Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 4, 2018 (Day 6)*

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


The science team rinses the Neuston net. (Photo: Brian Jones)

Wanting to repeat our sampling along blue-green convergence lines, we stayed in the same general vicinity as the previous day’s effort. Here is a short synopsis of some of the day’s activities.


By morning, the “tide line” we sampled yesterday had moved south by several miles. Upon finding the blue-green water interface (which was not as distinct as yesterday), we started our sampling with a neuston tow through a series of Sargassum patches. The tow went very well, and was brought on board—just in time for a morning squall ! The science team worked diligently through the wind and rain, which lasted approximately 30 minutes or so.


The CTD and rosette sampler being deployed over the side of the vessel. (Photo: Glenn Zapfe)

The skies soon cleared and we deployed the CTD and rosette sampler to collect profile data and water samples. The brief storm sufficiently broke up the Sargassum patches, so we cruised further south to collect our open water samples (neuston net, water samples, reflectance, frame trawl, etc.). Again, sample collection went relatively smoothly as the sea conditions improved throughout the day.



Science team members Eric Haffey, Verena Wang, and Glenn Zapfe measuring the weight of a Sargassum sample.

With calmer seas we revisited our Sargassum station and observed the formation of new weedlines, which were mostly thin lines of small clumps. Yesterday and earlier today, we noticed that even these small clumps usually had several small fishes associated with them, so we decided to sample down the “skinny” weedlines. One of our interests is the relationship between fish abundances and the ‘morphology’ or shape of Sargassum features (mats, lines, and clumps). The neuston tow through this small series of clumps yielded our highest catch of the trip so far; we collected numerous juvenile Sergeant Majors, Orangespotted Filefish, Planehead Filefish, and Sargassumfish, among others. We continued our work in the Sargassum habitat into the early evening, with an additional neuston tow and reflectance measures.



Dr. Frank Hernandez and Valeria Nunez inspect the sample collected from the Neuston net. (Photo: Brian Jones)

So where to go now? Although we have a second cruise later this summer (in July), our colleagues from the USF Optical Oceanography Lab will not be able to join us for that trip. Therefore, we decided to prioritize the collection of additional reflectance and backscatter data for the remainder of this cruise while we had their expertise on board. New remote sensing analyses suggested that the Loop Current region we visited earlier still had very high Sargassum biomass, so a decision was made to return to that area. After cleaning up and securing our gear on the back deck, the vessel set a course for the Loop Current where we hope to continue our sampling success tomorrow.

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