Arctic Life/Protista

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The kingdom Protista has long been the repository for all life forms that possess the cellular structures typical of eukaryotes (nucleus, mitochondria, chloroplasts), but look different from animals, fungi, or plants. It is now recognized that many of the traditional members of this kingdom need to be assigned elsewhere. In fact, there is good agreement that its members need to be subdivided into two groups – the kingdom Chromista and the kingdom Protozoa. As well, a number of other "traditional" protists have been assigned to the kingdom Plantae (e.g., green algae, red algae) or to the kingdom Fungi (e.g., Pneumocystis) based on genetic studies. However, because the process of revising the classification of protists is a work in progress, we have continued to place all of these groups in a single kingdom, retaining the name Protista. In an effort to simplify the discussion of this immensely diverse group of organisms, we have separated information on four broadly recognized groups of protists: algae, oomycetes, protozoans, and slime moulds.

Northern Algae & Allies

Three groups of protists dominate arctic environments: algae, oomycetes, and protozoans. We have compiled a list of major protist phylums which you may encounter in the Canadian Arctic. Please explore the pages below to learn more about protists and their impacts on Northern ecosystems.

Adaptations

Algal Life Preservers

How do diatoms stay afloat in arctic waters? They develop their own life preservers! Diatoms produce elaborate horns and projections that increase their surface area-to-volume ratio. This slows the rate at which diatoms sink and increases their chance of being carried higher in the water column by currents. Some species of diatoms sink less than 2 mm per day!

Algal Life Preservers
A diatom that grows on sea ice.

How do algae prevent freezing in cold arctic waters? Without an important adaptation, these algae would be at risk of becoming tiny popsicles! If ice develops in their cells, death is certain because of the damage caused by sharp ice crystals. To avoid freezing, algae lower the free water content of their cells by binding it to structures within the cell. This adaptation is especially effective in diatoms. As a result, these beautifully patterned, silica-shelled protists are commonly found living directly attached to the sea ice!

Algal Sunscreens
Sea lettuce, Ulva rigida, produces chemicals that act as sunscreen.

Sea lettuce, Ulva rigida, produces chemicals that act as sunscreen. Although sunlight is ordinarily a good thing for plant growth, there are risks. During the arctic spring and summer, when days last up to 24 hours, algae are at risk of serious sunburns! As a protective measure, many arctic algae produce amino acids and red carotenoid pigments. These compounds are able to absorb the dangerous ultraviolet rays, protecting the organism from DNA damage. Algae that live closer to the water's surface are more vulnerable to sunburn and thus tend to have more of these chemicals than those that live deeper in the water column. These natural sunscreens allow algae to make use of the long hours of sun for photosynthesis, without damage to their delicate tissues.

Cool Facts

An Icy Garden
Ice algae.

The large polar ice cap, and the many ice sheets of the Arctic Ocean, are home to a garden of algae. Consisting primarily of diatoms, these gardens cover the underside of the sea ice and even parts of the ice's interior. Growth of these ice algae begins in early March and peaks in May, after which time it declines rapidly with the ice melt. These ice algae serve as an important food source for marine crustaceans, worms, and fish.

Multi-Coloured Snow
"Watermelon snow" is caused by the green alga, Chlamydomonas nivalis.

Many people have seen yellow snow on their lawn thanks to neighbourhood pets, but snow can take on other hues in the Arctic due to the green algae that inhabit it. Many of these species, such as Hormidium subtile, are green, imparting this colour to the snow. But other algal species, like Chlamydomonas nivalis, produce red patches, while a rare grey colouration is the result of the growth of Mesotaenium berggrenii.

Sea Ghosts
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What is that ghostly glow seen in arctic marine waters at night? Tiny bioluminescent dinoflagellates! Some dinoflagellates in the genus Noctiluca are capable of creating light in response to mechanical stimulation. Normally, there are so few of these organisms that they go unnoticed, but sometimes these algae become very abundant. At such times, kayakers may find themselves amidst a blue-green glow of phytoplankton. Why do these phytoplankton produce light? It has been suggested that it is a defensive mechanism to ward off predators.

