International conférence on sargassum Thursday, October 24th, 2019 Day 1 - State of knowledge on Sargassum algae State of knowledge - biological, ecological and oceanographic data Fundamental knowledge about sargassum and related micro-organisms ---- Conférence Internationale sur les Sargasses Jeudi 24 octobre - Journée 1 État des lieux sur la connaissance des algues sargasses Table-ronde 1 Connaissance fondamentale des algues sargasses et des micro-organismes associés

1. IN SITU OBSERVATIONS OF DIVERSITY AND DISTRIBUTION OF
SARGASSUM AND ASSOCIATED FAUNA
AMY N.S. SIUDA
Eckerd College, St. Petersburg, Florida, USA
Collaborators:
DEBORAH S. GOODWIN, JEFFREY M. SCHELL, ANNETTE
GOVINDARAJAN, LAURA COONEY, KERRY WHITTAKER,
MADELYN TAYLOR, LINDSAY MARTIN, GRAYSON HUSTON

2. 10 different morphologies (Winge 1923)
2 holopelagic species (Parr 1934)
• S. fluitans (thorns on stem)
Forms - III , X
• S. natans (smooth stem):
Forms - I , II , VIII , IX
Schell et al. 2015 Oceanography
PELAGIC SARGASSUM DIVERSITYS.natansIS.fluitansIIIS.natansVIII

3. PELAGIC SARGASSUM DIVERSITY
Dibner et al. In Prep.
Mitochondrial genes (Cox3 and
Nad6) distinguish among forms
 reclassification?
Concatenated sequences:
• 0.349% divergence
S. natans VIII – S. natans I
• 0.698% divergence
S. natans VIII – S. fluitans III
• 0.698% divergence
S. natans I – S. fluitans III
Useful for identifying rare
variants?
Other genes. . . 16S and mt23S

4. PELAGIC SARGASSUM – IN SITU OBSERVATIONS
• Fall 1992 through Spring 2016
• > 7000 1-NM neuston tows
• new transatlantic cruise track in late
fall 2014 & 2015
• annually repeated cruise tracks
• 2x daily neuston tows (1200 & 0000)

5. Long-
term
30x
Long-
term
300x
Long-
term
Beached Sargassum
Windrows of Sargassum fragments
Dense Sargassum mat
composed of large branching
clumps
PELAGIC SARGASSUM – IN SITU OBSERVATIONS

6. PELAGIC SARGASSUM DISTRIBUTION
• Sargassum natans I
• Fall 1992 through Spring 2016
• essentially no S. natans I observed
in Caribbean

7. PELAGIC SARGASSUM DISTRIBUTION
• Sargassum fluitans III
• Fall 1992 through Spring 2016
• wider range than S. natans I
• found in Caribbean
• abundant in Florida Straits

8. PELAGIC SARGASSUM DISTRIBUTION
• Sargassum natans VIII
• Fall 1992 through Spring 2016
• abundant in tropical Atlantic,
Antilles Current, eastern Caribbean
• absent from Sargasso Sea
• observed in northern Gulf Stream,
off New England
• did not sample far western
Caribbean or Florida Straits after
early spring 2013

9. PELAGIC SARGASSUM DISTRIBUTION
Schell et al. 2015 Oceanography

10. PELAGIC SARGASSUM DIVERSITY & DISTRIBUTION
Govindarajan et al. 2019 PeerJ
• Aglaophenia latecarinata hydroid haplotypes
correlated with Sargassum form
• suggests that hydroid settlement occurs in
type-specific Sargassum source regions

11. PELAGIC SARGASSUM MOBILE FAUNA DENSITY & DIVERSITY
• 20,975 individuals
• 32 taxa (species or species groups)
• functional groups often dominated
by a single species
• Differences between form
• Differences between regions

12. PELAGIC SARGASSUM MOBILE FAUNA ABUNDANCE & DIVERSITY
Martin et al. In Prep
S. fluitans III S. natans VIIIS. natans I
RichnessAbundance

13. Martin et al. In Prep.
PELAGIC SARGASSUM MOBILE FAUNA DIVERSITY

14. Martin et al. In Prep.
PELAGIC SARGASSUM MOBILE FAUNA DIVERSITY
• density and diversity across regions does not correlate directly with
path of surface water flow
• pattern can be explained by simultaneous blooms in NERR and GOM

15. SUMMARY AND SIGNIFICANCE
• 3 common morphologies of Sargassum with distinct, but overlapping ranges
• all pelagic Sargassum is not the same! – may have different physiological tolerances
• critical information for modeling efforts
• suggests multiple source regions for recent pulses of Sargassum in Caribbean
• mobile fauna density, richness and community composition differ between
Sargassum forms and geographic regions
• interaction of previously rare with historically common Sargassum forms may lead
to shifts in mobile fauna diversity
• community composition may impact diversity at higher trophic levels

16. We thank the multitudes of
SEA Semester students & crew
for help with Sargassum collection.
This research was funded by
Sea Education Association and
Eckerd College.