Posted by: pointreyesscience | December 12, 2011

Batillaria Blog

Batillaria in a growth experiment

It’s true that few people care to get intimate with the muck at the bottom of Tomales Bay, but as for myself, I could not wait to spend my summer face to face with it. My interests in marine invasion ecology lead me to the Bodega Marine Lab where I was offered the opportunity to play in the mud for four months. I was thrilled at the prospect of getting up close and personal with the invasive Japanese mudsnail, Batillaria attramentaria. With bucket and sieve in hand I slogged forward, rain or shine, battling the Batillaria. Formally my job description entailed surveying the new population in Bodega Harbor and testing eradication methods on existing populations in Tomales Bay. In addition to this I also spent a lot of time researching and field-testing my own questions pertaining to the parasites that live within the snails. I was interested in observing infected and uninfected snail behavior.

My first trip to Tomales Bay was at Walker Creek. Before I even got the chance to sink my shoes into the mud, I could see shells littering the surface I was about to step on. Little did I know a small patch of mud could contain well over 1000 snails! I was soon to discover how quickly these snails are able to take over, inhabiting nearly every nook and cranny of the shoreline. In Tomales Bay Batillaria can be found living in brackish streams (a mix of fresh and salt water), salt marsh pannes, cobbled shores and on the expansive open mudflat. The snails inhabit the shoreline at varying densities from Walker Creek to Millerton on the eastern side of Tomales Bay, and from Indian Beach on the northwest side down to Inverness.

How did they get here?

In the 1930’s when the Pacific Oyster from Japan (Crassostrea gigas) became desirable for aquaculture on the west coast, Batillaria among other mudflat species from Japan arrived in the mud attached to the oyster shells. Batillaria ranges from Elkhorn Slough, California, all the way to Boundary Bay, British Columbia (Hanna 1966) at sites where Pacific oyster aquaculture was prevalent (Byers, J.E. 1999). Within the past 5-10 years however, Batillaria has spread to places where Crassostrea gigas has not been introduced. Heidi Weiskel from UC Davis and her research team found a new population in 2005 in San Francisco Bay and 2007 in Bodega Harbor. Using her research grant from the NPS, she started working on comparative studies, focusing on Tomales Bay as a critical reference population for the new populations.

A little natural history…

The snails graze along the mudflats like small herds of cattle, feasting on diatoms, or other photosynthesizing microalgae that cover the mud’s surface. Powered by an herbivorous diet, these snails can grow to sizes reaching 45mm. When new recruits emerge they are only visible to the snail-trained eye (less than a millimeter long!). When the snails reproduce their young develop directly from an egg as opposed to having a planktonic, or swimming stage. The direct development does play a role in limiting the species spread.

Tiny invader, big impacts

 Before Batillaria established its domain, the native California mud snail Cerithidea californica prevailed in Tomales Bay. After its introduction the snails were seen to coexist on the mudflat (Whitlatch & Obrebski 1980). Since then, the non-native has successfully taken over the flats of Tomales. Not only have these snails caused local extinctions of an ecologically similar species (Byers 2000), they have introduced a non-native parasite that has the potential to alter the mudflat community and possibly other levels of the food chain (Lafferty & Kuris 2009). The snails also cause a variety of habitat changes including an increase in hard substratum, as well as potential alterations to microalgal biomass (due to feeding habits) and competition with the infaunal community. The hard substrate created by their shells in some cases facilitates the invasion of other organisms, both native and non-native (Wonham et al. 2005) and may also affect shorebird foraging of what was once soft sediment.

Brightly marked Batillaria were used as part of a mark-recapture study

The spring months mark the re-appearance of the snails at Bodega Harbor. In the late fall the snails go under the mud and then reappear around May, a phenomenon unique to the new population found at Doran Beach (the snails at Tomales Bay are so abundant that they can be seen on the mudflat all year round). In the beginning of May, population surveys are carried out utilizing the same sampling protocol from year to year to maintain continuity. Methods include running a transect tape across the populated area and measuring vertical transects at random intervals. Sampling is done along the vertical transects, which entails sinking the sawed off top of a 5-gallon bucket into the mud and scooping up the surface with your hands. The sample is sieved (using a 2mm mesh) and the snails are put into a bag to be counted, sized and dissected in the lab. After the snails are dealt with in the lab all of our samples are put in the freezer for at least 24 hours and then disposed of using the designated protocol for marine invasive species.

