Photo of noble sea lemon
Sites and Critters

The noble sea lemon

I took the photo above recently at Alki Pipeline, in West Seattle.  It’s a noble sea lemon, Peltodoris nobilis, and it’s larger than any other specimen I’ve ever seen, at almost 20 cm in length. According to Andy Lamb and Bernard Hanby, who wrote every Pacific Northwest Diver’s go-to companion, Marine Life of the Pacific Northwest, noble sea lemons can actually grow to be up to 25 cm long.

Photo of noble sea lemon eating a sponge

Photo by Marquis McMurray. Source: http://slugsite.us/bow/nudwk533.htm

Noble sea lemons are a type of nudibranch, or sea slug. Closely related to snails and terrestrial slugs, nudibranchs come in a striking array of beautiful and vibrant coloration patterns. Many have frilly (functional) adornments, such the darker-colored, fuzzy gill rosette you see here on the noble sea lemon’s back.  (The word nudibranch actually means “naked gills.”) In the front, it has two rhinophores to detect odors. Because nudibranchs have lost their shell, they have developed alternative methods of defense, including blending into their surroundings and harboring chemical toxins, which they may produce themselves or harvest from their prey and reuse.

Nobles sea lemons generally feed on sponges (and sometimes detritus), but individuals apparently have quite specific preferences when it comes to their favorite sponge species. This one on the right appears to have found its prey species of choice! I love this photo from Marquis McMurray – the noble sea lemon there is chowing down so intensely on a sponge that its face is almost completely is buried in it! From what we can tell, noble sea lemons gain chemical defenses (toxins) from the sponges they eat. When they’re eating sponges, they contain doridosine, a toxin that was found to be lethal when injected into shore crabs and mice.

We took the above photo at about 25 ft. While I didn’t see a lot of sponges in the vicinity, I’ll certainly be looking out for potential prey items of the noble sea lemon on future dives.

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Map of Seattle circa 1851
Historical Context

Seattle before urbanization

This illustration from the Seattle Times (link to article) provides a fascinating window into what Seattle’s marine ecosystem might have looked like prior to urbanization. It’s a map of the Seattle area circa 1851, the year that the first white settlers arrived in the area.

There are some amazing distinctions here between the geography of the area at that time, and that of Seattle as we see it today. The entire area that was once a mud flat at the mouth of the Duwamish River is now filled in and inhabited. Harbor Island, a massive man-made structure where large cargo ships now dock and unload, did not yet exist. Without dredging, the southern parts of Elliott Bay were shallower than they are today. A cove exists on the north side of the bay where cruise ships now dock.

Here’s the same illustration next to a satellite map of modern day Seattle (click on it to make it bigger):

Map of Seattle circa 1851 next to satellite image of Seattle today

Left: Seattle circa 1851 (Source: Seattle Times). Right: Satellite image of Seattle today (Source: Google Earth)

With so much more soft sediment and so much less rocky habitat, I find myself wondering whether the rocky habitat species that are so common today – octopus, lingcod, rockfish – were barely present prior to urbanization. The area may have instead been dominated by seagrass beds and tidal mud flats, which support a very different biological community. With no long-term data sets spanning the length of the urbanization process, it may be hard to really know how the ecosystem has changed and what it looked like before the city of Seattle existed.  It’s fun to think about though!

 

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Photo of spotted ratfish
Sites and Critters

My friend the spotted ratfish

A few times recently when I’ve been out collecting sediment, I’ve had the feeling that I’m being followed.  Each time, I turn around and find one of these little guys in tow, hovering over the areas of sea floor that I’ve just disturbed by my sampling.  They’re called spotted ratfish (Hydrolagus colliei) and I’ve grown quite fond of them, despite their funny looks. They’re like my little underwater sidekicks, always interested in what I’m doing and standing by patiently as I do my work.  If the name weren’t already taken, I’d suggest we call them “dogfish” for their loyal underwater companionship.  But given their genus name, Hydrolagus (lagos means hare in Greek), I might instead just take to calling them water bunnies.

Photo of spotted ratfish

Photo by Linda Snook

Spotted ratfish are part of an ancient group of fish called Chimaeras, which are cartilaginous and most closely related to sharks. Their tails are long and skinny, providing limited propulsion. To swim, they instead flap their pectoral fins like a bird. They’re generally thought to favor crunchy foods like crabs and clams, but may also eat worms and other invertebrates in soft sediment. Similar to dogs, what keeps them hovering nearby is probably the hope that I’ll uncover something delicious as I’m sampling. Dog-like or not, though, I ignore the urge to reach out and pat them on the head. They have a venomous spine in front of their dorsal fin that can deliver a painful sting.

If ratfish look to you like weird mythological creatures concocted by the likes of Napoleon Dynamite, you wouldn’t be alone. The name Chimaera is, of course, borrowed from the Chimera in Greek mythology, a fire-breathing beast composed of parts from a snake, a lion, and a goat.  As wikipedia reports: “The term chimera has come to describe any mythical or fictional animal with parts taken from various animals, or to describe anything perceived as wildly imaginative or implausible.” I love that. Ratfish indeed look like the result of some wildly imaginative experiment, and it makes me love them all the more.

