Phytoplankton Food Quality Determines Time Windows for Successful Zooplankton Reproductive Pulses

Abstract

Recruitment success at the early life stages is a critical process for zooplankton demography. Copepods often dominate the zooplankton in marine coastal zones and are prey of the majority of fish larvae. Hypotheses interpreting variations of copepod recruitment are based on the concepts of "naupliar predation," "nutritional deficiency," and "toxic effect" of diatom diets. Contradictory laboratory and field studies have reached opposite conclusions on the effects of diatoms on copepod reproductive success, blurring our view of marine food-web energy flow from diatoms to higher consumers by means of copepods. Here we report estimates of copepod feeding selectivity and reproduction in response to seasonally changing phytoplankton characteristics measured in a highly productive coastal upwelling area off the coast of central Chile. The variable phytoplankton diversity and changing food quality had a strong and highly significant impact on the feeding selectivity, reproduction, and larval survival of three indigenous copepod species. Seasonal changes in copepod feeding behavior were related to the alternating protozoan-diatom diets, mostly based on dinoflagellates and ciliates during winter and autumn (low highly unsaturated fatty acids [HUFA]/polyunsaturated fatty acids [PUFA] availability), but switched to a diet of centric and chain-forming diatoms (high HUFA/PUFA availability) during the spring/summer upwelling period. Ingestion of diatom cells induced a positive effect on egg production. However, a negative relationship was found between egg hatching success, naupliar survival, and diatom ingestion. Depending on the phytoplankton species, diets had different effects on copepod reproduction and recruitment. In consequence, it seems that the classical marine food web model does not apply to some coastal upwelling systems.

Thermal tolerance of larval stages of the Chilean kelp crab Taliepus dentatus

“…Since survival in the plankton influences the arrival of recruits to adult populations, there is great interest in furthering our understanding of the physiology and ecology of early life history stages to improve management and conservation programs (Rumrill 1990, Morgan 1995. Factors such as temperature, food availability and quality, and predation can largely affect development and survival of larvae, their dispersal from the population of origin, and their chances of successfully completing metamorphosis after returning to shore (Thorson 1950, Pechenik 1987, Morgan 1995, Epifanio & Garvine 2001, Vargas et al 2006a,b, Emlet & Sadro 2006, O'Connor et al 2007). Sea temperature is probably the most important of these factors, as it influences all physiological and ecological processes of aquatic invertebrates and their life stages (Blaxter 1991, Somero 2002, O'Connor et al 2007, Pörtner & Farrell 2008.…”

Scaling copepod grazing in a coastal upwelling system: the importance of community size structure for phytoplankton C flux

“…Small copepods in the upwelling zone are mainly omnivorous, although as stated above, they can switch their diet to diatoms when the latter are abundant (Kleppel, 1993;Vargas et al, 2006), whereas large calanoid copepods prefer a more herbivore diet (diatoms) . Therefore, phytoplankton C can efficiently be transferred via grazing in highly productive upwelling systems, when small copepods are dominant, as in the coastal upwelling zone off Chile.…”

“…This analysis also showed that seasonal effects are important to determine grazing impact. Such seasonal variation takes place after shifts of copepod feeding to a more heterotrophic diet during conditions of low Chl-a (Vargas et al, 2006). Thus, transfer of phytoplankton through the pelagic food web via copepod grazing is not only more efficient during low Chl-a (autumn-winter), but it can also transfer more C through a heterotrophic pathway.…”

“…Feeding dynamics of zooplankton has been studied in relation to the quantity and quality of food, temperature and body size (Tirelli & Mayzaud, 2005;Vargas et al, 2006;Saiz & Calbet, 2007;Vargas et al, 2009).…”

“…Various works on different systems have suggested that herbivore-grazing exercises limited control over C flux in the marine food chain because most zooplankton are omnivorous & their feeding on heterotrophic diets predominates for a variety of situations, thus favoring microbial C pathways (González et al, 2000;Calbet, 2001;Calbet & Landry, 2004;Vargas et al, 2007). Although in strongly seasonal upwelling systems at times of the year (spring-summer) dominant zooplankton can shift their diet, such that herbivorous grazing on diatoms may greatly increase and thus serve as the C channel for higher trophic levels (Vargas et al, 2006).…”