Via PopSci, Let This Rube Goldberg Machine Show You How Cows Eat And Poop. This is Cow by Nova Jiang.

Watch more Rube Goldberg machines, kinetic sculptures, and chain reactions.

In this absolutely incredible footage from EarthTouchTV, watch hundreds of thousands of sardines off the coast of South Africa swarm at the center of an animal feeding frenzy. With Earth-Touch divers right in the middle of the action, large, hungry predators — sharks, dolphins, diving gannets, and a 20 to 30 ton Bryde’s whale — all take part in this intense and fascinating sardine run.

There are hours of nature and underwater videos in the archives.

To celebrate World Ocean Day 2013, director and animator Akiko McQuerrey created a Papa Cloudy stop-motion music video: Overfishing Song from Papa Cloudy’s Restaurant.

Overfishing—catching fish faster than they can reproduce—is an urgent and devastating issue, and may be the single biggest threat to ocean ecosystems… The global fishing fleet is operating at 2.5 times the sustainable level—there are simply too many boats chasing a dwindling number of fish.

What can we do to help? With more sustainable practices, our oceans can be healthy and plentiful for everyone. Recommendations from the Monterey Bay Aquarium suggest that we select sustainable fish from restaurants and stores, and diversify the kinds of fish we eat beyond just the popular choices.

To help make these choices easier, they created a Monterey Bay Aquarium Seafood Watch pocket guide and mobile app. They even have recipes and more information about how to solve our ocean challenges.

This week, the 5 year old discovered the science videos of Bite Sci-zed’s Alex Dainis, starting with this one: Echinoderm Show & Tell. When he immediately asked for more, we watched The Gas Laws, Dishes and Membranes and Why Red Blood Cells Look Like Donuts, above.

We’ve talked about red blood cells (and white blood cells) before, so some of this sounded familiar. And while some information is targeted towards older kids, the use of everyday objects and drawings provided enough familiarity to start our conversation…

Related watching: The Circulatory System, The Bloodmobile and BBC Knowledge Explainer DNA. Plus more videos about the body.

And the next time you have a donut, you’ll know how to make a red blood cell. Go forth, do science.

Called living fossils, horseshoe crabs are harmless creatures that have been swimming oceans for a few hundred million years. They predate dinosaurs and are closely related to spiders or scorpions. Every May and June, they crawl onto the beaches “from the Yucatan to Maine“ to mate and lay eggs in the sand in mass numbers.

At the same time, hungry Red Knot birds on the way to the Arctic from the southern tip of South America are looking for those millions of little green horseshoe crab eggs so that they can eat. The nourishment helps them gain energy so that they can finish their long migration and breed, as well.

In this KQED Science on the Spot, Rendezvous With Horseshoe Crabs, learn about these two species and what local teams are doing to protect the balance of their interdependency.

To learn more about horseshoe crab conservation efforts, check out Science Friday’s report: Beach Season For Horseshoe Crabs.