A review of a 30-year aquatic plant dataset
from the Santa Fe River
Eric Nagid
352-415-6962
[email protected]
Has submersed aquatic vegetation
(SAV) declined over time?
FWC – Invasive Plant Management Data
• What – Primarily surveying for exotic/invasive aquatic plants.
• The acreage of every exotic/invasive plant encountered is estimated.
• Presence/absence of every aquatic plant that is observed is recorded.
• Where – River Rise to Suwannee confluence.
• When – During growing season (April-October).
• How
• Presence/Absence: checklist.
• Exotic species acreage: Lines transects
via airboat and GPS.
• Who – 1 Surveyor from 1982-2009.
2 Different surveyors from 2010-present.
72 different species have been observed
Origin
Emergent
Submersed
Floating
Native
45
10
4
Exotic
6
4
3
Similarity of Plant Community by Year
Evidence for plant communities changes over time?
Analysis of similarity significantly different: (ANOSIM, p=0.001, R=0.574)
• Presence/Absence analysis extremely sensitive to minor differences.
• Some species come and go (e.g., Egeria).
• Human Error:
• Difficult to distinguish species that look similar (e.g., swamp lilies).
• Detection varies with water conditions (e.g., water clarity, flow)
• Experience – must know where to look for rare species.
So…has SAV declined over time?
Native Species of Submersed Aquatic Vegetation
Strap-leaf sagittaria (Sagittaria kurziana)
• Long, ribbon-like leaves
• Leaves have pointed tips
• White flowers and three-petaled and have long,
emersed stalks
Eel-grass, tape-grass (Vallisneria americana)
• Long, ribbon-like leaves
• Leaves have rounded tips
• Small, white female flowers reach the surface
on long, submersed flower stalks
Exotic Species of Submersed Aquatic Vegetation
Hydrilla (Hydrilla verticillata)
• Small leaves in whorls of 4 to 8 around the stem
• Leaf margins are distinctly saw-toothed
• Tiny white flowers on long stalks
East Indian hygrophila (Hygrophila polysperma)
• Square stems
• Leaves opposite
• Flowers are bluish-white to white, and have two
lips
Supposition: SAV coverage expands during periods
of drought and recedes during periods of floods.
2013
2011
2009
2007
2005
2003
2001
1999
1997
1995
1993
1991
1989
1987
1985
1983
1981
Discharge (cfs)
Stream Discharge and Acreage of Hydrilla/Hygrophila
cfs
2500
2000
1500
1000
500
0
Stream Discharge and Acreage of Hydrilla/Hygrophila
HYDR/HYGR
cfs
2500
80
70
2000
40
1000
30
20
500
10
2015
2013
2011
2009
2007
2005
2003
2001
1999
1997
1995
1993
1991
1989
1987
1985
0
1983
0
Acres
50
1500
1981
Discharge (cfs)
60
So…
• Inverse relationship exists between exotic SAV and discharge.
• Magnitudes of hydrilla coverage have declined over time.
• Should we expect exotic SAV to respond similarly to native SAV?
• Light: Hydrilla has a competitive advantage b/c it requires less light to grow.
• Anchoring: Native SAV have a competitive advantage in swift currents.
Other Factors:
• Effect of filamentous and epiphytic
algae?
• Decreases in dissolved oxygen and
grazer abundance in FL springs.