This week it has been very windy on the coast. As in hope-the-next-gust-doesn’t-arrive-while-I-am-still-holding-onto-the-door windy. Seriously, the other day I almost wrenched my shoulder when the wind caught a door I was walking through just as I opened it. I should have braced myself before opening that door. The wind also blows around dust and pollen, exacerbating everybody’s spring allergies.
Despite all that, the wind is a good thing because it is the driving force behind coastal upwelling, the oceanographic phenomenon that brings cold, nutrient-rich water from depth to the surface. Upwelled water provides the nutrients that primary producers such as phytoplankton require for photosynthesis. The simple equation is: Sunlight + nutrients = photosynthesis. With the days getting longer as we head toward the summer solstice, this is the perfect time of year to be a phytoplankter. (Note: a phyto- or zooplankter is any creature that lives as plankton)
It takes several days of sustained winds from the north to start upwelling along the coast. I record the temperature in one of my seawater tables every day and keep an eye out for decreases that might indicate upwelling. Given that it’s been crazy windy since Sunday (today is Wednesday) I thought today would be a good day to collect a plankton sample and see what’s going on.
What did I find? Lots of phytoplankton, right on schedule!
Most of these critters are diatoms, of which there were several different types. Diatoms are unicellular algae whose cells are encased in a fancy silica shell called a frustule. More on that later. In Monterey Bay, the first phytoplankters to bloom in the spring are usually diatoms; they can take advantage of upwelled nutrients to fuel rapid asexual division so their populations grow quickly. Photosynthetic creatures from diatoms to redwood trees can perform the biochemical magic of capturing light energy and converting it to chemical energy held in molecules containing fixed carbon (e.g., glucose). Diatom blooms provide food for grazing zooplankters such as copepods and krill. These small animals become food for any number of larger animals, and so on up the food chain, so in every sense possible the phytoplankton are the foundation upon which the entire marine food web is based. Interested in saving the whales? Then you should focus your energies on saving the phytoplankton. Seriously.
The largest object in the photo above is a large protozoan ciliate called a tintinnid. They also live in glass shells, only theirs is called a lorica (L: “body armor”). The tintinnids I see most frequently in tows from the Wharf have a clear goblet-shaped lorica that is entirely transparent. These tintinnids are big, for single-celled creatures, up to over 1 mm in length. That’s a lot bigger than some multicellular animals!
Tintinnids are frantic little swimmers. They are heavily ciliated, which means they can swim really fast. The one in the photo was tangled up in the phytoplankton and squashed under a cover slip, which conveniently retarded its motion, but in this video you can see its little cilia beating. I added a few seconds of a different tintinnid swimming solo to the end of the video clip, which will give you a better idea of how they swim.
Here are some other plankters from today’s sample:
Photo #1 – Diatoms. The large cell with the spines on both ends is Ditylum brightwellii, one of my favorite scientific names. Chaetoceros cells each have long spines at the corners of the cells. The spines link adjacent cells together, forming chains.
Photo #2 – Chaetoceros. At least two species of diatoms in the species Chaetoceros.
Photo #3 – Chaetoceros debilis(?). This species forms spiral chains.
Photo #4 – Assorted phytoplankton. In this photo the five roundish cells are the dinoflagellate Protoperidinium. They have two flagella, one in a groove that wraps around the cell and one that trails free. The two button-like cells near the center of the picture are (I think) the diatom Thalassiosira. There are two chains of Chaetoceros debilis and several other chain diatoms. That big opaque vaguely bullet-shaped object to the right of center? That’s a fecal pellet, probably from a copepod.
Speaking of copepods, as usual they were very abundant, both as adults and as larvae. In terms of numbers of individuals, copepods are likely the most abundant animals in the sea. Copepods are small crustaceans that feed on phytoplankton and are in turn eaten by many larger animals. In life they have beautifully transparent bodies, allowing us to see the beating heart. See for yourself:
And, finally, about those diatom frustules. As I mentioned above, a diatom’s frustule is a sculpted shell made of silica (SiO2). It comes in two parts, an epitheca and a hypotheca, that fit together like the two halves of a petri dish. In fact, I use a petri dish as a frustule model for my marine biology students; it is made of roughly the same substance and demonstrates the size relationship between the epitheca and hypotheca.
The large round centric diatoms best show the structure of the frustule. Here’s the best photo I was able to take today of one of the very large centrics, Coscinodiscus:
I hope that later in the season I can take some better photos of these diatoms. They are so beautiful that I really to do them justice. So much diversity early in the season makes me hope for a good productive season. We’ll see!