Abstract
Non-indigenous species (NIS) can impact marine biodiversity and ecosystem structure and function. Once introduced into a new region, secondary dispersal is limited by the physiology of the organism in relation to the ambient environment and by complex interactions between a suite of ecological factors such as presence of predators, competitors, and parasites. Early prediction of dispersal potential and future ‘area of impact’ is challenging, but also a great asset in taking appropriate management actions. Aerobic scope (AS) in fish has been linked to various fitness-related parameters, and may be valuable in determining dispersal potential of aquatic invasive species in novel environments. Round goby, Neogobius melanostomus, one of the most wide-ranging invasive fish species in Europe and North America, currently thrives in brackish and fresh water, but its ability to survive in high salinity waters is unknown to date. We show that AS in round goby is reduced by 30% and blood plasma osmolality increased (indicating reduced capacity for osmoregulation) at salinities approaching oceanic conditions, following slow ramping (5 PSU per week) and subsequent long-term acclimation to salinities ranging between 0 and 30 PSU (8 days at final treatment salinities before blood plasma osmolality measurements, 12–20 additional days before respirometry). Survival was also reduced at the highest salinities yet a significant proportion (61%) of the fish survived at 30 PSU. Reduced physiological performance at the highest salinities may affect growth and competitive ability under oceanic conditions, but to what extent reduced AS and osmoregulatory capacity will slow the current 30 km year-1 rate of advance of the species through the steep salinity gradient from the brackish Baltic Sea and into the oceanic North Sea remains speculative. An unintended natural experiment is in progress to test whether the rate of advance slows down. At the current rate of advance the species will reach the oceanic North Sea by 2018/2019, therefore time for taking preventative action is short.
Highlights
Non-indigenous species (NIS) can have strong impacts on marine biodiversity and ecosystem structure and functions [1,2,3]
By investigating the effect of salinity (0–30 PSU) on two physiological traits, namely Aerobic scope (AS) and osmoregulation, the present study provides a mechanistic assessment of the secondary dispersal potential of the species within the transition zone between the brackish Baltic Sea and the oceanic North Sea, which is characterised by a steep salinity gradient
The ANOVA model showed that maximum metabolic rate (MMR) and AS were significantly lower in treatments 25 and 30 PSU, compared to the reference treatment (10 PSU) (p = 0.010 and 0.006, respectively)
Summary
Non-indigenous species (NIS) can have strong impacts on marine biodiversity and ecosystem structure and functions [1,2,3]. Effective post-invasion actions are hindered by the difficulty of predicting the direction and rate of secondary dispersal (i.e. by natural migration or dispersal) following introduction into a new region. The key traits defining the physiological performance of a NIS must be identified, together with the responses of these traits to ambient environmental variation, if we are to accurately predict the ultimate distribution and potential impacts that may result from an invasion [19]. The fish (n = 9–10 in each group, Table 1) were kept for eight days at their final treatment salinity before blood sampling, a time period considered sufficient for their blood plasma osmolality level to be restored after the salinity change [49, 94, 95]. Osmolality was subsequently measured in a vapour pressure point osmometer (Vapor Pressure Osmometer 5600, Wescor, South Logan, USA)
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