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Oceanography 101

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Chapter 15 - Marine Communities in Benthic Environments

Smithsonian Ocean Portal:

What is a "Benthic Marine Community?"
-- An area where a group of marine organisms live and interact with each other on, near, or within the seafloor.

benthic means “relating to, or occurring at the bottom of a body of water (oceans, lakes)“
-- littoral (includes shore or nearshore)
-- neritic (seabed in shallow ocean/continental shelf)
-- limnetic (pertaining to lakes)
-- estuarine (pertaining to transition from river to ocean settings)
-- sub-littoral:(Below the littoral zone to a depth of 200 meters - include continental slope, continental rise, abyssal and hadal settings)

Marine Animals in Benthic Environments

Majority of animal species in that inhabit bentic envirornments are invertebrates (“animals lacking backbones”)
These organisms feed on other benthic organism (plants and animals), pelagic organisms (small fish and plankton forms), and decaying matter.
These animals are in turn eaten by a host of pelagic animals (secondary and tertiary tropic feeders)

Phylums of Invertebrates include:

Protozoa - Single cell
Porifera - Sponges – filter feeders
Coelenterada - Coral, Jellyfish
Annelida - Worms
Mollusca - Bivalves, squid, octopus, gastropods (things with shells or large cavities)
Arthropoda - Crabs, shrimp, spiders, scorpions
Echinodermata - Sea Stars, urchins and sea cucumbers (spiny skin)

Benthic Communities on Rocky Shores

Species are either:
-- Attached to bottom (e.g., anenomes, corals)
-- Move over seafloor (e.g., crabs, snails)

* Rocky Intertidal Zonation

Rocky shore sub divisions:
-- Spray and High tide zones
-- Middle tide zone
-- Low tide zone

Spray and Upper Tide Zone
-- Harsh-few organisms
-- Large Temp/Salinity Changes
-- Both Marine and Land Predators

Middle tide zone (Transition zone)
-- More Species Diversity
-- More Organisms

Low tide zone
-- Life is easy here!
-- Stable temp/salinity
-- Lots of Species Diversity
-- Space is limited

Communities on Sandy Beach Shores

* Sandy Beach Intertidal Zone
-- No stable, fixed surface
-- Burrowing provides more stable environment
-- Less risk of temperature extremes and drying out

Burrowing invertebrates include:
Mollusks - Soft body, hard shell (most, not all)
---Example: clams and mussels
Worms (annelids)
Sand Crabs

Shallow Offshore Benthic Communities

-- offshore sand bars (mostly inhabited by burrowing organisms)
-- rocky bottoms (host many attached organisms)
-- coralline reefs (complex, self-constructing communities)

Described as "rich ecosystems" because of the diversity and abundance of organisms in some of these environmental settings

Kelp and kelp forests
Attaches to rocky bottoms
Can grow up to 0.6 meters (2 feet) per day
Provides shelter for other organisms

Coral Reefs

Located in Tropical settings
-- require warm, clear, shallow water
-- Also provide sediments and food to deeper water settings

Corals are animals communities consisting of "Polyps" – each polyp is an individual coral animals
Corals produce calcium carbonate skeletal structures

Other "reef" forming animals include coralline algae (plants!), bryozoans, sponges, molluscs, and many others
Animals feeding on reef-forming organisms produce large quantities of sediment (building up reefs)

Importance of Coral Reefs

Largest structures created by living organisms
---- Great Barrier Reef, Australia, more than 1250 miles long
---- Florida Keys, Bahamas, many coastal Caribbean destinations
---- Atolls throughout the South Pacific and Indian Oceans
---- Coastlines of Red Sea, Persian Gulf, and Africa

Great diversity of species

Reefs protect shorelines and freshwater supplies

Coral Reefs are in Decline
30% healthy today, 41% healthy in 2000

Threats to coral reefs:

-- Hurricanes
-- Floods
-- Coral bleaching
-- Human encroachment and exploitation

Deep-Ocean Floor Communities

-- The deep ocean is largely unexplored
-- Light absent below 3300 feet
-- Temperature usually 28°F to 37°F
-- High pressure

Hydrothermal Vents

Abundance of “unusual” life forms
Life supported by Chemosynthesis

Microscopic organisms (base of local food chain) – thrive on hydrogen sulfide from vents
-- microbes manufacture sugar, carbon dioxide, and dissolved oxygen -

Hydrothermal Vent Species
-- Giant tubeworms
-- Giant clams
-- Giant mussels
-- Crabs

Vents active for years or decades

Animals species similar at widely separated vents

Larvae drift from site to site