Neustonic copepods (Labidocera spp.) discovered living residentially in coral reefs

Abstract

Pontellid copepods are archetypical representatives of the neuston—the highly specialized community living in the top 5–10 cm of the ocean surface. Their deep blue pigmentation and large eyes are unique adaptations to surface irradiation and carnivory, but poor prerequisites for survival in the transparent waters beneath the sea surface. Here, we report the discovery of three reef-associated representatives of this group—Labidocera bataviae A. Scott, 1909; L. pavo Giesbrecht, 1889; and Labidocera sp.—living residential in coral reefs. We (1) document the presence of Labidocera spp. for two separate coral reefs on two expeditions to Papua New Guinea, (2) describe their migration behavior and substrate preference, and (3) quantify the effects of benthic reef community composition on their abundance. All life stages of Labidocera spp. were 43 to 94 times more abundant at the reef sites compared to offshore sites. Although pontellids are generally considered non-migrators, Labidocera spp. showed discernible diel vertical migrations: living in reef substrates during the day, emerging into the water column at night (sometimes more than once), and returning to the substrate at dawn. Labidocera spp. showed a pronounced substrate preference for coral rubble, microalgae, and turf, over branching coral, massive boulder coral, and sand.