Kelp Communities

General Structure

• Dominant macro algae is Laminaria or Macrocystis
• Beds occur in up to 100 ft of water
• Often referred to as a kelp forest
• This community restricted to colder waters
• High latitudes on western sides of oceans, or further south on eastern sides

Effect of Wave Action

• Kelp are relatively fragile
• Restricted to deep water where wave action is reduced
• Can grow extremely fast, up to 20 in/day!
• Winter storms can remove many mature kelps
• Reproductive cycle involves alternation of generations

Structure of Kelp Forests

• Kelps form the canopy
• More shade tolerant species grow in understory
• A large number of invertebrates grow among holdfasts
• Epiphytes, bryozoans, gastropods, etc. grow on kelp
• Fish are abundant: Girabaldi, rockfish, kelp bass, California sheephead, etc.
• Much of detritus is exported elsewhere

Causes of Sea Urchin Barrens

• Explosions of sea urchin populations result in loss of kelp beds
• Declines in sea otters one possible cause
• Possibly the amount of drift kelp is less because of pollution
• Nutrients in pollution might favor urchins
• Over-harvesting of abalones
• Possibly sea urchin booms are just part of natural fluctuations.

Description

• Roughly from the surface to 650 ft below
• Photic zone overlaps and is sometimes covers same area
• Divided into neritic and oceanic.

General Biotic Structure

• Nearly all primary production occurs in the epipelagic itself
• Almost no outside inputs of organic matter in the oceanic part
• Suspension feeders and predators abound

Classification of the plankton

• Divided into phytoplankton and zooplankton
• Each is subdivided into 3 groups:

1. Net plankton (> 20 m m)
2. Nanoplankton (2-20 m m)
3. Picoplankton (0.2-2 m m)

• Net plankton further divided into 4 groups:

1. Megaplankton (20-200 cm)
2. Macroplankton (2-20 cm)
3. Mesoplankton (0.2-20 mm)
4. Microplankton (20-200 m m)

See Table 14.1

The Nekton

• Composed of larger, free-swimming organisms
• Some are planktivorous
• Others are predatory on other nekton
• Top carnivores include sperm whale & killer whale

Three Methods for Remaining in Epipelagic Zone

• Increase drag to reduce sinking rate
• Increase buoyancy
• Actively swim

Increasing Drag

• Being small automatically increases drag
• Being flat or bell-shaped
• Having long projections or spines
• Some phytoplankton form chains

Increasing buoyancy

• Store lipids (diatoms, copepods, fish eggs, larvae)
• Pockets of gas (Cyanobacteria)
• Excess lipids stored in liver or as blubber (certain fish, marine mammals)
• Swim bladders
• Control composition of body fluids: preferentially collect lighter salts as NH₄CL (dinoflagellates, salps, comb jellies, some squid)

Floaters (Neuston)

• Gas filled structure (Velella, Physalia)
• Mucous filled with bubbles (violet shell that eats Physalia)
• Swallow air (Glaucus, which eats by-the-wind sailor)
• Uses surface tension (water strider)

Senses

• Well developed eyes, even on some zooplankton
• Lateral line in Osteichthyes
• Echolocation in cetaceans

Coloration & camouflage

• Transparency
• Countershading
• Silvery sides
• Vertical bars (disrupts shape)
• Fly out of water

Rapid Swimming

• Streamlines appendages
• Smooth body surfaces
• Small scales or none at all
• Mucous to reduce drag (fishes)
• Very flexible fins or very firm fins
• Extensive & strong muscles with lots of myoglobin
• Digression: Body of some fishes warmed by countercurrent exchange (rete mirabile)

Vertical Migration

• Many zooplankton go deep during day, to surface at night
• Maybe predator avoidance behavior
• Maybe used to slow metabolism while in deep, cooler water
• Maybe to avoid toxins produced by certain dinoflagellates

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