Majestic undersea meadows and their hungry residents

Like most biology enthusiasts, I love an excuse to go into the field. So when given complete freedom to investigate any invertebrate question we wanted for our final project, I didn’t have to think twice before choosing to study invertebrates in seagrass meadows: a severely underappreciated ecosystem type.

Yes I know- seagrass sounds like just about the most uncharismatic thing there is. Grass isn’t very interesting at all…

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Figure 1. Boring land grass. Image: 1234RF Stock Images

… so grass under the sea probably isn’t that much more interesting, right? Perhaps these images might change your mind…


Some words that come to my mind from looking at these ones include “tranquil”, “majestic” and “lush”, which is a far cry from the average person’s conceptions of grass. So what’s the big deal with seagrass, and more importantly, what on Earth do invertebrates have to do with them?

Unlike seaweeds, seagrasses are marine angiosperms: land plants that have colonized the ocean. Different species of seagrasses are found all over the world with the exception of the high poles. As is apparent from the photos above, seagrass meadows are highly productive; the grasses harness energy from the sun, creating far more biomass per unit area than microscopic phytoplankton do in pelagic (open) waters. They also stabilize the sediment, and provide habitat for a diversity of life on the same order of magnitude as some coral reefs, from tiny invertebrates to juveniles of commercially important fish. Invertebrate herbivores (also known as grazers) living in seagrass meadows have one very important job- to eat! Grazers play the critical role of transferring all the nutritious food generated in seagrass meadows to animals higher up in the food web like fish. Juvenile fish that use seagrass meadows as nursery habitat eat lots and gain weight, and eventually they transport this biomass to pelagic waters when they are large enough to leave. In other words, seagrass meadows are important for creating biomass that ends up in open ocean, and grazers are a key player in this process.

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Snorkelling at the field site in Tsawwassen to collect seagrass-associated invertebrates for my experiment

Lucky for me, there is a seagrass meadow not too far away where I was able to get my field fix and collect my experimental organisms. The low tides that week were quite high so I ended up having to snorkel to catch them- no complaints there (aside from not being able to feel my face in the 6°C water). I also happened to visit in the middle of an algae bloom; the seagrass was looking pretty scummy from algae growing on the blades.

The most abundant grazers at the field site were the green eelgrass isopod Idotea resecata and the eelgrass limpet Lottia parallella. The results of my experiment showed that both actually prefer eating seagrass over algae, which may make seagrass at the site more vulnerable to decline from being strangled by the algae (More details here). Seagrass meadows are experiencing disastrous losses all around the world; since the 1940s, we have lost seagrass meadows on an order of magnitude of 10 000 km2 1. Despite this, they are not getting nearly as much attention from the media and general public as their charismatic counterparts, coral reefs. Along with conducting research to further understand factors causing their decline, creating public awareness and appreciation of their importance is crucial.

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Who needs a tropical reef fish aquarium when you can have a seagrass mesocosm instead?

Source

  1. Orth, R. et al. A Global Crisis for Seagrass Ecosystems. Bioscience 56, 987–996 (2006).
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A Real Estate Market as Brutal as Vancouver’s

Most millenials in Vancouver can relate: the low availability of decent, affordable housing in the city can sometimes make house-hunting feel like a brutal competition. I’ve had personal experience going to view an apartment and waiting in line amongst upwards of twenty other students to interview with a landlord, with the hope of “outcompeting” the others by proving that I am the best prospective tenant.
For invertebrates living in the rocky intertidal zone, competition for a nice place to live can be just as intense. Mobile organisms like shore crabs compete for shelter under cool, shady rocks, where they can avoid predators and direct sunlight (to avoid overheating)¹. Stationary animals like mussels and barnacles compete for space on rock surfaces to attach themselves; like those wealthy UBC students who are able to afford a one-bedroom apartment for over $3000 a month, some of these animals are able to live in more exclusive spots than others like gooseneck barnacles
However, no intertidal critter knows the struggle of finding a place to live like hermit crabs do. Not only do they still need to find spots under rocks, tidepools, and seaweed² like their cousins the shore crabs- they also need to find a gastropod (snail) shell to house their soft, de-calcified abdomen. This diagram shows what I am talking about- hermit crabs have a soft, asymmetrical abdomen (it looks like a tail) so that it can fit inside a snail shell. Which means that without a shell, they are a lot more vulnerable than their fully calcified (hard-shelled) cousins.

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       If you’ve ever wondered what a naked hermit crab looks like, this is it! The soft, decalcified abdomen (labelled “smooth tail” has no legs except for small ones used to grasp its shell from the inside. Source: The Hermit Crab Patch.

Seems pretty inconvenient, right? Not necessarily- many hermit crabs, such as Pagurus hirsutiusculus, can leave their shells behind as a defense mechanism when they feel threatened³. This is a great defense tactic if, for instance a fish had the snail shell in its jaws and the crab needs to get away.
In lab last week, we performed experiments on the hairy hermit crab Pagurus hirsutiusculus to determine the presence of interactive effects of temperature and salinity stress on behaviour (read more here!). One behaviour we measured was length of time it takes for a crab to retrieve its shell- a very important survival behaviour.
However when we tried to shake one little crab out of its shell, we noticed something hilarious- another larger, naked crab was trying to forcibly remove the littler one with its claws! I was astonished at how persistent the larger one was, even when we lifted it out of the water. I suppose it just goes to show competitive these animals are willing to be to get a suitable home.

