Author : Brittany Elizabeth Davis
Publisher :
ISBN 13 : 9780355967760
Total Pages : pages
Book Rating : 4.9/5 (677 download)
Book Synopsis Susceptibility of Juvenile Fishes to Environmental Change by : Brittany Elizabeth Davis
Download or read book Susceptibility of Juvenile Fishes to Environmental Change written by Brittany Elizabeth Davis and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Rockfish that inhabit seagrass beds may be particularly robust to environmental perturbation with an enhanced ability to compensate for alterations in PCO2 and DO compared to species living in more stable environments; however, studies on fishes in seagrass habitats are often overlooked compared to kelp forests or deep ocean waters when examining the effects of GCC conditions. I exposed rockfish to two PCO2 conditions (ambient [600] and high [1600 μatm PCO2]) across two levels of DO (normoxic [8.0] and hypoxic [4.5 mg l-1]) and measured physiological costs (cellular metabolism), behavioral responses (activity, exploration, and anti-predator responses), and predator-prey interactions (survival from cabezon [Scorpaenichthys marmoratus], a common predator of rockfish). I found evidence of short-term elevations in cellular metabolism, alterations in behavior, and susceptibility to predation in juvenile rockfish after acute acclimation to high PCO2 and hypoxic conditions. However, after 3-weeks of exposures, physiological and behavioral alterations were restored suggesting that rockfish likely possess plasticity in mechanisms to defend against wide changes in PCO2 and oxygen conditions. Our findings indicate local adaptation and life-history strategies are a critical factor in understanding species responses to future GCC conditions and whether a species is likely to be robust or sensitive. In chapter four, I investigated how GCC-correlated drought periods in California may influence fishes in the San Francisco Estuary-Sacramento/San Joaquin Bay-Delta rivers (hereafter Bay-Delta). GCC and drought periods may alter the Bay-Delta with increased in water temperature, sea level rise and reduced snowpack with less water outflow, both of which lead to saltwater intrusion and increased salinity regimes in the Delta. Already, a pelagic fish Delta Smelt (Hypomesus transpacificus), endemic to the Bay-Delta has precipitously declined, potentially to near extinction; however, it remains unclear how multiple drought stressors of high temperature and salinity interact to affect fish survival, and the influence Delta Smelt populations. Because the Bay-Delta is one of the most highly invaded ecosystems in the world, I also wanted to explore the effects of multiple drought stressors on non-native competitors and predators that influence Delta Smelt populations. Therefore, in this study I assessed the influence of elevated temperature (20°C) and salinity (12 ppt) as co-occurring stressors on the physiological performance of three Delta fishes: juvenile native, endangered Delta Smelt, and juvenile non-native Mississippi Silverside (Menidia beryllina) and Largemouth Bass (Micropterus salmoides). I determined species-specific vulnerability (i.e. tolerance) to elevated salinity and temperature, and characterized if the series in which stressors where experienced (e.g. initial warming, subsequent increased salinity, and vice-versa) affected the physiological tolerance of fishes. I found that each species had the capacity to tolerate a series of co-occurring stressors, and thermal history, not salinity, determined upper thermal tolerance. As expected, non-native fish were more thermally tolerant than native Delta Smelt; however, species-specific plasticity of upper tolerance was evident. Delta Smelt and Silversides rapidly reached new thermal tolerance baselines following 2-4 days of acclimation to 20°C, whereas Largemouth Bass upper tolerance was still increasing after 7 days of acclimation. Estimated thermal safety margins, that is, the buffer (i.e. temperature difference) between upper thermal tolerance and maximum habitat temperatures indicated, Delta Smelt have the narrowest margin for performance within Bay-Delta habitats, and with projected 2-3°C increases in temperature from GCC some thermal safety margins may become negative influencing the overall survival of the population. Since thermal history, and not salinity underlined physiological changes in California’s critically endangered Delta Smelt (H. transpacificus), the last chapter (five) focused exclusively on the effects of warming (a single stressor) on Delta Smelt behavioral responses and susceptibility to predation. The effects of temperature on individual and group movement behavior in prey fish can affect ecological interactions such as competition and predation. Therefore, in addition to understanding the effects of warming on physiology, it is important to understand how behavioral responses to warming may influence populations. We tested how high temperature experienced as constant (21°C) or fluctuated warming (as in a natural tidal cycle, daily 17-21°C) affects group structure of Delta Smelt shoals, anti-predator responses (i.e. conspecific alarm cue or predator-borne cue) and predation susceptibility from Largemouth Bass. This study quantified for the first time the free-swimming characteristics and group structure of Delta Smelt. In general, Delta Smelt did demonstrate shoaling behavior, remaining on average 2 body lengths from their nearest neighbor. There were significant effects of constant warming on both individual and structural behaviors; however, if warming was fluctuated in a manner closely mimicking that of the natural tidal cycle, Delta Smelt movement was not affected compared to the control group (held at ambient temperature, 17°C). Similarly, Delta Smelt’s response to conspecific alarm cue, predator cues, and a real-predation threat were also dependent on the type of warming treatment, such that significant mal-adaptive behaviors and increased predation mortality were exhibited under constant warming, but not fluctuated warming. While this last study proves important information about shoaling behaviors of Delta Smelt under warming, more importantly, from an experimental perspective, future studies should take care to match temperature treatments closer to real-world daily fluctuations when and where possible.
