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Shelf Areas (shelf + area)
Selected AbstractsMollusk species diversity in the Southeastern Pacific: why are there more species towards the pole?ECOGRAPHY, Issue 2 2003Claudio Valdovinos The most ubiquitous and well recognized diversity pattern at large spatial scales is the latitudinal increase in species richness near the equator and decline towards the poles. Although several exceptions to this pattern have been documented, shallow water mollusks, the most specious group of marine invertebrates, are the epitome of the monotonic decline in species diversity toward higher latitudes along the Pacific and Atlantic coasts of North America. Here we analyze the geographic diversity of 629 mollusk species along the Pacific South American shelf. Our analyses are based on the most complete database of invertebrates assembled for this region of the world, consisting of latitudinal ranges of over 95% of all described mollusks between 10° and 55°S. Along this coast, mollusk diversity did not follow the typical latitudinal trend. The number of species remained constant and relatively low at intermediate latitudes and sharply increased toward higher latitudes, south of 42°S. This trend was explained by changes in shelf area, but not by sea surface temperature, unlike the pattern documented for Northern Hemisphere mollusks. Direct sampling of soft bottom communities along the gradient suggests that regional trends in species richness are produced by increased alpha diversity, and not only by artifacts produced by the increase in sampling area. We hypothesize that increased shelf area south of 42°S, geographic isolation produced by divergence of major oceanic currents, and the existence of refugia during glaciations, enabled species diversification. Radiation could have been limited by narrow continental shelves between 10°,42°. Asymmetries in latitudinal diversity trends between hemispheres show that there is not a single general factor determining large-scale diversity patterns. [source] Aspects of the population biology of Cephalopholis fulva from the central coast of BrazilJOURNAL OF APPLIED ICHTHYOLOGY, Issue 3 2009J. N. Araújo Summary Age and size composition samples of Cephalopholis fulva from the central coast of Brazil were collected from research surveys and from line fishery landings between 1997 and 1999. The samples suggest that the submarine banks located further offshore are characterized by having fish larger than those caught in the continental shelf area. Although the oldest specimens were caught in the continental shelf area, only 34.6% of the specimens were older than 10 years as compared to 51.4% in the submarine banks. The observed size and age differences seem to be related to the lower fishing pressure on the submarine banks, although size composition bias resulting from different sampling procedures and different catchability between sites cannot be excluded. A resampling scheme was used to overcome the influences of size composition bias and to generate a three-dimensional plot of parameters as a means to compare the growth between the submarine banks and the continental shelf area; this plot showed no overlap between growth patterns of the two sites. The natural mortality (M) estimate based on the oldest specimen observed was 0.17 year,1. Total mortality (Z) estimated from catch-curve analyses using samples from both areas varied from 0.24 to 0.34 year,1, depending on the age range used. With this level of mortality, the C. fulva stock in the central coast area of Brazil was close to or already at the level of overexploitation in the late 1990s. [source] Relationships between morphological and sedimentological parameters in source-to-sink systems: a basis for predicting semi-quantitative characteristics in subsurface systemsBASIN RESEARCH, Issue 4 2009Tor O. Sømme ABSTRACT The study of source-to-sink systems relates long-term variations in sediment flux to morphogenic evolution of erosional,depositional systems. These variations are caused by an intricate combination of autogenic and allogenic forcing mechanisms that operate on multiple time scales , from individual transport events to large-scale filling of basins. In order to achieve a better understanding of how these mechanisms influence morphological characteristics on different scales, 29 submodern source-to-sink systems have been investigated. The study is based on measurements of morphological parameters from catchments, shelves and slopes derived from a ,1 km global digital elevation model dataset, in combination with data on basin floor fans, sediment supply, water discharge and deposition rates derived from published literature. By comparing various morphological and sedimentological parameters within and between individual systems, a number of relationships governing system evolution and behaviour are identified. The results suggest that the amount of low-gradient floodplain area and river channel gradient are good indicators for catchment storage potential. Catchment area and river channel length is also related to shelf area and shelf width, respectively. Similarly to the floodplain area, these parameters are important for long-term storage of sediment on the shelf platform. Additionally, the basin floor fan area is correlative to the long-term deposition rate and the slope length. The slope length thus proves to be a useful parameter linking proximal and distal segments in source-to-sink systems. The relationships observed in this study provide insight into segment scale development of source-to-sink systems, and an understanding of these relationships in modern systems may result in improved knowledge on internal and external development of source-to-sink systems over geological time scales. They also allow for the development of a set of semi-quantitative guidelines that can be used to predict similar relationships in other