Science Stories: Adventures in Bay-Delta Data

What lives in the mud?

(spoiler alert, not just clams)

By Rosemary Hartman, with advice from Betsy Wells.

Benthic samples (things that live in mud)

The Environmental Monitoring Program has been collecting data on water quality, nutrients, zooplankton, phytoplankton, and benthic invertebrates for almost 50 years. Data from the benthic invertebrate sampling program has been key to documenting the invasion of the clam Potamocorbula amurensis and corresponding decrease in phytoplankton (Carlton et al. 1990; Kimmerer and Thompson 2014). However, the program catches a lot more than just clams. They bring up crustaceans, worms, amphipods, isopods, and lot of other critters you have probably never heard of. All of their data are published regularly on the Environmental Data Initiative website (Wells 2024), and there is a lot to be learned by looking through it.

What does sampling look like?

It’s not easy to look at what lives in mud that is 20 feet under water. EMP’s intrepid crew uses a ponar grab – a pair of metal “jaws” that can be held open until it hits a solid surface (like the river bottom). Then the weighted jaws snap shut, picking up a healthy helping of mud and associated critters (Figure 1). The survey crew then dumps the mud out into a mesh tray and slowly washes the mud away, leaving the critters.

Figure 1. A gif demonstrating how a ponar grab works. A pair of metal "jaws" is lowered to the bottom of the water where it springs shut, scooping up a sample of mud and associated invertebrates.

What do they catch?

Well, when we look over the entire time period (1975-2023), 85% of the catch is made up of about 15 taxa (Figure 2, Figure 3). The most common is the invasive overbite clam, Potamocorbula amurensis. Second most common is a tube-dwelling amphipod, Americorophium stimpsoni. Next up is another amphipod, Amplesca abdita, followed by the polychaete worm Manayunkia speciosa. The rest of the “usual suspects” include some more polychaetes, several oligochaete worms, a few more amphipods, the Asian clam Corbicula flumninea, ostracods (also known as “seed shrimp”), and cumaceans (also called “comma shrimp).

Interestingly, there are also 41 species that have only ever been recorded once in the history of the program (Figure 4, Figure 5)! These include several crabs which are probably too fast to show up more frequently (Yellow rock crab – Metacarcinus anthonyi, blue-handed hermit crab – Pagurus samuelis, knobknee crestleg crab- Lophopanopeus leucomanus, and pea crab – Pinnixa scamit), the sea spider – Ammothea hilgendorfi, eleven different species of midge larvae (family Chironomidae), a dragonfly nymph (the blue dasher – Pachydiplax longipennis), and a few more worms and amphipods.

Figure 2. Percent of total catch over the entire history of the EMP program (1975-2023) made up by the 15 most common taxa. (Click to enlarge)

Figure 3. Some of the most common taxa collected by EMP's benthic survey. Clockwise from top life: Manayunkia speciosa (a polychaete worm), Limnodrillus hoffmeisteri (an oligochaete worm), Potamorbula amurensis (overbite clam), Nippoleucon hinumensis (a cumacean – comma shrimp), Corbicula fluminea (Asian Clam), and Americorophium spinicorne (Amphipod). All images from DWR's Environmental Monitoring program, used with permission.

Figure 4. A timeline of instances when a species was found once in the EMP program, and never again. (Click to enlarge)

Figure 5. A few taxa from the Delta that have only been seen once! The yellow rock crab, Metacarcinus anthonyi, the sea spider (Ammothea hilgendorfi) and midge larvae (family Chironomidae, several species). Yellow rock crab picture from Harmonic at English Wikipedia, (used under license CC BY-SA 3.0). Sea Spider picture from The Trustees of the Natural History Museum, London (used under license CC BY). Midge larvae image from CDFW's Stockton lab.

Who is Manayunkia speciosa anyway?

