8.3 Plankton, nekton, and benthos communities

Marine communities are diverse ecosystems teeming with life. From microscopic plankton to massive whales, these organisms play crucial roles in ocean food webs, nutrient cycling, and oxygen production. Their adaptations and interactions shape the marine environment.

Plankton, nekton, and benthos form the backbone of marine life. These groups showcase incredible diversity, from drifting algae to powerful swimmers and seafloor dwellers. Their ecological functions are vital for maintaining healthy oceans and supporting global biodiversity.

Marine Communities

Types of marine organisms

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• Plankton drift or float in water unable to swim against currents divided into phytoplankton (plant-like) and zooplankton (animal-like) includes diatoms copepods and jellyfish larvae
• Nekton actively swim independently of water currents encompasses fish (tuna salmon) squid and marine mammals (whales dolphins)
• Benthos live on or in the seafloor classified as epifauna (surface-dwelling) or infauna (sediment-dwelling) includes corals sea urchins and clams

Ecology of planktonic life

• Primary production phytoplankton form base of marine food webs generate ~50% of global oxygen
• Nutrient cycling facilitated by zooplankton vertical migration and fecal pellet transport to deeper waters
• Buoyancy adaptations include oil droplets gas-filled vesicles and flattened body shapes
• Reproductive strategies feature high reproductive rates and larval stages for many marine organisms
• Size range varies from microscopic (picoplankton) to large (jellyfish medusae)
• Bioluminescence common in deep-sea plankton for communication and predator deterrence

Nekton in marine ecosystems

• Trophic interactions act as predators and prey in complex marine food webs
• Biomass transport through vertical and horizontal migrations (salmon runs)
• Diverse groups include bony fish cartilaginous fish cephalopods marine reptiles and mammals
• Ecosystem services support commercial fisheries and tourism (whale watching)
• Swimming adaptations feature streamlined bodies fins flippers and muscular structures
• Sensory systems highly developed for navigation and prey detection (lateral line echolocation)
• Migratory patterns influence global nutrient distribution and ecosystem connectivity

Structure of benthic communities

• Zonation patterns vary across intertidal zones continental shelf and deep-sea habitats
• Substrate interactions include burrowing (bioturbation) and reef-building (corals oysters)
• Nutrient cycling through organic matter decomposition and sediment nutrient release
• Benthic adaptations include attachment mechanisms (byssus threads holdfasts) and protective structures
• Benthic-pelagic coupling links water column and seafloor via filter feeders and planktonic larval stages
• Community structures differ between hard substrates soft sediments and specialized habitats (hydrothermal vents)
• Ecosystem engineering species (kelp corals) create habitats for diverse communities
• Deep-sea benthic organisms adapt to high pressure low temperature and scarce food availability