Fish in the Bay – 2 December UC Davis Trawl – Part 3: The Bugs

It’s end of year, we just passed through solstice (21 December) and King Tide perihelion is coming on 2 Jan.  This is a rare chance to discuss a few things in greater detail.  A lot of critters I see on UC Davis trawls end up on the cutting room floor.  Bugs often are the losers: December report Part 1 was about Fish, Part 2 was the Tides.

This installment is about the bugs.  UC Davis trawls are fish surveys.  But, bugs are important, and the Hobbs crew always pulls up interesting bugs. (My definition of “Bugs” is very loose; generally, any invertebrate is a “bug” in my book.)

Lots of Crangon shrimp. I mentioned in the first post that native Crangon shrimp populations are up this year compared to non-native Palaemons and Exopalaemons.  Crangons are the sandy spotted ones in the photo.  A single clear-bodied Exopalaemon sits in the center position.

Huge gaps in shrimp knowledge. Crangon franciscorum (“Bay Shrimp” or “Grass Shrimp”) and Palaemon macrodactylus (Oriental Shrimp) are the two dominant shrimp species in the Bay-Delta system, according to various sources.  It has been long thought that Palaemons were introduced to SF Bay in early 1950s Korean-war-vintage ballast water.  Palaemons tend to dominate Lower South Bay during dry years. Native Crangons tend to bounce back after freshwater flushing.  It is not known how big or episodic must a flush be to favor Crangon populations.

Exopalaemon shrimp. Constant freshwater favors the other non-native Exopalaemon shrimp.  The Exopalaemon above was one of seven caught in Alviso Slough on December 2nd.  We always see some in fresher estuarine sloughs in Lower South Bay. The rounded (humped) rostrum is characteristic of this shrimp.

I found a concise presentation by Tiffany Brown and Kathy Heib about Exopalaemon modestus (Siberian Prawn):   According to the presentation, this true freshwater shrimp was introduced to the Bay-Delta around year 2000.

Palaemon shrimp.  These were two palaemons collected in a single trawl from Lower Coyote Creek (Coy 4 station).  I believe these are P. macrodactylus (aka: oriental shrimp).  They are definitely Palaemon genus.  Both show the distinctive Palaemon “steak-knife” rostrum. The larger one is tomato orange-red with big “boxer” arms, the smaller one is the more characteristic clear color.  I recall seeing similar colorful Palaemons last winter.  What is this?  My guess is that tomato Palaemons are mating ready males (or maybe females).

This group of Palaemons was caught in the main stem of Lower Coyote Creek later the same day.  There are no “tomato reds” in this group, but at least two of the eight have colorful “boxer” arms.  I presume that the name “macrodactylus” refers to these “big hands.”

I noticed big arms last January (photo above from Artesian Slough in January).  By May, big arms no longer seemed to be present.  Is this a seasonal Palaemon mating display?

Crangons don’t have boxer arms or a steak-knife rostrum.  A very different looking shrimp.

Another view.

Snail eggs stuck to a bryozoan.  Levi Lewis identified these little egg sacks as likely coming from some type of snail.  Back in the office, Jessica Donald nominated a likely candidate based on photos: Ilyanassa obsoleta – Eastern mud snail.

Eastern mud snails have been documented in SF Bay since at least 1907.  “the most abundant intertidal snail on SF Bay mudflats and lower reaches of marsh channels, where it is often found in large herds.”  … Feeds on diatoms and algal detritus and scavenges dead fish, crabs and other animal remains.

Snail egg closeup.  Some of the egg pouches are massed into larger balls.  Most are strung out along the branches of the mossy bryozoan.  Each jelly packet contains, maybe 50+ eggs from what I see in photos.  Can you imagine how many tiny snails will emerge?  How many become fish or shrimp food?  How many will grow to join the herds of algal grazing adult snails?

Tunicates / Sea Grapes.  The Hobbs net scraped up this ugly mess from the middle of Lower South Bay (station LSB-1).   Most of the mass is made up of tunicates (aka: Sea Grapes).  Thousands of them seem to show up in December or January.  The official Hobbs trawl count was 1000+ tunicates at this station.  There were many thousands of them if you tried to count each bud.

Tunicate clump.  These clumped masses of individual filter feeders seem to reproduce by budding.  I speculate that these are huge consumers of phytoplankton.  Tunicate populations “bloom” at the time of year when phytos decline sharply.  But, is this coincidence?

Tunicate close-up.  At first glance, I thought a worm-like parasite might be dwelling inside this Sea Grape.  But, I am pretty sure that is the tunicate gut.  I should have cut it open to verify.

Pile worm.  We see pile worms frequently, but they tend to get mangled in the trawl nets.  I was happy to see this one come out intact.  According to South San Francisco Bay Invertebrate Guide (p.8), this classic polychaete feeds on algae, bryozoans, sponges, small crustaceans, etc.  And, he, or she, is dinner to a fish or diving duck.

Ghost Shrimp.  By all accounts these shrimp are very good fishing bait, possibly the best.  Sturgeon are known to go crazy over them.  I did not know there are at least three varieties of Ghost Shrimp on California coasts, and I don’t know which of the three ghost shrimp species this one is.

This is another view.  Ghost shrimp are found on mud banks.  And, there is a fishing limit of 50 if you want to catch this very desirable shrimp:

Mud Crab.  This is either a Hemigrapsus or Harris crab.  I am still not proficient in telling the difference.  Native Hemigrapsus (“Hemi’s”) are more common in the Bay and prefer mud flats where this one was caught, so I will call this a “Hemi.”

Scale worm.  This polychaete could be native, depending on species.  Whether native or not, it is a bottom-dwelling scavenger and another good fish food.

Philine / Snot-Ball Snails.  We see Philine snails occasionally in the central parts of LSB.  This is a non-native “inside-out” gastropod snail (it has a small shell deep in the flesh). It goes by various names.  I tend to like the name invented by Jim Hobbs: “Snot-Ball Snail.”  According to some reports, they eat clams.

Synidotea laevidorsalis.  We almost always find big piles of these isopods around LSB.  They seem to congregate in huge numbers, probably over organic detritus.  According to SF Bay Benthic Guide, Synidotea are important food for young striped bass, starry flounder, king salmon, sturgeon and diving ducks.  I have a hard time believing that because they don’t look very nutritious.  And, I think they eat a lot more than hydroids.

Large masses of Synidotea look relatively disgusting to the untrained eye.

Synidotea closeup.  But individually, they are kind of charismatic.  I think of them as marine sowbugs / marine woodlice.  They cling, but they don’t bite … humans.

Zooplankton are the tiniest bugs.  Phytoplankton are the tiniest plants.   Too small to photograph!

This is our last working day before Christmas.  As I write, Ryan Mayfield, Jessica Donald, and Bryan Frueh just returned to from the Bay with a fresh batch of phyto and zooplankton samples.  Here are Ryan and Jessica with phyto samples ready for shipment.  This Bay won’t characterize itself and it never sleeps.

Happy Holidays everyone.  Happy New Year.  Don’t forget perihelion!



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