Influence of pore size of plankton nets and towing speed on the sampling performance of two high-speed samplers (Delfino I and II) and its consequences for the assessment of plankton populations

Is Oithona the most important copepod in the world's oceans?

“…Vertical net hauls are typically carried out at 0.5-1 m s -1 , but the higher speed of haul is not likely to produce significantly lower retention, and some research shows that retention may increase at higher tow speeds, even for the smallest metazoan zooplankton (Bernhard et al, 1973). Nevertheless, we believe that these data represent a reasonable estimate of likely net mesh selection effects on numbers and biomass for towed and vertically hauled nets.…”

“…Several studies have determined losses for smaller taxa (Saville, 1958;Vannucci, 1968;Bernhard et al, 1973;Evans and Sell, 1985;Nichols and Thompson, 1991;Krsinic and Lucic, 1994;Calbet et al, 2001)-up to 92% for Oithona, 78% for Microcalanus and 52% for Pseudocalanus. Krsinic and Lucic (Krsinic and Lucic, 1994), using a 250 µm net, estimate retention at only 1.2% for Oithona nana and 16.2% for calanoids (comprising 63.3% Paracalanus parvus and 31% Pseudocalanus elongatus).…”

“…Copepodite and adult stages of important groups such as Acartia, Calocalanus, Clausocalanus, Corycaeus, Microcalanus, Paracalanus, Pseudocalanus, Oithona, Oncaea, Temora and most harpacticoids, as well as polychaete larvae, invertebrate eggs and naupliar stages, are therefore undersampled or missed altogether in many studies. The consensus is that a mesh size of 75% of the width of the smallest animal to be sampled is required for quantitative sampling (Bernhard et al, 1973;Nichols and Thompson, 1991).…”

The Vertical Distribution of Zooplankton in Relation to Habitat Zones in the Area of the Atlantis II Deep, Central Red Sea

“…The contamination estimates (Weikert and John, 1981) were corroborated by recent investigations comparing vertical and horizontal tows, the latter yielding markedly smaller proportions of the following taxa: Appendicularia; Gastropoda (veligers); certain Pteropoda Euthecosomata, and Copepoda. Organisms may have entered in shallow water while the closed nets were being retrieved, or they may not have been removed when the nets were washed down after the preceding haul (Bernhard et al, 1973). Wet weight was measured by the method of Tranter (1962) after removal of occasional coelenterates and salps larger than 0.5 cm.…”