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Opportunistic assessment of El Niño effects on connectivity and recruitment

Dr. Crow White, Cal Poly San Luis Obispo
Dr. Benjamin Ruttenberg, Cal Poly San Luis Obispo
Dr. Danielle Zacherl, California State University Fullerton

February 1, 2016

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Roberto Calderon, an undergraduate marine biology student at Universidad Autonóma de Baja California, with measured whelks ready to be returned to the sea.

A long-standing question in marine ecology remains: From where does the next genera​tion of fish and shellfish originate? Answering this question is challenging because nearly all the marine fish and invertebrate species living along coastlines – rockfish, kelp bass, halibut, grouper, snapper, lobster, crab, urchin, abalone, clams and thousands of others – release microscopic larvae into the open ocean. Those larvae then disperse for weeks (abalone) to months (rockfish) to nearly a year (lobster) before settling back into coral reefs and kelp forests. They are too small and they travel too far to be tracked directly. The extent to which the next generation of fish in your local kelp forest is from elsewhere (that is, they were spawned by parents living in other kelp forests, and then dispersed here as larva) means that replenishment of your local reef is dependent on sustainable management of the other reefs. Overall, understanding these patterns of “connectivity” and “dependency” among reefs is critical for making smart decisions on how to best protect, fish and in general manage our coastlines.

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Kellet's whelk. Photo credit: Steve Lonhart/NOAA MBNMS.

To further complicate matters, a species’ pattern of connectivity changes from year to year. An example of such changes along the Pacific Coast of North America has to do with El Niños , which occur every few years and generate warm, north-flowing ocean currents that are hypothesized to transport marine larva up the coast. Thus, El Niños may make northern areas dependent on southern populations for new supplies of fish and shellfish.

Our research team is trying to figure out these patterns of connectivity, with particular focus on how El Niño events connect northern populations with southern spawning grounds. We are focusing our research on a predatory marine snail called Kellet’s whelk, which we chose for four main reasons:

  1. Kellet’s whelk is an emerging fisheries species of increasing economic value. About 100,000 whelk are harvested in California annually, up from nearly zero in the 1990s.
  2. Kellet’s whelk’s range spans the U.S.-Mexico border and a network of marine protected areas (no-fishing zones) in California, and the heart of its range lies in southern California, where pollution and fishing impacts can be intense. Understanding the patterns of connectivity and dependency within and among these areas can help guide international fisheries policy and sustainable marine management.
  3. Kellet’s whelk is expanding its range up the California coast. This range expansion is only a few decades old, and is hypothesized to be driven by a series of recent, strong El Niños (e.g., in 1982 and 1997) that generated exceptionally warm, north-flowing ocean currents along the coast. Climate models predict the frequency and intensity of El Niños along our coast to increase in the future.
  4. Finally, Kellet’s whelk’s biogeographic range and the biological characteristics of its larvae are remarkably similar to several other species with high cultural and economic value, such as sheephead, kelp bass and lobster. Thus, our study of Kellet’s whelk will help us understand the spatial patterns of connectivity of other species in California as well, and Kellet’s whelk’s northward range expansion may be a harbinger of future range expansions in these other species as the frequency and intensity of El Niño events increases over the 21st century.
To test the hypothesis that El Niño events drive northward patterns of connectivity and can promote range expansion in coastal marine species, we developed a multi-year Kellet’s whelk surveying and sampling program. Under this program, we are using SCUBA to conduct transect surveys for assessing patterns of whelk size and population abundance across the species’ range. Of particular focus, we are quantifying recruitment of Kellet’s whelk settlers (post-dispersal larvae) between historic and expanded range areas, and comparing the observed patterns with the El Niño conditions in each year. We also are sampling tissues from the recruits, and from the spawning adult populations, that can be analyzed genetically and with other molecular techniques to “assign” each recruit to a parent population.
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Cal Poly graduate student Katie Grady enters the water at one of our research sites.

We completed our first year of field research in summer 2015, following the weak 2014-15 El Niño. In Kellet’s whelk’s expanded range we recorded moderate numbers of Kellet’s whelk recruits that were patchily distributed. In support of our hypothesis, we expect to observe a stronger pattern of recruitment in the expanded range in summer 2016, following the strong 2015-16 El Niño – a pattern documented by one of our team members following the 1997-98 El Niño. We also found a relatively low but consistent adult spawning population abundance across the expanded range, suggesting that the range expansion is not temporary and that the recruits could have been spawned locally, not from the historic range. The molecular analysis of the tissue samples will help resolve this question. Our surveys also revealed that, within the species’ historic range, Kellet’s whelks are substantially larger at the Channel Islands versus along the mainland, and their population density is significantly higher in marine protected versus fished areas – important information for guiding sustainable management of the emerging Kellet’s whelk fishery. We presented some of these results at the Western Society of Naturalists meeting in November 2015.

Professors, and undergraduate and graduate students at universities in both California and Mexico, are all contributing to this project. The result is a research team that is highly interdisciplinary and strongly student-centered. Our hope is that we will generate information useful for understanding and sustainably managing coastal marine ecosystems in the face of climate change. Additionally, our ambition is that this multi-faceted project will train the next generation of scientists with the knowledge and skills needed for tackling 21st century problems in marine ecology, conservation and management.

Dr. Crow White​ and Dr. Ben Ruttenberg  are Assistant Professors in the Biological Sciences Department and Center for Coastal Marine Sciences at Cal Poly San Luis Obispo. Dr. Danielle Zacherl is a Professor in the Department of Biological Sciences at California State University, Fullerton. COAST provided funding for this project: Rapid Response Funding Program Award​ # COAST-RR-2014-001, December 2014. ​