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.