Abstract
Salinity drops in estuaries after heavy rains are expected to increase in frequency and intensity over the next decades, with physiological and ecological consequences for the inhabitant organisms. It was investigated whether low salinity stress increases predation risk on three relevant commercial bivalves in Europe. In laboratory, juveniles of Venerupis corrugata, Cerastoderma edule, and the introduced Ruditapes philippinarum were subjected to low salinities (5, 10 and control 35) during two consecutive days and, afterwards, exposed to one of two common predators in the shellfish beds: the shore crab Carcinus maenas and the gastropod Bolinus brandaris, a non-indigenous species present in some Galician shellfish beds. Two types of choice experiment were done: one offering each predator one prey species previously exposed to one of the three salinities, and the other offering each predator the three prey species at the same time, previously exposed to one of the three salinities. Consumption of both predators and predatory behaviour of C. maenas (handling time, rejections, consumption rate) were measured. Predation rates and foraging behaviour differed, with B. brandaris being more generalist than C. maenas. Still, both predators consumed significantly more stressed (salinity 5 and 10) than non-stressed prey. The overall consumption of the native species C. edule and V. corrugata was greater than that of R. philippinarum, likely due to their vulnerability to low salinity and physical traits (e.g., thinner shell, valve gape). Increasing precipitations can alter salinity gradients in shellfish beds, and thus affect the population dynamics of harvested bivalves via predator–prey interactions.
Highlights
Salinity is an important factor in shaping the boundaries of species distributions, influencing small and large-scale biotic interactions (Berger and Kharazova 1997; Smyth and Elliott 2016)
The total number of V. corrugata consumed by C. maenas was significantly larger in S5 and S10 than in S35, as was true for C. edule (Fig. 4a, Table 1)
The handling time to the first bite (HBT) differed significantly among treatments for V. corrugata (χ2: 6.12, df 2, p = 0.04), due to higher values in S35 compared to S10, and R. philippinarum (χ2: 5.55, df 2, p = 0.06), due to higher values in S35 compared to S5 (Fig. 4c, Table S1)
Summary
Salinity is an important factor in shaping the boundaries of species distributions, influencing small and large-scale biotic interactions (Berger and Kharazova 1997; Smyth and Elliott 2016). The shore crab has been an invasive species for over a decade in a fishing bed in Ría de Arousa (42° 29′25′′N, 8° 50′24′′W, Bañón et al 2008) It can cope with low salinities by efficient osmoregulation of its extracellular fluid (Jillette et al 2011; Klassen and Locke 2007), maintaining activity (Breen and Metaxas 2008; Curtis et al 2012) or avoiding short-term stress by an increased locomotor activity defined as halokinesis (Thomas et al 1981; McGaw et al 1999). We carried out laboratory experiments to investigate the predation activity and consumption rates of two predator species, C. maenas and B. brandaris, on juvenile bivalves previously exposed to short-term salinity stress levels that reflect those occurring in Galician shellfish beds. With regard to predator behaviour, the hypotheses tested were that (1) handling time and (2) rejection rate would be highest for the least stressed prey, and for the species with shells most resistant to crushing, R. philippinarum > C. edule > V. corrugata (Coffen-Smout 1998)
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