Bivalve questions make me happy as a clam!

Amanda Kahn

by Amanda Kahn, Invertebrate Zoology and Molecular Ecology Lab

In our Ask a Grad Student page, Leeanna asked a bunch of really good questions, and all revolve around bivalves.  Now, maybe you think you don’t know bivalves well enough to have them over for dinner, but I expect that many of you actually have had them FOR dinner!  Bivalves include clams, mussels, oysters, scallops, and other generally clam-shaped animals with two shells.  Class Bivalvia is within Phylum Mollusca, and its closest neighbors on the evolutionary tree are Classes Monoplacophora (extinct, snail-like animals), Polyplacophora (chitons), Gastropoda (snails and slugs), Scaphopoda (tusk shells), and Cephalopoda (octopuses and squids).  Too much information?  Too much information.  Sorry.  On to the questions!

Q: How do bivalves pump out water?

A: On each side of the foot inside of the bivalve (let’s say, for example, a clam), there are two big hollows, called mantle cavities.  On one end of the bivalve’s shell, there is an inhalant and exhalant siphon, which the clam uses to pump water in and out of the mantle cavities.

There is some heavy-duty pumping going on...water pumping, that is! From Mutts comic strip by Patrick McDonnell

Q: How do bivalves eat their food?

Do sponges have the nerve to eat?

Amanda Kahn

by Amanda Kahn, Invertebrate Zoology and Molecular Ecology Lab

Hi again.  I received a few questions in my previous post that I would like to address in this post.  A user named doughnutfan asked three great questions about sponges.

Q: Are the spicules themselves responsible for filtering out the food particles?

A: Sponge spicules do not filter food particles out of the water – what they do is support the cells that do.  I often think of sponges as skyscrapers (yes, I really do); it makes it a lot easier to visualize what different body parts of sponges are good for.  Spicules are like the beams and internal structures that support the skyscraper – they provide support and give the sponge its shape.  Spicules also make sponges hard to eat; very few animals can handle passing glass shards through their digestive systems!

Instead, what is responsible for filtering food out of the water is a type of cell called a choanocyte (ko-AN-oh-site).  It looks like a funny name at first, but it’s named after a group of microscopic single-celled organisms called choanoflagellates.  The choanocytes in sponges look just like the free-roaming choanoflagellates, but intsead of being solitary, single-celled organisms, sponge choanocytes are clustered together and work together to get food.  As a side note, the strong similarity between the way choanoflagellates and sponge choanocytes is no coincidence.  Currently, the favored hypothesis of how animals first evolved from single-celled organisms is that choanoflagellates evolved into sponges (specifically, the choanocytes in sponges). 

Birds of the Bering Sea: A Long Journey to an Arctic “Hotspot”

Nathan Jones

by Nathan Jones

May 25, 2008. Moss Landing, California – The Bering Sea is a long way from Moss Landing, California. It’s a long way from most anywhere, actually. To begin my summer of field work, I must first fly from San Francisco, California to Seattle, Washington. In Seattle I will change planes and fly to Anchorage, Alaska. From Anchorage I’ll catch a small propeller plane and fly low over the mountains, glaciers, and the vast wilderness of Southwest Alaska to stop briefly in King Salmon, where we will refuel, and then continue on out along the foggy Aleutian Island chain to land in Dutch Harbor, Alaska. I will then board a research vessel that will motor for fifteen hours out into the Bristol Bay portion of the Bering Sea and there, at last, I will begin my work. It will probably take me three long days.

Map of the Bering Sea near Alaska (NOAA)

Humans are not the only animals that eat fish, of course! Seabirds flock by the millions to feed on fish in the Bering Sea, and also on energy-rich krill (tiny crustaceans, similar to a shrimp). These krill grow to become so numerous in summer that they form dense undersea clouds that can stretch for miles. Krill, known to scientists as euphausiids, are eaten by fish; in fact, we feed them to our own pet goldfish, in dried and flaked form! They are also the favorite food of many whales, which use their thick baleen plates to strain these tiny creatures from the water in huge, lunging mouthfuls.

Birds and whales feed together in Alaska

Because they like to eat similar kinds of food, whales and seabirds can oftentimes be seen congregating to feed together in productive areas that contain especially large amounts of fish and euphausiids. Such places are usually characterized by turbulence and the mixing of cold(er) and warm(er) ocean water. What is it about the turbulent combination of cold and warm water that attracts the euphausiids and fish?

During the next two months I will spend most of my time on the ocean. I will be taking special interest in these foraging hotspots, trying to learn more about how seabirds find and exploit them.

If you’re interested in learning more, Nate recommends the following websites:

To learn more about the North Pacific/Bering Sea where Nate will be working, check out the National Pacific Research Board, Bering Climate, North Pacific Ocean Theme Page, and Arctic Change.

To learn more about wildlife, check out these resources for marine mammals, seabirds and fish.