Strong depth-related zonation of megabenthos on a rocky continental margin (∼700-4000 m) off southern Tasmania, Australia.
Assemblages of megabenthos are structured in seven depth-related zones between ∼700 and 4000 m on the rocky and topographically complex continental margin south of Tasmania, southeastern Australia. These patterns emerge from analysis of imagery and specimen collections taken from a suite of surveys using photographic and in situ sampling by epibenthic sleds, towed video cameras, an autonomous underwater vehicle and a remotely operated vehicle (ROV). Seamount peaks in shallow zones had relatively low biomass and low diversity assemblages, which may be in part natural and in part due to effects of bottom trawl fishing. Species richness was highest at intermediate depths (1000-1300 m) as a result of an extensive coral reef community based on the bioherm-forming scleractinian Solenosmilia variabilis. However, megabenthos abundance peaked in a deeper, low diversity assemblage at 2000-2500 m. The S. variabilis reef and the deep biomass zone were separated by an extensive dead, sub-fossil S. variabilis reef and a relatively low biomass stratum on volcanic rock roughly coincident with the oxygen minimum layer. Below 2400 m, megabenthos was increasingly sparse, though punctuated by occasional small pockets of relatively high diversity and biomass. Nonetheless, megabenthic organisms were observed in the vast majority of photographs on all seabed habitats and to the maximum depths observed--a sandy plain below 3950 m. Taxonomic studies in progress suggest that the observed depth zonation is based in part on changing species mixes with depth, but also an underlying commonality to much of the seamount and rocky substrate biota across all depths. Although the mechanisms supporting the extraordinarily high biomass in 2000-2500 m depths remains obscure, plausible explanations include equatorwards lateral transport of polar production and/or a response to depth-stratified oxygen availability.
CSIRO Wealth from Oceans Flagship, Hobart, Tasmania, Australia.
Ronald
R
Thresher
CSIRO Wealth from Oceans Flagship, Hobart, Tasmania, Australia.
Franziska
F
Althaus
California Institute of Technology, Pasadena, California, United States of America.
Jess
J
Adkins
CSIRO Wealth from Oceans Flagship, Hobart, Tasmania, Australia.
Karen
K
Gowlett-Holmes
CSIRO Wealth from Oceans Flagship, Hobart, Tasmania, Australia.
Phil
P
Alderslade
CSIRO Wealth from Oceans Flagship, Hobart, Tasmania, Australia.
Jo
J
Dowdney
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, United States of America.
Walter
W
Cho
California Institute of Technology, Pasadena, California, United States of America.
Alex
A
Gagnon
Museum of Victoria, Melbourne, Victoria, Australia.
David
D
Staples
CSIRO Wealth from Oceans Flagship, Hobart, Tasmania, Australia.
Felicity
F
McEnnulty
CSIRO Wealth from Oceans Flagship, Hobart, Tasmania, Australia.
Alan
A
Williams
D000818:Animals; D037421:Anthozoa / Q000502:physiology*; D018533:Biomass; D058448:Biota / Q000502:physiology*; D016000:Cluster Analysis; D057894:Coral Reefs; D017753:Ecosystem; D005580:Fossils; D005843:Geography; D008386:Marine Biology / Q000379:methods*; D011157:Population Dynamics; D054712:Salinity; D012623:Seawater / Q000737:chemistry; D013045:Species Specificity; D013648:Tasmania; D013696:Temperature