Ocean aggregations

by Laura Lilly

The CTD rosette is a popular aggregating/sampling stop for many of the ship’s scientists during all-night transects.

It’s a well-known fact that, in the ocean’s endless expanses of blue, creatures flock to any semblance of structure. Fishermen will tell you that some of the best places to drop a line are around buoys, kelp patties, and bottom rubble. Divers love oil rigs because they create platforms for mussels, barnacles, and sponges, which in turn attract fish and larger predators. Even seamounts concentrate upwelled nutrients and particles underwater, fueling productive hotspots for migratory fishes and sharks (side note: we just finished sampling in a region near the Davidson Seamount off Central California, which comes up to 1300 m below the ocean’s surface. Our work wasn’t related to the seamount, but perhaps we caught some seamount-related creatures in the MOCNESS). If you’ve been reading the news lately, you may have heard about the giant raft of aggregated pumice pieces that emerged from an underwater volcano near Tonga and is floating toward the Great Barrier Reef off Australia. Scientists believe that the pumice raft may actually help the Great Barrier Reef by collecting marine creatures as it floats, and then depositing them on the GBR, helping to repopulate a reef system that has suffered tremendously from climate change-related coral bleaching.

Zippy reappeared at the surface to an albatross welcoming party.

Yesterday we observed a different example of aggregation when we retrieved Zippy the Zooglider from his two-week excursion! Zippy had been doing continuous underwater up-and-down sampling patterns, so to recover him we had to program him to come up to the surface and float while we tracked down his GPS coordinates and spotted him from the ship (without running him over). But our human party wasn’t the first to spot him. We found Zippy by steaming toward the aggregation of albatrosses we saw sitting in the water nearby. Just like they had when we deployed Zippy, the albatrosses wanted to know why there was a giant orange missile-shaped carrot floating at the surface. We think one even took a bite – Zippy came back missing a small piece of wing! But somehow, even though they weren’t tracking GPS coordinates like we were, those albatrosses spotted Zippy before we did. Aggregation: it’s a marine life instinct.

Zippy gets picked up by the small boat crew.

We all participated in another form of aggregation two days ago: we had our third all-night sampling transect across another part of the (now evolved) ocean filament we are sampling. The transect was a typical all-night party/race of drawing water from CTD casts; filtering rapidly for carbon, nitrogen, and iron; and deploying zooplankton nets and preserving specimens – all before the next station 20 minutes away! We moved through everything successfully, though, and even managed to finish by dawn. Then most people slept all day.

Dolphins sometimes aggregate around our ship, too!

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