Turbidity and Salinity Affect Feeding Performance and Physiological Stress in the Endangered Delta Smelt

Abstract

Coastal estuaries are among the most heavily impacted ecosystems worldwide with many keystone fauna critically endangered. The delta smelt (Hypomesus transpacificus) is an endangered pelagic fish species endemic to the Sacramento-San Joaquin Estuary in northern California, and is considered as an indicator species for ecosystem health. This ecosystem is characterized by tidal and seasonal gradients in water parameters (e.g., salinity, temperature, and turbidity), but is also subject to altered water-flow regimes due to water extraction. In this study, we evaluated the effects of turbidity and salinity on feeding performance and the stress response of delta smelt because both of these parameters are influenced by water flows through the San Francisco Bay Delta (SFBD) and are known to be of critical importance to the completion of the delta smelt's life cycle. Juvenile delta smelt were exposed to a matrix of turbidities and salinities ranging from 5 to 250 nephelometric turbidity units (NTUs) and 0.2 to 15 parts per thousand (ppt), respectively, for 2 h. Best statistical models using Akaike's Information Criterion supported that increasing turbidities resulted in reduced feeding rates, especially at 250 NTU. In contrast, best explanatory models for gene transcription of sodium-potassium-ATPase (Na/K-ATPase)-an indicator of osmoregulatory stress, hypothalamic pro-opiomelanocortin-a precursor protein to adrenocorticotropic hormone (expressed in response to biological stress), and whole-body cortisol were affected by salinity alone. Only transcription of glutathione-S-transferase, a phase II detoxification enzyme that protects cells against reactive oxygen species, was affected by both salinity and turbidity. Taken together, these data suggest that turbidity is an important determinant of feeding, whereas salinity is an important abiotic factor influencing the cellular stress response in delta smelt. Our data support habitat association studies that have shown greater delta smelt abundances in the low-salinity zone (0.5-6.0 ppt) of San Francisco Bay, a zone that is also understood to have optimal turbidities. By determining the responses of juvenile delta smelt to key abiotic factors, we hope to aid resource managers in making informed decisions in support of delta smelt conservation.

Assessment of the Water Quality of Batang Rajang at Pelagus Area, Sarawak, Malaysia

“…High turbidity from anthropogenic sources limits light availability for photosynthesis and has significant negative impacts on aquatic fauna (Baoligao et al 2016;Gonzalez-Ortegon et al 2010;Hasenbein et al 2013;Kimbell & Morrell 2015;Madhu et al 2010). In the present study, turbidity was high at stations 1, 5, 6 and 7 (Figure 3).…”

Effects of Salinity on Some Haematological and Biochemical Parameters in Nile Tilapia, <i>Oreochromus niloticus</i>

“…There are variations in salinity tolerance among different species [8]. The physiological responses to high or low salinity levels in the aquatic environment have been studied in different fresh and marine species [9][10][11].…”

Spatio-Temporal Variability in a Turbid and Dynamic Tidal Estuarine Environment (Tasmania, Australia): An Assessment of MODIS Band 1 Reflectance

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