As I dive at sites around Seattle, even when I’m not collecting sediment, I’m amazed at how many spotted ratfish I see (at least 2-3 per dive). An article in the Seattle Times a few years ago highlighted the success of spotted ratfish in Puget Sound (article). Their population here is estimated at 200 million.  As Sandi Doughton, the author of the article, states, “that’s more than 30 [ratfish] for every woman, man and child in the state [of Washington].” Spotted ratfish have been a dominant species in bottom trawl surveys in Puget Sound for some time, particularly as other fish populations have plummeted. Information about their population trajectory is limited, but many believe that something about the changes we have made to the marine environment has provided this species with the conditions it needs to flourish and proliferate. Precisely what conditions these might be is unclear.

 

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Urchins in experimental "stalls"
This Week In The Lab

Urchins on leashes

Unfortunately, the urchin corrals (see previous post) proved unsuccessful.  After numerous adjustments to the design, escapees continued to find their way to freedom.  By the end, the only prototypes that were successful at containing urchins were also trapping algae and confining other species that will need to move freely in and out of experimental plots in the field.  So, I’ve moved on to plan B: urchins on leashes.

Tethered urchin

Tethered urchin

This is a rather sad alternative, as it requires piercing the side of the test (exoskeleton) of urchins and threading it with monofilament line. While it seems likely that this is uncomfortable for them, a close look at their anatomy gives me reassurance – the area that I’m puncturing is basically a hollow cavity without organs. Urchins are also very different from us in their make up, and a limited exposure of the interior part of their body to the surrounding environment does not have the same implications for them as it does for us.  Indeed, the individuals I have tethered are recovering well and appear to be going about life as usual.

The method I’m using is borrowed from previous work by Nick Shears, Russell Babcock, and Anne Salomon.  Shears and Babcock describe the method in a paper they published in Oecologia in 2002 (link). Anne Salomon was also gracious enough to offer some additional tips via email based on her experiences tethering purple urchins, Strongylocentrotus purpuratus.

While urchin tethering has been used successfully in several previous studies, it has primarily been used as a means for quantifying predation on urchins themselves.  This is a common technique in marine ecology; Remember the goat they put into the T-Rex enclosure in Jurassic Park? It’s kind of like that but with lots of replicates and on a much smaller scale. By tethering urchins and placing them in the field, previous studies have evaluated relative rates of predation on urchins across different sites. (It’s only relative because the process of tethering may itself alter predation rates).

In my case, however, the question is not about predation on urchins, but about the impact of urchin feeding on the rest of the biological community. In other words, I’m not interested in how many goats the T-Rex will eat – but in how the goats impact the grass and flowers and shrubs when they are present.  Goats have a big impact on the biological community (just type ‘rent a goat’ into your google browser if you want proof); How about urchins?

In order to use tethered urchins as an experimental “treatment” in the field, I need to first see whether being tethered affects their feeding behavior.  So this is what I’m doing now at MaST aquarium. I’ve got 24 “stalls” housing individual urchins.  Half of them are tethered and half are not.  They have each been given a pre-weighed quantity of food.  I am running multiple trials of this lab experiment, but in each trial, I re-weigh the remaining algae from each urchin stall to see how much they’ve eaten after a few days.  I should have a comparison of feeding rates between tethered and un-tethered urchins compiled and available within a few weeks. Assuming all goes well, it will then be off to field for these little guys, where they’ll have the opportunity to eat their way through macroalgae that has grown wild. Just like rent-a-goats.

Urchins in stalls with algae

Tethered and untethered urchins in their stalls with pre-weighed pieces of macroalgae.

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Photo of hydroids
Recent Research

Hydroid assemblages in Spain’s harbors versus natural rocky habitats

Here’s a cool recent paper from Cesar Megina and colleagues: Harbours as marine habitats: hydroid assemblages on sea-walls compared with natural habitats. Megina et al. compared communities of hydroids in harbors and natural rocky habitats along the southern coast of Spain.

Photo of hydroids

Photo by Peter Southwood

Quick interlude – if you’re wondering what hydroids are, here’s a good overview.  They’re essentially colonies that grow in a vast variety of shapes, sizes and structures. The colonies are comprised of lots of little polyps, but often have a medusoid phase as well, like a jellyfish.

OK, back to the story… Cesar Megina and colleagues from Spain and Italy sampled hydroids at multiple harbors and natural rocky sites on the Iberian Peninsula. They found that hydroid assemblages in harbors tended to be comprised of species that formed small colonies and put a higher proportion of their energetic effort towards reproduction. Conversely, the hydroid species growing in natural rocky habitats away from cities tended to be those that form large colonies, put proportionally less effort into their reproductive stage, and have a greater capacity for competition with other benthic organisms for space.

Harbors also tended to support a higher proportion of non-indigenous hydroid species.  This is a finding that has been extended across multiple taxa and in several other parts of the world (I’ll post soon about a recent paper on this subject from the Pacific Northwest).

Megina et al. note that they were surprised to find high species richness of sessile hydroids in harbors in southern Spain.  As the field of urban marine ecology expands, it would be interesting to see whether this is a finding that carries over to other parts of the world.

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This Week In The Lab

Enrichment plot samples are here!

That’s right, the first 8 week samples from the enrichment plots are in and it’s time to get to work. Here’s what the inside of our lab fridge looks like right now to give you a sense of what lies ahead:

Photo of fridge full of sediment samples

Each one of those bags needs to be sieved, sorted, and analyzed for macrofauna.  I definitely have my work cut out for me!  But I’m excited to see what critters I’ll find in there.  Thanks so much to Rhoda Green and Dave Thoreson for their help setting up the enrichment plots and collecting these samples with me.  And another thanks to Rhoda for coming into the lab to stare at tiny sediment grains for hours on end with me.

More soon!

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