Isotopic Perspectives on the Foundation of Estuarine Dependent Fish Biomass:

Macrophytes Versus Microphytes

David Hollander, Elon Malkin, Susan Murasko, Ernst Peebles

College of Marine Science

University of South Florida

St. Petersburg, FL 33701

Project Objective: Determine the key primary producer(s) that

support economically-important juvenile fish in SW Florida’s tidal rivers

Fishing in Southwest Florida: A Billion Dollar Industry

•Estuarine-Dependent Life–Adult’s spawn at coast–Larvae migrate to rivers–Juveniles occupy rivers

•Climatic & Human Impacts–SW Florida Hydrology •Wet vs. Dry Seasons

–Anthropogenic nutrient inputs •Oligotrophic vs. Eutrophic

Why do fish occupy tidal rivers?

Migration

Migration

Adults

Tidal RiversTidal Rivers

JuvenilesJuveniles

New Orleans

Coast

TampaBay

Gulf of Mexico

Larvae

•Abundant vascular plants occupy these habitats– Do these provide the basis of food-webs?

Tidal Rivers: Vegetated Nursery Habitats

•Juvenile Fish utilize vegetated tidal rivers as nurseries•Juvenile Fish eat benthic invertebrates (Gut Study)

Benthic Inverts.

Benthic invert. feeder

Juvenile

–What 1o producers support these ecosystems?

•Abundant vascular plants occupy these habitats– Do these provide the basis of food-webs?

Tidal Rivers: Vegetated Nursery Habitats

•Juvenile Fish utilize vegetated tidal rivers as nurseries•Juvenile Fish eat benthic invertebrates (Gut Study)

Benthic Inverts.

Benthic invert. feeder

Juvenile

–What 1o producers support these ecosystems?

Macrophytic food web?

?Vascular PlantsMacrophytes?

Abundant Vascular Plants (Macrophytes) may support food web

•Freshwater delivers nutrients to these habitats– Potential Changes to Nutrient Flows:

– Natural hydrology (Wet season Hi vs. Dry season Lo)– Anthropogenic nutrient loading (Oligotrophic vs. Eutro)

Tidal Rivers: Nutrient Flow

Nutrient Delivery

JuvenileInverts.

•Freshwater delivers nutrients to these habitats– Potential Changes to Nutrient Flows:

– Natural hydrology (Wet season Hi vs. Dry season Lo)– Anthropogenic nutrient loading (Oligotrophic vs. Eutro)

Tidal Rivers: Nutrient Flow

Nutrient Delivery

JuvenileInverts.

•Nutrient delivery supports microalgal blooms

MicroalgaeMicrophytes

•Freshwater delivers nutrients to these habitats– Potential Changes to Nutrient Flows:

– Natural hydrology (Wet season Hi vs. Dry season Lo)– Anthropogenic nutrient loading (Oligotrophic vs. Eutro)

Tidal Rivers: Nutrient Flow

Nutrient Delivery

JuvenileInverts.

•Nutrient delivery supports microalgal blooms

?MicroalgaeMicrophytes? Microphytic food web?

Microalgae (Microphytes) may support food web

Florida’s Tidal Rivers: 2 Potential Nutritional Influences

Juvenile Fish Nursery

Florida’s Tidal Rivers: 2 Potential Nutritional Influences

Watershed Plants

Macrophytes•Marshgrass•Mangroves•Upland tree detritus

Macrophyticfood web

Juvenile Fish Nursery

Florida’s Tidal Rivers: 2 Potential Nutritional Influences

Hydrology & Nutrient Driven

MicrophytesMicroalgae•Benthic Microalgae •Phytoplankton (POM)

Microphyticfood web

Watershed Plants

Macrophytes•Marshgrass•Mangroves•Upland tree detritus

Macrophyticfood web

Juvenile Fish Nursery

Florida’s Tidal Rivers: 2 Potential Nutritional Influences

MicrophytesMicroalgae•Benthic Microalgae •Phytoplankton (POM)

Microphyticfood web

Watershed Plants

Macrophytes•Marshgrass•Mangroves•Upland tree detritus

Macrophyticfood web

Which 1o producers support fish biomass in tidal rivers? Microphytes vs. Macrophytes?

