daphnia. spike walker. 2005© microscopy uk or their contributors. assessing the ecological risk of...

Daphnia. Spike Walker. 2005© Microscopy UK or their contributors.

Assessing the Ecological Risk of the Effects of Climate Change on

Zooplankton in Lake Champlain

Alex GibsonMark RasmussenBen ShermanJosh StewartBrittany A. Weldon

ENSC 202Spring, 2009

Increasing water temperatures in Lake Champlain due to climate change will alter zooplankton

populations and cause subsequent food web disruption at higher trophic levels.

Overview

Climate Change Zooplankton in Lake Champlain Trophic cascades and food web Population dynamics Food sources and phytoplankton Predation Invasive species Conclusions & recommendations

Climate Change

The Greenhouse Effect: Visible light passes through the earths atmosphere and is either absorbed or reflected into the atmoshphere.

Examples: 1. Comparison of Lakes at Varying Altitudes

○ Characteristics/morphometry determine zooplankton biomass potential.

- Higher latitudes nutrient deficient.- Lower latitudes nutrient rich.

2. Photoperiod influences biomass.

Compensating for increased amounts of greenhouse gases, the mass balance of the earth is disrupted.

Compensate managing of inputs and outputs by increasing temperature.

Since a thicker blanket of greenhouse gasses have reduced energy loss to space, atmospheric adjustments in the form of temperature increase, have responded to the change.

Implications for the Northeast

Unique Characteristics Numerous freshwater ecosystems Dense concentrations of people History of intensive land use practices Extensive Forests

*Climate change has the potential to disrupt the dynamic input/output regime agitating natural freshwater systems through the creation of a variety of feedback mechanisms

Effect on Lake Temperature in Lake Champlain Increased global

mean temperature Increased seasonal

variability Increased

cloudiness and precipitation, more runoff

More runoff leads to higher base flow warmer water temp.

Zooplankton Microscopic

invertebrates Fill a critical niche in

Lake ecosystem Principle species in

Lake Champlain calanoid copepods, cyclopoid copepods, Daphnia, Bosmina, Sididae,and Leptodoridae

(Carling, et al. 2004)

Daphnia.

Calanoid CopepodBosmina

Trophic Cascades

Definition: suppression of prey abundance as a result of predators

in a food web.

Factors: Spatial and Temporal-high spatial heterogeneity

-deviation from linear food chain -high resource availability

and quality

Predictors of Zooplankton Biomass and Community Structure 1. CLIMATE 2. Nutrient Concentration 3. Predation

Work in concert to determine lakes trophic state.

Population Dynamics

Earlier spring warmingRotifer vs CladoceranPhotoperiodEdible algae

SedimentationRotifer vs Cladoceran

Spring Warming

Dynamics

Sedimentation

Rotifer vs CladoceranClay interactions

Food Sources Phytoplankton, main food source

Increases in phytoplankton growth related to concurrent increases in water temperature (Dale and Swartzman, 1984)

Perform at a higher than normal rate of photosynthesis in waters with a higher than optimal temperature

Lake Baikal, Siberia- the world’s largest freshwater lake

Monitored since 1945 Dramatic temperature

increases Large size of lake-

resistance to temperature changes

Importance of long-term monitoring

Phytoplankton Biomass Chlorophyll a and

Secchi discs used to measure phytoplankton biomass

Found to increase 300% since 1979 in Lake Baikal (Hampton, et al, 2008)

Earlier Spring Peak Earlier Spring, high

base flow, warmer waters

Allows for earlier first peak in phytoplankton growth

Longer growing season Overall increase in phytoplankton biomass

- - - Phytoplankton normal conditions, − Phytoplankton in thermally loaded conditions. (Dale, Swartzman, 1984)

– phytoplankton, - - - zooplankton (Dale, Swartzman, 1984)

Phytoplankton & Zooplankton Herbivorous

zooplankton peak follow phytoplankton peak

Larger carnivorous zooplankton feed on herbivorous zooplankton

Earlier zooplankton peak

Zooplankton Biomass

Decreasing Copepods and Rotifers

Increasing Cladocerans

Fewer large cladocerans, more smaller

(Hampton, et al, 2008)

Zooplankton Decrease in Biomass

Mean and minimum values decrease with temperature

Maximum values increase high peak

At Max - High variability in Daphnia at high temperatures due to shorter period and larger amplitude (peak)

(Norberg, DeAngelis. 1995)

Why are zooplankton decreasing if phytoplankton

are increasing?

