Subscribe: Journal of Plankton Research - Advance Access
Preview: Journal of Plankton Research - Advance Access

Journal of Plankton Research Advance Access

Published: Tue, 21 Nov 2017 00:00:00 GMT

Last Build Date: Tue, 21 Nov 2017 05:46:00 GMT


Resting eggs in free living marine and estuarine copepods


Marine free living copepods can survive harsh periods and cope with seasonal fluctuations in environmental conditions using resting eggs (embryonic dormancy). Laboratory experiments show that temperature is the common driver for resting egg production. Hence, we hypothesize (i) that seasonal temperature variation, rather than variation in food abundance is the main driver for the occurrence of the resting eggs strategy in marine and estuarine copepod species; and (ii) that the thermal boundaries of the distribution determine where resting eggs are produced and whether they are produced to cope with warm or cold periods. We compile literature information on the occurrence of resting egg production and relate this to spatio-temporal patterns in sea surface temperature and chlorophyll a concentration obtained from satellite observations. We find that the production of resting eggs has been reported for 42 species of marine free living copepods. Resting eggs are reported in areas with high seasonal variation in sea surface temperature (median range 11°C). Temporal variation in chlorophyll a concentrations, however, seems of less importance. Resting eggs are commonly produced to cope with both warm and cold periods and, depending on the species, they are produced at the upper or lower thermal boundaries of a species’ distribution.

“Fake prey”: planktonic ostracods negatively affect the predatory performance of Chaoborus larvae


Previous laboratory experiments have indicated that Chaoborus larvae may be confused when exposed to a single prey species at a high density, resulting in decreased attack efficiency. Here, we hypothesized that a prey less vulnerable to Chaoborus larvae, such as Physocypria schubarti ostracods, could affect the predatory performance of Chaoborus on a more vulnerable prey, such as Ceriodaphnia silvestrii neonates. We predicted that fewer neonates would be ingested by Chaoborus larvae in the presence of ostracods at high densities due to the decreased attack efficiency caused by the confusion effect. This hypothesis was tested by combining predation assays and direct visual observations of live organisms. There was a significant decrease in the consumption of neonates when they were offered together with ostracods at high densities; however, this was not related to the ingestion of ostracods as an alternative prey or to decreased attack efficiency on neonates caused by the confusion. The energy wasted due to the numerous attacks on the ostracods (“fake prey”) possibly led the chaoborids to exhaustion, reducing their predatory performance on neonates. In ecological terms, high densities of ostracods in the water column may theoretically minimize the strong impact of Chaoborus sp. larvae on more vulnerable prey.