Marine life

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General characteristics of a large marine ecosystem (Gulf of Alaska)

Marine life refers to the plants, animals and other organisms that live in the ocean. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms produce much of the oxygen we breathe and probably help regulate the earth's climate. Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land.

Marine life ranges in size from the microscopic, including plankton and phytoplankton which can be as small as 0.02 micrometres and are both important as key primary producers of the sea, to huge cetaceans (whales, dolphins and porpoises) which in the case of the blue whale reach up to 33 metres (109 feet) in length.

Marine life is an object of study both in marine biology and in biological oceanography. In biology many phyla, families and genera have some species that live in the sea and others that live on land. Marine biology classifies species based on the environment rather than on taxonomy. For this reason marine biology encompasses not only organisms that live only in a marine environment, but also other organisms whose lives revolve around the sea. Biological oceanography is the study of how organisms affect and are affected by the physics, chemistry, and geology of the oceanographic system. Biological oceanography mostly focuses on the microorganisms within the ocean; looking at how they are affected by their environment and how that affects larger marine creatures and their ecosystem.[1] Biological oceanography is similar to marine biology, but is different because of the perspective used to study the ocean. Biological oceanography takes a bottom up approach (in terms of the food web), while marine biology studies the ocean from a top down perspective. Biological oceanography mainly focuses on the ecosystem of the ocean with an emphasis on plankton: their diversity (morphology, nutritional sources, motility, and metabolism); their productivity and how that plays a role in the global carbon cycle; and their distribution (predation and life cycle).[1][2][3] Biological oceanography also investigates the role of microbes in food webs, and how humans impact the ecosystems in the oceans.[1]

Microscopic life[edit]

As inhabitants of the largest environment on Earth, microbial marine systems drive changes in every global system. Microbes are responsible for virtually all the photosynthesis that occurs in the ocean, as well as the cycling of carbon, nitrogen, phosphorus and other nutrients and trace elements.[4]

Microscopic life undersea is incredibly diverse and still poorly understood. For example, the role of viruses in marine ecosystems is barely being explored even in the beginning of the 21st century.[5]

A teaspoon of seawater contains about one million viruses.[6] Most of these are bacteriophages, which are harmless to plants and animals, and are in fact essential to the regulation of saltwater and freshwater ecosystems.[7] They infect and destroy bacteria in aquatic microbial communities, and are the most important mechanism of recycling carbon in the marine environment. The organic molecules released from the dead bacterial cells stimulate fresh bacterial and algal growth.[8] Viral activity may also contribute to the biological pump, the process whereby carbon is sequestered in the deep ocean.[9]

Marine bacteriophages are viruses that live as obligate parasitic agents in marine bacteria such as cyanobacteria.[10] Their existence was discovered through electron microscopy and epifluorescence microscopy of ecological water samples, and later through metagenomic sampling of uncultured viral samples.[10][11] The tailed bacteriophages appear to dominate marine ecosystems in number and diversity of organisms.[10] However, viruses belonging to families Corticoviridae,[12] Inoviridae[13] and Microviridae[14] are also known to infect diverse marine bacteria. Metagenomic evidence suggests that microviruses (icosahedral ssDNA phages) are particularly prevalent in marine habitats.[14]

Bacteriophages, viruses that are parasitic on bacteria, were first discovered in the early twentieth century. Scientists today consider that their importance in ecosystems, particularly marine ecosystems, has been underestimated, leading to these infectious agents being poorly investigated and their numbers and species biodiversity being greatly under reported.[15]

Microorganisms constitute more than 90% of the biomass in the sea. It is estimated that viruses kill approximately 20% of this biomass each day and that there are 15 times as many viruses in the oceans as there are bacteria and archaea. Viruses are the main agents responsible for the rapid destruction of harmful algal blooms,[16] which often kill other marine life.[17] The number of viruses in the oceans decreases further offshore and deeper into the water, where there are fewer host organisms.[9]

The role of phytoplankton is better understood due to their critical position as the most numerous primary producers on Earth. Phytoplankton are categorized into cyanobacteria (also called blue-green algae/bacteria), various types of algae (red, green, brown, and yellow-green), diatoms, dinoflagellates, euglenoids, coccolithophorids, cryptomonads, chrysophytes, chlorophytes, prasinophytes, and silicoflagellates.

Zooplankton tend to be somewhat larger, and not all are microscopic. Many Protozoa are zooplankton, including dinoflagellates, zooflagellates, foraminiferans, and radiolarians. Some of these (such as dinoflagellates) are also phytoplankton; the distinction between plants and animals often breaks down in very small organisms. Other zooplankton include cnidarians, ctenophores, chaetognaths, molluscs, arthropods, urochordates, and annelids such as polychaetes. Many larger animals begin their life as zooplankton before they become large enough to take their familiar forms. Two examples are fish larvae and sea stars (also called starfish).

Plants and algae[edit]

Microscopic algae and plants provide important habitats for life, sometimes acting as hiding and foraging places for larval forms of larger fish and invertebrates.

Algal life is widespread and very diverse under the ocean. Microscopic photosynthetic algae contribute a larger proportion of the world's photosynthetic output than all the terrestrial forests combined. Most of the niche occupied by sub plants on land is actually occupied by macroscopic algae in the ocean, such as Sargassum and kelp, which are commonly known as seaweeds that create kelp forests.