One of the top players in our benthic team is the polychaete worm, Manayunkia speciosa (first picture in Figure 3). If you’re not familiar with polychaetes, they are in the same phylum as earthworms (the annelids) but a different class (Polychaeta, not Oligochaeta). You can tell the difference because the oligochaetes are very “worm shaped” without a clear head and with only a few hairs. Polychaetes, on the other hand, have a lot of spines and hairs all over them. They sometimes have leg-like fins that ungulate along their sides, and they always have a distinct head. In the case of M. speciosa, he is a tube-dwelling worm, which means he sticks a bunch of sand and mud into a little house in the bottom of the river and lets his long, wavey feelers stick out, catching bits of food as they wave by. Most types of polychaetes are salt-water critters, but M. speciosa prefers freshwater, so he is found primarily in the freshwater stations sampled by EMP (Figure 6). M. speciosa is particularly important to the broader ecology of the Delta because they can carry the nasty salmon disease Ceratonova shasta, a myxozoan parasite (Foott 2017; Stocking et al. 2006).

Figure 6. Average catch per meter squared (log-transformed) of M. speciosa at all of EMP’s freshwater stations since 2000. (Click to enlarge)

One of the curious things about M. speciosa is that he can be very common, but not in every year. Looking at the average catch per m² from all the freshwater stations, it can vary from a low of 7 individuals in 1978, to a high of 4,387 individuals per square meter in 1991 (Figure 7)! But why do we see these big swings? A lot of critters in the Delta have population swings based on how much rain we get, so we see patterns based on water year type (broad categories of precipitation from critically dry to wet, indicated by colored point shapes on Figure 7). We see that a lot of the really high population spikes in M. speciosa are during critically dry years. Other researchers have found that M. speciosa seems to do better in slow-moving water (Alexander et al. 2014), so maybe they get flushed out during high-flow years? But other high population years are categorized as “wet” or “above normal”, so that can’t be the only factor. An experiment by Malakauskas et al. (2013) found that while they can get dislodged at high flows, they have high survivorship after being dislodged, so high flow events might just spread them around.

The highest abundance of M. speciosa occurs in the late winter and spring (Figure 8) – the periods of highest flow in the Delta. This is a little different than the pattern of abundance in the Great Lakes – one of the few other places they’ve been studied – where the peak abundance was in May-August (Schloesser et al. 2016). A study of lab-reared M. speciosa found they have an annual life cycle and can reproduce throughout the year, but had highest egg production in the spring and summer, with babies staying in their mother’s tube for 4-6 weeks before emerging (Willson et al. 2010).

Figure 7. Average CPUE of M. speciosa in all the freshwater stations sampled by EMP from 1975-2023. (Click to enlarge)

Figure 8. Mean CPUE of M. speciosa by month for all the freshwater stations sampled by EMP, 2000-2023. (Click to enlarge)

M. speciosa seems to prefer fresh water, and California has a lot of fresh water outside of the Delta. Where else is it found? The Surface Water Ambient Monitoring Program (SWAMP) conducts benthic invertebrate surveys all over the state – sponsored by the State Water Board and implemented by CDFW. It turns out that in over 34,000 samples collected by SWAMP since the year 2000, M. speciosa has only been found 118 times, and most of those detections were in the Delta (Figure 7). However, research conducted on the Klamath River in northern California has found a lot of M. speciosa on that river, particularly in the slower reaches downstream of a major dam (Alexander et al. 2014; Stocking and Bartholomew 2007), so the lack of detections may be more “not knowing what to look for” than not being there. M. speciosa is also quite small, and may be too small to be caught in SWAMP’s sampling gear on a regular basis.

Figure 9. Samples collected by the Surface Water Ambient Monitoring Program from 2000-2023 showing catch of polychaetes (including M. speciosa). Grey points indicated samples without polychaetes, colored circles indicating samples with polychaetes, with larger circles having more individuals. (Click to enlarge)

I wish I could end this blog post with a clear graph of something that is driving abundance of M. speciosa, but after two days of playing with the data, I haven’t found anything useful. So I will leave you with links to the data and so you can figure it out for yourself! Let me know if you have any ideas.

Check out EMP's website for more annual reports and more background information!