The above population survey was conducted in Tomales Bay in 2008, providing a wealth of information concerning the established population, which was used to compare to the two new populations in San Francisco Bay and Bodega Harbor.  In May of 2010, Heidi Weiskel and I conducted the survey in Bodega Harbor at Doran Beach where the relatively new population exists. The population survey enables us to track its rate of spread, distribution and demographic characteristics. Information regarding sex, size and infection rate can be accounted for. In particular, the snails at Bodega Harbor provide a unique opportunity to test predictions concerning founder populations (for example, how quickly they spread, what their distribution patterns are, and how their size class structure changes over time).

Eradication

Prior to the 2010 field season, teams of volunteers handpicked and sieved for snails at Doran Beach, removing more than 10,000 pounds of snails! Because the population at Doran Beach is still relatively small, there’s a push to test different eradication methods in order to control the spread.

Funded by the California Sea Grant, a team of scientists from the Bodega Marine Lab spent the 2010 field season testing a device dubbed –“The Super Sucker”. This low-tech machine includes a gas-powered motor attached to a 5-gallon pail, complete with sieve, intake hose and bike break throttle. Two trial experiments were run, one at Doran Beach (low density <10 snails/m2) in Bodega Harbor and one at Walker Creek (high density >1000 snails/m2) in Tomales Bay. The experiments compared handpicking versus the “Super Sucker”, running methods of eradication simultaneously.  We hypothesized, as most would, that anything would be faster than tediously picking up snails by hand. We also thought that the Super Sucker would be able to pick up tinier snails that a hand-picker may not see.

During the trials the Super Sucker performed well, picking up small and large snails (3mm and bigger) with little sediment. However, technical glitches and difficulty while maneuvering the machine during the trails slowed its efficiency. Not until we conducted the trials in a more uniform density (Walker Creek) did comparisons between the two methods become clear. In a 10 minute time period it seemed that I was able to clear a 2m x 1m patch handpicking as fast as the Super Sucker could. However, not until we took our samples to the lab were we able to conclude that in both low and high density areas, handpicking was at par or slightly MORE efficient than the “Super Sucker” at eradicating snails. Also the frequency of smaller sized snails (5-10mm) being eradicated was the same across both methods. When comparing the Super Sucker across densities, it seemed to be much more effective in high density areas and on flat muddy surfaces as opposed to coarser surfaces that contain many pebbles or sand that are vacuumed up along with the snails and can clog the hose and sieve

The "Super Sucker" was used to remove the invasive snails

Moving forward…

The small engine was the biggest constraint controlling the Super Sucker’s efficiency. Sucking up water and mud was a huge strain on the motor requiring more fuel than anticipated. Maneuverability was also a challenge on the mudflat. Dragging equipment on a plastic sled through varying terrain (marsh, stream, mud and stones) was difficult and frustrating at times! Without further modification and a more powerful motor the device will not achieve higher efficiency than hand picking. Testing the Super Sucker proved to be a valuable exercise as now time and funds can be re-directed toward other methods of eradication such as molluscicides, heating and raking.

It’s likely that humans moving between infected and uninfected areas carried the snails to different locations creating the new populations. Therefore, it’s imperative that we inform ourselves about what species belong where and to act accordingly, especially when non-native and invasive species are concerned. It’s critical to keep this in mind when we are in Tomales Bay, whether we are kayaking, exploring or researching. Always be sure to thoroughly clean off gear, equipment and boots before entering another water body. We all need to work together to stop the spread!

For more information about Batillaria attramentaria in Tomales Bay you may contact Heidi Weiskel at UC Davis (hwweiskel@ucdavis.edu).

Finally I’d like to thank the hardworking team of researchers who have contributed their time, support, sweat and tears- Chris Pollio, Christy Bowles, Ted Grosholz, and Heidi Weiskel.

Katie Houle

References:

Byers, J. E. (1999). The distribution of an introduced mollusc and its role in the long-term demise of a native confamilial species. Biological Invasions 1(4): 339-353

Byers J.E. (2000) Competition between two estuarine snails: implications for invasions of exotic species. Ecology 81: 1225–1239

Hanna G.D. (1966) Introduced mollusks of Western North America. California Academy of Sciences Occasional Paper 48: 108

Lafferty K.D. and Kuris A.M. (2009) Parasites reduce food web robustness because they are sensitive to secondary extinction as illustrated by an invasive estuarine snail. Philosophical Transactions of the Royal Society of Biology 364: 1659–1663

Whitlatch R.B. and Obrebski S. (1980) Feeding selectivity and coexistence in two deposit feeding gastropods. Marine Biology 58: 219–225

Wonham, M. J., O’Connor, M. & Harley, C.D.G. (2005) Positive effects of a dominant invader on introduced and native mudflat species. Maring Ecology Progress Series 289: 109–116

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