systems where data from individual system segments are missing or lacking. [source] Species richness of marine Bryozoa in the continental shelf and slope off Argentina (south-west Atlantic)DIVERSITY AND DISTRIBUTIONS, Issue 1 2000Juan López Gappa Abstract., A total of 246 marine bryozoan species was recorded within an area of the south-west Atlantic between 35° and 56°S, and between the coast of Argentina and 50°W. The distribution pattern of benthic stations surveyed during the most important cruises in the area shows that the sampling effort has been biased towards southern shelf areas off Santa Cruz and Tierra del Fuego, as well as around the Malvinas (Falkland) islands. The littoral zone, Patagonian gulfs and the continental shelf off Chubut, Río Negro and Buenos Aires state received less attention, and should be surveyed more intensively in the future. Only 2% of the species can be regarded as non-indigenous, all of them inhabiting biofouling communities in harbour environments. With the exception of some thoroughly surveyed localities, the number of species recorded for different areas of the coast, shelf and slope is estimated to be just a small fraction of the actual number of species present. A distinct diversity gradient was found, with species-rich stations located only in the southern shelf. Highest diversity occurred in shelf areas dominated by coarse sediments, and along a high-productivity shelf-break front. A remarkable decrease in species richness was found in inner and middle shelf areas off Chubut, Río Negro and Buenos Aires state. This pattern may be related to the Pacific origin of the Magellanic fauna, since the diversity of bryozoans is higher in the Pacific than in the Atlantic Ocean. The trend of species richness is, however, overemphasized by the fact that the least diverse faunistic assemblage occurs in areas where surveys have been relatively less frequent. An up-to-date checklist of species recorded for the study area is included. [source] An individual-based model of the early life history of mackerel (Scomber scombrus) in the eastern North Atlantic, simulating transport, growth and mortalityFISHERIES OCEANOGRAPHY, Issue 6 2004J. Bartsch Abstract The main purpose of this paper is to provide the core description of the modelling exercise within the Shelf Edge Advection Mortality And Recruitment (SEAMAR) programme. An individual-based model (IBM) was developed for the prediction of year-to-year survival of the early life-history stages of mackerel (Scomber scombrus) in the eastern North Atlantic. The IBM is one of two components of the model system. The first component is a circulation model to provide physical input data for the IBM. The circulation model is a geographical variant of the HAMburg Shelf Ocean Model (HAMSOM). The second component is the IBM, which is an i-space configuration model in which large numbers of individuals are followed as discrete entities to simulate the transport, growth and mortality of mackerel eggs, larvae and post-larvae. Larval and post-larval growth is modelled as a function of length, temperature and food distribution; mortality is modelled as a function of length and absolute growth rate. Each particle is considered as a super-individual representing 106 eggs at the outset of the simulation, and then declining according to the mortality function. Simulations were carried out for the years 1998,2000. Results showed concentrations of particles at Porcupine Bank and the adjacent Irish shelf, along the Celtic Sea shelf-edge, and in the southern Bay of Biscay. High survival was observed only at Porcupine and the adjacent shelf areas, and, more patchily, around the coastal margin of Biscay. The low survival along the shelf-edge of the Celtic Sea was due to the consistently low estimates of food availability in that area. [source] Ecological relevance of laboratory determined temperature limits: colonization potential, biogeography and resilience of Antarctic invertebrates to environmental changeGLOBAL CHANGE BIOLOGY, Issue 11 2010D. K. A. BARNES Abstract The relevance of laboratory experiments in predicting effects of climate change has been questioned, especially in Antarctica where sea temperatures are remarkably stable. Laboratory studies of Southern Ocean marine animal capacities to survive increasing temperature mainly utilize rapid temperature elevations, 100 ×,10 000 × faster than sea temperature is predicted to rise. However, due to small-scale temperature fluctuations these studies may be crucial for understanding colonization patterns and predicting survival particularly through interactions between thermal tolerance and migration. The colonization of disjunct shelves around Antarctica by larvae or adult drift requires crossing or exposure to, rapid temperature changes of up to 2,4 °C over days to weeks. Analyses of responses to warming at varying rates of temperature change in the laboratory allow better predictions of the potential species have for colonizing disjunct shelf areas (such as the Scotia Arc). Inhabiting greater diversities of localities increases the geographic and thermal range species experience. We suggest a strong link between short-term temperature tolerance, environmental range and prospects for surviving changing environments. [source] THE STRUCTURAL STYLE OF SEDIMENTARY BASINS ON THE SHELVES OF THE LAPTEV SEA AND WESTERN EAST SIBERIAN SEA, SIBERIAN ARCTICJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2005D. Franke A total of 11,700 km of multichannel seismic reflection data were acquired during three recent reconnaissance surveys of the wide, shallow shelves of the Laptev and western East Siberian Seas in the Siberian Arctic Ocean. Three seismic marker horizons were defined and mapped in both shelf areas. Their nature and age were predicted on the basis of regional tectonic and palaeoenvironmental events and corroborated using onshore geology. To the north