Chapter 15 Animals of the Benthic Environment Coral Reef Deep Sea Rocky and sandy shores

Animals of the Benthic Environment-Overview Benthic communities include a variety of habitats. Corals need specific environmental conditions. Hydrothermal vents support diverse communities that rely on chemosynthesis.

Distribution of Benthic Organisms More than 98% of 250,000 known marine species live in or on ocean floor Benthic organisms live mainly on continental shelves. Their distribution is affected by surface ocean currents.

Distribution of Benthic Organisms Benthic biomass matches surface chlorophyll distribution.

What Communities exist along Rocky Shores? Epifauna Attached to substrate (e.g., marine algae) Move over sea floor (e.g., crabs, snails) Moderate diversity of species Greatest animal diversity at tropical latitudes Greatest algae diversity at mid-latitudes

Intertidal Zonation The physical and biological conditions cause horizontal bands of organisms to form in the intertidal waters. Physical conditions determine the organisms found in the upper bands Biological conditions determine the organisms found in the lower bands.

Zonation Spray zone – above spring tide zone Intertidal zone area between high and low tide.

Intertidal Zonation Intertidal zone High tide zone – relatively dry Middle tide zone – covered by all high tides & exposed by all low tides Low tide zone – usually wet

Spray Zone Spray zone = Supratidal zone Organisms Avoid drying out Many animals have shells Few species of marine algae Periwinkles Limpets Rock louse

High Tide Zone Animals have shells to avoid drying out. Marine algae—rock weeds with thick cell walls Rock weeds colonize first Sessile animals establish later Barnacles Rock weed

Middle Tide Zone More types of marine algae Soft-bodied animals Acorn Barnacles and mussels Acorn Barnacles Mussels

Middle Tide Zone Tidal pools are common Sea anemones are inhabitants of the tidal pools. Stinging nematocysts on tentacles poison prey

Middle Tide Mussel Bed and Sea Star Carnivorous snails and starfish will move into this area to feed Sea stars love to feed on mussels

Middle Tide Zone Also find other inhabitants in the middle tidal zone Hermit crabs Sea urchins

Low Tide Zone Abundant algae and surf grass Many animals hidden by seaweed and sea grass

Low Tide Zone Various shore crabs Scavengers

Physical Environment of Sediment-Covered Shores Sediment size related to wave and current strength Greater the wave and current strength the larger the sediment Course boulder beaches Sand beaches Salt marshes Mud flats High energy Low energy

Intertidal Zonation and Common Organisms

What Communities Exist along Sediment-Covered Shores? Infauna – burrowing animals No stable, fixed surface Burrowing provides more stable environment Less risk of temperature extremes and drying out Same marine worm (Annelida) in two pictures

Sandy Beach Organisms and Adaptations Bivalve mollusks Soft body, hard shell Example: clams and mussels Greatest number in low tide regions Annelid worms

Sandy Beach Organisms and Adaptations Crustaceans Segmented body, hard exoskeleton, paired jointed limbs Sand crabs common

Sandy Beach Organisms and Adaptations Echinoderms Spiny skin Five tapered legs Example: starfish and heart urchin

Sandy Beach Organisms and Adaptations Meiofauna (interstitial organisms) Live in spaces between sediment particles Small, feed on bacteria Polychaetes, mollusks, arthropods, nematodes

Mud Flats Eelgrass and turtle grass common Bivalves and other mollusks Fiddler crabs

What Communities Exist on the Shallow Offshore Ocean Floor of a Rocky Coast? Subtidal zone – zone below the tides Rocky bottom Organisms Kelp Attaches to rocky bottoms with strong holdfast Stipes and blades supported by pneumatocysts (gas filled floats)

Shallow Offshore Ocean Floor Communities Kelp forests – beds of giant brown bladder kelp and bull kelp Fast growing Highly productive ecosystems Shelter for variety of organisms

Kelp Distribution

Rocky Bottom Shallow Offshore Ocean Floor Communities Lobsters Large, spiny antennae Live in water deeper than 20 meters (65 feet) Scavengers Also feed on live animals

Rocky Bottom Shallow Offshore Ocean Floor Communities Oysters Sessile bivalve mollusks Thick shell Food for sea stars, fish, crabs, and snails Oyster beds – empty shells with living generation on top