 

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       A naked Pagarus hirsutiusculus trying to yank another tenant out of its current shell.

However, house-hunting for these rocky intertidal crustaceans is not all ruthlessness… This hilarious BBC snippet shows tropical hermit crabs lined up in order of size to switch shells that they all have outgrown- this level of cooperation is remarkable for backbone-less critters!

 

 

 

Unfortunately, at the end of the switcheroo, one individual is without a shell and has to settle for one that’s a bit too big and has a hole… as a broke university student who’s had to settle for suboptimal basement suites in this real estate market, I can relate.

Sources
1. Steinberg, M. K. & Epifanio, C. E. Three’s a crowd: Space competition among three species of intertidal shore crabs in the genus Hemigrapsus. J. Exp. Mar. Bio. Ecol. 404, 57–62 (2011).
2. Meschkat, C., Fretwell, K. & Starzomski, B. Hairy hemit crab Pagurus hirsutiusculus. Biodiversity of the Central Coast (2014). Available at: http://www.centralcoastbiodiversity.org/hairy-hermit-crab-bull-pagurus-hirsutiusculus.html. (Accessed: 12th March 2017)
3. Story, R. M. & Steitz, T. A. © 19 9 2 Nature Publishing Group. Nature 355, 242–244 (1992).

Four tips on how to be a great intertidal ecologist

For some, there exists a misconception that all marine biologists scuba dive in the tropics and chase dolphins into the sunset. Case in point: I did a brief Google image search of “marine biologist” and there were the top few hits:

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Screenshot of “marine biologist” from Google Image search

 

Coral reefs are undoubtedly beautiful and a globally important habitat type. However some fail to realize how much more there is to ocean biodiversity, and best of all, that we really don’t need to venture further than our coastal back yards to see some fascinating creatures co-existing. Last week our intertidal walk at Aguillar Beach saw representatives across nine invertebrate phyla, including porcelain crabs, Idotea isopods, four species of anemone, bryozoans, polychaete worms, and several species of shrimp.

While visiting the beach can be fun for everyone, with these four pointers you can increase your chances of seeing cool things and be great intertidal ecologist:

 

 

  1. Tide tables are your best friend.

If you’re interested in studying intertidal or subtidal organisms, planning field days according to the tides is necessary to ensure that you’ll be able to see as much as possible. Each ~12.5 hour tidal cycle has two low tides and two high tides. The best time to see things is just before the lowest tide because this is when most of the shoreline is exposed. This allows the opportunity to see habitat zonation patterns to the greatest extent possible as opposed to only the ones living in the high intertidal zone (which might be limited to two species of algae and some mussels and barnacles).

2. Be adventurous (while keeping safety a priority)

Sometimes we have to brave rough conditions to see the most interesting things- this can mean sacrificing sleep to visit the intertidal zone at a midnight low tide in below freezing temperatures, or trekking across slippery seaweeds and sharp barnacles while being chased by an incoming tide. Last week at Brady’s Beach we eagerly joined Chris who travelled to the more exposed side of the sea stacks to check out the Gooseneck barnacles and California mussels. This is prime habitat for these two species- the high wave action and spray means that salty water makes it higher up the rocks, and therefore the mussels are able to exist out of the reach of hungry sea stars. I think we might have made the poor field trip staff at Bamfield a little nervous by our hanging out at that spot because the tide was coming in fast and rough, but it was well worth it.

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Figure 1. Chris telling Kephra, Keila, and Emily tales of gooseneck barnacles, California mussels, and Nucella snails at the highly exposed sea stacks. Note everyone has their PFD zipped up (safety first). Photo by Sharon Kay.

  1. Look around! Be curious!

I’ve gained tons of new knowledge, theory, and practical skills over my years as a biology undergrad. But the most valuable thing I’ve learned by far (and best of all, one you don’t need a bachelor’s degree to learn!) is how to be sensitive to my surroundings and notice little details. Whether you’re at a remote marine research station or walking across campus, there are small critters to be found if you look super closely, and interesting patterns everywhere that likely can be explained by biology. While dredging in Trevor Channel to sample for benthic invertebrates, I happened to look inside a butter clam shell with a bunch of crap inside, and noticed this tiny brittle star. Critters that small are easy to miss if you’re not looking carefully!

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A brittle star (Class Ophiuroidea) smaller than my pinky

While walking in the intertidal zone, turn over rocks, peek inside tidepools, and keep your face as close as it can possibly get to the ground without detracting from your ability to see or your nose hitting the rocks, whichever comes first (see Figure 2). Inevitably, you will start to notice patterns- some organisms live higher up, some lower down. Some grow on top of others. Some don’t seem to like the light, others love it. Make a note of what you notice!

 

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Figure 2. Optimal distance for spotting interesting animals in the intertidal zone

 

 

  1.  Ask lots of questions

This tip is the natural follow-up to tip #3. After looking around and noticing interesting patterns, the next step is to ask why so you as the intertidal ecologist can find the answer. That’s how science works!