References and further reading:

• Alexander JD, Hallett SL, Stocking RW, Xue L, Bartholomew JL. 2014. Host and Parasite Populations After a Ten Year Flood: Manayunkia speciosa and Ceratonova (syn Ceratomyxa) shasta in the Klamath River. Northwest Sci. 88(3): 219-233, 215. .
• Carlton JT, Thompson JK, Schemel LE, Nichols FH. 1990. Remarkable invasion of San Francisco Bay (California USA) by the Asian clam Potamocorbula amurensis. I. Introduction and dispersal. Mar Ecol Prog Ser; 66: 81-95.
• Foott JS. 2017. Ceratonova shasta and Parvicapsula minibicornis (Phylum Cnidaria: Myxosporea ) infectivity for juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Upper Sacramento River: July – November 2016. Anderson, CA. : US Fish and Wildlife Service. California-Nevada Fish Health Center.
• Kimmerer WJ, Thompson JK. 2014. Phytoplankton growth balanced by clam and zooplankton grazing and net transport into the low-salinity zone of the San Francisco Estuary. Estuaries Coasts; 37: 1202-1218.
• Malakauskas DM, Willson SJ, Wilzbach MA, Som NA. 2013. Flow variation and substrate type affect dislodgement of the freshwater polychaete, Manayunkia speciosa. Freshwater Science. 32(3): 862-873.
• Schloesser DW, Malakauskas DM, Malakauskas SJ. 2016. Freshwater polychaetes (Manayunkia speciosa) near the Detroit River, western Lake Erie: Abundance and life‐history characteristics. Journal of Great Lakes Research. 42(5): 1070-1083.
• Stocking RW, Bartholomew JL. 2007. DISTRIBUTION AND HABITAT CHARACTERISTICS OF MANAYUNKIA SPECIOSA AND INFECTION PREVALENCE WITH THE PARASITE CERATOMYXA SHASTA IN THE KLAMATH RIVER, OREGON–CALIFORNIA. Journal of Parasitology. 93(1): 78-88. doi: https://doi.org/10.1645/ge-939r.1
• Stocking RW, Holt RA, Foott JS, Bartholomew JL. 2006. Spatial and Temporal Occurrence of the Salmonid Parasite Ceratomyxa shasta in the Oregon–California Klamath River Basin. Journal of Aquatic Animal Health. 18(3): 194-202.
• Wells E, Interagency Ecological Program. 2024. Interagency Ecological Program: Benthic invertebrate monitoring in the Sacramento-San Joaquin Bay-Delta, collected by the Environmental Monitoring Program, 1975-2023. ver 4. Environmental Data Initiative.
• Willson SJ, Wilzbach MA, Malakauskas DM, Cummins KW. 2010. Lab Rearing of a Freshwater Polychaete (Manayunkia speciosa, Sabellidae) Host for Salmon Pathogens. Northwest Sci. 84(1): 183-191, 189.

More underappreciated data!

This is the second blog in our series on underutilized datasets from IEP.

San Francisco Bay Study’s Crab Catch dataset

Curated by Kathy Hieb and Jillian Burns

The San Francisco Bay Study has been sampling with otter trawls and midwater trawls throughout the San Francisco Bay, Suisun Bay, and Delta since 1980. Their fish data have been used in a number of scientific studies, regulatory decisions, and journal articles. However, did you know they measure and count crabs in their nets too?

Bay Study’s stations are all categorized as “Shoal” (shallow areas) or “Channel” (deeper samples). Crabs are collected by otter trawl, which is towed along the bottom of the water, scraping up whatever demersal fishes and invertebrates it comes across. Truth be told, it’s not the best way to catch crabs, because most crabs like hiding under rocks where they are out of the way of the net, but it does give us a metric of status and trends of some of the most common species of crabs, including the Pacific rock crab (Cancer productus), the graceful rock crab (Cancer gracilis, also known as the slender rock crab), the red rock crab, and everyone’s favorite, the Dungeness crab (Metacarcinus magister).

After the net has been towed on the bottom for five minutes, it’s brought on board the boat and the biologists count, measure, and sex the crabs they’ve caught (Figure 1). This can be tricky, because crabs can be FAST! Especially the smaller Dungeness crabs (Figure 2). The biologists have to be careful and pick up the crabs by their back side to avoid getting pinched by their claws, which definitely takes practice.

