10.3 Marine symbioses and species interactions

Marine symbioses are fascinating partnerships between different species in the ocean. From cleaner shrimp and fish to coral and algae, these relationships shape marine ecosystems. Some benefit both partners, while others favor one at the expense of the other.

These symbiotic interactions play crucial roles in marine environments. They enable life in extreme habitats like deep-sea vents and contribute to the biodiversity of coral reefs. However, climate change and pollution threaten many of these delicate partnerships, potentially disrupting entire ecosystems.

Types and Examples of Marine Symbiotic Relationships

Types of marine symbiotic relationships

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• Symbiosis involves close and long-term interactions between two or more species which can be beneficial, neutral, or harmful to the organisms involved
• Mutualism occurs when both species benefit from the relationship
  • Cleaner shrimp remove parasites and dead skin from fish gaining nutrition and protection from predators in return (cleaner shrimp and fish)
  • Zooxanthellae algae live within coral tissues providing nutrients and oxygen through photosynthesis while coral provides shelter and compounds for algal photosynthesis (zooxanthellae and coral)
• Commensalism happens when one species benefits while the other remains unaffected
  • Remora fish attach to sharks using a suction disc gaining transportation and access to food particles without typically affecting the sharks (remora fish and sharks)
  • Barnacles attach to whale skin benefiting from increased water flow and access to food particles generally leaving the whales unaffected (barnacles and whales)
• Parasitism involves one species (parasite) benefiting at the expense of the other (host)
  • Isopods attach to and feed on tonguefish tongue replacing it and impairing the fish's feeding ability (isopods and tonguefish)
  • Sacculina (parasitic barnacle) infects and castrates crabs diverting the crab's energy towards nurturing the parasite (sacculina and crabs)

Ecological Significance and Adaptations in Marine Symbioses

Significance in marine ecosystems

• In coral reefs, mutualism between corals and zooxanthellae enables the formation and maintenance of the reefs as the algae provide up to 90% of coral's energy requirements
• Diverse symbiotic relationships contribute to the high biodiversity found in coral reef ecosystems
• Deep-sea hydrothermal vent communities rely on symbioses between chemosynthetic bacteria and various vent animals like tubeworms and clams
  • The bacteria oxidize hydrogen sulfide or methane to produce energy
  • Vent animals depend on their bacterial symbionts for nutrition
• These symbioses allow life to thrive in the absence of sunlight in deep-sea environments

Adaptations for marine symbiosis

• Chemical communication and signaling play a key role in establishing symbioses
  • Organisms secrete compounds to attract and recognize symbiotic partners
  • Bobtail squid release mucus containing sugars and amino acids to attract Vibrio fischeri bacteria which colonize the squid's light organ and produce bioluminescence (bobtail squid and bioluminescent bacteria)
• Host organisms develop specialized structures to accommodate symbionts
  • Hydrothermal vent tubeworms (Riftia pachyptila) lack a digestive system and instead have a specialized trophosome organ housing chemosynthetic bacteria
• Immune system modulation allows hosts to distinguish between beneficial symbionts and potential pathogens
  • The Hawaiian bobtail squid's immune system recognizes and tolerates Vibrio fischeri bacteria while eliminating other bacteria to maintain a specific symbiotic relationship

Environmental impacts on marine symbioses

• Climate change can disrupt temperature-sensitive symbioses
  • Rising sea temperatures cause coral bleaching where zooxanthellae are expelled from coral under thermal stress leading to coral mortality and reef degradation if bleaching events are prolonged
  • Ocean acidification affects calcification and growth of symbiotic organisms weakening reef structure as calcification is reduced in coral-algal symbiosis
• Pollution alters symbiotic relationships
  • Nutrient pollution from sources like agricultural runoff favors algal growth over coral leading to algal dominance
  • Chemical pollutants and oil spills disrupt chemical signaling impairing communication and hindering the establishment and maintenance of symbioses
• Healthy symbiotic relationships contribute to marine ecosystem resilience by providing functional redundancy and adaptability
  • Disruption of key symbioses can trigger ecosystem shifts and reduce resilience
  • Loss of coral-algal symbiosis can cause a shift from coral to algal-dominated reefs
  • Reduced resilience leaves ecosystems more vulnerable to further disturbances