Seasonal and spatial patterns in cellular energy allocation in the estuarine mysid Neomysis integer (Crustacea: Mysidacea) of the Scheldt estuary (The Netherlands)

The seasonal and spatial patterns in cellular energy allocation of the estuarine mysid Neomysis integer (Leach, 1814) were investigated in the Scheldt estuary over a 2-year period. Using the recently developed cellular energy allocation (CEA) assay, energy reserves (protein, lipid and sugar) and energy consumption (as derived from the cellular respiration rate) were integrated into a general indicator of physiological stress. Total energy reserves were relatively unaffected by sampling season or location, whereas the individual energy reserve fractions of N. integer were differentially influenced by sampling location and season. Seasonal effects were apparent for mysid weight and were related to the population biology, whereas spatial effects on the weight of N. integer may depend on pollution-induced effects on cellular energy allocation in the two most upstream sites (Bath and Doel). These upstream sites coincide with the most polluted part of the sampled area and were characterized by a significant increase in energy consumption, resulting in a significantly lower CEA. Due to the recent amelioration in the oxygen concentration at these sites, it can be expected that N. integer will migrate further upstream, similar to what is observed in other European estuaries. It will, therefore, be important to assess the physiological consequences and potential population effects on mysids from these polluted areas in the Scheldt estuary. This study provides evidence that the CEA assay has potential under field conditions as an in situ biomarker of pollutant effects.