Offshore Habitats Research Articles

Diversity of Benthic Foraminifera on the Georgia Continental Shelf

Research Article| June 01, 1974 Diversity of Benthic Foraminifera on the Georgia Continental Shelf BARUN K. SEN GUPTA; BARUN K. SEN GUPTA 1Department of Geology, University of Georgia, Athens, Georgia 30602 Search for other works by this author on: GSW Google Scholar RICHARD T. KILBOURNE RICHARD T. KILBOURNE 1Department of Geology, University of Georgia, Athens, Georgia 30602 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1974) 85 (6): 969–972. https://doi.org/10.1130/0016-7606(1974)85<969:DOBFOT>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation BARUN K. SEN GUPTA, RICHARD T. KILBOURNE; Diversity of Benthic Foraminifera on the Georgia Continental Shelf. GSA Bulletin 1974;; 85 (6): 969–972. doi: https://doi.org/10.1130/0016-7606(1974)85<969:DOBFOT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Two indices of species diversity, the species number s and the Shannon-Wiener function H̄, bring out the difference between the benthic foraminiferal assemblages on the inner part of the Georgia continental shelf and those on the middle and outer parts. The diversity values rise from the shoreline to water depths of about 15 m. From 15 m to the shelf edge (at about 50 m) and beyond, the values remain steady or increase very slightly, with s nearly 50 and H̄ nearly 3. This may be explained by the fact that in terms of variations in water temperature, salinity, and substrate conditions, the nearshore habitat on the Georgia shelf is much more “unstable” or “unpredictable” than the offshore habitat. Such differences in diversity gradients could be expected in comparable late Tertiary foraminiferal assemblages. Foraminiferal equitability values on the different parts of the Georgia shelf do not show any distinct trends. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The fauna of the 100 feet beach clays

I. Introduction. The marine and estuarine clays and sands associated with the 100 feet beach in Scotland have been exhaustively treated in papers and monographs by Brady, Crosskey, Robertson, and others. These workers all remark on the curiously mixed character of their fossil fauna. This contains forms now living in Arctic seas as well as those of more temperate climate, and species of both littoral and off-shore habitats. Although Robertson (8, p. 283) thought that in the clays from at least one locality the deep-water forms were to be found at a lower level than the littoral species, this can by no means be universally established and in general there appears to be no clear separation. The arctic nature of the fauna seems to have become almost a popular belief, in spite of Robertson's criticism (8, p. 114), because of the presence of a few arctic species. But, although due regard must be paid to the significance of minorities, the character of a population is primarily determined by the kind of individuals comprising the bulk of its members. Existing fossil lists, consisting as they usually do, of the names of species recognised in the clays, can at the best give only a very limited and often unsatisfactory picture of the true nature of the population. In 1938 extensions of the sewer system in the Paisley district exposed a number of new sections in the 100 feet beach clays. These were examined by Dr M. Macgregor, Mr W. Fisher and myself

The passamaquoddy tidal-power project

The colonial ascidian Didemnum sp. has colonized northwestern Atlantic coastal habitats from southern Long Island, New York, to Eastport, Maine. It is also present in offshore habitats of the Georges Bank fishing grounds. It threatens to alter fisheries habitats and shellfish aquacultures.Observations in a tide pool at Sandwich, MA from December 2003 to February 2006 show that Didemnum sp. tolerates water temperatures ranging from ≤ 1 to > 24°C, with daily changes of up to 11 °C. It attaches to pebbles, cobbles, and boulders, and it overgrows other tunicates, seaweeds, sponges, and bivalves. From May to mid July, colonies appear as small patches on the bottoms of rocks. Colonies grow rapidly from July to September, with some growth into December, and they range in color from pink to pale yellow to pale orange. Colony health declines from October through April, presumably in response to changes in water temperatures, and this degenerative process is manifested by color changes, by the appearance of small dark brown spots that represent clumps of fecal pellets in the colony, by scavenging by periwinkles, and by a peeling-away of colonies from the sides of cobbles and boulders. At Sandwich, colonies died that were exposed to air at low tide. The species does not exhibit this seasonal cycle of growth and decline in subtidal habitats (40–65 m) on the Georges Bank fishing grounds where the daily climate is relatively stable and annual water temperatures range from 4 to 15 °C. Experiments in the tide pool with small colony fragments (5 to 9 cm2) show they re-attach and grow rapidly by asexual budding, increasing in size 6- to 11-fold in the first 15 days. Didemnum sp. at Sandwich has no known predators except for common periwinkles (Littorina littorea) that graze on degenerating colonies in the October to April time period and whenever colonies are stressed by desiccation.The tendencies of the ascidian (1) to attach to firm substrates, (2) to rapidly overgrow other species, (3) to tolerate a wide temperature range, (4) to be free from predation, and (5) to spread by colony fragmentation combine to make it a potential threat to benthic marine habitats and aquacultures. Didemnum sp. is known to overgrow mussels, oysters, and sea scallops, and it likely envelops other bivalves too.