kingdom Protista.
    • Predominantly complex and benthic.
  • Seaweeds vary greatly in size:
    • From a few millimeters to giant kelps of the eastern Pacific, reaching lengths over 60 meters.
    • Some species grow up to 1 meter daily.

Morphology of Seaweed

  • Thallus: Refers to an individual seaweed, encompassing the whole organism.
  • Holdfast: Specialized structure that attaches to benthic substrates, not universal to all species.
  • Stipe: Tubular and flexible structure that moves with currents, analogous to a plant stalk.
  • Frond/Blade: Leaf-like structure involved in capturing light and absorbing nutrients.
  • Pneumatocysts: Air sacs that provide buoyancy and allow the seaweed to float.

Classification of Seaweeds

1. Photosynthetic Pigments

  • Chlorophyta (Green Seaweeds): Use chlorophylls for photosynthesis.
  • Phaeophyta (Brown Seaweeds): Contain accessory pigments called fucoxanthins, contributing to their coloration.
  • Rhodophyta (Red Seaweeds): Characterized by pigments such as phycoerythrin and phycocyanin.

2. Carbon Storage Molecules

  • Chlorophyta: Store starch as a food reserve.
  • Phaeophyta: Store laminarin and mannitol.
  • Rhodophyta: Store Floridian starch.

3. Cell Wall Composition

  • Chlorophyta: Cell walls composed of cellulose, along with other polysaccharides and proteins.
  • Phaeophyta: Cell walls made of alginate, used in products like toothpaste and pills.
  • Rhodophyta: Cell walls consist of agar and carrageenan, used in food and pharmaceuticals.

Specific Types of Seaweeds

Chlorophyta (Green Algae)

  • Contains chlorophylls a and b.
  • Stores starch within plastids.
  • Cell walls made of cellulose.
  • Many species inhabit freshwater environments.
  • Examples:
    • Caulerpa sertularioides (siphonous green algae)
    • Halimeda tuna (calcareous alga)
    • Chara spp. (stoneworts): features stem-like thallus and leaf-like fronds.

Phaeophyta (Brown Algae)

  • Use chlorophyll a, b, and fucoxanthin, the latter contributing to their yellow-brown color.
  • Store carbon as laminarin and mannitol.
  • Predominantly marine, prevalent in rocky shore ecosystems of colder waters.
  • Example: Macrocystis pyrifera (giant kelp) forms extensive forests.

Rhodophyta (Red Algae)

  • Out of approximately 6000 species, primarily marine.
  • Use chlorophylls in addition to phycoerythrin and phycocyanin.
  • Store carbohydrates as Floridian starch.
  • Cell walls predominantly composed of agar and carrageenan.
  • Economically significant as food (e.g., Porphyra) and for industrial uses (e.g., as gelling agents).

Introduction to Seagrasses

  • Seagrasses are rooted, flowering plants that produce seeds.
  • Evolved from land-based higher plants that have recolonized marine environments.
  • Thrive in shallow water environments of bays and estuaries, often limited by light availability and water turbidity.
  • Narrow species diversity with only 58 species across 11 genera.
  • Critical ecological roles, including serving as nursery habitats for juvenile fish and invertebrates.

Herbivory and its Impacts on Benthic Primary Producers

General Concepts

  • Herbivory impacts on macroalgae diversity and biomass yield, both positive and negative.
  • Various levels of herbivores, including macro, mega, and meso-abundance have implications on the ecosystem's productivity.

Specific Case Studies

  • Examined herbivory across different benthic primary producers:
    • Interactions with seagrasses and effects of dominant herbivorous species.
    • Comparisons of seagrass and coral reef systems across geological time periods, considering herbivore evolution and functional roles in grazing.

Additional Topics in Marine Biology

Species Interactions and Trophic Webs

  • Understanding the intricate relationships between species:
    • Interactions include predation, parasitism, herbivory, competition, mutualism, and commensalism.
  • Predation: Refers to positive-negative interactions where one organism benefits at the expense of another.
    • Can be regulated through numerical, functional, and aggregative responses depending on prey density.
  • Parasitism: Infection of host organisms by parasites, with complex life cycles involving various hosts.
    • Affects host fitness and reproductive capabilities.

Competition and Its Implications

  • Contrast between different interaction types that can influence aquatic ecosystems:
    • Intraspecific: within species and Interspecific: among different species.
  • The concept of Niche refers to the ecological role and requirements of a species.
  • Competition can lead to differential access to resources, driving adaptation and evolution.

Mutualism and Commensalism

  • Mutualistic relationships can enhance survival and reproductive success for both species involved.
    • Examples include the clownfish-anemone relationship.
  • Commensalistic interactions benefit one species while the other is unaffected.
    • Such as remoras adhering to larger fish.

Defensive Strategies Against Predation

  • Survival tactics employed by prey species:
    • Crypsis for camouflage.
    • Escape responses to avoid predation.
    • Defensive adaptations, whether mechanical (spines) or chemical (toxins).

Conclusion

  • Implications of species interactions, particularly herbivory, competition, and mutualism, are vital components in maintaining the complexity and resilience of marine ecosystems.
  • Understanding these relationships contributes to deeper ecological insights and conservation strategies.

Values and Complexities of Marine Ecosystems: It is crucial to appreciate the intricate balance of these interactions within marine biology, where each species plays a role in the sustenance of ecological frameworks.