Juvenile Fish Nursery

Hydrology & Nutrient Driven

Weeki wachee

Alafia

Myakka

CharlotteHarbor

Tampa Bay

Gulf OfMexico

Research Strategy

Field Studies•Ecosystem wide sampling during wet & dry season

–Vascular Plants, Microalgae, Fish

Weeki wachee

Alafia

Myakka

CharlotteHarbor

Tampa Bay

Gulf OfMexico

Research Strategy

Field Studies•Ecosystem wide sampling during wet & dry season

–Vascular Plants, Microalgae, Fish

•3 Rivers with variable nutrient states

EutrophicOligotrophic

AlafiaMyakkaWwachee

Weeki wachee

Alafia

Myakka

CharlotteHarbor

Tampa Bay

Gulf OfMexico

Research Strategy

Field Studies•Ecosystem wide sampling during wet & dry season

–Vascular Plants, Microalgae, Fish

•3 Rivers with variable nutrient states

EutrophicOligotrophic

AlafiaMyakkaWwachee

Analytical Approach•Stable isotopes of organic C, N, S

–Reflects trophic relationships & nutrient sources

Weeki wachee

Alafia

Myakka

CharlotteHarbor

Tampa Bay

Gulf OfMexico

Research Strategy

Field Studies•Ecosystem wide sampling during wet & dry season

–Vascular Plants, Microalgae, Fish

•3 Rivers with variable nutrient states

EutrophicOligotrophic

AlafiaMyakkaWwachee

Which 1o producers support fish biomass in tidal rivers? Microphytes vs. Macrophytes?

Analytical Approach•Stable isotopes of organic C, N, S

–Reflects trophic relationships & nutrient sources

Mesotrophic Myakka: Wet Season

Mesotrophic Myakka: Wet Season

-5-3-113579111315

δ15N

,

‰ A

IR

6N:2C

FishRed Drum

Mojarra

Silverside

Sand Seatrout

-35 -30 -25 -20 -15δ13 C, ‰ PDB

-5-3-113579111315

•Macrophyte δ13C range constrained vs. Fish

6N:2C

δ15N

,

‰ A

IRMacroMangroves

Marshgrass

Upland Trees

-35 -30 -25 -20 -15δ13 C, ‰ PDB

Mesotrophic Myakka: Wet Season

-5-3-113579111315

-35 -30 -25 -20 -15

•POM covers δ13C range of Fish•POM supports Fish in the Wet Season

δ15N

,

‰ A

IR

δ13 C, ‰ PDB

6N:2C

MicroPOM

BMA

Mesotrophic Myakka: Wet Season

Mesotrophic Myakka: Dry Season

-5-3-113579111315

δ15N

,

‰ A

IR

6N:2C

FishRed DrumMojarraSilversideSand SeatroutSpotted StroutMulletSpot

-35 -30 -25 -20 -15δ13 C, ‰ PDB

Mesotrophic Myakka: Dry Season

-5-3-113579111315

•Macrophytes may contribute to some Fish

δ15N

,

‰ A

IR

6N:2C

MacroMangroves

Marshgrass

Upland Trees

-35 -30 -25 -20 -15δ13 C, ‰ PDB

Mesotrophic Myakka: Dry Season

-5-3-113579111315

s

•BMA may contribute to some Fish

δ15N

,

‰ A

IR

6N:2C

MicroPOM

BMA

-35 -30 -25 -20 -15δ13 C, ‰ PDB

Mesotrophic Myakka: Dry Season

•BMA & Macrophytes both seem to contribute to fish•Third tracer needed

6N:2C

s

Micro

MacroMangroves

Marshgrass

Fish

-35 -30 -25 -20 -15δ13 C, ‰ PDB

-5-3-113579111315

δ15N

,

‰ A

IR Mesotrophic Myakka: Dry Season

POM

BMA

Mesotrophic Myakka: Dry Season Sulfur

-5-3-113579111315

3 8 13 18

s

•Sulfur data distinguishes between BMA & Macrophytes•BMA supports Fish in the Dry season

