Unit 11The Marine Environment

The diversity of marine life

The ocean is home to a wide variety of organisms

Marine organisms range from microscopic bacteria and algae to the largest animal in the world (blue whale)

Number of known marine species: 250,000

Video on Bioluminescence

Classification of living things

Organisms can be classified into one of three domains of life:

Archaea

Bacteria

Eukarya

Classification of living things

Organisms can also be classified into one of five kingdoms:

MoneraProtoctistaFungiPlantaeAnimalia

Classification of living things

Taxonomic classification includes the following increasingly specific groupings:

KingdomPhylum (Division for plants)ClassOrderFamilyGenusSpecies

Taxonomic classification of selected organisms

Category Human Killer whale Giant kelp

Kingdom Animalia Animalia Protoctista

Phylum Chordata Chordata Phaeophyta

Subphylum Vertebrata Vertebrata

Class Mammalia Mammalia Phaeophycae

Order Primates Cetacea Laminariales

Family Hominidae Delphinidae Lessoniaceae

Genus Homo Orcinus Macrocystis

Species sapiens orca pyrifera

Classification of marine organisms

Marine organisms can be classified into one of three groups based on habitat and mobility:

1. Plankton (floaters)Phytoplankton (drifting plants and algae)Zooplankton (drifting animals)

2. Nekton (swimmers)3. Benthos (bottom dwellers)

Plankton: Examples

Phytoplankton Zooplankton

Nekton: Examples

Benthos: Examples

Life cycle of a squid

Squid experience benthic, planktonic, and nektonic stages

Squid are considered meroplankton (partially planktonic)

Organisms that spend their entire lives as plankton are holoplankton)

Distribution of species on Earth

The land has more species because it has greater environmental variability than the ocean

Most ocean species are benthic because of greater environmental variability compared to pelagic environments

Adaptations of organisms to the marine environment

The marine environment presents many challenges to organisms because seawater:

Is dense enough to support organismsHas high viscosityExperiences variations in temperature and salinityContains variable amounts of dissolved gasesHas high transparencyHas a dramatic change of pressure with depth

Marine organisms have various adaptations for the conditions of the marine environment

Need for physical support

Condition:Seawater is dense enough to support marine organisms

Adaptations:Many marine organisms lack rigid skeletons, appendages, or vast root systemsInstead, they rely on buoyancy and friction to maintain their position within the water column

Seawater’s viscosity controlled by temperature

Condition:Seawater’s viscosity (resistance to flow) is strongly affected by temperature

Cold water has higher viscosity than warm water, so is more difficult to swim through

Warm water has lower viscosity, so organisms tend to sink within the water column

Seawater’s viscosity controlled by temperature

Adaptations:Many warm-water organisms have ornate appendages to stay afloatMany cold-water organisms are streamlined to swim more easily

Warm-water copepod

Cold-water copepod

Seawater’s viscosity and adaptations of phytoplanktonCondition:

Phytoplankton must remain in sunlit surface waters

Adaptations:Small size increases surface area to volume ratio

Appendages increase frictional resistance

Tiny droplet of low density oil increases buoyancy

Variations in temperature

Condition:Coastal water temperatures vary more than the open ocean or at depth

Adaptations:Many coastal organisms can withstand a wide temperature range (are eurythermal)Most open ocean and deep-water organisms can withstand only a small temperature range (are stenothermal)

Variations in salinity

Condition:Coastal environments experience greater salinity variation than the open ocean or at depth

Adaptations:Many shallow-water coastal organisms can withstand a wide salinity range (are euryhaline)

Most open ocean and deep-water organisms can withstand only a small change in salinity (are stenohaline)

Osmosis

Condition:Osmosis is the movement of water molecules through a semipermeable membrane from lower to higher concentrationsOsmosis removes water from hypotonic organismsOsmosis adds water to hypertonic organisms

OsmosisAdaptations:

Dissolved gases: Oxygen

Condition:Marine animals need oxygen to survive

Adaptations:Many marine animals use gills to extract dissolved oxygen from seawaterMarine mammals must breathe air

Abundance of dissolved oxygen and nutrients with depth

Seawater’s high transparency

Condition:Seawater has high transparency

Adaptations:Transparency

Camouflage

Countershading

Migration (DSL)

Camouflage

Countershading

The deep scattering layer (DSL)

Organisms within the deep scattering layer undertake a daily migration to hide in deep, darker waters during daytime

Increase of pressure with depth

Condition:Pressure increases rapidly with depth

Adaptations:Most marine organisms lack large compressible air pockets inside their bodiesWater-filled bodies exert the same amount of pressure as is pushing inward, so marine organisms do not feel the high pressure at depth

Divisions of the marine environment

Main divisions:

Pelagic (open sea)

Benthic (sea bottom)