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Florida Bay Seagrass Die-off Summary

David Rudnick

Everglades National Park

RECOVER Annual Science Meeting

March 1, 2016

Turtlegrass Die-off During the Summer of 2015

Turtlegrass Detritus Produced with Die-off

BlackwaterSound

Calusa Key Basin

Eagle Key Basin

Twin Key BasinRabbit Key Basin

Johnson Key Basin

Crane Key Basin

Whipray Basin

Rankin Lake

Madeira Bay

TURTLEGRASS DIE-OFF LOCATIONS1987-1990 vs. 2015 EVENT

1987

From: P. Hall 2015, FWRI2015

Everglades National ParkSouth Florida Natural Resources Center

Comparison to 1987

From B. Furman

Estimated Thalassia Die-off Area (Jan. 2015)

Seagrass mortality and algal blooms:

hypothesized causes

and feedback loops

mortality

Thalassia

dominance,

high biomass

& respiration

Increase

sediment

suspens

low

freshwater

flow

Increase

sediment

suspens

nutrient

input

Increasesediment

suspens

high

salinity

Increasesediment

suspens

Oxygen (DO)

deficiency,

sulfide

production

Events inhibit DO

Sulfide toxicity

supply sSEAGRASS

MORTALITY

Sediment

destabilizationSediment

destabilization

Increased

sediment

suspension

Increased

sediment

suspension

Increased

algal

blooms

Increased water

column

nutrients

Decreased

LIGHT

penetration

Detritus

decomposition,

oxygen uptake,

nutrient release

2015: Low Rain and High Salinity

From: K. Kotun

Salinity gauge

Creek flow gauge

TRTR

365 d

ay m

ovin

g s

um

of 5 c

reek flo

w(x

1000 a

cre

-feet)

100

200

300

400365d moving sum 5 creek flowflow below MFL thresholdWY01-13 Average MFL threshold

J F M A M J J A N DS OM J J A N DS O J F M A M J J A N DS O J F M A M J J A S O

2012-2015 Conditions - Florida BayTaylor River Salinity & MFL Flow

2012-2015 Conditions - Florida BayTaylor River Salinity & MFL Flow

105,000 acre-feet MFL rule threshold

Lowest value ever recorded since the 5 creek flow

gauges were installed in 1996.

August 2015 – 77,602 acre-feet

Average

Record High Salinity in North-Central Florida Bay

During the Summer of 2015

Mapping Florida Bay SalinityMapping Florida Bay Salinity

11

Late

July 2015

Difference

from

2006 – 2014

Average

(Jun – Aug)

> 50 Practical

Salinity Units

(psu)

5 10 15 20 25 30 35 40

Salinity

-30 -20 -10 0 10 20 Salinity minus average

Seven

Palm

Seven Palm

Rankin

Rankin

From Madden,

Stachelek,

Kelly

Percent Saturation Dissolved Oxygen at Buoy Key (2015)

140

120

100

80

60

40

20

0

From P. Carlson, V. Absten

Sediment Porewater Sulfide Concentrations (mM) in Die-off Areas.

Values > 2 mM are toxic to Thalassia testudinum.

Rankin Lake

From P. Hall and B. Furman, FWRI

Conclusions

� A die-off of Thalassia testudinum began in July 2015 in north-central

Florida Bay

� By January 2015, the location and spatial extent of this die-off was

similar to that of the 1987-1990 die-off

� Thalassia die-offs are hypothesized to occur in high biomass beds,

which develop in association with sustained high salinity and

relatively high nutrients

� The lethal agents proximately causing die-off are anoxia and sulfide

toxicity

� High salinity decreases dissolved oxygen supply and increases the risk

of anoxia via stratification

� With nutrient release from decomposing seagrass detritus, Florida

Bay is now poised for potential large-scale algal blooms

2015 Conditions - District Rainfall Distribution

Low

High

• Taylor Slough & Florida Bay received the lowest amounts of rainfall

• 25-45 inches since May 2014 compared to District-wide average of 80 inches

Total Rainfall

(Radar Estimated)

May 2014 - November 2015

Station BK: Anoxic event development

Jun-2010 Jun-2011 Jun-2012 Jun-2013 Jun-2014 Jun-20150

6

12

18

24

Num

ber

of

hours

per

day

wit

h D

O <

0.5

mg/l

Station BKHours of anoxic conditions per day

Never suboxic more than 12

hours per day:

2010 - 2012

Possible

sensor failure

Suboxic conditions

persist for > 3 months

Everglades National ParkSouth Florida Natural Resources Center

Detrital Mats

Everglades National ParkSouth Florida Natural Resources Center

Date

Palm

er

Dro

ught

Se

verity

In

de

x (

PD

SI)

