Abstract
Copepods are among the most abundant and diverse groups of mesozooplankton in the world's oceans. Each species has a certain depth range within which different individuals (of the same life stage and sex) are found. Lipids are accumulated in many calanoid copepods for energy storage and reproduction. Lipid content in some species increases with depth, however studies so far focused mostly on temperate and high-latitude seasonal vertically migrating copepods and compared lipid contents among individuals either from coarse layers or between diapausing, deep-dwelling copepods and individuals found in the photic, near-surface layer. Here we examined whether lipid contents of individual calanoid copepods of the same species, life stage/sex differ between finer depth layers within the upper water column of subtropical and Arctic seas. A total of 6 calanoid species were collected from samples taken at precise depths within the photic layer in both cold eutrophic and warm oligotrophic environments using SCUBA diving, MOCNESS and Multinet. Measurements of lipid content were obtained from digitized photographs of the collected individuals. The results revealed significant differences in lipid content across depth differences as small as 12–15 meters for Mecynocera clausi C5 and Ctenocalanus vanus C5 (Red Sea), Clausocalanus furcatus males and two clausocalanid C5s (Mediterranean Sea), and Calanus glacialis C5 (Arctic). We suggest two possible explanations for the differences in lipid content with depth on such a fine scale: predator avoidance and buoyancy.
Highlights
Copepods are among the most abundant metazoans on earth [1]
The lipid content was significantly different among depths in the Mediterranean copepods C. furcatus males and the clausocalanids "C5 right" and "C5 left" (Fig. 5–7, Table II)
This study shows, for the first time, differences in lipid content among individuals found at finely segregated depths within the photic layer in several calanoid copepod species
Summary
Copepods are among the most abundant metazoans on earth [1]. Many copepods are herbivorous and form an important trophic link between phytoplankton and fish [1]. It is generally believed that lipids play a role in copepod buoyancy [7,8,9,10,11]. Several studies reported that lipid content in some species increased with depth [3,6,10,13,14,15,16], sometimes suggesting a role in buoyancy control [10]. These studies focused mostly on copepods from temperate and high latitudes exhibiting seasonal vertical migration. The comparisons of lipid contents were so far examined only among coarse depth layers, or between diapausing copepods that dwell in deep waters and those found in the photic, near-surface layer
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