Sites and Critters

All that lives in a handful of mud

Most coastal cities are built at the mouths of rivers and in estuarine systems where soft sediment was the dominant marine habitat type historically. Though we’ve added all sorts of artificial structures to these landscapes and altered urban shorelines considerably, mud and sand habitats are sometimes still evident in some coastal cities, either at low tide, or if you look carefully through the water to the seafloor below from piers and boardwalks. Initially, this soft sediment substrate will probably look rather boring and featureless, not to mention “icky.” There couldn’t be much living in that stuff, right?

Believe it or not, soft sediment environments are incredibly diverse. In a single sediment core sample (a cylindrical area of sediment that’s only a few inches wide and maybe half a foot deep), I find more invertebrate species than I typically find on an entire artificial reef in Puget Sound. They’re modest creatures – small and unassuming, often cryptic, and typically not as colorful as their ostentatious, rock-dwelling counterparts. Regardless, soft sediment organisms, termed “infauna”, are an important part of urban marine landscapes.

Over the last few years, I’ve had the pleasure of becoming more closely acquainted with some of these critters as I’ve sorted through sediment samples from West Seattle. The samples are part of a larger experiment that I promise to report more about soon, but in the meantime, I want to share with you some of my favorite “infaunal” organisms. Specifically, they are the current winners of 3 categories for which I’ve had running lists over recent years:

Category #1: Most frightening

WINNER: Glycerid worms

If I were a marine organism about the size of an ant, there is little I can imagine that would be more frightening than a glycerid worm. These fierce predators construct complex networks of burrows in soft sediment, which they move through rapidly. Remember the movie Tremors from the early 90s? This is like Tremors the real version. When glycerids find their prey, they shoot out their pharynx complete with four terrifying fangs (pictured to here). They’re known as bloodworms. This is said to be because of the ceolomic fluid you can sometimes see through their body wall, which contains hemoglobin and is the color of blood. I wouldn’t be surprised is the true origin of their name is more morbid than that, though. At least they seem to want blood when I’m handling them in the field… Remind me not to re-watch Tremors anytime soon.

Teeth of a glycerid worm. Photo: Marcos Daniel

Teeth of a glycerid worm. Photo: Marcos Daniel

Glycerid worm, Photo: David Fenwick

Glycerid worm, Photo: David Fenwick


Category #2: Most adorable / cutest

WINNER: Euphilomedes ostracods

Since teddy bears weren’t in the running, we have the next best thing. Ostracods are tiny crustaceans that live inside a little circular house; sort of like a seed with legs. The genus I tend to encounter is Euphilomedes spp. and is relatively large, reaching well over a millimeter in diameter. It may not sound like much, but in the world of ostracods, these are giants. Life for Euphilomedes ostracods tends to consist of puttering around between sediment grains, presumably in search of food.

Ostracod, Photo: Ajna Rivera

Euphilomedes ostracod, Photo: Ajna Rivera


Category #3: Most elegant

WINNER: Tellina clams

Though clams in Puget Sound come in all shapes and sizes, one stands out with its elongated figure, smooth, shiny shell, and occasional radiating pink patterns. Though the Tellinid pictured here is from the Bahamas, it’s Puget Sound relatives are no less elegant.

Tellina radiata, Photo: Bill Frank

Tellina radiata, Photo: Bill Frank


These are just a small selection of the many critters that inhabit muddy and sandy marine habitats. The softs sediments we see in urban marine environments may look like a lonely place to call home, but these critters are by no means alone. It’s amazing to see all that lives in a handful of mud!

Photograph of algae presses
Sites and Critters

Red macroalgae artwork… and some science

Algae presses are a cool and creative way to document macroalgal specimens you encounter in the field (and they make great gifts too!). These specimens came from a dive site near Centennial Park in Elliott Bay, Seattle. They represent some of the more common and dominant species I see growing on riprap. I made the presses by placing them on thick paper between two pieces of plywood held together by bolts that I then tightened as the algae dried.

These are presses of red algae species I commonly find on riprap in Seattle.  Tiny pieces of these algae are mixed into adjacent sediments.

