1. Oceanic Necton
Necton: These include all organisms that are capable of moving against water currents.
This is as supposed to the plankton covered in previous lectures… Also, here
we will primarily consider organisms distributed in the epipelagic zone of the
open ocean… (i.e. off shore, top 200 meters or so of open ocean…)

2. Oceanic Necton
Holoepipelagic – Fishes that spend their entire life in the epipelagic.
These fishes usually lay floating
eggs and have epipelagic larvae
(planktonic)…
They are usually most abundant in
surface waters of the tropics and sub-
tropics.
Also include fishes like thresher shark,
Mackerel shark, blue shark, most flying
Fish, swordfish, etc.

3. Oceanic Necton Meroepipelagic - fishes that spend only part of
their life in the epipelagic.
Some will spawn in inshore waters
(e.g. whale shark)
Others will enter the epipelagic
zone only at certain times of the day
(e.g. some deep ocean fishes)
Yet others will spend only parts
of their life in the epipelagic.
(e.g. salmon)

4. Oceanic Necton – other components besides fishes
Marine mammals - Nectonic mammals include whales (order Cetacea), and seals
and sea lions (order Pinnipedia).
[most of these are of course “meroepipelagic-like”, although this
term is usually reserved for fishes]
Other marine mammals like sea otters (order Carnivora) and
manatees and dugongs (order Sirenia) occupy inshore areas all
the time and are not considered pelagic…
Marine reptiles – Nectonic reptiles primarily include turtles and sea snakes.
Marine reptiles also include iguanas
And saltwater crocodiles, but these
Again inhabit inshore areas and are
Not considered pelagic…
Marine reptiles were probably a lot
More common about 60 million years
Ago…

5. Oceanic Necton – other components besides fishes
Marine birds – Although technically birds are not considered as part of the necton,
a large number of them spend major parts of their lives over the ocean,
and often feed on marine organisms (some diving up to 100 meters for
their food!)… Because of their potential impact on these marine systems,
they do need to be considered…
Marine invertebrates – Most invertebrates are not good swimmers and as such are
often classified as plankton… There are however a number of
cephalopod mollusks with swimming abilities that allow them to be
classified as part of the necton.

6. Oceanic Necton – some basic concepts
Environmental conditions significant to the necton:
* three-dimensionality of the medium
* transparency of the medium
* lack of shelter from predators
* absence of physical boundaries or structures
Adaptations of organisms need to take all these into account…
Good control of buoyancy and increased locomotion.
streamline bodies, gas bladders in fishes, lipid filled livers in sharks,
air channels in the bones of marine birds…
Well developed sensory systems.
vision, hearing, olfaction…
Defense using camouflage.
color patterning, and alteration of body shape to reduce shades…