Biomass is decreasing

↓ Larger zooplankton species (Daphnia)

↑Smaller zooplankton species (Bosmina)

Warmer water conducive to the growth of…

Blue-Green Algae Growth rate ↑ as water warms Concurrent P overloading ↓ Water clarity, ↓ dO2 Leads to ↓ diatoms & green algae Blue-green lower nutritional value Most zooplankton feed selectively on

others …Apparent increase of phytoplankton

and decrease in zooplankton

Predation Migration due to predation Predator migration- insect larvae of the Notonecta- preys on zooplankton in the shallows during

the during the day.- At night moves to open water to prey on

zooplankton

The adult form of the Notonecta also known as the water bug

Migration by zooplankton Zooplankton like Tropocyclops and

Polyarhra migrate vertically during day and night.

Tropocyclops (copepod) migrate to the bottom of the lake/pond during the day and at night spread equally in the water

Known as typical migration

Migration of zooplankton Polyarhra moves to the surface during

the day and spread out during the night. Known as reverse migration Zooplankton migrate to avoid predators

like fish which also increases their fitness.

At night zooplankton spread out because night predation is more difficult for predators

The abundance of zooplankton in Johnson pond at noon

Temperate and oxygen levels of Johnson

pond during the day and night

Surface water was warmer during the day than bottom of the pond.

At night water was the same temperature allowing the movement of zooplankton

Oxygen levels where higher on the bottom during the day but at night oxygen levels were found to be higher near the surface.

With increase temperatures zooplankton migration cycle would be altered allowing for opportunities for predation and lower the overall fitness of zooplankton.

Predation-comparing warmer/cold water lakes Ice cover- helps to reduce the predation

on zooplankton by shortening the growing season of phytoplankton

Canadian lakes have less predation then Danish lakes which have a warmer climate

Increase temperature will allow a longer time for predation of zooplankton

What can we expect in Lake Champlain with an increase in predation? Increased predation would lead to a

decrease in zooplankton abundance and biomass.

Less grazing on phytoplankton and algal biomass should increase

More turbid conditions and greening of lakes

A decline in invertebrates and amphibians

Zooplankton community composition determined by two major factors

PredationResource limitation

Energy moves in direction of arrow

Source: Lake Champlain Basin Program 2008

Predation -

What has a more significant impact on zooplankton?PredatorsResource Availability

How can this be determined?Manipulate predator populations AND food

sources in an existing system

Case Study: Vanni 1987

Increased food availabilityPhytoplankton levels were raised by elevating

available nutrients

Addition of planktivorous bluegill sunfish

Zooplankton populations measuredCladoceransCopepodsRotifers

Cladocerans Copepods Rotifers

Results Zooplankton density primarily driven by

resource limitationMost species saw population rise as a result of

elevated food levels, even with added predators

Species composition significantly affected by predationAll Cladoceran species reached larger mature

body size in the absence of sunfishAverage size Cladocerans initiated reproduction

was smaller in the presence of predator species

Case Study: Elser & Carpenter 1988

Removal of Piscivorous largemouth bass

Addition of planktivorous minnowsComparison between study lake (Tuesday)

and reference lake (Paul) that naturally exhibits manipulated fish populations

Results

Paul lake = dashed lines, Tuesday lake= solid line, vertical line = spring manipulation

Source: Elser & Carpenter 1988

Results Before manipulation:

larger zooplankton present at low levels

Smaller sized species represent most of biomass

After Manipulation: Shift towards larger mean body size

Higher concentration of larger species than before

Invasive Predators

Alosa pseudoharengus Dreissena polymorpha

Case Study: Beisner et al. 2003

Lake Champlain: Invasive Alewife is exploiting the Rainbow Smelt population

Crystal and Sparkling Lake (WI): Invasive Rainbow Smelt is interfering with indigenous Alewife population

Zooplankton data taken before and after the invasion was studied

Findings

(D) = Daphnia, (CL) = non-daphnid cladocerans, (CAL) = Calanoid Copepods, (CYC) = Cyclopoid Copepods

Source: Beisner et al. 2003

Zebra Mussels

Solid line = Observed impacts, Dotted line = Potential impacts (+) = Taxa benefitting from zebra mussels, (-) = Taxa exhibiting adverse effects due to zebra mussels Source: MacIsaac 1996.

Possible Impacts on Zooplankton

Reduction in zooplankton biomass Direct - ingestion of smaller taxa

(copepod nauplii)May alter species composition

Indirect - Filtration of suspended solids and phytoplankton could result in food limitation

Conclusions Large zooplankton populations are likely to

decrease Reduce food sources for higher trophic

levels Reduction of species dependent on large

zooplankton Increase in species feeding on small taxa Significant changes in lake species

composition!

Recommendations!

Long term monitoring in Lake Champlain

Efforts to decrease P loading

Practice best management processes to reduce invasives and further disruption

More $$ for research!!!

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