These are presses of red algae species I commonly find on riprap in Seattle. Tiny pieces of these algae are mixed into adjacent sediments.

Riprap, the rocky material that makes up jetties, breakwaters, and seawalls, supports an abundance and wide diversity of red macroalgae.  One of the questions I’ve been most interested in testing is whether the red macroalgae growing on riprap get incorporated into neighboring soft sediments.  I recently collected sediment samples along transects extending perpendicularly from riprap installations (see earlier post), and I’m happy to say that I have a finding to report!  After weeks of sorting through the sediment samples, I have found that the amount of red macroalgae that is mixed into soft sediment decreases as you move away from riprap.

The next step is to identify whether these differences in algal content might influence the community of organisms that live in soft sediment.  In ecology, food webs that are altered by the influx of resources from adjacent habitats are said to be “subsidized” or influenced by “spatial subsidies.”  (I’ll write a post soon to give more background on the spatial subsidies literature.)

To test for spatial subsidies, I’ll be conducting field experiments in which I enrich soft sediment plots with fixed volumes of shredded red macroalgae. At the end of 8 and 16 weeks, I’ll be collecting core samples from these enrichment plots and testing for differences in community structure. More to come on that.  In the meantime, I’m excited to say riprap-originating algae do in fact make it to neighboring soft sediments… what is their affect there?  The answer to that is coming soon!

This Week In The Lab

Soft sediments – they’re alive!!!

On Aug 3, I told you about the dives we’d done to collect soft sediments.  Tube of macrofauna in ethanolSince then I’ve spent many an hour in the lab processing the samples we collected.  Processing involves (1) quantifying the volume of riprap-originating algal material in each sample, (2) quantifying sediment grain size, (3) identifying each type of shell hash, and (4) identifying and counting all macrofauna.

Macrofauna are organisms that live in soft sediment.  Until just a few years ago, I had no idea how many critters actually live embedded in sand and mud. From above, the soft sediment landscape appears barren, almost devoid of life.  But it’s actually alive in a way I never imagined – at a tiny scale.  After many hours of picking through sand and mud in my sediment cores, I am again amazed at the density and diversity of macrofaunal life forms.  They come in all shapes and sizes, colors and textures, life histories and strategies.  Worms, clams, snails, amphipods, ostracods, sea cucumbers, and more!  It’s overwhelming.

For now, I’m simply pulling specimens out of sediment samples and storing them in ethanol (as in the photo), but I’ll be identifying them over the coming months and look forward to sharing.  Their stories are bazaar, amazing, surreal – from vicious hunters with exploding mouth parts to little arthropods that spend their entire lives moving about the seafloor in the organic equivalent of a hamster ball. I’ll highlight my favorites as they arise.  Stay tuned!

This Week In The Lab

Does algae and shell hash from riprap make it into neighboring sediments?

You can find subtidal riprap all over the place in urban marine ecosystems.  It’s often like a patchy network of little islands in a sea of soft sediment.  On each of the islands is vibrant hub of reef-associated species – fish, algae, invertebrates of all shapes, colors, and sizes.  Collectively, these riprap-dwelling species generate a lot of biomass, particularly in the form of algae and shell hash.  Eventually, I’ll be testing whether these materials alter the soft sediment communities nearby.  But for now, I simply want to test whether the materials produced by riprap-dwelling organisms make it into adjacent habitats.

Divers entering water to collect soft sediment

This was my reason for embarking on a series of dives recently at Alki Pipeline and Elliott Bay Marina’s breakwater.  With the invaluable help of two dive buddies, Rhoda Green and Dave Thoreson, I was able to get my hands on lots and lots of dirt!  At each site, we lay out three transects extending perpendicularly from riprap.  We collected core samples at 1m, 7m, and 15m along each transect and put them into plastic bags.  After a lot of heavy lifting, we got the samples back to the lab, where I sit now (procrastinating by writing this) with my work cut out for me.  Over the coming weeks, I’ll be sorting through the sediment, quantifying algae, shell hash, sediment grain size, and macrofauna.

I’ll keep you posted on findings as they arise. For now, it’s time for me to get busy.