To predict temporal dynamics of holopelagic <em>Sargassum</em> blooms and their development across the Great Atlantic <em>Sargassum</em> Belt, one must understand the environmental tolerances and growth rates of different morphotypes under varying environmental conditions. We conducted a series of experiments exposing three common holopelagic <em>Sargassum</em> morphotypes to different temperature (21 to 30 degrees C) and salinity (26 to 40 ppt) conditions. Tolerance of <em>Sargassum</em> was assessed by two methods: a daily health metric was calculated from changes in a specimen’s blade and float count and coloration patterns, and growth rates were estimated from pre- and post-treatment wet weights. Morphotypes exhibited different responses to treatment conditions. <em>S. natans I<em> has a narrow salinity tolerance (32 to 40 psu) and a wide tolerance for colder temperatures (20 to 28 degC).  <em>S. natans I<em> does not tolerate salinities below 30 psu and temperatures above 32 degC. <em>S. natans VIII<em>  has a wide salinity tolerance (28 to 40 psu) and narrow temperature (24 to 32 degC) tolerance favoring warm conditions.  <em>S. fluitans III<em> has a wide salinity (28 to 40 psu) and temperature (20 to 28 degC) tolerance.  <em>S. fluitans IIII<em> does not tolerate salinities below 26 psu and temperatures above 32 degC. Additional experiments of longer duration and with varying nutrients, using specimens from across holopelagic <em>Sargassum</em>’s geographic range, are necessary to understand growth ecology and parameterize models.

Primary Presenter: Jeffrey Schell, Sea Education Association (jschell@sea.edu)

Authors:

Jeffery Schell, Sea Education Association  (jschell@sea.edu)

Amy Siuda, Eckerd College  (siudaan@eckerd.edu)

Deborah Goodwin, Unaffiliated  (goodwins@gmail.com)

Rebecca Volk, Sea Education Association  (becvolkh@gmail.com)