I. Challenges of Life in the Sea
Every habitat has its own unique set of
characteristics & presents special challenges to
the organisms that live there.
A. Planktonic Organisms: organisms that drift
in the water
B. Nektonic Organisms: organisms that swim
in the water
C. Benthic Organisms: organisms that live on
the ocean floor
II. Salinity
Marine organisms have adapted to maintain the
proper balance of water & salt within themselves
A. Osmocomformers: organisms whose
internal concentrations of salt changes as
the salinity in the water changes
http://www.daltonstate.edu/faculty-staff/jadams/Biol%203500/Projectable%20images/Chapter%206/sharks-psd.png
III. Temperature
Metabolic reactions proceed faster at higher
environmental temperatures & slow down
dramatically as it gets colder
A. Ectotherms: (poikilotherms)
- cold blooded organisms
- as temperatures in the water fluctuate
so does their body temp.
- become sluggish in unusually cold
water
B.
Endotherms: (homeotherms)
- warm blooded organisms
- use respiration to maintain heat
- MAMMALS – blubber reduces heat
loss
Marine Life Zones
 A life zone is a region that contains
characteristic organisms that interact with one
another and with their environment
A. Supratidal – from the high tide mark to
the sand dunes behind the beach
1. Sand very dry
2. Movement of sand in this location is
due primarily to the winds
B.
Intertidal Zone – exposed to the
atmosphere during low tide and covered
by water during high tide
1. Absorbs the direct assault of waves
striking the beach
2. Breaking waves release their energy
here
3. Broken shells litter this area
Strand Line – marks the highest point
where water washes up on the beach and
separates upper beach from the intertidal
zone
C. Subtidal Zone – the coastal life zone
that remains underwater
1. beneath the lowest low tide and is
continuously covered by offshore
water
2. extends as far out as the sand is moved
by wave action
D. Pelagic Zone – the largest life zone in
the ocean
1. covers the entire ocean of water above
the sea bottom
2. this is the area where large schools of
fish and pods of marine mammals
swim freely
3. includes the Neritic Zone (0 –
200meters out to sea past the
intertidal zone) and the Oceanic Zone
(200 meters +)
E.
Neritic Zone – region that lies above the
continental shelf
1. most of the world’s commercial
fishing occurs in this zone
2. much of this zone is sunlit
F.
Oceanic Zone – this region is beyond
the neritic zone and includes most of
the open ocean
1. the upper portion of this zone is called
the photic (meaning “light”) zone;
most light penetrates up to 200m
2. the lower portion is called the aphotic
(meaning “no light”) zone
 the deepest part of the ocean floor
is the ocean basin or abyssal plain
 Benthic Zone – includes the entire
sea floor, from the shallow
intertidal zone to the deep ocean
basin