Plants that survive in the sea are often found in shallow waters, such as the seagrasses (examples of which are eelgrass, Zostera, and turtle grass, Thalassia). These plants have adapted to the high salinity of the ocean environment. The intertidal zone is also a good place to find plant life in the sea, where mangroves or cordgrass or beach grass might grow. Microscopic algae and plants provide important habitats for life, sometimes acting as hiding and foraging places for larval forms of larger fish and invertebrates.

Invertebrates[edit]

Main article: Marine invertebrates

As on land, invertebrates make up a huge portion of all life in the sea. Invertebrate sea life includes Cnidaria such as jellyfish and sea anemones; Ctenophora; sea worms including the phyla Platyhelminthes, Nemertea, Annelida, Sipuncula, Echiura, Chaetognatha, and Phoronida; Mollusca including shellfish, squid, octopus; Arthropoda including Chelicerata and Crustacea; Porifera; Bryozoa; Echinodermata including starfish; and Urochordata including sea squirts or tunicates.

Fungi[edit]

Main article: Marine fungi

Over 1500 species of fungi are known from marine environments.[18] These are parasitic on marine algae or animals, or are saprobes on algae, corals, protozoan cysts, sea grasses, wood and other substrata, and can also be found in sea foam.[19] Spores of many species have special appendages which facilitate attachment to the substratum.[20] A very diverse range of unusual secondary metabolites is produced by marine fungi.[21]

Vertebrates[edit]

Fish[edit]

Main article: Fish

Fish anatomy includes a two-chambered heart, operculum, swim bladder, scales, eyes adapted to seeing underwater, and secretory cells that produce mucous. Fish breathe by extracting oxygen from water through gills. Fins propel and stabilize the fish in the water. Fish fall into two main groups: fish with bony skeletons and fish with cartilaginous skeletons.

A reported 32,700 species of fish have been described (as of December 2013),[22] more than the combined total of all other vertebrates. About 60% of fish species are saltwater fish.[23]

Reptiles[edit]

Main article: Marine reptile

Reptiles which inhabit or frequent the sea include sea turtles, sea snakes, terrapins, the marine iguana, and the saltwater crocodile. Most extant marine reptiles, except for some sea snakes, are oviparous and need to return to land to lay their eggs. Thus most species, excepting sea turtles, spend most of their lives on or near land rather than in the ocean. Despite their marine adaptations, most sea snakes prefer shallow waters nearby land, around islands, especially waters that are somewhat sheltered, as well as near estuaries.[24][25] Some extinct marine reptiles, such as ichthyosaurs, evolved to be viviparous and had no requirement to return to land.

Birds[edit]

Main article: Seabird

Birds adapted to living in the marine environment are often called seabirds. Examples include albatross, penguins, gannets, and auks. Although they spend most of their lives in the ocean, species such as gulls can often be found thousands of miles inland.

Mammals[edit]

Main article: Marine mammal

There are five main types of marine mammals.

References[edit]

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  2. ^ Menden-Deuer, Susanne. "Course Info." OCG 561 Biological Oceanography. Web. 22 Oct. 2014. <http://www.gso.uri.edu/ocg561/>.
  3. ^ Miller, Charles B., and Patricia A. Wheeler. Biological Oceanography. Second ed. Chinchester, West Sussex: John Wiley & Sons, 2012. Print.
  4. ^ "Functions of global ocean microbiome key to understanding environmental changes". www.sciencedaily.com. University of Georgia. December 10, 2015. Retrieved December 11, 2015. 
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  6. ^ Shors p. 4
  7. ^ Shors p. 5
  8. ^ Shors p. 593
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  11. ^ Wommack, K. Eric; Russell T. Hill; Terri A. Muller; Rita R. Colwell (April 1996). "Effects of sunlight on bacteriophage viability and structure". Applied and Environmental Microbiology (United States of America: American Society for Microbiology) 62 (4): 1336–1341. PMC 167899. PMID 8919794. 
  12. ^ Krupovic M, Bamford DH (2007). "Putative prophages related to lytic tailless marine dsDNA phage PM2 are widespread in the genomes of aquatic bacteria". BMC Genomics 8: 236. doi:10.1186/1471-2164-8-236. PMC 1950889. PMID 17634101. 
  13. ^ Xue H, Xu Y, Boucher Y, Polz MF (2012). "High frequency of a novel filamentous phage, VCY φ, within an environmental Vibrio cholerae population". Appl Environ Microbiol 78 (1): 28–33. doi:10.1128/AEM.06297-11. PMC 3255608. PMID 22020507. 
  14. ^ a b Roux S, Krupovic M, Poulet A, Debroas D, Enault F (2012). "Evolution and diversity of the Microviridae viral family through a collection of 81 new complete genomes assembled from virome reads". PLOS ONE 7 (7): e40418. doi:10.1371/journal.pone.0040418. PMC 3394797. PMID 22808158. 
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  17. ^ www.cdc.gov. Harmful Algal Blooms: Red Tide: Home [Retrieved 2014-12-19].
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  19. ^ Kirk, P.M., Cannon, P.F., Minter, D.W. and Stalpers, J. "Dictionary of the Fungi". Edn 10. CABI, 2008
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  21. ^ San-Martín, A.; S. Orejanera; C. Gallardo; M. Silva; J. Becerra; R. Reinoso; M.C. Chamy; K. Vergara; J. Rovirosa (2008). "Steroids from the marine fungus Geotrichum sp". Journal of the Chilean Chemical Society 53 (1): 1377–1378. 
  22. ^ http://www.fishbase.org
  23. ^ http://www.worldwatch.org/node/784
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