Abstract
Red tide blooms caused by the toxic dinoflagellate Karenia brevis are natural disturbance events that occur regularly along Florida’s west coast, often resulting in massive fish kills and marine mammal, seabird, and sea turtle mortalities. Limited prior work on the ecological effects of red tides suggests they play an important role in structuring ecosystem dynamics and regulating communities, however specific effects on prey populations and potential alterations to predator-prey interactions are unknown. We surveyed the prey fish assemblage of a top marine predator, the common bottlenose dolphin (Tursiops truncatus), in shallow seagrass habitat in Sarasota Bay, Florida, during 2004–2019, collecting data on prey density, species composition, K. brevis cell densities, and environmental variables. Across eight distinct red tide bloom events, resistance, resilience, and the ecological effects on the prey assemblage varied depending on bloom intensity, season, and frequency. Prey assemblage structure showed significant and distinct short-term shifts during blooms independent of the normal seasonal shifts in prey structure seen during non-bloom conditions. Canonical correspondence analysis indicated a strong influence of K. brevis density on assemblage structure. Blooms occurring primarily in the summer were associated with less initial prey resistance and higher than average annual catch per unit effort (CPUE) 1–3 years following bloom cessation, with bloom frequency prolonging the time needed to reach higher than average annual CPUE. Regardless of season, recovery to pre-bloom prey abundances occurred within 1 year. Sample-based rarefaction and extrapolation indicated significant differences in prey diversity among summer bloom events. This study is a first step in identifying differences in resistance, resilience, and the ecological effects of multiple red tide bloom events of various temporal scales and intensity on a dolphin prey assemblage. Improved understanding of the influence of red tides on estuarine structural dynamics and function can better inform management, and potentially guide mitigation efforts post-bloom.
Highlights
Much work has focused on the dynamics of single species or guilds of species at the same trophic level, the direct and indirect disturbance effects on the dynamics of populations linked by predator-prey interactions, across different trophic levels, are not as well understood (Commander and White, 2020)
In response to a recent severe bloom event in 2018–2019, the first major red tide to occur in the summer months in the Sarasota Bay area since 2006, this study evaluates the populationand community-level effects of red tide on a prey assemblage of a year-round, long-term resident bottlenose dolphin (Tursiops truncatus) community
Using data from long-term surveys of K. brevis across the study area, we identified eight distinct red tide blooms that affected the Sarasota Bay study area between 2003 and 2019
Summary
Disturbance events are recognized as playing a crucial role in the formation and maintenance of ecological communities (Connell and Slatyer, 1977; Sousa, 1984; White and Jentsch, 2001; Callaway et al, 2002; Borer et al, 2006; Miller et al, 2011; Steudel et al, 2012; Johnke et al, 2014). Recent ecosystem modeling suggests K. brevis blooms along the west Florida shelf can impose top-down food web effects, causing trophic cascades, as well as changes in community structure and biodiversity (DiLeone and Ainsworth, 2019). These studies suggest a pattern of ecological effects on fish abundance, diversity, and/or community structure due to severe red tides; it is unknown how generalizable these results are to red tide blooms of differing intensity, season (timing), duration, and frequency. Understanding resistance, resilience, and the ecological effects of red tides, including population/community level effects and potential alterations to predator-prey interactions, across multiple bloom events can lend insight into regime patterns, better inform management, and potentially guide mitigation efforts following a severe disturbance event (Stevens et al, 2016)
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