Reconstruction of trophic pathways between plankton and the North Iberian sardine (<i>Sardina pilchardus</i>) using stable isotopes

Abstract

SUMMARY: Feeding on phyto-and zooplankton by juvenile (< 1 year old) and adult sardines (Sardina pilchardus) was inferred from analyses of natural abundance of stable carbon and nitrogen isotopes in samples from the northwestern Iberian Peninsula (Spain) collected at the beginning of the upwelling season and peak spawning period of sardine. Plankton samples were fractionated through nets of 20, 200, 500, 1000 and 2000 µm mesh-size and the muscle protein of individual sardines was isolated before isotopic determinations. Up to six planktonic components and two sardine feeding types were identified from the modes in the frequency distributions of isotope abundance values. Also, the most probable pathways for carbon and nitrogen flows between compartments were analysed. The resulting food web revealed a relatively large degree of omnivory, both in plankton and sardine components, which confirms that complex trophic interactions could also occur in pelagic upwelling ecosystems. Young sardines had isotope abundance values clustered around a single mode in the frequency distribution, while adult sardines displayed two main modes. These modes are interpreted as representative of two extreme feeding types: one related to the individual capture of zooplankton prey and the other to unselective filter-feeding. Although both types of feeding could include micro-(20-200 µm) and mesozooplankton (200-2000 µm) prey, phytoplankton appears to be ingested mainly by filter-feeding. However, even adult sardines must be mainly zoophagous to achieve the observed isotopic abundance values, taking into account current assumptions on stable isotope enrichment through trophic levels. From the differences in the resulting pathways using either carbon or nitrogen isotopes, we interpreted that sardines acquire most of the protein nitrogen from zooplankton while a substantial fraction of their carbon would derive from phytoplankton. These interpretations agree with the information available for this species on the gut contents and the anatomy of the filtering apparatus.Key words: phytoplankton, zooplankton, clupeids, stable isotopes, food web, upwelling, NE Atlantic. RESUMEN: RECONSTRUCCIÓN DE LAS CONEXIONES TRÓFICAS ENTRE EL PLANCTON Y LA SARDINA DEL NORTE DE LA PENÍNSULA IBÉRICA (SARDINA PILCHARDUS) A TRAVÉS DEL ANÁLISIS DE LAS DISTRIBUCIONES DE FRECUENCIA DE LA ABUNDANCIA NATURAL DEISÓTOPOS ESTABLES. -A partir de las medidas de la abundancia natural de isótopos estables de carbono y nitrógeno se reconstruyó la alimentación de juveniles (< 1 año de edad) y adultos de sardina (Sardina pilchardus) a partir de fito-y zooplancton en el noroeste de la península Ibérica. Las muestras de plancton y sardinas fueron tomadas al comienzo de la época de afloramiento y durante el máximo de freza de la sardina. Previamente a las determinaciones isotópicas, el plancton fue fraccionado por tamaños a través de tamices de 20, 200, 500, 1000 µm de luz de malla y, en el caso de las sardinas, se tomaron muestras de la proteína muscular. A partir de las modas en...

Domoic acid accumulation in the sardine Sardina pilchardus and its relationship to Pseudo-nitzschia diatom ingestion

“…Sardines are primarily filter-feeders, whose diet composition is closely related to plankton availability (Varela et al 1988(Varela et al , 1990. In terms of biovolume, sardine diet is mostly supported by mesozooplankton organisms, which are assimilated more efficiently than phytoplankton (van der Lingen 1998, Bode et al 2004). However, it is numerically dominated by organisms smaller than 200 µm, with large quantities of phytoplankton being consumed (Garrido 2003).…”

Feeding of European pilchard (<em>Sardina pilchardus</em>) in the northwestern Mediterranean: from late larvae to adults

“…Ecological models based on trophic web interactions and capable of quantitatively describing the structure and function of exploited marine ecosystems (e.g. Ecopath/Ecosim, see Banaru et al 2012, Coll et al 2006 have described sardine in the northwestern Mediterranean as a key species in the trophic web but, with the exception of data from Lee (1961) used in Banaru et al (2012), these models have used data on the diet of sardine from regions other than the northwestern Mediterranean, such as the eastern Mediterranean (Demirhindi 1961) and the Atlantic coast of Spain (Bode et al 2004, Garrido et al 2008. Moreover, detailing the ontogenetic fractions of key species included in the models (e.g.…”

“…It is one of the most important fish resources throughout its range in the northeastern Atlantic, from the North Sea to the Senegalese coast, including the Mediterranean and the Black Seas. Studies of its feeding dynamics have been conducted on the Atlantic coast of Spain, where the diets of juvenile and adult sardine have been found to consist entirely of plankton (Bode et al 2004, Garrido et al 2007 and where adults are able to perform both filter and particulate feeding. Due to this difference between stages, the adults show a greater fraction of phytoplankton in their stomachs than the juveniles do.…”

Laboratory investigations on the effect of prey size and concentration on the feeding behaviour of Sardina pilchardus

“…Previous studies based on stomach content (Varela et al 1988, Garrido 2003, Cunha et al 2005) and stable isotope analyses (Bode et al , 2004 have shown that sardines have a highly diverse diet, dominated in terms of biovolume by micro-and mesozooplankton prey. High numbers of phytoplankton cells, ABSTRACT: Laboratory experiments were conducted to study the effects of different prey types and concentrations on the feeding behaviour of the Iberian sardine Sardina pilchardus.…”