Streams (Rivers)• Stream = water flowing downhill in a

defined channel.

• Amount of flow significant. Usually varies seasonally. (wet season & dry season)

• Substrate important. (bedrock, gravel, silt)

• Amount of floating particles (turbidity) is important.

What physical conditions do flow, substrate, & turbidity affect?

Energy in Streams• Photosynthesis can occur in stream via

periphyon (attached “algae”) or macrophytes (larger multicellular photosynthesizers).

What conditions need to occur for photosynthesis to happen in stream?

• Most streams heavily dependent on external organic matter inputs (leaf litter) to support their food webs.

N. Amer. vs. S. Amer. Streams• How do temperature and sunlight vary

between temperate N. America and tropical S. America?

• How does precipitation vary between temperate N. America and tropical S. America?

• How do leaf litter inputs vary between temperate N. America and tropical S. America?

N. Amer. Stream Food Web

periphyton

grazinginsects &

crustaceans

grazingfishes

bacteria& fungi

fine organic matter

collectinginsects, crust.,nematodes, &

annelids

leaf litter

predatoryinsects &

crustaceans

dissolved organiccompounds

runoff orgroundwater entry

coarseorganic matter

bacteria& fungi

conditioning(microbial colonization)

shreddinginsects &

crustaceans

“predatory”fishes

S. Amer. Stream Food Web

periphyton

grazingFISHES &

crustaceans

bacteria& fungi

fine organic matter

detritivoreFISHES, crust.,nematodes, &

annelids

leaf litter

dissolved organiccompounds

runoff orgroundwater entry

coarseorganic matter

bacteria& fungi

conditioning(microbial colonization)

herbivoreFISHES &

crustaceans

“predatory”FISHES

Relatively few aquatic insects.

?

Aquatic InsectO-rama

@ lower trophic levels

Fish O-rama@ lower trophic

levels

Estuaries• Estuary = semi-enclosed body of water

where freshwater from land drainage dilutes sea water.

• Amount of stream flow again significant. Usually varies seasonally. (wet season & dry season)

• Tidal and wave activity also significant.

• Salinity varies.

• Much organic matter deposited (mud).

Sea Grass Beds• Seagrasses live completely submerged

and can tolerate fully marine water.

• Require a soft particulate substrate and low turbidity.

Coral Reefs

• Reef = a solid outcrop in shallow water reached by sunlight.

• Coral Reef = a solid outcrop created by the action of coral animals in shallow water reached by sunlight.

• Coral reefs require shallow, 23-25 º C, clear water (low in nitrogen).

• Very sensitive to perturbation and stress.

Coral Animals

flatback reef

reefface

Fringing Coral Reefs

Acropora palifera Forms

Coral Bleaching

Coral Reef Food Webs• Primary producers = algae in corals,

periphyton (algae), and macrophytic algae.

• External inputs = plankton from open water (usually very important)

• Trophic patterns very complicated.

• Cleaner fishes.

• Coral eaters

(parrot fishes).