Marine Ecology

• Divisions of the Marine Environment

  • Pelagic - Open water
  • Benthic - Seafloor
• Pelagic Waters


  • Characterized by Depth
• Adaptations of Marine Organisms

  • Water's Transparency
  • Daily Vertical Migrations of the Deep Scattering Layer, which often contains copepods krill, types of fish
• Fish and Osmoregulation


  1. Osmosis is the diffusion of water across cells

  2. Freshwater fish continuously absorb water, internal cells saltier than surrounding water

  3. Marine fish naturally lose water, internal cells less saline than surrounding water, water wants to move out of fish cells

  4. Marine fish continuously drink seawater to replenish water in cells, secrete oceanic salt from their gills

  5. Fish in estuaries must be able to do both
• Plankton


  Animals that float with ocean currents, unable to swim against currents, examples: diatoms, dinoflagellates, jellyfish etc.
• Nekton


  Animals that are active swimmers, able to swim against ocean currents
• How do Marine Organisms Avoid Sinking

  1. May increase buoyancy using gas containers, rigid gas containers, swim bladders, nautilus uses an external shell filled with air to stay afloat, cuttlefish have internal air chambers

  2. Floating Zooplankton (microscopic) like foraminifera with calcium carbonate tests that are chambered, create spines to help them float, copepods with shrimplike crustacean bodies, segmented bodies, jointed legs, control buoyancy using secreted oils

  3. Active swimming by trapping water and expelling it, like squid blowing water out of a siphon, fish curving body from front to back like a wave, using caudal, dorsal, pelvic and pectoral fins
• Caudal fin designs in fish

  • Rounded fin - slow, maneuverable, flexible
  • Truncate fin - OK maneuverability, fast
  • Forked fin - fast, OK maneuverability
  • Lunate fin - fast, limited maneuvering, rigid
  • Heterocercal fin - top heavy, causes lift, limited maneuvering
• Adaptations for Finding Prey


  • Mobility: Lungers (wait for prey and pounce) versus Cruisers (actively seek prey)
  • Swimming speed - generally proportional to size, normally swim slowly when cruising, can move very fast for short time
  • Body Temperature - most fish cold-blooded (poikilothermic), some are warm-blooded (homeothermic) which increases power output of muscles
• Pelagic Waters


  • Characterized by Light
• Adaptations of Deep-Water Nekton


  • Mainly fish that consume detritus or each other, lack of abundant food limits size and number of organisms
  • Bioluminescence - photophores produce light, may help search for food, attract prey, patrol territory, communicate, seek mates, escape predators
  • Large, sensitive eyes, large sharp teeth, expandable bodies, hinged jaws - can ingest species larger than they are
• Adaptations for Deep Sea Gigantism


  • Tendency for animals in the deep ocean to be larger than their shallow water counterparts, likely due to food scarcity, reduced predation, increased dissolved oxygen, lowered ocean temperatures
• Adaptations to avoid predation


  1. Schooling - move in same direction and evenly spaced, school may appear as single larger unit, confuses predator, ensures males are present to fertilize eggs

  2. Spines - some may be venomous, armor - strong exoskeletons

  3. Camouflage - reflection, countershading, distraction, red coloration, active camouflage, translucence
• Sexual reproduction


  Exchange of gametes (sperm and eggs), fish can lay eggs and then fertilize them, gametes released into the water column
• Hermaphroditic Reproduction


  Some organisms possess both sexual organs (gonads), have both gonads at the same time or switch sexes at some point in their life
• Asexual reproduction


  No exchange of genetic material, cloning - genetically identical copies, fission - organism splits in half, budding - organism forms an outgrowth that breaks away
• Holoplankton


  Live as plankton their entire life cycle, e.g. copepod
• Meroplankton


  Live as plankton for a part of their life cycle, e.g. crab larvae (zoea and megalops) are planktonic, live on the benthos as an adult
• Symbiosis


  Close and prolonged association between two organisms of different species, three types: parasitism, mutualism, commensalism
• Parasitism


  When one species benefits from the association and the other is at a disadvantage, tend to live in or on the host, steal the host's food or consume the host's tissue
• Mutualism


  When both species benefits from the association, e.g. corals have symbiotic algae, shrimp can clean parasites from other fish
• Commensalism


  When one species benefits from the association and the other is not benefitted or harmed, e.g. remoras hitching a ride on a larger fish, hermit crab shell covered in anemones
• Poikilotherms

  Body as warm as the surrounding
• Homeotherms

  Body warmer than the surrounding water
• Strategies to evade predation


  • Schooling
  • Spines
  • Armor
  • Poison and venom
  • Camouflage
  • Reflection, countershading, distraction, red coloration, active camouflage, translucence
• Sexual reproduction


  • Exchange of gametes (sperm and eggs)
  • Fish can lay eggs and then fertilize them
  • Gametes released into the water column
  • Either eggs or sperm
• Hermaphroditic Reproduction


  • Some organisms possess both sexual organs (gonads)
  • Have both gonads at the same time
  • Nudibranchs
  • Or changes sex at some point in their life
  • Clownfish generally change from male to female
• Asexual reproduction


  • No exchange of genetic material
  • Cloning
  • Genetically identical copies
  • Fission - Organisms splits in half
  • Budding - Organism forms an outgrowth that breaks away
• Asexual reproduction


  • Corals
  • Salps
• Holoplankton


  Live as plankton their entire life cycle
• Meroplankton


  Live as plankton for a part of their life cycle
• Meroplankton


  • Crab larvae (Zoea and Megalops) are planktonic live on the benthos as an adult
• Plankton


  • Copepod with eggs
• Symbiosis


  Close and prolonged association between two organisms of different species
• Types of symbiosis


  • Parasitism
  • Mutualism
  • Commensalism
• Parasitism


  • When one species benefits from the association and the other is at a disadvantage
  • Tend to live in or on the host
  • Steal the host's food or consume the host's tissue
• Parasitism


  • Cymothoid isopod replaces the tongue of the fish and feeds on the blood of the host
• Mutualism


  • When both species benefits from the association
  • Corals have symbiotic algae - Algae produce food for the coral and the coral protects the algae
  • Shrimp can clean parasites from other fish
• Commensalism


  • When one species benefits from the association and the other is not benefitted or harmed
  • Remoras hitching a ride on a larger fish
  • Hermit crab shell covered in anemones
• More benthos beneath areas of high primary productivity


  • Mainly on continental shelves
  • Affected by surface ocean currents