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Before Christmas I was invited to speak at one of the monthly public talks hosted by the Seymour Marine Discovery Center. I'm always happy to be asked to speak to students or the public, so my default answer to these requests is "Yes!" Usually for this kind of presentation I get to choose the topic, but this time my name came up because one of the Seymour Center staffers came up with "bees, banana slugs, and bat stars" so that's what I was given to work with. When my brain took hold of this topic and these very disparate animals, the common theme that came to mind was . . . wait for it . . . reproduction. So yes, this is going to be another sex talk.

What this means is that I need to provide some information on the talk and photos so that the Seymour Center can start publicizing the event, which is in March. Banana slugs are still in the mix, and I don't have any pictures of them, so this afternoon I took advantage of a break between storms to go hiking in the forest and look for slugs. I'd been feeling a little cabin fever for the past few days because of the rain and my own recovery from bronchitis which sapped all of my energy, so I was grateful for an excuse to leave my desk and get outside for a bit.

I headed out to the Forest of Nisene Marks State Park, knowing that where there are redwood trees there should also be banana slugs, especially after all the rain we've had recently. You know how when you're looking for something you can't find it, and when you're not looking for it you see them all over the place? That's how this hike began. It turns out that looking for banana slugs under a deadline makes them very hard to find. And I did have a deadline, as I'd promised to have the blurb and photos for my talk ready today.

After about half an hour of slowly meandering along the trails and getting distracted by all the fungi that popped up after the rains, I did see a banana slug:

Banana slug (Ariolimax sp.) at The Forest of Nisene Marks State Park. 7 January 2016 © Allison J. Gong
Banana slug (Ariolimax sp.) at The Forest of Nisene Marks State Park.
7 January 2016
© Allison J. Gong

That is such a gastropod face! Banana slugs are really cool (and ectothermic, too) animals. One of my buddies in grad school kept one for a pet in our office bullpen; we called it Terry, because slugs are hermaphrodites and deserve androgynous names. Terry really liked eating mushrooms and lettuce.

Banana slugs, and all of the terrestrial snails and slugs, are pulmonate ("lung") gastropods. Most of their marine relatives, with whom I spend so much quality time in the lab and in the field, are prosobranch ("gill in front") gastropods. The nudibranchs and sea hares, which are so photogenic and conspicuous, are opisthobranch ("gill on back") gastropods. As these names imply, the prosobranchs and opisthobranchs possess gills (although they are very different kinds of gills) and thus live in water. The pulmonates don't have gills; they live on land and breathe air. [There are aquatic pulmonates, too. Only a few are marine, and most live in fresh water. They have to come to the surface to breathe.]

So, what is the lung of a banana slug? It's actually the mantle cavity, that oh-so-molluscan feature, that in prosobranchs contains the gill(s). In the pulmonates, the mantle cavity is highly vascularized, as you'd expect from any gas-exchange surface, and opens to the outside by a hole called a pneumostome.

Here's the pneumostome of my first banana slug of the afternoon:

Anterior region of a banana slug (Ariolimax sp.), showing the pneumostome on the right side of the mantle. 7 January 2016 © Allison J. Gong
Anterior region of a banana slug (Ariolimax sp.), showing the pneumostome on the right side of the mantle.
7 January 2016
© Allison J. Gong

The pneumostome is always on the right side of the animal's mantle. You can actually watch it open and close as the slug breathes.

I found a second slug about an hour into the hike.

Banana slug (Ariolimax sp.) at The Forest of Nisene Marks State Park. 7 January 2016 © Allison J. Gong
Banana slug (Ariolimax sp.) at The Forest of Nisene Marks State Park.
7 January 2016
© Allison J. Gong

See? No pneumostome on the left side.

If I'd had the time, I would have put the slugs together to see if they'd mate. It is a sex talk I'm prepping for, after all. Heck, what would be even better would be to find two slugs already in copulo. No such luck today, though. What's good about not finding everything that I was looking for today is that it gives me incentive to keep going out to search for it. And in the meantime, I've got to start studying up on local fungi. I saw so many different kinds of mushrooms today that now I'm motivated to fill in this particular gap in my knowledge. Might as well take advantage of the El Niño rains, right?

At 07:40 on Tuesday 5 January 2016, the sandbar at the mouth of Younger Lagoon broke open for the first time this rainy season. The Younger Lagoon Reserve (YLR) is located directly west (or "up the coast," as we say; the terminology gets a little weird because the coastline runs east-west in Santa Cruz) of the Marine Science campus of UC Santa Cruz. The actual lagoon is Y-shaped, and while it receives run-off from land, including from the adjacent agricultural fields, for most of the year it is cut off from the Pacific Ocean by a thick sand bar.

Map of UC Santa Cruz's Marine Science campus and adjacent Younger Lagoon Reserve.
Map of UC Santa Cruz's Marine Science campus and adjacent Younger Lagoon Reserve.

This week California has been glorying in the might of El Niño, which has been bringing heavy rain to most of the state and lots of snow in the Sierra Nevada. As the first new moon of the year tomorrow creates the usual extreme high and low tides, we've been treated to some spectacualr waves on the coast. However, it's not the incoming tidal surge that causes the lagoon to break through; if that were the case, then the sand bar would be broken open, or at least seriously eroded, more often than it is. Rather, it's the surge of fresh water, the accumulation of heavy rain and run-off, coming from the top of the lagoon that breaches the sand bar from the upstream side.

This photo was taken on Tuesday by staff of the Younger Lagoon Reserve:

Temporary channel through the sand bar at the mouth of Younger Lagoon. 5 January 2016 © Younger Lagoon Reserve
Temporary channel through the sand bar at the mouth of Younger Lagoon.
5 January 2016
© Younger Lagoon Reserve

You can see that the ocean is rushing through the channel and mixing with the brown stagnant water from the lagoon. Those two tiny white dots on the far side of the channel are snowy egrets. The same egrets also appear in this video that I shot from the overlook which is the closest I can get to the lagoon itself without trespassing on the Reserve:

The break through the sand bar is a temporary thing. This photo and my video were taken around mid-day on Tuesday. Later in the afternoon I looked down on the lagoon from a more distant vantage point and already the sand had begun to accumulate again. Today the lagoon broke through again, and the YLR staff took another great photo from down in the reserve:

Channel through the sand bar at the mouth of Younger Lagoon. 7 January 2016 © Younger Lagoon Reserve
Channel through the sand bar at the mouth of Younger Lagoon.
7 January 2016
© Younger Lagoon Reserve

This being the first break-through of the sand bar this season, the water running out was pretty stagnant and nasty. In fact, as I drove in Tuesday morning I noticed a strong smell of H2S permeating the entire lab complex, and wondered if the construction workers had hit a sewer line. Obviously, the first breach of the sand bar releases all of that gunky, H2S-laden water into the ocean, where it flows right past our seawater intake.

I've long wondered what nutrient levels are in the lagoon at different times of the year, and whether or not conditions in the lagoon affect our seawater quality at the marine lab. I used to think that there might be a correlation between nutrient input from the lagoon and the occasional gunky algal bloom that clouds our seawater and makes life difficult for animals and aquarists alike. However, seeing for myself how little actual water exchange there is between the lagoon and the ocean when the sand bar breaks open, I'm pretty certain now that any nutrients from the lagoon would be quickly diluted to the point of having no effect on productivity in the ocean. Besides, those pesky algal blooms are a regional phenomenon, occurring over large swaths of coastline. Still, it would be interesting to study how nutrient levels within the lagoon fluctuate throughout the year. Maybe I can get a student to take this on as a senior thesis project.

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