Animals of the Pelagic Environment  

Making a living--Adaptations Staying Above the Seafloor   

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Eating   

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Gas Containers Floaters Swimmers (nekton) Mobility Speed Temperature

Group Behavior   

Reproduction Schooling Migrations

Adaptations 

To make a living organisms must meet the following challenges:    

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1) where to live 2) what food to eat and how to obtain it 3) how to avoid predators 4) where, how, when to reproduce

They are strongly influenced by the usual factors: temperature, density, etc.

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Planktonic forms: Zooplankton 

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Zooplankton are the animals of the plankton. They cannot swim against the currents. Every major phylum of the animal kingdom is represented Their size ranges from micrometers (protists) to tens of meters ("Jellies")

Zooplankton Continued... 

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Zooplankton typically grow fast, and this is very dependent on the food supply Distribution - Zooplankton typically occur in patches with a high density of organisms, but they may accumulate along a particular depth e.g., the pycnocline, DSL

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Common Zooplankton   

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Copepods and euphausids (krill) Foraminifera and radiolarians Transparent forms or "Jellies". There are the so-called true Jellies (Cnidaria) and the Ctenophores, or comb-jellies Salps and tunicates

True Nekton 

This group can regulate both their horizontal and vertical position, and include:     

Fish Molluscs (squid, cuttlefish, nautilus) Reptiles Marine Birds Marine Mammals (>50% of time at sea)

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Buoyancy 

4 groups, based on vertical positioning: 

Size-Independent 

This includes the smallest organisms  

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Primarily the smaller zooplankton So small they don’t sink very rapidly

Adaptations are size- and shape-related

Gas Containers Floaters (no hard parts)-neutrally buoyant Swimmers

Buoyancy: Gas Containers  

Use a gas chamber to regulate depth (buoyancy)--similar to a diver’s BCD Limited to about 500 m depth (the crush depth) for nautilus

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Buoyancy: Fish Bladders  

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A special case of gas containers, as most fish swim instead NOT found in fish that swim all the time such as tuna Below about 7000 m, the gas is replaced by fat Can be rapidly or slowly adjusted

Buoyancy: Floaters  

Contain very little hard tissue Includes: 

Coelenterates Siphonophores  Scyphazoans 

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Tunicates Ctenophores Chaetognaths (usually placed in zooplankton group)

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Coelenterates-->Siphonophores   

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Bodies are more than 95% water Use a pneumatophore for buoyancy Colonial organism, with specialized individuals Includes nematocysts (stingers)

Coelenterates-->Scyphazoans   

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True jellyfish Don’t contain a float-bag Uses muscular contraction of the bell to provide movement Capable of explosive growth by asexual budding

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Tunicates     

Also called sea squirts, salps Are chordates, but don’t have a spine Use jet propulsion Can grow up to 40% per day in size! Can be important for export of organic material to depth

Ctenophores   

Also called “comb jellies”, sea gooseberries Always pelagic, marine Carnivorous

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Chaetognaths  

Also called arrow worms very important carnivores, intermediate step between small zooplankton and fish

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Nekton (true swimmers) 

Squid

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Fishes Marine Mammals All of these groups expend more energy to maintain buoyancy

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Adaptations for Feeding 

Mobility and Speed are largely dependent on 3 factors:   

Length:Width (barracuda vs. sunfish) Caudal Fin morphology Red vs. white muscle mass

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Body Temperature 

Tuna are an example of countercurrent heat exchange systems

Body Temperature  

The opposite extreme are cold-water fishes that use antifreeze These glycoproteins bind to small ice crystals in the cell, keeping them from forming bigger crystals

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Marine Mammal Adaptations 

Marine Mammals: spend more than 50% of the time at sea     

Cetaceans (obviously) Pinnipeds Sea Otters Sirenians (manatees, dugongs, Stellar sea cow [extinct]) Polar Bears

Breathing 

Deep diving mammals have evolved to reduce oxygen consumption by:     

Increasing blood volume, capacity “gliding” as they dive Shutting off unnecessary organs during dives Developing flexible ribs No nitrogen narcosis

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Behavioral Adaptations 

Schooling: found in over 2000 species of fishes    

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Reduce the predator-prey encounter rate Less likely to eat any given individual May appear as a “single” organism Confusing to predators

Can be reproduced using simple rules on a computer

Behavior: Migration

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Behavior: Abduction 

Some organisms “borrow” another one to enhance survival

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