-6

-4

-2

0

2

4

61

95

0

195

1

195

2

195

3

195

4

195

5

195

6

195

7

195

8

195

9

196

0

196

1

196

2

196

3

196

4

196

5

196

6

196

7

196

8

196

9

197

0

197

1

197

2

197

3

197

4

197

5

197

6

197

7

197

8

197

9

198

0

198

1

198

2

198

3

198

4

198

5

198

6

198

7

198

8

198

9

199

0

199

1

199

2

199

3

199

4

199

5

199

6

199

7

199

8

199

9

200

0

200

1

200

2

200

3

200

4

200

5

200

6

200

7

200

8

200

9

201

0

201

1

201

2

201

3

201

4

201

5

201

6

Florida Keys

Lower East Coast

Everglades

Climatology

Was drought a factor in 1987?What about other drought years?We need a continuous response

variable for die-off severity…

Data from NOAA

Anoxic Bottom Water in

North-Central Florida BayRankin July 30, 2015

0.00

2.00

4.00

6.00

8.00

10.00

RK1 RK3 RK4 RK5 RK7

Site

DO

mg/L

Surface

Bottom

41 42 4241

41

50 58 4250 61

Salinity

values

Stratification of water column likely important factor for die-off

Site: Rankin Lake; July 30, 2015

Everglades National ParkSouth Florida Natural Resources Center

TURTLEGRASS DIE-OFF LOCATIONS1987-1990

Modified from Robblee, et al. 1991

BlackwaterSound

Calusa Key Basin

Eagle Key Basin

Twin Key BasinRabbit Key Basin

Johnson Key Basin

Crane Key Basin

Whipray Basin

Rankin Lake

Madeira Bay

subsequent

monitoring areas

die-off areas

Long-term set up factors

• Stable, high salinity promotes Thalassia dominance• Nutrient supply promotes high biomass with high

respiratory demand (especially root, rhizome)

Seagrass mortality and algal blooms: hypothesized causes and feedback loops

Long-term set up factors

• Stable, high salinity promotes Thalassia dominance• Nutrient supply promotes high biomass with high

respiratory demand (especially root, rhizome)

Proximate triggers

• Anoxia and associated sulfide appear to be the primary lethal agents

• Anoxia promotes sulfate reduction, producing toxic sulfide

• Dissolved oxygen (DO) supply (saturation) decreases with increasing temperature and salinity

• DO demand increases with temperature• High night-time DO demand when low light (cloudiness,

short photoperiod in autumn)• Stratification can yield rapid anoxia at bottom• High salinity (density) bottom water and low wind promote

stratification

Seagrass mortality and algal blooms: hypothesized causes and feedback loops

Long-term set up factors

• Stable, high salinity promotes Thalassia dominance• Nutrient supply promotes high biomass with high

respiratory demand (especially root, rhizome)

Proximate triggers

• Anoxia and associated sulfide appear to be the primary lethal agents

• Anoxia promotes sulfate reduction, producing toxic sulfide

• Dissolved oxygen (DO) supply (saturation) decreases with increasing temperature and salinity

• DO demand increases with temperature• High night-time DO demand when low light (cloudiness,

short photoperiod in autumn)• Stratification can yield rapid anoxia at bottom• High salinity (density) bottom water and low wind promote

stratification

Feedbackloops propagate more die-off

• Seagrass mortality produces decaying detritus that consumes more DO and produces more sulfide

• Nutrient release from detritus stimulates algal blooms that decreases light and seagrass DO production

• Sediments are destabilized with seagrass mortality and resuspended, further decreasing light

Seagrass mortality and algal blooms: hypothesized causes and feedback loops

Everglades National ParkSouth Florida Natural Resources Center

• Map shows how much salinity levels deviate from average conditions*

• Darker the pink coloration, the higher above average the salinity

• Average salinity – 35 psu

• In July, salinities exceeded 50 psu in large area of central Florida Bay

• Salinity as high as 72 psu measured at Garfield Bight

Mapping Florida Bay Salinity Mapping Florida Bay Salinity

Late

July 2015

* (2006-2014)

Everglades National ParkSouth Florida Natural Resources Center

Everglades National ParkSouth Florida Natural Resources Center

Everglades National ParkSouth Florida Natural Resources Center

Dissolved Oxygen

SUMMER 2015

0=Mean BB

0<Mean BB≤1

1<Mean BB≤2

2<Mean BB≤3

3<Mean BB≤4

4<Mean BB≤5

Johnson KeyBasin

Twin KeyBasin

Rabbit KeyBasin

Rankin Lake

Whipray Basin

FALL 2015

0=Mean BB

0<Mean BB≤1

1<Mean BB≤2

2<Mean BB≤3

3<Mean BB≤4

4<Mean BB≤5

Johnson KeyBasin

Twin KeyBasin

Rabbit KeyBasin

Rankin Lake

Whipray Basin

Florida Bay Algal Bloom Location

Florida Bay Algal Bloom Location

34

Algae Bloom

Region: One month

after the

hypersaline event

Seven Palm

Rankin Lake

BloomsNo

Blooms

Sept 14-17 2015

Everglades National ParkSouth Florida Natural Resources Center

Region of Recent Fish Kills

35

Seven Palm

Rankin Lake

Striped

Mullet

Gulf Toadfish

Pinfish

Florida Bay Conceptual Ecological Model

Pesticides & MercuryNitrogen and

Phosphorus Inputs

Slime Mold Infection of Thalassia >

with > Salinity

PinkShrimp

Benthic Grazers

Seagrass Community

Water Quality Condition

Sea Level Rise

Major Hurricanes

Flagler Railway

(Keys' fill)

Water Management Agriculture

Recreation & Fisheries

Fishing Pressure

Thalassia

Overgrowth

ThalassiaMass

Mortality

Bioaccumulation

Fish Populations

Fish-EatingBirds

Upper

Trophic

Level

Shift

> Nitrogen &

Phosphorus

< Ruppia

& Halodule

Development

>Suspended Sediment

Algal Blooms

< Light PenetrationContinued

Seagrass Mortality

Cycle Causing

Seagrass Habitat Loss

> Filter Feeding

Altered Salinity Regime