17 Biodiversity and Conservation of the Ocean

Notes for Marine Biology: Function, Biodiversity,

EcologyBy Jeffrey S. Levinton

©Jeffrey S. Levinton 2001

Biogeographic Factors

• Geographic isolation + strong environmental gradients -- isolate groups of species

• Present day world -- mostly north-south trending coasts, fairly strong latitudinal temperature gradient, offshore habitat lower in nutrients

• Produces coastal biogeographic provinces (temperature, current systems, geographic isolation)

• Provinces can be species boundaries, statistical construct of different species assemblages

ARCTICALEUTIAN

OREGONIAN

CALIFORNIAN

70N

60N

50N

40N

30N

1. Pt. Barrow2. Cape Romanzof3. Nunivak Island4. Hagemeister Island5. Prince William Sound6. Dixon Entrance7. Vancouver Island8. Puget Sound9. Cape Flattery10. Cape Mendocino11. Monterey Bay12. Point Conception13. Punta Eugenia14. Cabo San Lucas

Provinces (named in red) of the Pacific coast of North America

Horseshoecrab

Americanoyster

Seasidesparrow

Diamondbackterrapin Toadfish Black sea

bass

Province boundaries: can = species boundaries, can = genetic boundaries within species

Establishment of Biogeographic Barriers 1

• Many coastal provinces are maintained by barriers to dispersal, combined with temperature breaks (e.g., Point Conception, California, Cape Hatteras, Massachusetts)

Establishment of Biogeographic Barriers 2

• Many coastal provinces are maintained by barriers to dispersal, combined with temperature breaks (e.g., Point Conception, California, Cape Hatteras, Massachusetts)

• Larger scale barriers originate from geological upheavals (e.g., Isthmus of Panamá, which arose ca. 3 million years ago), resulting in isolation and speciation (in Panamá, many paired species on Pacific and Caribbean sides of Isthmus)

Components of Diversity

• Within-habitat component refers to the number of species living in the same habitat type

• Between-habitat component refer to the number of species living in all habitat types

• A within-habitat study might be comparing the number of species that live in muddy bottoms on the shelf versus the abyssal bottom

Diversity Gradients

• Latitudinal Diversity Gradient - one of the most pervasive gradients. Number of species increases towards the equator

• Gradient tends to apply to many taxonomic levels (species, genus, etc.)

Species

Genera

Families

1,000

100

10

Latitude

Num

ber

Bivalve diversity versus latitude

Other Diversity Differences• Between-Ocean differences. Pacific biodiversity

appears to be greater than Atlantic, although the specifics are complex

• Within-Ocean differences. From a central high of biodiversity in the SW Pacific, diversity declines with increasing latitude and less so with increasing longitude, away from the center

• Inshore-Estuarine habitats tend to be lower in diversity than open marine habitats

• Deep-sea diversity increases, relative to comparable shelf habitats, then decreases to abyssal depths

Explanations of Diversity Differences• Short-term ecological interactions - presence of

predators might enhance coexistence of more competing species, competitor might drive inferior species to a local extinction

Explanations of Diversity Differences 2• Short-term ecological interactions - presence of

predators might enhance coexistence of more competing species, competitor might drive inferior species to a local extinction

• Greater speciation rate - might explain higher diversity in tropics. Center of origin theory argues that tropics are source of most new species; some of which may migrate to higher latitudes

Explanations of Diversity Differences 3• Short-term ecological interactions - presence of

predators might enhance coexistence of more competing species, competitor might drive inferior species to a local extinction

• Greater speciation rate - might explain higher diversity in tropics. Center of origin theory argues that tropics are source of most new species; some of which may migrate to higher latitudes

• Lower extinction rate - might also explain major diversity gradients

Explanations of Diversity Differences 4• Short-term ecological interactions - presence of predators

might enhance coexistence of more competing species, competitor might drive inferior species to a local extinction

• Greater speciation rate - might explain higher diversity in tropics. Center of origin theory argues that tropics are source of most new species; some of which may migrate to higher latitudes

• Lower extinction rate - might also explain major diversity gradients

• Area - Greater area might result in origin of more species, but also lower extinction rate of species living over greater geographic ranges (having higher population sizes)

Explanations of Diversity Differences

• Habitat stability - A stable habitat may reduce the rate of extinction, because species could persist at smaller population sizes

• Sea-level fluctuations - sea level fluctuations, such as during the Pleistocene, might have created barriers during low stands of sea level, leading to isolation and speciation. This mechanism has been suggested as increasing the number of species in the SW Pacific in coral reef areas.