Biology

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The kingdom Protista, as we have defined it, includes all those organisms that are not bacteria, animals, true fungi, or green plants. Many protists are motile and feed on other organisms, which makes them appear animal-like. Other protists, such as algae, are plant-like and obtain their energy directly from the sun. Most protists are unicellular, meaning that they perform all the basic tasks of life, including feeding, locomotion, and reproduction, within a single cell – their body. However, some protists form multicellular colonies of considerable complexity. In fact, the largest photosynthetic organisms in the Arctic are not land plants, but are multicellular protists – algae.

Algae

Algae usually occur in the water (fresh, marine, or brackish) where they may be part of the planktonic (most microscopic algae) or benthic (e.g., kelps) community. Various types of algae also grow on moist soil and rocks, or as endosymbionts within the bodies of protozans or invertebrates. Other algae form symbiotic associations with fungi to produce composite organisms called lichens.

In general, algae have rigid cell walls, typical eukaryotic nuclei, and chloroplasts. Motile species of algae use flagella as their locomotory organelles. Algae can be either autotrophic or heterotrophic, but most are photoautotrophic and require light and carbon dioxide as their primary source of energy and carbon. The vegetative body of multicellular alga is called the thallus and may reach several metres in length.

Algae reproduce both asexually and sexually. Asexual reproduction takes place in three different ways: the thallus may simply fragment with each piece growing into a new individual; the thallus may reproduce by means of sporulation; or it may propagate by binary fission, in which the nucleus divides and subsequent division of the cytoplasm occurs.

Fragmentation of an algal cell.
Binary fission of an algal cell.
Algal reproduction via sporulation.
Oomycetes
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Oomycetes have diploid hyphae and a cell wall composed of cellulose. Members of this group reproduce asexually via diploid zoospores formed in a sporangium. Sexual reproduction (from which the group derives its name) occurs when male and female reproductive structures meet. Nuclei pass from the male to the female organ through a fertilization tube, then fuse in pairs to form diploid nuclei. One or more thick-walled oospores then develop in the female organ. These oospores serve as dormant survival structures, capable of producing either diploid hyphae or a sporangium that releases diploid zoospores, in times of environmental stress.

Protozoa
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Protozoans are usually motile, and are often unicellular, although some form multicellular colonies. They thrive in a variety of habitats, with one common characteristic – available water. High moisture levels are necessary because protozoans are very sensitive to desiccation. Most are free-living and inhabit freshwater and marine environments. They make up a large part of the plankton in the Arctic and thus are a key part of polar food webs.

The presence of ectoplasm and an outer membrane (pellicle) gives their bodies structure and strength. Some species have one nucleus, but others have two. Most have contractile vacuoles for osmoregulation, especially freshwater forms. Most species are able to produce cysts that are resistant to extreme temperatures and desiccation. There are a few sessile species, but most move using cilia, flagella, or pseudopodia. Asexual reproduction is achieved primarily through binary fission, while sexual reproduction involves gamete cell fusion (e.g., flagellates, amoebae) and conjugation (e.g., ciliates) in which gametic nuclei are exchanged between individuals.

Slime Moulds
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The vegetative phase of all cellular slime moulds is an amoeboid cell. These cells employ either asexual or sexual reproduction, depending on environmental conditions. During sexual reproduction, two cells of different mating types fuse to create a diploid cell. When another amoeboid cell comes into contact with this diploid cell, it is consumed and a giant cell forms. Meiosis follows and a macrocyst is formed in which haploid spores develop. Sexual reproduction rarely occurs in the Arctic because it requires damp conditions to take place. In drier environments, haploid amoeboid cells cease feeding and clump together to form a slug-like pseudoplasmodium, from which a stalked fruiting body forms. Spores contained in this fruiting body are released from the head, which sits atop the stalk.

In contrast to the above description of the pseudoplasmodium, the plasmodium phase of the acellular slime mould is diploid. This mass gives rise to a fruiting body in which haploid spores are produced via meiosis. These spores germinate and produce motile flagellate cells called swarm cells, which fuse to form a diploid gamete, which then produces another plasmodium.