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The Daily Bucket is a regular feature of the Backyard Science group.  It is a place to note any observations you have made of the world around you.  Snails, fish, insects, weather, meteorites, climate, birds and/or flowers.  All are worthy additions to the bucket.  Please let us know what is going on around you in a comment.  Include, as close as is comfortable for you, where you are located.
May 2013
Salish Sea
Pacific Northwest

The plankton is blooming in this spring sunshine, and I'm finding all sorts of life waking up. Last time I showed you pictures of the "pastures of the sea" out in the bay, the drifting plant life, the phytoplankton. Today we'll take a close look at Copepod, the most important and by far the most numerous of the grazers of that phytoplankton.

The impact of Copepods in aquatic ecosystems can not be overstated. In biomass, nothing compares, except possibly their Crustacean cousin the krill, which are much larger in size, and have populations more pelagic and geographically specific. I don't see krill much in these inland waters. But copepods are evident all year round, in any plankton tow, and in spring their populations explode. The photo above is typical for this time of year.

Crustaceans are a group of arthropods. While other arthropods are mostly terrestrial or freshwater, Crustaceans are mostly aquatic, and primarily marine. Think crabs, shrimp, and lobsters, rather than insects, spiders and centipedes.

How do I get the samples? Usually people take plankton samples from boats, but I drag a fine mesh net through the water at a dock, back and forth at least 20 times. I'm benefiting from the vigorous tidal flushing in these waters that distributes the plankton pretty well.

The water flows out through the mesh and the plankton gets trapped inside, becoming more concentrated than it is in the ocean (kind of like corralling cattle in a pen). Turbulence and swishing gets it into the bottle.

This means what I see in my field of view under the microscope is much more densely packed, not to mention squashed into a two dimensional world between the slide and cover slip, so I like to look at it quickly, before crowding affects their behavior and structure too much. Being larger than the phytoplankton, the copepods and other zooplankton ("animal drifters") feel the effects of crowding more. Copepods are about 1 mm in length.

I call them grazers, but that's a bit misleading. Unlike cattle, zooplankton have to hunt down and capture their "grass", since the phytoplankton they feed on is drifting, and even sometimes moving out of their way. Some copepods are even omnivorous, feeding on smaller animals too. So copepods have appendages that enable them to move very quickly and to capture food (as well as avoid predators - you can imagine, with their huge biomass, how important they are to fish and invertebrates in the ecosystem, who can't take advantage of the phytoplankton bounty directly).

tail bristles

Besides for propulsion, their appendages help them sense vibrations in the water. They also have a single red eyespot.

above, eye
Here's a different species of copepod, which orients more laterally on the slide. We can see the appendages, eye and digestive tract at a different angle.
side view
Like all arthropods, copepods have an exoskeleton which does not grow. They go through a series of moults, each time increasing in size. This is the transparent exoskeleton left over from one of the 5-6 moults before reaching full adult size.
Even the larvae go through a series of moults. This is a copepod nauplius larva. You can get a sense of relative size by comparing these various stages to the single-celled diatoms in the background (some are in colonial chains).
cop naup
The fuller story of a copepod would take you back to the egg case, which is pretty cool, but unfortunately I haven't seen one yet in my samples this spring. I will keep looking. They must be out there since we have larvae in the samples. There are also lots more kinds of zooplankton, and I'll post some microphotos of them in future Buckets...a view into the invisible world all the fish and whales and sharks and such depend upon.


I'm kicking off a possible new Daily Bucket publishing protocol, publishing a few hours earlier so our Easterly folk can see it before their day is half over. That means I won't be replying to comments until it's Pacific Time morning, but for sure, I will join you soon. Let's see how we like this publishing schedule.

What's happening in nature in your backyard lately?

Originally posted to Backyard Science on Sun May 26, 2013 at 05:00 AM PDT.

Also republished by Community Spotlight.

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