subtidal communities hard bottom kelp forests. figure 10.22

Subtidal Communities

Hard Bottom

Kelp Forests

Figure 10.22

Subtidal Zone

• The part of the continental shelf that is always covered by water – from the low tide mark to the shelf break

(150m or 490 ft)

Subtidal Zone

• Temperature varies from place to place due to its shallowness

• Bottom still affected by waves, tides and currents

• Very productive areas – nutrients & light

Subtidal Zone

• Hard Bottom Communities– Kelp Forests

– Other: Soft Bottom Communities

Seagrass Beds (addressed later)

Hard-Bottom Subtidal Communities

• Less common than soft-bottom

• Submerged extension of rocky intertidal, hard parts of organisms (oyster shells, calcareous algae)

• Sometimes called “reefs” – not coral

Kelp

• Kelp = large brown seaweed

• Large holdfast to hold onto the rocky bottom

• Long stipes

• Fronds… 20-30m (65-100ft)

• Go through two stages in their life cycle

Laminaria

Laminaria

Alaria (edible)

Geographic Kelp Distribution

Kelp Communities

• Arranged in distinct layers

• Giant kelp forms in deeper waters– reduced wave action– Forms a canopy

Kelp Communities

Several species of kelp-community fishes sheltering near giant kelp, Macrocystis.

© Galina Barskaya/ShutterStock, Inc.

Fig. 13.23

Figure 13.23

Kelp:Baja, CA

Figure 13.25

Kelp Communities

• Below the effects of waves and tides, kelp communities dominate in temperate areas.

General structure of a West Coast kelp forest, with a complex understory of plants beneath the dominant Macrocystis or Nereocystis.

Fnft

Kelp Communities

• Many organisms

• Sea Urchins = most important grazers or herbivores

Fig. nft

Sea Urchins

• What leads to population explosions?– Absence of their predators– Overfishing, less seals & sea lions, killer

whales eat sea otters, more urchins

Figure 13.26

Kelp Communities

Trophic relationships of some dominant members of a southern California kelp community.

Kelp Communities

Trophic relationships of the common

members of a New England kelp community.

Fig. 13.20

Pictoral Food Web ExamplePictoral Food Web Example

PRIMARY PRODUCERS PRIMARY CONSUMERS 2ND LEVEL CONSUMERS 3RD LEVEL CONSUMERS

KELP SEA URCHINS SEA OTTERS KILLER WHALES

MICROSCOPIC ALGAES SMALL FISH LARGE FISH