Wednesday, June 28
Currents, light, food resource, tidal fluxes--so many different factors influence the types and numbers of zooplankton found in nearshore waters. We only have a few days to explore the diversity of forms and lifestyles of marine zooplankton in the vicinity of San Juan Island, and none of us have much experience identifying these creatures. So after thoughtful discussion, we decided to collect from as many places as we could, night and day, and to catalogue what we find using digital imaging equipment in the lab. We studied coastal plankton field guides first, to figure out which sized nets (150,300, and 500 micron mesh) to deploy. We learned how to run the hydraulic system on a 25 ft aluminum boat, the Auklet, and were checked out on various safety protocols. Now we're ready to collect plankton!
Thursday, June 29
We towed several different sized nets from the Auklet this morning, seeking creatures from 150 to 500 microns (0.15 - 0.50 mm) in length. We were not disappointed. After towing the net at a fairly shallow depth through a series of slicks (alternating smooth and rough water due to the concentration of organic material at the surface by ocean currents), we segregated the various tows to different jars for later exploration. We followed the same protocol in the evening; once night had fallen around 10 PM, we towed several times from the Auklet, anticipating catching a different suite of planktonic life. We look forward to sorting through the samples now stored in the sea table tomorrow.
Friday, June 30
We started sorting samples from yesterday in earnest this morning. Even though we'd inspected the bottles quickly when we set up the bubbling system, we are continually surprised by the diversity of creatures encountered in the petri dishes.
A jellyfish-like ctenophore (see the movie)was lurking near the bottom of the first daytime tow jar, its ciliated combs moving gently against the mass of copepods also pressed against the glass surface. We used a cut-off plastic pipette to transfer the ctenophore to the "black box", an 6" by 15" plastic aquarium covered on three sides with black tape and lit from above. Once in the more spacious container, the globe-shaped creature moved smoothly through the water, its luminescent combs sparkling with its steady swimming.
Another night-time find, a sea butterfly, lilted up and down in its brightly colored internal organs visible against its nearly translucent, rubbery body. Its form reminded me of a slug from the nearby forest, though its quick, smooth motion belied any terrestrial movement. The clione is a Pteropod, a pelagic mollusc, which is found throughout the northern oceans of the world.
Copepods from the daytime tow were endless, with many variations on the shrimp like body and bulbous eyes. These abundant crustaceans, many of which resemble tiny shrimp or lobsters, darted quickly, making photography difficult. We put several in alcohol to slow them down, so as to capture them on film. The night tow yielded an equally abundant set of young crabs, or zoea (see the movie). With sharp, defensive spines adorning their heads and a frenetic, seemingly random swimming pattern, they remind me of battalions of confused soldiers without a leader.
Saturday, July 1
Though we aerated our samples from the last day in a flowing seawater table, unfortunately, they quickly began to rot. So we tossed the jars and did a couple of vertical tows off the Labs dock.
Sunday, July 2
We night-lighted again tonight, in search of creatures other than crab zoea. Many of the young crabs had now developed to the megalopa stage, one step closer to the benthic lifestyle. They thronged the light, making it difficult for us to pick out the sinuous, bright orange polychaetes and delicate gelatinous creatures. A spawning nereid worm, some 25 cm in length, pulsed along the surface of the water, its powerful legs shining with the glow of our underwater light. A shrimp attacked it, sparring with its front legs and shaking the worm violently. The worm slid away with a powerful motion, and continued to release its sperm at the water's surface.