0 2000 4000 6000 8000 10,000

15

10

5

Num

ber

of s

eagr

ass

spec

ies

Km

Example of evidence supporting the center of origin theory. Number0f seagrass species with distance downcurrent from Torres Straight

Eutrophic

OligotrophicNum

ber

of s

peci

es

Area (hectares)

Species-area effect: Danish ponds and lakes.

Within-ocean coral reef diversity gradients. Pacific coral reefs

After Hughes, 2001, Science

Conserving Marine Biodiversity

• In many habitats the number of species present is poorly known and severely underestimated

• Need methods of recognizing species. Morphology has limited use, but molecular markers are being used commonly to distinguish among species

Conserving Marine Biodiversity 2Value of biodiversity

• Aesthetic value of diverse ecosystems• Many species play crucial roles in elemental

cycling• Loss of species at apex of food chains has

drastic top-down effects on marine systems• Loss of species that are structural elements in

communities (e.g., corals, seaweeds, seagrasses) might cause loss of many more species

Marine Invasions

• Invasion is the arrival of a species to an area that has not lived there previously

• Invasions are increasing in frequency

• Invasions often result in the arrival of species with strong local ecological effects

• Invasions eventually homogenize the biota world-wide

Properties of Successful Invaders 1• Vector - a means of transport must be

available, e.g., ballast water of ships, ability to disperse (e.g., planktotrophic larvae)

Properties of Successful Invaders 2• Vector - a means of transport must be available,

e.g., ballast water of ships, ability to disperse (e.g., planktotrophic larvae)

• Invasion frequency - because most arrivals do not result in invasion success, frequency of arrival is important

Properties of Successful Invaders 3• Vector - a means of transport must be available,

e.g., ballast water of ships, ability to disperse (e.g., planktotrophic larvae)

• Invasion frequency - because most arrivals do not result in invasion success, frequency of arrival is important

• Ecological compatibility - invading species need an appropriate habitat in which to colonize and propagate

Properties of Successful Invaders 4• Vector - a means of transport must be available, e.g.,

ballast water of ships, ability to disperse (e.g., planktotrophic larvae)

• Invasion frequency - because most arrivals do not result in invasion success, frequency of arrival is important

• Ecological compatibility - invading species need an appropriate habitat in which to colonize and propagate

• Survival of initial population variation - initial fluctuations of small population size results in extinction of invading species

Invasions are Common

• Ship ballast water has many potentially invading species

• Transport of commercially exploited mariculture species resulted in transport of other species as well

• Canals are important routes for invaders. Suez Canal facilitated invasions, mainly from Red Sea to Mediterranean Sea

Invaders can have significant effects

• Periwinkle Littorina littorea invaded New England, USA from Europe. Now most common rocky shore snail and has significant effects on seaweed communities

• Shore crab Carcinus maenas invaded from northern Europe to become common all over the world

• Freshwater zebra mussel, Dreissena polymorpha invaded from eastern Europe to North America, has exerted strong effects on water column, and on native mussels

Invasion routes of species of the crab genus Carcinus maenas from European waters to sites around the world

Conservation Genetics• Genetic markers (e.g., DNA sequences, length fragment

polymorphisms in mitochondrial DNA) allow identification of populations

• This allows species identification, identification of different migrating stocks of fishes, turtles, and marine mammals

• Examples: Green turtle females shown to home to the same nesting beaches, after migrations of thousands of km to feeding grounds; fishing of Loggerhead turtles in eastern Atlantic shown to deplete nesting turtles in Florida; stocks of migrating humpback whales have been identified

The End