Exploring Pelagic Organisms

Pelagic Organisms and Their Adaptations

• Pelagic organisms make up the majority of the ocean's biomass, including phytoplankton and other photosynthesizing microbes.
• These organisms live in the upper sunlit surface waters and serve as the primary food source for other marine life.
• Pelagic organisms must remain in the sunlit layers of the ocean, requiring them to swim or float to avoid sinking.
• Many marine animals have evolved specific functions to help with buoyancy and avoid sinking, such as using gas containers or swim bladders.
• Examples of animals with gas containers for buoyancy include the spear Allah, nautilus, and cuttlefish.
• Some fish have swim bladders directly connected to the esophagus, allowing for rapid buoyancy changes, while others fill their swim bladders through blood vessels for slower changes.
• Zooplankton produce fats or oils to float with minimal energy expenditure, while nektonic organisms have evolved streamlined shapes and fins to avoid sinking and provide lift.
• Floating zooplankton with shells called tests are abundant in the deep ocean and make up a significant portion of the ocean's biomass.
• Radialarian and foraminifera zooplankton have tests made of silica or calcium carbonate, allowing them to remain buoyant in the water.
• Copepods, microscopic shrimp, make up the majority of the ocean's zooplankton biomass and have special adaptations for filtering food particles from the water.
• Krill, another type of zooplankton, are abundant in Antarctica and play a critical role in the food web, serving as a food source for many organisms, including whales and birds.
• Cnidarians, such as the Portuguese Man O'War and jellyfish, are soft-bodied organisms with stinging tentacles, and they fall into two basic groups: hydras and jellies.

Adaptations for Swimming in Marine Organisms

• Swimming mechanisms of marine organisms include muscular contractions, water entering and forced out of their cavities
• Medusas, like Portuguese man-of-war, use a sail-like structure for directional movement
• Different swimming organisms include fish, squid, sea turtles, and marine mammals
• Flying squids trap water in their mantle cavity for propulsion
• Fish use different fin designs for stabilization, steering, balance, and thrust
• Different swimming motions include S-shaped and L-shaped, used by various organisms
• Predatory fish have different muscle tissue colors for different swimming strategies
• Swimming speed is generally proportional to the size of the fish
• Cold-blooded fish are typically not fast swimmers, while warm-blooded fish are more efficient
• Deepwater nekton have adapted to perpetual darkness by using bioluminescence to attract prey and mates
• Deepwater nekton have large, sensitive eyes, sharp teeth, expandable jaws, and a large belly for scarce food
• Schooling is an adaptation used by smaller fish to confuse predators and appear larger in numbers