Polar habitats often have very rich nutrient levels that are seasonally productive.

Long seasonal periods of darkness reduce primary productivity to low levels

Biological diversity is lower than other regions, probably because many species cannot survive the extreme conditions.

Freezing temperatures increase salinities... allowing marine waters to be < 0°C.

Polynyas are open spots of water surrounded by sea ice. These are important for air breathing marine animals.

Those that are successful tend to be very abundant. Whales make feeding migrations into polar regions in the spring, and leave for warmer waters before winter.

Some examples of polar marine biodiversity

Ice associated krill (Family Euphausiidae) are important grazers of algae that accumulate on the undersides of floating sea ice.

A single krill can clear one square foot of ice algae in approximately 10 minutes.

Icefish (Family Channichthyidae) have glycoproteins that act as antifreeze to allow survival at temperatures below freezing.

They lack hemoglobin but in the low temperatures at which they live, their blood carries enough dissolved oxygen to survive

Antarctic toothfish (Family Nototheniidae) are the most common fish in the Antarctic.

Most are bottom dwellers feeding on invertebrates and occasionally algae. These fish are an important source of food for penguins, seals and toothed whales.

Weddell seal, Leptonychotes weddelli, has thick blubber that allows survival in the extreme cold.

These seals attain weights of 900 to 1,000 pounds on a diet of fish and squid. They are eaten by killer whales

Leopard seal, Hydrurga leptonyx, a very large top-end predator with a vicious reputation (eats penguins and other seals, along with fish).

Polar bears (Ursus maritimus) hunt marine mammals and may swim long distances offshore.  Climate change and loss of ice may threaten this species.

 

The Open Sea includes life forms associated with the "pelagic division" of the marine realm.  By definition, this is away from the influence of coastal habitats.

The pelagic realm is a three-dimensional, nutritionally dilute habitat with low rates of primary production and few obvious physical niches.

Remember the parts of the ocean

In the open ocean, the divisions are linked to light levels

(Recall from lecture 2):

Epipelagic (upper 150 - 200 m or so... linked to the photic zone)

Mesopelagic (150/200 - 1000 m)

Bathypelagic (1,000 - 4,000 m)

Abyssopelagic (4,000 - 6,000 m)

Hadal (in the trenches)

Two major groups of marine animals in this region include the zooplankon and the nekton

Zooplankton are represented by more than 5000 species of:

permanent holoplankton (including all three protozoan phyla, cnidarians, ctenophores, chaetognaths, crustaceans, and invertebrate chordates)

meroplanktonic stages of invertebrates and fishes

Most nekton are vertebrates, and most marine vertebrates are teleost fishes.

Where is life found in the open ocean?

Within the center of the large, semi-enclosed, oceanic current gyres is the epipelagic, or photic, zone

Geographic patterns of distribution for life in the open ocean are broadly defined by unique combinations of water temperature and salinity

This can be seen by looking at the distribution of six closely related species of krill

Krill are an essential part of oceanic food webs

Given the 3-D nature of the habitat, also consider the vertical distribution of pelagic animals... most are near the surface in the epipelagic (photic) zone

Although the epipelagic zone accounts for less than 10% of the ocean’s volume, most pelagic animals are found there

Most are countershaded carnivores that are effective swimmers, so many species are more broadly distributed than the more discretely distributed zooplankton.

How countershading works:

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