Juvenile weakfish Cynoscion regalis distribution in relation to diel-cycling dissolved oxygen in an estuarine tributary

Abstract

Shallow estuarine waters that serve as nurseries for fishes along the Atlantic and Gulf coasts of the USA can undergo wide diel dissolved oxygen (DO) fluctuations (< 2 to ~20 mg O 2 l -1 ) during summer. In this study, the distribution of juvenile weakfish Cynoscion regalis was investigated in relation to diel-cycling DO during summer 2001 in a mesohaline tributary of Indian River Bay, Delaware, USA. Weakfish were collected at 3 sites (upper, middle, and lower) along the ~5 km length of Pepper Creek on 15 d using an otter trawl. Near-bottom DO was monitored continuously over the summer, every 15 min, using multi-parameter sondes. Peak abundance of weakfish coincided with the greatest frequency, intensity, and spatial extent of severe diel-cycling hypoxia events (< 2 mg O 2 l -1 ). Severe hypoxia first occurred in early June in the upper creek and recurred there almost daily for periods of 1 to 4 h until early September. Whenever bottom DO was > 2.0 mg O 2 l -1 , weakfish were more abundant at the upper site than at the middle and lower sites, which also experienced severe hypoxia but at much lower frequency. However, under all environmental conditions they were absent from the upper site whenever bottom DO was < 2 mg O 2 l -1 , and returned within 2 h of DO exceeding 2 mg O 2 l -1. Daily up-and down-creek movement occurred over a distance of ~1 km. These findings indicate an avoidance threshold of ~2.0 mg O 2 l -1 for juvenile weakfish and demonstrate very temporally dynamic DO-related movement. Their rapid return to these areas as DO conditions improve, and relatively high density in tidal tributary headwaters, suggests that these relatively small areas provide important habitat for fishes.

Effects of hypoxia on Mnemiopsis leidyi, ichthyoplankton and copepods: clearance rates and vertical habitat overlap

“…Without an oxygen gradient, there were no areas of higher DO concentrations that were available to organisms as refuges from either low-DO stress or predation (Tyler & Targett 2007). A lack of refuges may be especially important for motile organisms such as fish larvae (Breitburg 1994) and copepods (Decker et al 2003), which actively avoid nonlethal oxygen concentrations that are physiologically stressful (Miller et al 2002).…”

Diel hypoxia in marsh creeks impairs the reproductive capacity of estuarine fish populations

“…with oscillations between 0 and as much as 20 mg l -1 in salt marsh creeks (Gardner & Gorman 1984, D'Avanzo & Kremer 1994, Timmerman & Chapman 2004, Tyler & Targett 2007.…”

Combined impact of ultraviolet radiation and increased nutrients supply: a test of the potential anthropogenic impacts on the benthic amphipod Amphitoe valida from Patagonian waters (Argentina)

“…Under a high input of nutrients, macroalgae respond enhancing their growth and consequently their biomass (Pardal et al, 2000). If the level of nutrient input is highly elevated, the increment in biomass could be deleterious, producing hypoxia or anoxia as a result of oxygen depletion (Malone, 1987;Deegan, 2002;Diaz and Rosenberg, 2008), affecting the survival of organisms living on and near macroalgae (Diaz and Rosenberg, 2008), or causing migration, in the case of mobile organisms, to other parts of the intertidal (Pardal et al, 2000;Tyler and Targett, 2007). In a study performed in the eastern Atlantic Ocean (Pardal et al, 2000) it was observed that an increase in macroalgae biomass may favor A. valida populations, enhancing their growth production; however, extensive blooms, affecting the whole area of distribution of this species, had a strong negative impact and might result in their disappearance.…”