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Land-Ocean Interactions: The known and unknown impacts of multiple human activities on marine biodiversity. Heike K. Lotze Dalhousie University Halifax, Canada. History of change in estuaries. NCEAS (National Center for Ecological Analysis and Synthesis). How to explore the Past.

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Land-Ocean Interactions: The known and unknown impacts of multiple human activities on marine biodiversity

Heike K. Lotze

Dalhousie University

Halifax, Canada


History of change in estuaries

NCEAS (National Center for Ecological Analysis and Synthesis)

how to explore the past
How to explore the Past
  • Paleontological records
  • Archaeological records
  • Historical records
  • Ecological records
  • Cultural periods
  • Relative abundance
ecosystem degradation
Ecosystem degradation

Lotze et al. in preparation

resource depletion and habitat loss
Resource depletion and habitat loss












Lotze et al. in preparation

degradation of water quality
Degradation of water quality
  • Sediment cores
  • Hydrographic data

Lotze et al. in preparation

species invasion
Species invasion

Lotze et al. in preparation

present state of degradation
Present state of degradation

Relative abundance

Lotze et al. in preparation

shifts in diversity
Shifts in diversity

Lotze et al. in preparation

human drivers
Human drivers

Lotze et al. in preparation


Lotze et al. in preparation

the future
The Future

Where are we going?

1 temporal acceleration
1. Temporal acceleration

How much will our impact increase

before leveling off?

nutrient loading
Nutrient loading

Since 1960:

  • Nitrogen flow in terrestrial ecosystems doubled
  • Phosphorus flow tripled

Human-produced Reactive Nitrogen

Millennium Ecosystem Assessment 2005

oxygen depleted areas
Oxygen-depleted areas

Global increase since 1900

Diaz et al. 2004, GEO Year Book 2003

harmful algal bloom

Harmful algal blooms

Public health events

Fish events

Coral events

Invertebrate events

Mollusc events

Sea turtle events

Seagrass events

Bird events

Mammal events

Harmful algal bloom

Increase since 1970

HEED 1998

degradation of water quality1
Degradation of water quality

Lotze et al. in preparation

diversity decline with eutrophication
Diversity decline with eutrophication

Eutrophication gradient

Worm & Lotze, in press

are we tipping the balance
Are we tipping the balance?

The rise of slime…?

2 spatial expansion
2. Spatial expansion

How far will we spread our impacts?

rivers nutrient loading
Rivers: nutrient loading

Increase in Nitrogen transport to river mouths

Millennium Ecosystem Assessment 2005

coasts oxygen starved zones
Coasts: oxygen-starved zones

Oxygen depletion key:  Annual / Episodic / Periodic / Persistent

GEO Year Book 2003

open ocean atmospheric deposition
Open ocean: atmospheric deposition

Reactive nitrogen deposition in 1993 (mg N m-2 yr-1)

Galloway and Cowling 2002

deep sea nitrogen enrichment
Deep sea: nitrogen enrichment

Deep-water Redfield ratio in North Atlantic Ocean exhibits rising N:P, possibly related to increased atmospheric N deposition

Pahlow & Riebesell 2000, Science

reaching global limits
Reaching global limits?


=> estuary

=> inshore

=> offshore

=> deep sea

Global consequences…?


  • Nutrient loading
  • Exploitation
  • Habitat destruction
3 multiplication
3. Multiplication

How will our multiple impacts interact?

acceleration of algal blooms


Filter feeder


Filter Feeder


Climate change

Annual algae

Annual algae


Habitat destruction


Nutrient loading

Acceleration of algal blooms

Lotze & Milewski 2004

interacting climatic and ecological controls
Interacting climatic and ecological controls

Increasing temperature enhances:

  • algal recruitment and growth
  • the nutrient effect
  • the grazing effect

Lotze & Worm 2002

potential for surprises

Caribbean food web containing 30% of species

and 11% of the interactions.

Bascompte et al. 2005

Potential for surprises?

Can we predict and manage

multiple interactions among

multiple human drivers and

multiple species?

4 sustainability
4. Sustainability

How much un-degraded river, estuary,

and inshore area do we needto

sustain marine diversity and

goods & services?

population declines
Population declines

In 22 out of 28 estuaries designated as National Estuary Programme sites in the USA, declines of fish and wildlife populations are now considered to be high or medium-priority problems

Kennish 2002


Worse-case scenario:

Can we do without them?


Best-case scenario:

Can we restore them?

reversing nutrient pollution
Reversing nutrient pollution
  • Tampa Bay, FL
  • 10-fold reduction of nitrogen loading from municipal waste
  • Increase in water clarity
  • Reduction of phytoplankton productivity
  • Reduction in cyanobacterial blooms
  • Recovery of seagrass

Cloern 2001


Reversing nutrient pollution

  • Thames and Forth River estuaries, UK
  • Increase in oxygen
  • Recovery of fish stocks

Cloern 2001


The Known

  • Where we come from
  • Where we are today
  • Where we are going if current trends continue
  • Recovery is possible

Thus, whatever the UU’s, we should use the K’s to act today and turn negative trends around.