δ15N

,

‰ A

IR

6N:0S

MojarraSilversideSpotted Strout

Micro

MacroBMA

MangrovesMarshgrass

δ34 S, ‰ CDT

Fish

Conclusion: Microalgae Support Juvenile Fish Biomass

Benthic Deposit Feeders

Invert Feeders

Juvenile Fish

•Fish and Inverts do not change feeding behavior

Conclusion: Microalgae Support Juvenile Fish Biomass

•Fish and Inverts do not change feeding behavior

Benthic Deposit Feeders

Invert Feeders

Juvenile Fish

Wet Season Nutrient Delivery ON

POM BLOOM

POM DominatedSediments

DepositionalSystem

Conclusion: Microalgae Support Juvenile Fish Biomass

Benthic Deposit Feeders

Invert Feeders

Juvenile Fish

Dry Season Nutrient Delivery OFF

BMA DominatedSediments

POM BLOOM

Benthic Nutrients

•Fish and Inverts do not change feeding behavior

Conclusion: Microalgae Support Juvenile Fish Biomass

Benthic Deposit Feeders

Invert Feeders

Juvenile Fish

Wet Season Nutrient Delivery ON

POM BLOOM

POM DominatedSediments

DepositionalSystem

Dry Season Nutrient Delivery OFF

BMA DominatedSediments

POM BLOOM

Benthic Nutrients

•Fish and Inverts do not change feeding behavior

Mesotrophic vs. Oligotrophic Rivers

Mesotrophic Myakka

•Moderate nutrient delivery during wet season

–POM supports Fish

Mesotrophic vs. Oligotrophic Rivers

•Moderate nutrient delivery during wet season

–POM supports Fish

Mesotrophic Myakka Oligotrophic Weeki wachee

•Low nutrient delivery during wet season

–What supports Fish?

•What 1o producers support Fish in oligotrophic systems?

Oligotrophic Weeki wachee:

δ13 C, ‰ PDB

Mesotrophic Oligotrophic-3-113579111315

-5-35 -30 -25 -20

-3-113579111315

-5-35 -30 -25 -20

δ15N

,

‰ A

IROligotrophic Rivers: POM Deposition OFF

Myakka Wet Season Wwachee Wet Season

Oligotrophic Weeki wachee:

δ13 C, ‰ PDB

Mesotrophic Oligotrophic-3-113579111315

-5-35 -30 -25 -20

-3-113579111315

-5-35 -30 -25 -20

δ15N

,

‰ A

IR

•Less Fish catches during sampling (Myakka 3X)

Fish

Oligotrophic Rivers: POM Deposition OFF

Myakka Wet Season Wwachee Wet Season

Oligotrophic Rivers: POM Deposition OFF

Oligotrophic Weeki wachee:

Myakka Wet Season Wwachee Wet Season

δ13 C, ‰ PDB

Mesotrophic Oligotrophic-3-113579111315

-5-35 -30 -25 -20

-3-113579111315

-5-35 -30 -25 -20

δ15N

,

‰ A

IR

•Less Fish catches during sampling (Myakka 3X)•Not enough nutrients for sig. wet season phytoplanktic algal blooms•Only partial POM contribution; BMA supports fish in wet season

Micro Fish

POM

BMA

Conclusions & Implications•Microalgae support juvenile fish in tidal rivers

–POM supports Fish during wet season (freshwater nutrient flow)

–BMA supports Fish during dry season (access to benthic nutrients)

•Ecosystem-wide stable isotopes & Management

–Quantifies ecology; supports mathmatical models

–Stronger than species-specific studies; supports NOAA’s future goals

–Links Ecology to biogeochemistry of ecosystems