Effects of warming and nutrient enrichment on trophic

production in coastal waters

Laura DobroskiJuly 24, 2014

Aquatic Trophic Levels

http://www.teachoceanscience.net/teaching_resources/education_modules/aquatic_food_webs/learn/

Metabolic Theory of Ecology

• Temperature, body size affect individual metabolic rate

• Individuals’ metabolism can be scaled up to ecosystem level (Brown et al. 2004)

Climate change?

Trophic Production with Warming

O’Connor et al. 2009

Previous Work

O’Connor et al. 2009• Outdoor microcosms,

altered temperature and nutrients

• Measured effects on primary and secondary consumers’ biomass

• Conclusion: temperature alone can shift food web structure IF sufficient nutrients

Marañón et al. 2014• Analyzed

phytoplankton biomass/C fixation data in polar, temperate, tropical regions

• Conclusion: resources > temperature, which are not independent

Seasonal Variation

• Summer temperature increase equal to spring

• Will spring results hold true in summer?

• Modify O’Connor experiment:– Season– Fewer nutrients– Duration

http://oconnorlab.weebly.com/temperature-and-food-webs.html

Ambient +2 OC

+4 OC

Control Control

Control

+ Nutrients + Nutrients

+ Nutrients 20 μm N 1 μm P

Ambient +3 OC

+5 OC

Control Control

Control

+ Nutrients + Nutrients

+ Nutrients 40 μm N 2 μm P

Temperature

6/2/2014 0:00 6/4/2014 0:00 6/6/2014 0:00 6/8/2014 0:000

5

10

15

20

25

30

35

40

Avg same-temp tank temps

Ambiantplus 3plus 5

Time

Tem

p (

C)

Sampling Methods

Phytoplankton• Fluorometric

determination of [Chl a]

• Sampled on days 1, 2 and 4

Macrozooplankton• Filtered 2 L each in

63 μm mesh• Copepods, rotifers,

and cladocera• 2 10-mL replicate

subsamples in Ward counting wheel, averaged

Results – Lower Nutrient Addition

0.00

5.00

10.00

15.00

20.00

25.00

Time (Days)

[Chl

a] (

ug/L

)

1 2 4

Figure 1 Average chlorophyll a concentrations in water samples on days 1, 2, and 4 with standard error, with nutrient addition of 20 μm N and 1 μm P.

Relationship with nutrients is significant (p<0.05)

Results – Lower Nutrient Addition

Figure 3 Average macrozooplankton concentrations in same-temperature water samples on day 4 with standard error, with nutrient addition of 20 μm N

and 1 μm P.

Avg [Macro], Day 4

Figure 2 Average chlorophyll a concentrations in same-temperature water samples on day 1 with standard

error, with nutrient addition of 20 μm N and 1 μm P.

Relationships with nutrients are significant (p<0.05)

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

200.00

Temperature

Zoop

lank

ton/

L Ambient +2 OC +4 OC

0.00

5.00

10.00

15.00

20.00

25.00Avg [Chl a], Day 1

Temperature

[Chl

a] (

ug/L

)

Ambient +2 OC +4 OC

Results – Higher Nutrient Addition

0.00

5.00

10.00

15.00

20.00

25.00

Time (Days)

[Chl

a] (

ug/L

)

1 2 4

Figure 4 Average chlorophyll a concentrations in water samples on days 1, 2, and 4 with standard error, with nutrient addition of 40 μm N and 2 μm P.

Relationship with nutrients is significant (p<0.05)

Results – Higher Nutrient Addition

Avg [Macro], Day 4

Figure 5 Average chlorophyll a concentrations in same-temperature water samples on day 1 with standard

error, with nutrient addition of 40 μm N and 2 μm P.

Figure 6 Average macrozooplankton concentrations in same-temperature water samples on day 4 with standard error, with nutrient addition of 40 μm N

and 2 μm P.Relationship with nutrients is significant (p<0.05)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

Temperature

Zoop

lank

ton/

L Ambient +2 OC +4 OC

0.00

5.00

10.00

15.00

20.00

25.00Avg [Chl a], Day 1

Temperature

[Chl

a] (

ug/L

)

Ambient +2 OC +4 OC

Strength of Nutrients’ Enhancement with Temperature

0

2

4

6

8

10

12

14Chl a, Day 1

Lower

Higher

Temperature

Prop

ortio

n of

Con

trol

Ambient +2-3 OC +4-5 OC0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6Macrozooplankton, Day 4

Lower

Higher

Temperature

Prop

ortio

n of

Con

trol

Ambient +2-3 OC +4-5 OC

Discussion

• Nutrients affect biomass more than temperature does

• Sufficient resources needed for temperature to affect biomass– Possibly only found at

unnatural nutrient levels (sewage, runoff, etc.)

• Control switch from bottom-up to top-down

• Warming did not affect zooplankton biomass– Optimal temperature?– Methods?

Optimal Temperature

Experiment Ambient Upper Temperature

O’Connor 20 OC 26 OC

Single Nutrient

27 OC 32 OC

Double Nutrient

30 OC 34 OC

Heinle 1969

Improvements

• Measurement (biomass vs. counting)• Productivity

Acknowledgements

Suzanne ThompsonScott EnsignNathan HallMike Piehler

Questions?

http://blog.nature.org/science/2013/02/01/oceans-and-climate-change-protecting-the-invisible/