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CHAPTER 15 Animals of the Benthic Environment
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Distribution of benthic organisms
Fig. 15.1 More benthic productivity when closely beneath areas of high surface primary productivity Mainly on continental shelves Affected by surface ocean currents
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Benthic organisms on rocky shores
Epifauna (on top) Attached to substrate (e.g., marine algae) Move on/over seafloor (e.g., crabs, snails) Moderate diversity of species Greatest animal diversity at tropical latitudes Greatest algae diversity at mid-latitudes
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Epifauna Intertidal zonation (rocky shore)
Fig a
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Epifauna Spray zone (supratidal) Have to avoid drying out
Fig. 15.2b Spray zone (supratidal) Have to avoid drying out Many animals have shells Very few species of marine algae
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Epifauna High tide zone Avoid drying out so animals have shells
Marine algae—rock weeds with thick cell walls
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Epifauna Middle tide zone More types of marine algae
Soft-bodied animals
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Epifauna Low tide zone Abundant algae
Many animals hidden by sea weed and sea grass Crabs abundant in all intertidal zones
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Benthic organisms on sediment-covered shores
Similar intertidal zones to that of rocky shores Less species diversity Greater number of organisms Mostly infauna – burrow into sediment Microbial communities Coquina (Donax)
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Intertidal zonation (sandy shore)
Fig. 15.8
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Benthic organisms on sediment-covered shores
Energy level along shore depends on Wave strength Longshore current strength Wave/current energy determines habitat… Coarse boulder beaches Sand beaches Salt marshes Mud flats Fine-grained, flat-lying tidal flat more stable than high energy sandy beach
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Sandy beaches Animals burrow Bivalve mollusks Annelid worms
Crustaceans Echinoderms Meiofauna
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Mud flats Eelgrass and turtle grass common Bivalves and other mollusks
Fiddler crabs
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Shallow ocean floor Continental shelf Mainly sediment covered
Kelp forest associated with rocky seafloor Also lobsters Oysters
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Figure 15.14a,b
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Figure 15.14c
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Coral reefs Most coral polyps live in large colonies
Hard calcium carbonate structures cemented together by coralline algae
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Coral reefs Coral reefs limited to Warm (but not hot) seawater
Sunlight (for symbiotic algae) Strong waves or currents Clear seawater Normal salinity Hard substrate
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Reef-building corals Fig
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Symbiosis of coral and algae
Coral reefs made of algae, mollusks, foraminifers as well as corals Hermatypic coral mutualistic relationship with algae – zooxanthellae Algae provide food Corals provide nutrients Soft coral polyp (Lobophytum compactum). Green shows the polyp tissue, while the red shows the zooxanthellae.
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Importance of coral reefs
Largest structures created by living organisms Great Barrier Reef, Australia, more than 2000 km (1250 m) long Great diversity of species Important tourist locales Fisheries Reefs protect shorelines
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Humans and coral reefs Activities such as fishing, tourist collecting, sediment influx due to shore development harm coral reefs Sewage discharge and agricultural fertilizers increase nutrients in reef waters Hermatypic corals thrive at low nutrient levels Phytoplankton overwhelm at high nutrient levels Bioerosion of coral reef by algae-eating organisms Coral covered with macroalgae
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Other problems Smoothering by dredging, runoff
Fishing practices, harvesting Pollution Global warming
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Worm Reefs Sabellariid worms (Phragmatopoma caudata) form shallow reefs St. Augustine to south end of Biscayne Bay Provide habitat for many organisms
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Sabellariid worms – polychaete worms
Adult worms (3/4 - 2 in. long) build reefs on limestone and coquina formations, jetties Build sand hoods over tubes to reduce desiccation at low tide. Protective tubes made of sand, joined to neighbors to build rigid, wave resistant structures. 15,000 to 60,000 worms per m2 Live up to 10½ years. Thais (oyster drill) is an important predator
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Benthic organisms on the deep seafloor
Little known habitat – only accessable via dredge and some submersibles and ROVs Bathyal, abyssal, hadal zones Little to no sunlight About the same temperature About the same salinity Oxygen content relatively high Pressure can be enormous Bottom currents usually slow
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Food sources in deep seafloor
Most food sinks from surface waters Low supply and “patchy” Fig
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Deep-sea hydrothermal vent biocommunities
First discovered 1977 Chemosynthesis Archaea use sea floor chemicals to make organic matter Unique communities Tube worms Giant clams and mussels Crabs Microbial mats
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Figure 15.27
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Archaea use sea floor chemicals to make organic matter
Chemosynthesis Archaea use sea floor chemicals to make organic matter Figure 15.25b
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Global hydrothermal vent fields
Fig
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Deep-sea hydrothermal vent biocommunities
Vents active for years or decades Animals species similar at widely separated vents Larvae drift from site to site “Dead whale hypothesis”
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How do organisms go from one hydrothermal vent to another?
“Dead whale hypothesis” – Dispersal of vent organisms Pelagic eggs/larvae disperse to other food patches or vent fields Methane-bearing springs on continental shelves and slopes are more common than originally thought Possible dispersal to carcasses – support vent organisms Take years to decompose Use as "stepping stones Whale carcass with worms, sea cucumbers
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Figure 15.C Fish carcass On ocean floor
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Deep-sea hydrothermal vent biocommunities
Life may have originated at hydrothermal vents Chemosynthesis also occurs at low temperature seeps Hypersaline seeps Hydrocarbon seeps Subduction zone seeps
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Figure & 15.29
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Beneath the sea floor Deep biosphere Microbes live in porous sea floor
Might represent much of Earth’s total biomass In may 2008, prokaryotes were reported in mud cores extracted from between 860 to 1626 meters beneath the sea floor off Newfoundland. Cells were fold denser than in terrestrial cores of similar depth and about 5-10% of the cells were dividing. beneath-the-oceans.html
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