8 research outputs found
Multivariate statistical analysis of net diatom species distributions in the Southwestern Atlantic and Indian Ocean
Vertical net haul diatom assemblages from near South Georgia, and from between Africa and Antarctica, were examined and compared. Variation among South Georgia stations was examined by principal component, cluster and canonical discriminant analyses. Diatom distributions provide evidence for at least two distinct water masses. The region north of the island is characterized by neritic, temperate diatoms and by an assemblage with low species diversity. The region south of the island is characterized by oceanic, antarctic species and relatively high species diversity. The regions are most distinct to the west of the island, intergrading east of the island. Within the north-south division, five station groupings were detected on the basis of distribution of dominant net diatoms. By comparing classical species ecological categorizations to results of principal component analysis, a “neritic-oceanic” factor was identified from net diatom distributions. This factor was common to both areas in spite of the fact that Biscoe and Agulhas collections were from different seasons.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46982/1/300_2004_Article_BF00446041.pd
Morphological adaptation of a planktonic diatom to growth in Antarctic sea ice.
Chaetoceros dichaeta Ehrenberg is one of the
most important planktonic diatom species in the Southern
Ocean, making a significant contribution to the total biomass
in the region. Our observations on both field and
culture material have revealed the existence of a specialized
form of C. dichaeta adapted to living in sea ice. This
sea ice form differs from the planktonic form by the shape
and orientation of the setae and the aperture length between
sibling cells. Thus, the diameter of the chain is equivalent
to the apical axes of the cells and is accompanied by a two
order of magnitude decrease in minimal space requirement.
Here, we report for the first time on the extraordinary
overwintering strategy of a planktonic diatom in sea ice
facilitated by its rapid morphological adaptation to
changing environmental conditions. This morphological
plasticity enables it to thrive in the confined space of the
sea ice brine matrix and retain its numerical dominance in
recurrent growing seasons and has likely evolved to
optimally exploit the dynamic ecosystem of the seasonally
ice-covered seas of the Southern Ocean