Once all the crabs are counted and measured, they are entered into a database that goes back to 1980. Bay's Study's Dungeness crab data have been used to help manage the commercial crab fishery because fisheries-independent data is valuable. From 1975 to 1978, an estimated 38-82% of the Dungeness crabs in the central California region rear in the San Francisco Estuary each year (Wilde and Tasto 1983). This dataset was also very helpful in tracking the introduction, expansion, and decline of the Chinese mitten crab (Eriocheir sinensis), which briefly took over the brackish regions of the estuary but declined as rapidly as it arrived (Figure 3. Rudnick et al 2003). Bay Study's crab data has also been combined with other datasets to see how the estuarine community as a whole responds to climate patterns and human impacts (Cloern et al. 2010).

However, a lot of questions remain to be asked of this dataset. Why did we see such high catch of Dungeness crabs in 2013 and 2016? What are the drivers between the lesser-studied crabs, such as the graceful rock crab? How does the salinity preference of each species of crab differ (Figure 4)? If you want to investigate these questions yourself, data are available on the CDFW file library website. But be careful, the data have a few hiccups in them, such as changes to sampling sites over time, missing samples during period of boat break-downs, and other caveats. Be sure to read the metadata and make sure you understand the data before using them.

Further reading

• Baxter, R., K. Hieb, S. Deleon, K. Fleming, and J. Orsi. 1999. Report on the 1980-1995 fish, shrimp and crab sampling in the San Francisco Estuary (PDF), Interagency Ecological Program Technical Report 63. Stockton, California. 503 pages. 
• Cloern, J. E., K. A. Hieb, T. Jacobson, B. Sanso, E. Di Lorenzo, M. T. Stacey, J. L. Largier, W. Meiring, W. T. Peterson, T. M. Powell, M. Winder, and A. D. Jassby. 2010. Biological communities in San Francisco Bay track large-sale climate forcing over the North Pacific (PDF). Geophysical Research Letters 37(L21602):6 pages.
• Cloern, J. E., and A. D. Jassby. 2012. Drivers of change in estuarine-coastal ecosystems: Discoveries from four decades of study in San Francisco Bay. Reviews of Geophysics 50(4):RG4001. 
• Rudnick, D. A., K. Hieb, K. F. Grimmer, and V. H. Resh. 2003. Patterns and processes of biological invasion: The Chinese mitten crab in San Francisco Bay. Basic and Applied Ecology 4(3):249-262.
• Rudnick, D., T. Veldhuizen, R. Tullis, C. Culver, K. Hieb, and B. Tsukimura. 2005. A life history model for the San Francisco Estuary population of the Chinese mitten crab, Eriocheir sinensis (Decapoda: Grapsoidea). Biological Invasions 7(2):333. doi:
• Rudnick, D. A., K. M. Halat, and V. H. Resh. 2000. Distribution, Ecology and Potential Impacts of the Chinese Mitten Crab (Eriocheir sinensis) in San Francisco Bay. Technical Completion REPORT UCAL-WRC-W-881, University of California. 
• Wild, P. W, & Tasto, R. N. (1983). Fish Bulletin 172. Life History, Environment, and Mariculture Studies of the Dungeness Crab, Cancer Magister, With Emphasis on The Central California Fishery Resource. UC San Diego: Library – Scripps Digital Collection.

Some data just needs a little love

IEP collects a lot of data. Most people who work in the estuary have probably heard of FMWT’s Delta Smelt Index, or the Chipps Island salmon trawl, or the EMP zooplankton survey. But those “big name” surveys are only part of what we do at IEP! This is the first blog post in a series on “underappreciated” datasets where we highlight some of the data you might not be familiar with.

Yolo Bypass Fish Monitoring Program’s Drift Invertebrate survey

By Nicole Kwan, Brian Schreier, and Rosemary Hartman

In most of the estuary, we concentrate on invertebrates and other fish food that live under the water. However, in streams and rivers the contribution of terrestrial invertebrates falling into the water from surrounding vegetation and aquatic insects that ‘hatch’ on the surface of the water to metamorphose into their terrestrial adult form are also important food sources for fish, particularly Chinook Salmon and Sacramento Splittail. The Yolo Bypass, a large managed floodplain near Sacramento, is located on the boundary between the estuary and the river. As such, the Yolo Bypass Fish Monitoring Program (YBFMP) tracks both aquatic zooplankton and terrestrial drift invertebrates.

