Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 2, 2018 (Day 4)*

*Note: these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.

Greetings from the Loop Current! Thanks to calm seas and plenty of Sargassum, we were able to get right to work after breakfast. Here is a short synopsis of some of the day’s activities.

Neuston 2

The science team hauls a Sargassum sample aboard the ship. (Photo: Brian Jones)

This morning found us in the Loop Current at approximately 26° N, 88° W, and in the midst of numerous weedlines. Conditions were somewhat similar to yesterday in that there were no large, continuous lines of Sargassum. Instead, there were long series of relatively large patches lined up along convergence slicks. We cruised around briefly looking for suitable sampling habitat and we were joined for a while by a large group (30-40) of what appeared to be Pantropical Spotted Dolphins (we are lacking in marine mammal expertise on board, so our best guess!). Finding a nice set of Sargassum patches, we got right to work, starting with a pair of short neuston tows. Again, we collected relatively few fish, which seems to be a theme for this area. While fishing with our Sabiki rigs, we collected a juvenile Rainbow Runner and a few juvenile Almaco Jacks. We observed numerous large Mahi Mahi swimming between the Sargassum patches, as well as a few unidentified triggerfishes feeding on the canopy edges.  It was a race to get any small fish we hooked onto the vessel while being chased by the Mahi. After collecting a few juveniles, we sampled a few of the larger fish, collecting blood, liver, and muscle tissue for stable isotope analyses, and the stomachs for diet analyses.

Sargassum associated fish.jpg

Two common Sargassum-associated fishes, the Planehead Filefish (left) and the Sargassumfish (right), both collected today. (Photos: Olivia Lestrade)

After lunch we set our camera system adrift in a Sargassum patch while collecting more reflectance and backscatter data, then we cruised to an ‘open water’ location and repeated our sampling ops. Interestingly, our frame trawl sampler, which we anticipated would collect juvenile fishes, came aboard with many larval fishes stuck to the cod end mesh. We noticed larval Surgeonfish (Acanthuridae), Tuna (Thunnus sp.), Triggerfish (Balistidae), and Squirrelfish (Holocentridae), among others. There were also many crab zoea and stomatopods, as well as a brown ‘film’ coating part of the net, possibly an indication of Trichodesmium, also called “sea sawdust” (a filamentous cyanobacteria).

Mengqiu

Mengqiu Wang and Xingxing Han collect reflectance and backscatter data from Sargassum and open water habitats. (Photo: Josh Bierbaum)

After collecting some additional reflectance data at the open water location, we decided to steam back north towards the Gulf coast. Patches of Sargassum streamed by as we cruised along, reminding us of the considerable Sargassum biomass we observed in the Loop Current. Our goal for the next few days is to locate similarly productive sampling sites in different regions for comparison.

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