Lecture 20: Open Waters

• Despite scarce nutrients, the open ocean accounts for a large percentage of primary production.
• Temperate waters have higher primary production due to the thermocline.
• Stable, shallow pycnocline of tropics limits nutrients
• Lower nutrient availability in open ocean means wider primary producer base compared to coastal waters.
• Use of Acoustic Signals Sources as a means to get an idea of what is in the open ocean
• Two groups dominate the open ocean: plankton and nekton
• Temperate primary productivity fluctuates with the nutrient supply

  1. as temp decreases, depth of mixed layers becomes deeper
  2. as mixed layer goes deeper, nutrient mixing increases
  3. as nutrients become available, phytoplankton blooms
  4. as phytoplankton increases, zooplankton grazers increase
• Food webs are simple in temperate and more complex in tropics due to the tropics being more stable (more stable = more speciatation)
• Zooplankton classified by length of stay in plankton

  Meroplankton: larval stage only

  Holoplankton: always a plankton
• Larger holoplaknton include jellyfish, krill, nudibranchs, and pteropods
• Neuston are plankton that live close to the water's surface (Man of war jellyfish, purple sea snail)
• Copepods as grazers
• Zooplankton have daily vertical migrations due to UV light exposure, avoiding predation, change of position, re-growth of phytoplankton, and saving energy
• Staying afloat in the open ocean:

  1. Swimming (some phytoplankton, zooplankton, nekton)
  2. Frictional drag (at low Reynold's numbers, drag dominates and thus increased surface area will slow sinking)
  3. Buoyancy (incorporation of fats and oils, reduction in heavy materials, replacement of heavy ions with lighter ions, gas floats)
• Some deep sea creatures that lack a swim bladder reduce their bones
• Nekton squid and tuna
• Tuna and Billfishes are regional endotherms: use of the sarcoplasmic reticulum for futile cycling of calcium, where there is a release of calcium, and addition of ATPase, and the conversion of ATP into ADP releases heat.
• Sunfish and Manta Rays as Nekton
• Sunfish have a modified caudal fin and prominent dorsal and anal finds
• Manta Rays feed on small fishes and plankton that they channel into their mouths with large labial flaps
• Culpeiform fishes: sardines, herrings, shad
• Types of fish formations:

  1. Aggregations (multispecies)
  2. Shoals (same species)
  3. Schooling (all oriented in the same direction and swim synchronously for protection, food location, and reproduction)
• 4 major categories of Crypsis in Pelagic Zones

  1. Transparency (transmission of a high percentage of background light through interior of the animal)
  2. Mirroring (reflective components of the body)
  3. Cryptic coloration (surface waters countershading and deep waters with red/black bodies)
  4. Counterillumination (production of light)