The YBFMP collects drift invertebrates year-round from two sites to compare the seasonal variations in densities and species trends of aquatic and terrestrial invertebrates between the Sacramento River and the Yolo Bypass. The crew piles into a boat and heads out, then tows a rectangular net that sits half-in, half-out of the water for ten minutes along the surface. Sometimes, when flows are really high, they can simply hold the net out on the side of their fish trap for ten minutes and let the water flow through it instead of towing it (Figure 1). The crew then rinses the sample into a bottle, preserves it with formalin, and sends it to a contracted lab for identification and enumeration (counting all the bugs under a microscope).

Figure 1. YBFMP scientist Anji Shakya sampling drift invertebrates in high flows next to the fish trap. Image credit - Naoaki Ikemiyagi Department of Water Resources.

There are a lot of interesting questions we can ask with these data, such as, what time of year do we catch the most chironomids (midges) (Figure 2)? Or, how does community composition and abundance differ between the Sacramento River and Yolo Bypass (Figure 3), and how does that relate to differences in hydrology and water quality?

Figure 2. Log-transformed catch-per-unit-effort of chironomid midges caught in drift net samples in the Yolo Bypass Toe Drain and Sacramento River at Sherwood Harbor. Note the abundances of chironomids in the spring on the Yolo Bypass. The Bypass tends to have higher abundances than the Sacramento River in the spring, but lower abundances in the summer. Sampling in summer and fall only started in more recent years. Click on image to enlarge.

Figure 3. Catch per unit effort of organisms in the drift net categorized by taxonomic order and plotted over time. Insects dominate both the River and the Bypass samples, but the Bypass has consistently higher abundance of drift invertebrates. Click on image to enlarge.

One particularly unexpected thing we’ve seen in the data is high abundances of snails in the samples. Snails normally live on the bottom of the water or on vegetation, so seeing them floating on the surface was surprising. We see a lot of variation in snail abundances between years, and we’re not sure why (Figure 4). The wet years of 2017 and 2019 had particularly high snail catch, but other wet years weren’t similar. A fun mystery for someone to investigate!

Figure 4. Mean (+/- one standard error) CPUE of snails (class Gastropoda) in drift net samples from the Yolo Bypass. Water year classes (Wet - W, Dry - D, or Average - A) is noted with letters under each bar. Notice how snail catch was very high during the wet years of 2017 and 2019, but also during the dry year of 2013 and the average year of 2003. Click on image to enlarge.

If you want to check out this data for yourself, it has been published on the EDI data repository and will be updated regularly. However, keep in mind that sample frequency, contracting labs, and methods have changed slightly over time. Be sure to read the metadata so you fully understand the data before using it. If you have any questions, just reach out! We’re nice people and we love talking about our data and helping others use it.

Further Reading

• Benigno, G. M., and T. R. Sommer. 2008. Just add water: sources of chironomid drift in a large river floodplain. Hydrobiologia 600(1): 297-305.
• Goertler, P. A. L., T. R. Sommer, W. H. Satterthwaite, and B. M. Schreier. 2018. Seasonal floodplain‐tidal slough complex supports size variation for juvenile Chinook salmon (Oncorhynchus tshawytscha). Ecology of Freshwater Fish 27(2):580-593.
• Goertler, P., K. Jones, J. Cordell, B. Schreier, and T. Sommer. 2018. Effects of Extreme Hydrologic Regimes on Juvenile Chinook Salmon Prey Resources and Diet Composition in a Large River Floodplain. Transactions of the American Fisheries Society 147(2):287-299.
• Sommer, T. R., W. C. Harrell, A. M. Solger, B. Tom, and W. Kimmerer. 2004. Effects of flow variation on channel and floodplain biota and habitats of the Sacramento River, California, USA. Aquatic Conservation 14(3):247-261.
• For more key findings from the Yolo Bypass, check out the YBFMP Story Map