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…)

Oceanic Necton

Holoepipelagic – Fishes that spend their entire life in the epipelagic.

These fishes usually lay floatingeggs and have epipelagic larvae(planktonic)…

They are usually most abundant insurface waters of the tropics and sub-tropics.

Also include fishes like thresher shark,Mackerel shark, blue shark, most flyingFish, swordfish, etc.

Oceanic NectonMeroepipelagic - 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)

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 allthe time and are not considered pelagic…

Marine reptiles – Nectonic reptiles primarily include turtles and sea snakes.

Marine reptiles also include iguanasAnd saltwater crocodiles, but theseAgain inhabit inshore areas and areNot considered pelagic…

Marine reptiles were probably a lot More common about 60 million yearsAgo…

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.

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…