Halosphaera viridis, Ditylum brightwellii and other phytoplankton in the north-eastern North Atlantic in spring: sinking, rising and relative abundance
Jenkinson, I.R. (1986). Halosphaera viridis, Ditylum brightwellii and other phytoplankton in the north-eastern North Atlantic in spring: sinking, rising and relative abundance, in: Muus, K. (Ed.) Proceedings of the 20th European Marine Biology Symposium: Nutrient Cycling. Processes in Marine Sediments, Hirtshals, Denmark, 9-13 September 1985. Ophelia: International Journal of Marine Biology, 26: pp. 233-253
In: Muus, K. (Ed.) (1986). Proceedings of the 20th European Marine Biology Symposium: Nutrient Cycling. Processes in Marine Sediments, Hirtshals, Denmark, 9-13 September 1985. Ophelia: International Journal of Marine Biology, 26. Ophelia Publications: Helsingør. ISBN 87-981066-4-3. 477 pp., more
In: Ophelia: International Journal of Marine Biology. Ophelia Publications: Helsingør. ISSN 0078-5326, more
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Document type: Conference paper
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| Abstract |
For a period when the spring bloom was recovering, after destruction of the summer thermocline by strong winds, at a station (51°00'N, 13°00'W) in the Porcupine Seabight, net phytoplankton was recorded from ~100-m thick layers from the surface to 1020 m. Net phytoplankton was also caught sequentially at nine discrete depths from 0 to 100 m. The phytoplankton was examined fresh on board and ashore after preservation. Taxa were ascribed by estimation (limitations of this method are discussed) to four categories of biomass abundance. The phytoplankton in samples from above 200 m was dominated by Ditylum brightwellii, and below this depth by Halosphaera viridis, large solitary centric diatoms, or D. brightwellii. The percentage of Ditylum present in fresh samples as 'spherical masses' (SMs) within frustules was estimated. This percentage was >-99% below the newly formed summer thermocline, and -70% or less above. This bimodal distribution of SM percentage in samples may represent different in situ physiological states in Ditylum above and below the thermocline, due to a difference in mean light levels. A newly developed apparatus for determining the maximum sinking rate of phytoplankton populations was tested on board using three experimental approaches. The results given illustrate some merits and problems of the methodology. Maximum sinking rate in vitro was between 64 and 134 m. day-1, the material first to sink consisting of a variety of the taxa present, but with no Halosphaera, suggesting that sinking might have occurred as multispecific aggregates. Rising material consisted solely of Halosphaera. Maximum sinking speed in situ, estimated from vertical distribution of phytoplankton in hauls, was estimated as at least 39 m. day-1 at the station worked. From the time of the photographed arrival of phytodetritus at the bottom at another Seabight station (Lampitt 1985), maximum sinking speed is estimated at roughly 80 m.day-1, consistent with in vitro rates within the wide limits given. Rising Halosphaera represents an upward organic flux whose magnitude, along with that of fluxes of any associated materials such as nutrients and radionuclides, is unknown. |
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