7.2 Marine arthropods: crustaceans and their relatives

Marine arthropods, especially crustaceans, are incredibly diverse and adaptable creatures. With over 67,000 species, they inhabit various marine environments, from shallow coral reefs to the deep sea. Their segmented bodies and jointed appendages allow for specialized functions and diverse locomotion.

Crustaceans play vital roles in marine ecosystems as filter feeders, grazers, predators, and decomposers. Their complex life cycles often involve planktonic larval stages before metamorphosis into adult forms. Economically, crustaceans are crucial in fisheries, aquaculture, and the ornamental trade.

Marine Arthropods: Crustaceans

Features of marine arthropods

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• Segmented body divided into head, thorax, and abdomen enables flexibility and specialized functions
• Jointed appendages allow for diverse locomotion (walking, swimming, grasping) and feeding strategies
• Exoskeleton made of chitin provides protection and support, must be molted for growth
• Crustacean body plan adapted for various lifestyles and habitats
  • Head contains sensory organs (antennae, compound eyes) and feeding structures (mandibles, maxillae)
  • Thorax bears walking legs and swimmerets (pleopods) for locomotion and carrying eggs
  • Abdomen houses additional swimmerets (pleopods) and ends in a tail fan (uropods, telson) for swimming and steering

Diversity of crustaceans

• Over 67,000 described species showcase incredible diversity and adaptability
• Found in various marine habitats from intertidal zones to deep-sea environments (coral reefs, pelagic zones)
• Ecological significance spans multiple trophic levels and ecosystem functions
  • Primary consumers include filter feeders (barnacles, krill) and grazers (amphipods, isopods)
  • Secondary consumers and predators (crabs, lobsters, shrimp) transfer energy up the food web
  • Decomposers and scavengers contribute to nutrient cycling and break down organic matter
  • Keystone species (sea otters, coral-dwelling crabs) maintain balance and structure of communities

Crustacean life cycles

• Larval development often involves planktonic stages (nauplius, zoea, megalopa) before metamorphosis into adult form
• Reproductive strategies vary among crustacean groups
  • Sexual reproduction with separate sexes and mating behavior (courtship rituals)
  • Brooding females carry fertilized eggs until hatching
  • Direct development in some species (amphipods, isopods) where offspring resemble miniature adults
• Molting (ecdysis) is necessary for growth, involves shedding of exoskeleton
  • Vulnerable period during molting process as new exoskeleton hardens

Economic impact of crustaceans

• Fisheries target major species (shrimp, lobsters, crabs) and contribute significantly to global seafood industry
  • Sustainable management practices (quotas, size limits, seasonal restrictions) ensure long-term viability
• Aquaculture farming of crustaceans (shrimp, prawns, crayfish) is a rapidly growing sector
  • Challenges include disease management and environmental impacts (habitat destruction, pollution)
• Other economic uses include bait for recreational and commercial fishing and the ornamental trade (hermit crabs, cleaner shrimp)