The aims of this study were to describe the reproductive cycle of the European anchovy (Engraulis encrasicolus) off the south coast of Sicily and determine whether intra-and inter-annual reproductive trait variations, if any, are adaptive responses which maximize reproductive success under environmental fluctuations. Biological data were collected from purse seine and mid-water pelagic trawl commercial catches landed in Sciacca (Sicily) over 6 yr (1997)(1998)(1999)(2000)(2001)(2002) at fortnightly intervals, analysing a total of 84 581 individuals. No inter-annual changes in length at first reproduction were observed, with a mean pooled value of 11.26 cm for both sexes being found. Spawning intensity, indicated by gonadosomatic index, condition factor and length-weight relationships, seem to be governed by food availability prior to spawning. Anchovy reproductive investment was limited by the area's low primary production. There was a synchrony between reproductive cycle and temperature. Water warming marks the onset of a period of high water stability in the area, and its later cooling marks the onset of a period with low water stability. The relationship between reproductive cycle and temperature is therefore probably a reproductive strategy having evolved to ensure that spawning takes place during the period of the year when water column stability is higher, favouring food concentration and egg and larval retention in the spawning areas.

Unialgal and mixed cultures of the toxic dinoflagellate Alexandrium minutum and the non-toxic dinoflagellate Prorocentrum micans were cultured under phosphate (P) limitation (<1 µM), in the presence or absence of the copepod Acartia clausi. The aim was to determine the possible effects of interspecific competition, predation and nutrient limitation on the production of Paralytic Shellfish Poisoning (PSP) toxin by A. minutum. The growth rate of A. minutum was higher in the cultures of A. minutum and copepods than in the mixed cultures of A. minutum and P. micans, which indicates that A. minutum was more negatively affected by interspecific competition than by predation. Toxin content per cell in A. minutum increased in all cultures, but toxin production rate was higher in cultures with P. micans and/or A. clausi. Toxin concentration in A. minutum increased as PO 4 3 -concentration diminished. In the mixed cultures with copepods, analyses of toxin content in the copepods showed that at cell toxin contents lower than approximately 20 fmol cell -1 , mainly cells of A. minutum were ingested by copepods, whereas at higher toxins content per cell, copepods fed mainly on P. micans. We conclude that one of the possible advantages of toxin production by A. minutum under P limitation is to enhance interspecific competition, by redirecting grazing pressure to non-toxic phytoplankton species. It would allow a possibly low competitive ability of A. minutum to be offset under low nutrient concentrations. KEY WORDS: Dinoflagellates · Phosphorus · Nutrients · Toxins · Copepods · Predation · Interspecific competitionResale or republication not permitted without written consent of the publisher

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A field study was carried out to determine the relative importance of both food quantity and food quality to reproduction of the copepod Euterpina acutifrons. The total protein concentration of the seston 3 to 20 µm size fraction was used as the indicator of food available for copepods in the field. Food quality was quantified by comparing the amino acid (AA) composition of females, eggs and the seston 3 to 20 µm size fraction, and by considering the species composition of the phytoplankton community. Egg production rate was mainly determined by food concentration. However, for the same food concentration, a reduced egg production rate was observed when there were more differences between the AA composition of eggs and females. Hatching success was correlated only with food quality. A higher hatching success was obtained when the similarity between the AA composition of eggs and females and between the AA composition of females and seston was higher. However, a reduced hatching success was observed when the proportion of diatoms in the phytoplankton was higher than 70%. Therefore, food quality limitation was due to an AA imbalance in the natural seston and, perhaps, due to the presence of inhibitory compounds. Copepods were food limited for long periods of the year. Food quality mainly limited copepod reproduction in spring and early summer, whereas food quantity limited reproduction at the end of autumn and early winter. In summer and early autumn the reproductive success of copepods was higher.

Several experiments were performed to determine the effects of cell toxin concentration, composition and toxicity of Alexandrium minutum on ingestion rate, egg production, hatching success and naupliar fitness of the copepod Acartia clausi. A combination of A. minutum and nontoxic algae (Prorocentrum micans, Tetraselmis suecica and Isochrysis galbana) was used as food. Copepods ingested a higher amount of A. minutum cells as the concentration of these toxic dinoflagellates increased, and also in response to decreasing total food concentration available for the copepods. A positive relationship was obtained between A. minutum cells ingested by copepods and total toxin concentration per copepod. Hatching success and naupliar production were lower when copepods ingested a higher amount of toxic dinoflagellates. This negative effect could has been due to the accumulated toxins in the egg and copepod tissues, and was higher when A. minutum had a higher cell concentration of GTX1. Finally, the results obtained from nauplii incubated with T. suecica and I. galbana showed that nauplii hatched from females fed non-toxic food (T. suecica and I. galbana) reached copepodite stage earlier than those nauplii hatched from females fed with a combined of toxic (A. minutum) and non-toxic (T. suecica and I. galbana) food. KEY WORDS: Dinoflagellate · Copepod · Toxins · PSP · ReproductionResale or republication not permitted without written consent of the publisher

The essential amino acid composition (EAA) of females and eggs of Euterpina acutifrons and their food was analyzed on copepods fed with different microalgae and collected from the field. There were not significant differences in the EAA of females, but the EAA of eggs varied according to food source. As predicted by homeostasis theory, a higher reproductive success was observed as the EAA of females and food became more similar. This chemical homeostasis explains the selective retention of amino acids observed in copepods, tells why conversion efficiencies of ingested nitrogen may vary according to the food source, and shows the importance of food quality on reproductive success in copepods.

This study was carried out during an autumn bloom of Dinophysis acuminata in the Galician Rías Bajas (NW Spain). The main objective was to determine whether any of the predominant zooplankton species could ingest and transfer toxins through the pelagic food web. Grazing experiments showed that the copepods Temora longicornis and Oithona nana and the tintinnid Favella serrata fed on Dinophysis spp. whereas the copepods Acartia clausi and Euterpina acutifrons did not. However, only F. serrata seem to profit from the ingestion of the toxic dinoflagellates. Field populations of F. serrata increased whereas T. longicornis and O. nana densities declined after the toxic outbreak. Okadaic acid content found in the seston size fractions 100-200, 200-300 and 300-1000 µm showed a good correlation with F. serrata. These results confirm the hypothesis that tintinnids can transfer dinoflagellates toxins to higher trophic levels in the pelagic food web. The importance of faecal pellets with undigested dinoflagellates as an alternative pathway to transmit toxins to pelagic or benthic organisms is mentioned.

ABSTRACT. We collected females of the marine copepod Euterpina acutifrons monthly from November 1994 to January 1996 at a station located in Ria de Vigo (Spain). A trade-off between egg size and egg number was found. As food concentration measured as mean fluorescence in the water column diminished, mean number of eggs per sac carried per female decreased, whereas mean egg size increased. An experiment carried out with adult females cultured at different food concentrations confirmed the field results, and also showed that as egg size increased, there, was an increase in naupliar body length at hatching; nauplii developed faster to first copepodite stage, and net reproductive rate was higher. Therefore, the reproductive strategy of directing more energy toward offspring size rather than offspring number, at low food concentrations, clearly increases reproductive success.