Living on the edge: feeding of subtropical open ocean copepods

Abstract

The objective of this study was to provide quantitative information on environmental feeding rates of warm water oceanic epipelagic copepods. We determined clearance rates at 23 °C for various particle size ranges in shipboard studies in the western oligotrophic subtropical Atlantic Ocean for females of the calanoid species Clausocalanus furcatus and Mecynocera clausii. These in situ clearance rates were then applied to the various particle size ranges of environmental particle spectra of auto‐ and heterotrophs at different depths from three stations in the western Atlantic. After calculating the metabolic demands of each of these two copepod species and applying an assimilation efficiency of 90%, we determined that C. furcatus meets its metabolic demands in all six cases, and M. clausii in two of six cases. Clausocalanus furcatus would also meet its energy demands at 25 °C, where it is often found, while M. clausii at 20 °C, where it is regularly found, would cover its metabolic needs in four of six cases. It is hypothesized that these species, and most likely most of the other co‐occurring copepod species, are limited in their abundance by food availability, or, better said, are ‘living on the edge’ in relation to food abundance.

Oxygen consumption in relation to motion of marine planktonic copepods

“…At 20°C, the occasionally moving Oncaea spp. females (inactive 74.4% of the time, Paffenhöfer et al 2006) metabolized on average 10.5% of their body weight per day, the continuously but slowly moving and feeding current-creating P. aculeatus females (0.33 mm s -1 , Paffenhöfer et al 1996) metabolized 15.1%, and the continuously fast-moving C. furcatus females (6 to 10 mm s …”

“…These experiments were used to calculate the clearance rates (Frost 1972) to be applied to natural food abundances in order to determine their food intake (Table 1). Clearance rates for Clausocalanus furcatus originated from in situ studies in the subtropical open ocean (Table 1, Paffenhöfer et al 2006).…”

“…Are previously quantified ingestion rates (Paffenhöfer et al 2006) sufficient to support the metabolic expenditures presented in this study? Using particle concentrations (µgC l -1 ) quantified for the range from 2 to 40 µm ESD at 3 different stations at 2 different depths in the western tropical and subtropical Atlantic Ocean where Clausocalanus spp.…”

“…Oncaea spp. females are motionless/sinking for 74.4 ± 8.3% (SE) of the time during light hours at 20°C (Paffenhöfer et al 2006). Morris et al (1985) calculated that at a swimming speed of 5.2 body lengths s -1 the metabolism of the copepod Pleuromamma xiphias (6 mm prosome length) was 3.1. times higher that its standard (non-moving) metabolism.…”

“…So far, evaluations of metabolic expenditures in relation to motion have been based on fluid dynamics theory. ) of P. aculeatus females at 20°C at various particle size ranges feeding on different phytoplankton species at total concentrations ranging from 5 to 15 µgC l -1 and comparative data for C. furcatus females at 23°C, feeding on in situ particles (Paffenhöfer et al 2006 most advanced modeling effort for copepod swimming expenditures was made by Morris et al (1985). They included variables such as mechanical energy required for appendage movement, kinetic energy dissipation in the fluid, and metabolic costs of swimming in their assessment.…”