Scales of spatial and temporal variability in the nighttime distribution of siphonophores in the north Atlantic Ocean at Bermuda /
Siphonophores were enumerated in open net and closing net collections from Bermuda, 1986-1993. A total 118 meter net collections were evaluated, which were collected a) on one Summer night in each of 1986, 1989, and 1991, b) one night per month during 1991-92, and c) on 3 consecutive Summer nights...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1995.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=742145231&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Siphonophores were enumerated in open net and closing net collections from Bermuda, 1986-1993. A total 118 meter net collections were evaluated, which were collected a) on one Summer night in each of 1986, 1989, and 1991, b) one night per month during 1991-92, and c) on 3 consecutive Summer nights of 1992. In addition, 195 MOCNESS collections were evaluated from 4 cruises in different seasons during 1992-93. The mean biomass of siphonophores in the meter net collections was 1.4 ︢0.6 ml 100 M-3, or about 20 ︢10% of the total catch volume (WDV). Calycophorae species were most abundant. The 6 most common species: Chelophyes appendiculata, Eudoxoides mitra, Lensia subtilis, Eudoxoides spiralis, Bassia bassensis, and Abylopsis eschscholtzi, comprised >67% of all individuals. Mean numerical abundance or WDV of siphonophores varied little on space scales of 30-50 miles (between Hydrostation-S and BATS station), or during 3 consecutive Summer nights, but variability increased seasonally and interannually and over space scales >100 miles. On a time scale of hours, species groups from midnight (21:0003:00) were less variable than those collected near dusk and dawn; dusk collections were distinct from those made after midnight. In the monthly collections, 3 seasonal groups were detected, with a Winter group being the most distinct from the others. Although only about I % of the siphonophores collected in the open nets were retained by the larger mesh MOC-10 nets, 41 Calycophorae and 11 Physonectae species were represented. E. mitra and C appendiculata were the 2 most common species overall; together they equalled 38% of total calycophore numbers. Four of the 10 most common species make diel vertical migrations, but overall >67% of the WDV biomass and >80% of the numbers of most siphonophore were found in the upper 100 m. While many species co-occurred, they did not always co-vary in abundance. Polygastric and eudoxid generations of the same species usually co-varied in the open net collections, but this was not always the case in the MOCNESS net. The distribution of some species was correlated with seasonal patterns of temperature/salinity structure (i.e. the depth of mixed layer) and biological factors (i.e. salp bloom) but not to moonlight. |
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| Item Description: | Vita. "Major Subject: Oceanography". |
| Physical Description: | xiv, 216 leaves : illustrations, maps ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |