Name that WoRM!

Billie Swalla

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Billie is the Interim Director of Friday Harbor Laboratories, a Professor of Biology at University of Washington, and is an editor of WoRMS, The World Register of Marine Species. She is also an instructor at FHL, teaching Marine Genomics Research Apprenticeships and Comparative Invertebrate Embryology courses.

In the Swalla Lab, we conduct research on several topics including the biodiversity of marine invertebrates. This consists of cataloging different marine species and making our findings known to others who are interested in the results, such as ecologists, marine biologists, and policy makers (Appeltans et al. 2012). Biodiversity has been in the news the past twenty years, and is increasingly important in a world of climate change and ocean acidification. How does a scientist describe and study biodiversity? Does it matter that we know how many marine species exist?    How many marine animals are there, and are there any left to describe? These are global questions, but they’re local biodiversity questions too. For example, how many hemichordate species are there in the San Juan Islands? Do we have any invasive species here? What is their effect on the local species?

Figure 1 – Dr. Amanda Rychel, a former graduate student in the Swalla lab (front), Dr. Billie Swalla (middle), and Brock Roberts (back), a former Swalla lab undergraduate now in graduate school at U.C. Berkeley, dig for hemichordates. Photo by Darren Begley.

I am an editor of WoRMS, The World Register of Marine Species, and update it as part of my professional duties.       There are over 120 editors, and at least two others have worked extensively at Friday Harbor Laboratories: Claudia Mills, an expert in marine zooplankton, and Gretchen Lambert, an expert in tunicates. Several years ago, all of the WoRMS editors together published a manuscript describing all of the species that are currently known, and made an educated guess about those that are currently unknown (Appeltans et al. 2012.) This paper describes 750,000 known marine species and estimates that there are at least 250,000 undescribed marine species. It is sobering that we are still trying to describe all of the world’s marine invertebrate species while many of them are going extinct or being decimated by disease (see TideBites #5.)

I’m the expert that helps identify, describe, and catalogue the tunicates (Shenkar and Swalla, 2011) and hemichordates, two invertebrate groups that are closely related to vertebrates. Humans are vertebrates, so you can think of the groups that I work on as your invertebrate cousins! When I moved to the University of Washington and Friday Harbor Labs in 1999, none of the hemichordates that live here had names. My challenge was to find and categorize the species that live here.

What is a hemichordate? They are marine worms that are related to echinoderms (sea stars, sea urchins, and sea lilies). They are notoriously difficult to find, even if you have a known location for them (Figure 1.) Their larval stage is echinoderm-like and as adults they look more like chordates. They have half of the chordate features; gill slits at some life stage, a dorsal neural tube, and a post-anal tail (Figure 2.) They live buried in sand or mud, and many scientists don’t even know that hemichordates are living in their study areas.

Figure 2. Hemichordate worm dug from Bambridge Island by the FHL Comparative Invertebrate Embryology course of 2010. Note the short proboscis in the lower right. This is the “head” end of the worm. It has a short “neck” region behind the proboscis and then a long posterior region, the “abdomen.” Photo by graduate student Julia Merkel.

There is a population of hemichordates that live in Padilla Bay, WA, which is the muddy bay to your right as you’re racing to the Anacortes ferry.   At low tide you can see the shallow and muddy nature of the bay, and the hemichordate worms that live there must burrow down at low tide to avoid dessication. These hemichordates were first described as an East Coast species, Saccoglossus bromophenolosus, named by Dr. Gary King in 1995 for the chemicals that they produce. We quickly showed with molecular methods that the Padilla Bay species is S. bromophenolosus, and was probably imported by the shellfish industry in the early 1900’s (Smith et al. 2003.) Smith et al. 2003 showed that the East Coast species, S. bromophenolosus, is only present in Willapa Bay and Padilla Bay in Washington (Figure 3.) This study was done by an enterprising undergraduate student, Shannon Smith.

Figure 3. Pacific Northwest Saccoglossid locations. S. bromophenolosus, a species native to the East Coast, is found only in Padilla Bay and Willapa Bay as far as we know. S. pusillus is found from San Diego to Vancouver Island, and is a native species. Figure from Smith et al. 2003. Since 2003, we’ve also found S. pusillus in Friday Harbor, right in front of Friday Harbor Laboratories.

Only an expert can tell these animals apart, and correct identitification is important for knowing how many species there are and what their ranges may be. We also need to be aware that there may be invasive species that were introduced from afar, and native species not yet discovered in a particular area. My research lab examined a Canadian hemichordate species and showed that it was Saccoglossus pusillus, first described from southern California in 1908 (Smith et al. 2003.) We’ve shown that this species’ range extends all the way from San Diego to Vancouver Island, and the same species has been found in a dredge right in Friday Harbor near FHL.

We are continuing to look for new populations of hemichordates. Sometimes we go back to very old scientific literature and find that the worms are still found in the locations that were originally described. In 2013, we discovered a new population of hemichordates living at the far end of False Bay, on San Juan Island, WA. This is the first report of hemichordate worms living in the intertidal on San Juan Island. These worms have been called Glossobalanus berkeleyi by some scientists, but may have also been described as Balanoglossus occidentalis. This worm recently graced the cover of a scientific journal, for an article on micro-RNAs in hemichordates (Peterson et al. 2013.) When there is a question raised about what a worm is, we use both morphological and molecular tools to decide which species it is. We read the original description of the species, study the current worm, and do DNA analyses to figure out its identity.

In summary, it’s not always easy to identify a particular marine invertebrate but it is important to have experts who continue to study the different species that we have on planet Earth. Friday Harbor Labs scientists have been active in documenting marine biodiversity on global and local scales. We hope that you’ve learned a little bit about the hemichordate worms that are found here in the San Juan Islands!

Information from these publications is cited in this issue of Tide Bites:

Appeltans, W. et al. (120 authors alphabetical, including Lambert, G., Mills, C.E. and B.J. Swalla). 2012. The magnitude of global marine species diversity. Current Biology 22(23): 2189-2202.

Peterson, K.J., Su Yi-H., Arnone M.I., Swalla B.J., and B. King. 2013. microRNAs support the monophyly of enteropneust hemichordates. J. Exp. Zoolog. B Mol. Dev. Evol. 9999B: 1–7.

Shenkar, N. and B.J. Swalla. 2011. Global Diversity of Ascidiaea. PLoS 1. 6:6 e20657

Smith, S.E., Douglas, R., Burke da Silva, K. and B.J. Swalla. 2003. Morphological and molecular identification of enteropneust worms (Hemichordata: Harrimanidae) in the Pacific Northwest. Can. J. Zool. 81:133-141.