Migratory and grazing behavior of copepods and vertical distribution of phytoplankton

The vertical distribution and grazing activity of copepods was studied during the summer of 1985 throughout the North Sea. In most areas, copepods did not vertically migrated and their vertical distribution followed that of the phytoplankton which was restricted to the upper 20-30 m. This behavior may be a consequence of barely sufficient or limiting food concentrations (about 200 mg multiplied by m-3. The diel grazing patterns as a function of variations in phytoplankton are described for the dominant zooplankton species: Calanus finmarchicus, Oithona similis, Temora longicornis, Pseudocalanus elongatus, Acartia spp., Centropages hamatus, Microsetella spp</i

Calculations of zooplankton grazing rates according to a closed, steady-state, three-compartment model applied to different¹⁴C methods

A re-examination of the numerical example of the three-compartment model by CONOVER & FRANCIS (1973) showed that the warning by these authors for the misuse of radio isotopes in transfer studies within food chains is incorrect and based on a misinterpretation of their results. There is no difference in the estimate of transfer rate by use of specific activities or by use of total radioactivities observed in each compartment.After adapting the formulae developed by CONOVER & FRANCIS, their model was used to illustrate deviations of the programmed grazing rate in 3 types of grazing experiments; a) with 14C present only in the phytoplankton at the start of the experiment, b) with 14C only in the water, and c) with 14C in both phytoplankton and water. Up to a duration of the grazing experiment of 2 hours, and at various light conditions and grazing pressures, deviations were small and did not exceed 4%. These results are not directly applicable to practical work because the quantitatively important loss by egestion of radioactive material was not accounted for, only losses by respiration were incorporated in the closed, steady-state model.Best calculations of the community filtering rate (fraction of the volume of the grazing vessel swept clear per day) were generally obtained with the formula (with t in hours) lsquo((DPM zoo at time t)/(DPM phyto at 0+DPM phyto at t)/2)×24/trsquo, applicable to all three types of grazing experiments considered

A simplified ¹⁴C method for grazing measurements on natural planktonic populations

The method used consists of adding highly radioactive material (40 µCi/l NaH14CO3) to sea water with its natural concentrations of zoo- and phytoplankton, incubating this water in the light, separating zoo- from phytoplankton after 1h or at the most 2h and measuring the radioactivity of both. Under such conditions, the concentration of the tracer in phytoplankton can be simplified as a linear function of time, and that of the zooplankton as a parabolic function of time. This simplification leads to an overestimation of grazing of at most 2-3%. Comparisons with the Coulter Counter method are given and discussed

Etude écologique d'un brise-lames de la côte belge: 1. Description et zonation des organismes

The studied break-water is an ecological system, exposed at high variable and extreme conditions: exposed medium, often violent wind, very cold in winter and sometimes hot during summertime. Even more, the coast water is polluated by the mouth of the Schelde. The fauna here is essentially northern, very reduced in relation to species, but with an abondance of individuals, specialized to this extreme conditions. This few species are distributed in very precise zones on the breakwater. We put the attention on these animal and plant-associations, caracteristic for each important species

Copepod composition, abundance and diversity in Makupa Creek, Mombasa, Kenya

The taxonomic composition, abundance and spatio-temporal distribution of copepods were analysed from monthly zooplankton samples collected in Makupa creek and Mombasa Harbour (Makupa creek was until recently subjected to considerable dumping of domestic and industrial waste). At least 51 copepod species belonging to 38 genera in the families Calanoida (25), Harpacticoida (5), Poecilostomatoida (7) and Cyclopoida (1) were identified. The most common genera were Acartia, Acrocalanus, Corycaeus, Oncaea and Oithona. Copepods bloomed in the wet months of November and April (75 to 158/m³). Abundance was consistently high near the creek mouth and low within the creek enclosure. Copepod diversity (H’) was slightly higher (2.00 to 2.57) during September, November, December, January, May and June and lower (1.30 to 1.95) in the remaining months. Evenness (J) was, however, relatively constant (0.67 to 0.84) during the entire sampling period. These results point to suppressed copepod diversity and abundance in Makupa Creek, and possible reasons for this, which may include environmental degradation caused by pollution, are presented