From the edge of darkness to the black abyss
Marine scientists census 17,500+ species and counting. Explorers report deep sea teeming with species that have never known light; Describing all new species in a cup of deep seafloor mud “a daunting challenge;” Discovered: jumbo “Dumbo” octopod and its new-to-science cousin; Historic 1st global ocean Census: Oct. 2010. Census of Marine Life scientists have inventoried an astonishing abundance, diversity and distribution of deep sea species that have never known sunlight – creatures that somehow manage a living in a frigid black world down to 5000 meters (three miles) below the ocean waves. Revealed via deep-towed cameras, sonar and other vanguard technologies, animals known to thrive in an eternal watery darkness now number 17,650, a diverse collection of species ranging from crabs to shrimp to worms. Most have adapted to diets based on meager droppings from the sunlit layer above, others to diets of bacteria that break down oil, sulfur and methane, the sunken bones of dead whales and other implausible foods. Five of the Census’ 14 field projects plumb the ocean beyond light, each dedicated to the study of life in progressively deeper realms – from the continental margins (project COMARGE: Continental Margins Ecosystems) to the spine-like ridge running down the mid-Atlantic
(MAR-ECO: Mid-Atlantic Ridge Ecosystem Project), the submerged mountains rising from the seafloor (CenSeam: Global Census of Marine Life on Seamounts), the muddy floor of ocean plains (CeDAMar: Census of Diversity of Abyssal Marine Life), and the vents, seeps, whale falls and chemically-driven ecosystems found on the margins of mid-ocean ridges and in the deepest ocean trenches (ChEss:Biogeography of Deep-Water Chemosynthetic Systems). The number of records in OBIS (Ocean Biogeographic Information System), the Census’ inventory of marine life observations, falls off dramatically at deeper depths — a function of the dearth of sampling done in the deep sea. OBIS today records 5,722 species for which all observations are deeper than 1,000 meters and 17,646 species for which all observations are deeper than 200 meters, the depth where darkness stops photosynthesis. While the collective findings are still being analyzed for release as part of the final Census report in London, Oct 4, 2010, scientists say patterns of the abundance, distribution and diversity of deep-sea life around the world are already apparent. “Abundance is mostly a function of available food and decreases rapidly with depth,” says Robert S. Carney of Louisiana State University, co-leader of the Census project COMARGE, studying life along the world’s continental margins. Abundance in the deep sea requires one or more of the following:
* Swift current, which increases an animal’s chance of encountering food; * Long-lived animals, populations of which grow numerous even on a meager diet; * Abundant food in higher layers that either settles to the depths or to which deep animals can migrate; * An alternative to photosynthesis of food, such as chemosynthetic production. With respect to distribution, Dr. Carney says the composition of faunal populations changes with depth, likely a consequence of physiology, ecology and the suitability of seafloor habitat condition for certain animals. “Diversity is harder to understand. Although the mud on the deep sea floor appears monotonous and poor in food, that monotonous mud has a maximum of species diversity on the lower continental margin. To survive in the deep, animals must find and exploit meager or novel resources, and their great diversity in the deep reflects how many ways there are to adapt.” Specific discoveries, some beautiful and all pushing back the frontiers of the unknown, illustrate the results of voyages by the five Census projects exploring the dark deep sea. Heading the list: At 1,000 to 3,000 meters: A very large specimen of a rare, primitive octopod, commonly called “Dumbos” because they flap a pair of large ear-like fins to swim, akin to the cartoon flying elephant. The jumbo Dumbo netted by Census explorers was estimated to be nearly two meters long and, at 6 kg, the largest of only a few specimens of the species ever obtained. Altogether, nine species of gelatinous “Dumbos” were collected on the Mid-Atlantic Ridge, including one that may be new to science. These animals rank among the largest in the deep sea.
Sometimes, almost all creatures collected in hauls of mud from the abyssal plains are new to science, says CeDAMar expert David Billett of the the UK’s National Oceanography Centre. “The abyssal fauna is so rich in species diversity and so poorly described that collecting a known species is an anomaly,” says Dr. Billet. “Describing for the first time all the different species in any coffee cup-sized sample of deep-sea sediment is a daunting challenge.” “There is both a great lack of information about the ‘abyss’ and substantial misinformation,” says Dr. Carney. “Many species live there. However, the abyss has long been viewed as a desert. Worse, it was viewed as a wasteland where few to no environmental impacts could be of any concern. ‘Mine it, drill it, dispose into it, or fish it — what could possibly be impacted? And, if there is an impact, the abyss is vast and best yet, hidden from sight.’ “CoML deep realm scientists see and are concerned.” Census of Marine Life. Started in 2000, the Census is an international science research program with the goal of assessing and explaining the diversity, distribution and abundance of marine life. It is supported by private sources and government agencies the world over. The Census of Marine Life 2010: A Decade of Discovery, to be released in London in October 2010, will address three questions: • What lived in the ocean? • What lives in the ocean? • What will live in the ocean? news from chinese.eurekalert.org
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