Discovery and dynamics of a cryptic marine copepod-parasite interaction

Abstract

Parasitism is increasingly recognized as a critical element of ecosystem dynamics but remains understudied due to observational limitations, especially in rapidly fluctuating marine plankton populations. We combined 3 new techniques—in situ imaging microscopy, automated classification, and empirical dynamic modeling—to quantify interactions between Oithona spp. and the rhizarian parasite Paradinium spp. at hourly resolution for over 1 yr in the Southern California Bight. We investigate the time scales, host population effects, and potential environmental drivers of infection. Our study suggests that Paradinium spp. is consistently present in the local copepod population at low levels throughout the year and that the parasite exerts control on the host population on a 22-23 d lag—a delay consistent with known Oithona spp. generation times. The interaction strength was pronounced at higher temperatures, suggesting that Paradinium spp. will have a significant role in local ecosystem dynamics as surface ocean temperatures rise.