The lost generation of Calanus pacificus: Is the diatom effect responsible?

Abstract

An apparent mismatch between periods of high reproduction (spring) and high copepodite abundance (autumn) has been observed for the copepod Calanus pacificus in Dabob Bay, Washington, U.S.A. This persistent pattern leads to a lost generation of progeny that are produced in spring but do not recruit to the juvenile and adult populations, and this is likely due to a combination of factors including advective losses, predation mortality, and nonviability of progeny. Here we test the hypothesis that observed detrimental effects of diatoms on the viability of copepod embryonic and naupliar stages (the diatom effect) are the primary reason for the observed patterns of reproduction and abundance. Furthermore, we test how assumptions about egg production rate and naupliar viability can affect calculations of copepod recruitment. To test these hypotheses, we developed a numerical model to quantitatively explore how certain parameters may have affected the population of C. pacificus population in Dabob Bay. Predation mortality was the most significant contributor to population losses, while advective losses and naupliar viability were of lesser importance, and the model results were more sensitive to parameterization of naupliar viability than egg production rate. Although brief instances of low naupliar viability caused a 25-30% reduction in cumulative stage I copepodite abundance over time when compared with the assumption of persistent high naupliar viability, the lost generation of C. pacificus in Dabob Bay is likely due to predation mortality, not the diatom effect.

Diatom‐produced allelochemicals trigger trophic cascades in the planktonic food web

“…On the other hand, Calanus finmarchicus fed on S. marinoi during its mesocosm bloom (Ray et al ). Predation had a stronger effect on the recruitment success of Calanus than diatom allelopathy throughout the spring bloom conditions (Pierson et al ).…”

“…In fact, several field studies have shown that copepods can reject the most abundant phytoplankton, particularly certain PUA-producing species (Leising et al 2005b). On the other hand, Calanus finmarchicus fed on S. marinoi during its mesocosm bloom (Ray et al 2016 success of Calanus than diatom allelopathy throughout the spring bloom conditions (Pierson et al 2007).…”

“…This phenomenon is considered an anti-grazer defense (Miralto et al 1999;Ianora et al 2004;Ianora et al 2012). However, the extent of diatominduced deleterious effects varies widely among copepod species and experiments (Leising et al 2005b;Pierson et al 2007;Sommer 2009;J onasd ottir et al 2011;Taylor et al 2012). Flynn and Irigoien (2009) have proposed instead that the main target of PUA are the primary herbivores, microzooplankton.…”

Aldehyde-induced insidious effects cannot be considered as a diatom defence mechanism against copepods

“…Any impact of consumption of PUA+ diatoms by copepods in the field may only occur briefly and be of importance only under certain conditions , notably when only diatoms are present as food for the otherwise prey-selective copepods. Pierson et al (2007) also argued that, in general, predation upon copepods (topdown effect) is likely to be more important for the loss of a specific generation than diatom-induced (i.e. bottom-up) mortality.…”

Survey of the allelopathic potential of Mediterranean macroalgae: production of long-chain polyunsaturated aldehydes (PUAs)

“…However, it is import to consider that the extent of deleterious effects varies widely among copepod species and experiments (e.g. Pierson et al, 2007;Sommer, 2009;Taylor et al, 2012).…”