Abstract

In the Mediterranean basin, the globally increasing temperatures are expected to be accompanied by longer heat waves. Commonly assumed to benefit cold-limited invasive alien species, these climatic changes may also change their feeding preferences, especially in the case of omnivorous ectotherms. We investigated heat wave effects on diet choice, growth and energy reserves in the invasive red swamp crayfish, Procambarus clarkii. In laboratory experiments, we fed juvenile and adult crayfish on animal, plant or mixed diets and exposed them to a short or a long heat wave. We then measured crayfish survival, growth, body reserves and Fulton’s condition index. Diet choices of the crayfish maintained on the mixed diet were estimated using stable isotopes (13C and 15N). The results suggest a decreased efficiency of carnivorous diets at higher temperatures, as juveniles fed on the animal diet were unable to maintain high growth rates in the long heat wave; and a decreased efficiency of herbivorous diets at lower temperatures, as juveniles in the cold accumulated less body reserves when fed on the plant diet. Heat wave treatments increased the assimilation of plant material, especially in juveniles, allowing them to sustain high growth rates in the long heat wave. Contrary to our expectations, crayfish performance decreased in the long heat wave, suggesting that Mediterranean summer heat waves may have negative effects on P. clarkii and that they are unlikely to boost its populations in this region. Although uncertain, it is possible that the greater assimilation of the plant diet resulted from changes in crayfish feeding preferences, raising the hypotheses that i) heat waves may change the predominant impacts of this keystone species and ii) that by altering species’ trophic niches, climate change may alter the main impacts of invasive alien species.

Highlights

  • MethodsCollection and maintenanceCrayfish collection was carried out under the permit no. 211/2014/CAPT from Instituto da Conservacão da Natureza e das Florestas

  • The metabolic processes and the stoichiometric balance of ectotherms are both strongly influenced by temperature

  • In the short heat wave the median proportion of plant material assimilated by juveniles increased to 0.099 (BCI = 0.004–0.538) and in the long heat wave it increased even more to 0.275 (BCI = 0.012–0.709; Fig 2a)

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Summary

Methods

Collection and maintenanceCrayfish collection was carried out under the permit no. 211/2014/CAPT from Instituto da Conservacão da Natureza e das Florestas. Crayfish collection was carried out under the permit no. Crayfish were captured with dip-net sweeps in rice field ditches near Samora Correia (38 ̊52’N, 8 ̊51’W), before the main reproductive episode in the fall [39]. Adults were collected on the 30th of May 2013 (total body length: 60-90mm) and immature juveniles from the previous autumn cohort on the 25th of July 2013 (total body length: 40 to 45mm), when average water temperatures range from 18 to 23 ̊C and maximum water temperature averages 25 ̊C [39]. Crayfish were acclimatized for two months at room temperature Adults were maintained individually in 1.5L aquaria and entered the experiment on the 31st of July 2013, while juveniles were maintained in groups of 15 individuals in 5L aquaria and entered the experiment on 1st of October 2013

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