of the Laptev Sea, the Gakkel Ridge, an active mid-ocean ridge which separates the North American and Eurasian Plates, abruptly meets the steep slope of the continental shelf which is curvilinear in plan view. Extension has affected the Laptev Shelf since at least the Early Tertiary and has resulted in the formation of three major, generally north-south trending rift basins: the Ust'Lena Rift, the Anisin Basin and the New Siberian Basin. The Ust'Lena Rift has a minimum east-west width of 300km at latitude 75°N and a Cenozoic infill up to 6 s (twt) in thickness. Further to the NW of the Laptev Shelf, the downthrown and faulted basement is overlain by a sub-parallel layered sedimentary succession with a thickness of 4 s (twt) that thins towards the west. Although this area was affected by extension as shown by the presence of numerous faults, it is not clear whether this depression on the NW Laptev Shelf is continuous with the Ust'Lena Rift. The Anisin Basin is located in the northern part of the Laptev Shelf and has a Cenozoic sedimentary fill up to 5 s (twt) thick. The deepest part of the basin trends north-south. To the west is a secondary, NW-SE trending depression which is slightly shallower than the main depocentre. The overall structure of the basin is a half-graben with the major bounding fault in the east. The New Siberian Basin is up to 70 km wide and has a minimum NW-SE extent of 300 km. The sedimentary fill is up to 4.5 s (twt) thick. Structurally, the basin is a half-graben with the bounding fault in the east. Our data indicate that the rift basins on the Laptev Shelf are not continuous with those on the East Siberian Shelf. The latter shelf can best be described as an epicontinental platform which has undergone continuous subsidence since the Late Cretaceous. The greatest subsidence occurred in the NE, as manifested by a major depocentre filled with inferred (?)Late Cretaceous to Tertiary sediments up to 5 s (twt) thick. [source] Conserving a subpopulation of the northern Atlantic cod metapopulation with a marine protected areaAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2009Liuming Hu Abstract 1.Marine reserves can play an important role in the conservation of subpopulations of marine fish metapopulations. The population spatial structure of northern Atlantic cod of Newfoundland and Labrador has characteristics of a metapopulation. Subpopulations of northern Atlantic cod on the continental shelf were decimated by decades of overfishing, and have not recovered. The remaining northern cod are concentrated in coastal areas. 2.A Marine Protected Area (MPA) was established in Gilbert Bay, Labrador by the Government of Canada in 2005 to protect the bay's resident subpopulation of northern Atlantic cod. Conservation of Gilbert Bay cod will help protect the genetic diversity of the northern cod metapopulation. 3.Unlike some other MPAs, Gilbert Bay is not a harvest refugium or ,no-take' reserve. Aboriginal subsistence fisheries for salmonids with a bycatch of cod are allowed in designated areas of the MPA. A recreational fishery for Atlantic cod by angling open to all people is under consideration. Management of the MPA must ensure that fishing activities do not endanger the local cod population. 4.The population dynamics of Gilbert Bay cod were simulated using an age-structured Leslie matrix model to estimate the total mortality under various recreational fishing scenarios. The level of sustainable harvest by a recreational fishery depends on the natural mortality of the Gilbert Bay cod population, which is unknown. Therefore, there is risk in permitting a recreational fishery in the MPA. 5.There may be benefits to the northern cod metapopulation, if the Gilbert Bay subpopulation is allowed to rebuild to the carrying capacity of the bay. If the abundance of Gilbert Bay cod exceeds the level which the local marine ecosystem can support, some cod may emigrate from the bay and recolonize adjacent coastal areas. The potential for Gilbert Bay cod to recolonize continental shelf areas is less certain. Copyright © 2008 John Wiley & Sons, Ltd. [source] Influence of point-source sediment-supply on modern shelf-slope morphology: implications for interpretation of ancient shelf marginsBASIN RESEARCH, Issue 5 2009Cornel Olariu ABSTRACT Present sea-floor bathymetry indicates that the continental-shelf and shelf-break morphology have some unique and predictable characteristics in areas with and without high sediment supply. Using a global bathymetry dataset in open shelf areas in front of rivers that discharge over 25 × 106 tons of sediment per year, five distinct accretionary types of shelf-break are distinguished based on along-shelf gradient variability and inferred shelf-break trajectory. Morphological characteristics of river-mouth shelves (compared with adjacent areas lateral to the immediate fairway of the river) are: (1) an overall lower gradient and greater width, and (2) a relatively high slope gradient/shelf gradient ratio. The exceptions are shelves with active shelf-edge deltas; these are narrower, steeper and have an attenuated shelf break in front of rivers. These observations are at seismic scale and have direct implications for the recognition and positioning of principal cross-shelf, supply fairways on ancient shelves or shelf margins, and therefore the potential by-pass routes for deepwater sands. Higher slope/shelf gradient ratios in areas of actively accreting margins, where the shelf-break is more prominent and easier to recognize on seismic data compared with adjacent areas, predict areas with high sediment supply. Along-strike morphological changes on supply-dominated shelves suggest that identification of the sediment-feed route and depocenter relative to the shelf break during a relative sea level cycle are critical for understanding/predicting the 3-D architecture of the shelf-slope-basin floor clinoform. [source] | |||||||||||||