Effects of the Blob on settlement of spotted sand bass, Paralabrax maculatofasciatus, to Mission Bay, San Diego, CA

RESEARCH ARTICLE Effects of the Blob on settlement of spotted sand bass, Paralabrax maculatofasciatus, to Mission Bay, San Diego, CA Anthony Basilio1, Steven Searcy1*, Andrew R. Thompson2 1 Environmental and Ocean Sciences, University of San Diego, San Diego, California, United States of America, 2 Fisheries Resources Division, Southwest Fisheries Science Center, NOAA Fisheries Service, La Jolla, California, United States of America a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Basilio A, Searcy S, Thompson AR (2017) Effects of the Blob on settlement of spotted sand bass, Paralabrax maculatofasciatus, to Mission Bay, San Diego, CA. PLoS ONE 12(11): e0188449. https://doi.org/10.1371/journal.pone.0188449 Editor: Heather M. Patterson, Department of Agriculture and Water Resources, AUSTRALIA Received: July 13, 2017 Accepted: November 7, 2017 Published: November 27, 2017 Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. * Abstract The West Coast of the United States experienced variable and sometimes highly unusual oceanographic conditions between 2012 and 2015. In particular, a warm mass of surface water known as the Pacific Warm Anomaly (popularly as “The Blob”) impinged on southern California in 2014, and warm-water conditions remained during the 2015 El Niño. We examine how this oceanographic variability affected delivery and individual characteristics of larval spotted sand bass (Paralabrax maculatofasciatus) to an estuarine nursery habitat in southern California. To quantify P. maculatofasciatus settlement patterns, three larval collectors were installed near the mouth of Mission Bay, San Diego CA, and retrieved weekly from June–October of 2012–2015. During ‘Blob‘ conditions in 2014 and 2015, lower settlement rates of spotted sand bass were associated with higher sea surface temperature and lower wind speed, chlorophyll a (chl a) and upwelling. Overall, the number of settlers per day peaked at intermediate chl a values across weeks. Individual characteristics of larvae that settled in 2014–2015 were consistent with a poor feeding environment. Although settlers were longer in length in 2014–15, fish in these years had slower larval otolith growth, a longer larval duration, and a trend towards lower condition, traits that are often associated with lower survival and recruitment. This study suggests that future settlement and recruitment of P. maculatofasciatus and other fishes with similar life histories may be adversely affected in southern California if ocean temperatures continue to rise in the face of climate change. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: Funding was provided by a faculty research grant from the University of San Diego to Steven Searcy as well as from support by the Department of Environmental and Ocean Sciences at the University of San Diego. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Introduction A central goal of marine ecology and fisheries biology is to understand factors that contribute to variability in population size [1]. For many marine organisms understanding causes of fluctuations in abundance is complicated by a two-part life history with pelagic larvae that develop offshore and settle to benthic juvenile/adult habitats [2–5]. The number of larvae that reach settlement is a critical factor contributing to future year-class strength [3, 6–8], although postsettlement processes can also be an important source of variation [9, 10]. PLOS ONE | https://doi.org/10.1371/journal.pone.0188449 November 27, 2017 1 / 15 Settlement of spotted sand bass, Paralabrax maculatofasciatus Competing interests: The authors have declared that no competing interests exist. Settlement success is dependent on a variety of processes including egg production [11, 12] physical transport and retention of larvae [6, 13–18], and larval mortality [19]. Even small variations in larval mortality can lead to large changes in the number of individuals that survive this period [20]. Larval mortality may be caused directly by predation [21], as well as indirectly through environmental conditions such as water temperature and food supply [22–27]. Food availability is particularly important to larval survival because larvae have high metabolic rates and low energy reserves [28]. At elevated water temperatures, metabolic rates are faster, thereby increasing energetic requirements and increasing risk of starvation [22, 23, 25, 29, 30]. After only a few days without food, the larvae of some fish species reach a "point of no return" and are unable to survive [31–33]. Water temperature and food availability may also affect larval survival by influencing growth rates and physiological condition [34–37]. The growth mortality hypothesis [38] suggests that if mortality is lower for larger individuals, then faster growing individuals of a given age will have a lower probability of mortality than slower growing individuals of the same age [39]. Larger individuals may be able to detect and respond to predators more effectively [21, 40], obtain food and withstand starvation [21, 41, 42], although, some studies suggest that larger larvae may actually have higher mortality [39, 43–45]. Finally, larvae with faster growth may be exposed to overall lower levels of predation by quickly growing out of this vulnerable life history stage [38, 46, 47]. Increased sea surface temperature (SST), may also be related to poor larval growth conditions by indicating periods with low upwelling and potential stratification of the water column [48, 49]. During upwelling events, increased supply of nutrients to the surface water can spur phytoplankton growth and support a trophic pyramid that includes zooplankton and many fish species [50]. When upwelling ceases, SST and stratification increase, and there is decreased productivity [48]. Indeed, previous work indicates that during a long-term shift from a cool to a warm water regime as the result of changing Pacific Decadal Oscillation there was an overall 46% reduction in volume of phyto- and zooplankton and a corresponding decline in abundance of many species of larval rockfish (Sebastes sp.) [51]. Understanding how settlement is affected by environmental conditions such as water temperature is especially important to gain insight into how warming ocean conditions may impact marine populations. In the northeast Pacific Ocean, during the winter of 2013–14, weakened winds and unusually high sea level pressure formed a region where heat was retained in surface water. This mass of warm water, known as “the Blob”, reached coastal wate (...truncated)