A new paper in Limnology and Oceanography by Rodrigo Gonçalves and Thomas Kiørboe revises the currently prevailing understanding of how copepods perceive their prey. This new insight implies a different understanding of prey seize spectra in copepods.
Copepods perceive and capture individual phytoplankton prey rather than automatically filtering them out of suspension. A seminal paper published in Science in 1982 demonstrated that copepods that generate a feeding current may perceive their phytoplankton prey remotely through chemical signals, and subsequent studies suggested a mechanism. This has since been the accepted description of prey perception in copepods. However, a critical review of the literature now reveals that the evidence for that mechanism is anecdotal and new observations have further demonstrated that it is most likely wrong. Instead, copepods perceive prey cells when they touch them with the setae on their feeding appendages. Only then is a capture response elicited. This implies that the dining sphere of a copepod is much smaller than hitherto assumed, and that it is governed by the length of the setae rather than the size of the prey. This is significant for how we must interpret prey size selection in copepods, and has implications for mechanistic descriptions of prey size spectra in trait-based models.
The paper can be found here:
Gonçalves RJ, Kiørboe T (2015) Perceiving the algae: How feeding-current feeding copepods detect their nonmotile prey. Limnol. Oceanogr 60: doi: 10.1002/lno.10102