Life History Traits of the Stygophilous Amphipod Synurella ambulans in the Hyporheic Zone of the Lower Reaches of the Upper Sava River (Croatia)

Abstract

Estimating the growth and population dynamics of crustaceans is important for understanding the role of species in ecosystems and for conservation and monitoring purposes. This study investigated temporal and spatial variation in population dynamics (growth rate, instantaneous mortality rates, and longevity) of the stygophilous freshwater amphipod Synurella ambulans (F. Müller, 1846), and influencing environmental factors. Seasonal sampling was conducted from December 2018 to October 2019 at two sampling sites (Jarun and Medsave) along the Sava River in northwestern Croatia. A Bhattacharya cohort analysis was applied to the length-frequency data using the FISAT software package. At least four cohorts were distinguished during the year. The possible influence of environmental factors on growth parameters was investigated using Canonical Correspondence Analysis (CCA), which revealed that the important environmental factors influencing S. ambulans abundance were water temperature and dissolved oxygen concentration. The average total body length (TBL) of females was 4.25 mm, while the TBL of males was 3.34 mm. The asymptotic length (L∞) and growth coefficient (K) were estimated to be 6.30 mm and 0.92 year−1 for females and 5.40 mm and 0.59 year−1 for males, respectively, at the Jarun site. L∞ and K were estimated to be 7.20 mm and 0.34 year−1, respectively, for females and 4.00 mm and 1.20 year−1, respectively, for males at the Medsave site. Estimated total mortality (Z) for each sex had higher values for males than females at both sampling sites. The lack of ecological knowledge on S. ambulans populations and relationships with invertebrate communities in the hyporheic zone of the large river ecosystems emphasises the importance of a detailed study for protecting this species and its vulnerable ecotonal groundwater-connected environment.

Energy Status of Stygophilous Amphipod Synurella ambulans as a Promising Biomarker of Environmental Stress in the Hyporheic Zone

“…The opposite was observed in the population of S. ambulans from site 2-DOWN, which showed less variable seasonal adenine nucleotide concentrations (with the exception of AMP), possibly due to more stable conditions at the microlocation with upwelling properties. Expressed as the ratio of adenine nucleotide concentrations, AEC showed significant differences between two studied populations of S. ambulans in all seasons except summer (Table 2), which might be related to more stable environmental conditions during the summer and to the resting physiological state after the active reproductive period in the spring [48].…”

“…However, significantly higher K eq in spring at the site 1-UP could be related to reproductive efforts that are shown to present a considerable energetic demand. Indeed, a study on the population dynamics of S. ambulans in the HZ of the Sava River showed the highest reproductive peak in this season [48].…”