Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 1, 2018 (Day 3)*

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

Frank Hernandez

Dr. Hernandez scanning the horizon for signs of Sargassum (Photo: Carla Culpepper)

 

Today we woke up along the northwest edge of the Loop Current (approximately 26° 38′ N, 88° 19′ W) and quickly found patches of Sargassum in the area. Here is a short synopsis of some of the day’s activities.

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Dr. Dillon uses a Horizontal Niskin Sampler to collect water near a Sargassum patch. (Photo: Glenn Zapfe)

Sargassum was plentiful in our region, though again we did not find very large mats or weedlines. Multiple lines of surface convergence were observed, and along these frontal features were rows of smaller Sargassum clumps with an occasional larger patch (5-10 m long) interspersed in between. After searching for a few hours, we decided to sample a set of these larger patches. Sunny skies allowed for good reflectance measures; the CTD cast and water collection proceeded smoothly. During these ops, we did not see many fish associated with the Sargassum mats, and our fish collecting ops confirmed this.  Our neuston net pulled in a large of Sargassum, approximately 143 kg (that’s over 300 lbs)! It took the better part of the day to procss this much algae. In spite of this high biomass collected, there were very few fish present: we found a few juvenile Sergeant Majors and Tripletails (but little else).

Tripletail

A juvenile Tripletail (Lobotes surinamensis) collected in a neuston net towed through Sargassum. (Photo: Frank Hernandez)

Today we deployed our camera system for the first time within a Sargassum mat; this is a simple camera set up with 2 GoPro cameras filming under the Sargassum canopy. Scanning through the video, we again saw only a few fish over the course of 30 minutes or so (Tripletail, Amberjack, among others). Lastly, we sampled using hook-and-line fishing with Sabiki rigs, and collected a pair of Hardtail juveniles and several juvenile Almaco jacks (4 anglers fishing for 30 minutes). We were able to collect blood, liver and muscle tissue samples from these larger juveniles for later stable isotope and protein/fatty acid analyses.

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R/V Point Sur Marine Tech Josh Bierbaum, Ph.D. student Mengqiu Wang, and Dr. Xingxing Han deploy small boat ops to collect data from a Sargassum patch. (Photo: Olivia Lestrade.)

In short, all of our sampling gear indicated the same result today–just not many fish associated with Sargassum in this region today. It’s difficult to speculate why at the moment, but one of our objectives is to examine spatial variability in Sargassum-associated fish assemblages, so these data, along with the environmental data (salinity, temperature, etc.) will prove very useful.

Today we also deployed a small boat from the Point Sur to get “up close” measurements of reflectance and backscatter from Sargassum and open water habitats. This worked very well–a special thanks to Mengqiu and Xingxing for adding this new set of observations to the project! We may use the small boat again in the coming days to collect these and other in situ measurements.

So our first Sargassum habitat sampling was a success, even though it was “light” in the fish department. We hope for continued calm seas and golden algae in the days to come!

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