MESOZOOPLANKTON GRAZING IN THE SOUTHERN CALIFORNIA BIGHT .2. GRAZING IMPACT AND PARTICULATE FLUX

Citation
Mr. Landry et al., MESOZOOPLANKTON GRAZING IN THE SOUTHERN CALIFORNIA BIGHT .2. GRAZING IMPACT AND PARTICULATE FLUX, Marine ecology. Progress series, 115(1-2), 1994, pp. 73-85
Citations number
78
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Marine & Freshwater Biology",Ecology
ISSN journal
0171-8630
Volume
115
Issue
1-2
Year of publication
1994
Pages
73 - 85
Database
ISI
SICI code
0171-8630(1994)115:1-2<73:MGITSC>2.0.ZU;2-3
Abstract
Mesozooplankton grazing on phytoplankton, as inferred from gut pigment contents and gut evacuation rates, was studied in relation to primary production and particulate export flux on 6 cruises in the Santa Moni ca Basin, California, USA. Gut evacuation rates did not vary significa ntly among different taxa or size classes examined and were consistent with extrapolations of published temperature relationships. Shipboard incubations with cultured phytoplankton and net-collected zooplankton indicated a seasonal difference in the extent to which gut passage co nverts chlorophyll to non-fluorescent by-products. In autumn experimen ts, only about 5% of ingested chlorophyll could not be recovered as ph aeopigment. In winter-spring experiments, approximately 70% of ingeste d chlorophyll (chl) was destroyed. In contrast, other indices of pigme nt destruction, the ingestion rates of a dominant copepod species and the ratio of water-column phaeopigment:silica fluxes, did not reveal a significant gut passage effect during winter-spring cruises. Mesozoop lankton community grazing impact varied from 1.7 to 7.3 mg chi m(-2) d (-1), with higher grazing during the winter-spring period (mean = 5.8 mg chi m(-2) d(-1)) as compared to the autumn (mean = 2.3 mg chi m(-2) d(-1)). On average, mesozooplankton grazing accounted for a loss of 1 1.7% of chlorophyll standing stock d(-1) with a 6 cruise range of 6 to 18% d(-1). Mesozooplankton grazing on phytoplankton accounted for 29 to 44% (mean = 39%) of measured primary production for the winter-spri ng cruises, but only 16 to 24% (mean = 19%) of production in the autum n. From measured phaeopigment fluxes into sediment traps below the eup hotic zone, only 27.5% (range 23 to 32%) of this grazing on phytoplank ton could be accounted for as export flux. Thus, in terms of contribut ion to particulate flux or remineralization, most mesozooplankton graz ing in the Santa Monica Basin was functionally equivalent to that of m icrozooplankton. Direct grazing on phytoplankton contributed 15 to 38% of carbon flux into sediment traps during winter-spring and 8 to 13% during autumn. Nonetheless, if feeding on nonpigmented prey is conside red from the available information on carbon:phaeopigment ratios of fr esh fecal pellets, over 70% of the carbon flux to traps could have a m esozooplankton grazing origin.