17 Biodiversity and Conservation of the Ocean Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton

Factors in Biodiversity Although local patterns of species diversity are often explained in terms of short-term dynamic interactions, regional patterns are probably as much explained by the balance of speciation and extinction Speciation usually requires some degree of isolation of populations, which results eventually in reproductive incompatibility between them. Habitat change or destruction, widespread diseases, biological interactions, or random fluctuations of population size may cause extinction

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 the sum of many species coinciding boundaries, or a statistical construct of different species assemblages

Provinces (named in red) of the Pacific coast of North America ARCTIC 70N ALEUTIAN 1. Pt. Barrow 2. Cape Romanzof 3. Nunivak Island 4. Hagemeister Island 5. Prince William Sound 6. Dixon Entrance 7. Vancouver Island 8. Puget Sound 9. Cape Flattery 10. Cape Mendocino 11. Monterey Bay 12. Point Conception 13. Punta Eugenia 14. Cabo San Lucas 60N 50N OREGONIAN 40N CALIFORNIAN 30N Provinces (named in red) of the Pacific coast of North America

Establishment of Biogeographic Barriers 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 Panama, which arose ca. 3 million years ago), resulting in isolation and speciation (in Panama, many paired species on Pacific and Caribbean sides of isthmus)

Relating Geography to Evolutionary History The relation of geography to speciation can be accomplished by relating evolutionary trees to patterns of geographic occurrence

Left: Species A occupies a central island and successive colonizations of nearby islands and local divergence results eventually in the evolution of 7 species in the time sequence from top to bottom; tree on right shows relationships between species, which could be constructed from similarities in DNA sequences

Relating Geography to Evolutionary History Examples of results: Importance of barriers: different groups of evolutionarily related species found on east and west side of the Pacific, resulting from long-term geographic isolation; most closely related species found on either side of Isthmus of Panama, which arose about 3 million years ago

Relating Geography to Evolutionary History Examples of results: On within-species level: trace genetic markers and fossils - shows dispersal 3.5 million years ago from Pacific to Atlantic, then extinction by glaciers on Atlantic side in New England-Nova Scotia 18,000 years ago, then recolonization of this area from European side of Atlantic about 4000 years ago (figure on next slide)

Persistent boundary can isolate populations of several species

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 toward the equator Gradient tends to apply to many taxonomic levels (species, genus, etc.) Pattern is persistent, but differs for different groups over same latitudinal gradient

Bivalve diversity versus latitude

Within the Pacific Ocean, species diversity in coral reefs declines in all directions from an Indo-Pacific diversity maximum

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: estuaries 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 Complex recent historical events may explain some current regional differences in species diversity (e.g., breakdown of biogeographic barriers, followed by large-scale dispersal; Pacific-N. American invasion 3.5 my ago).

Explanations of Diversity Differences 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 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)

Eutrophic Number of species Oligotrophic Area (hectares) Species-area effect: Danish ponds and lakes; Eutrophic lakes support more species

Explanations of Diversity Differences Habitat stability - a stable habitat may reduce the rate of extinction, because species could persist at smaller population sizes (possible explanation of deep-sea maximum of species richness) 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

Is There a Center of Origin? Center of Origin Hypothesis: high diversity centers are places where more species are produced and retained and also a source of colonization to peripheral regions where diversity is lower

15 10 5 Number of sea grass species 0 2000 4000 6000 8000 10,000 Km Example of evidence supporting the center of origin theory; number of sea grass species with distance downcurrent from Torres Straight

*D. Jablonski et al., Science 314, 102 -106 (2006) Evidence from Fossil Record Jablonski et al.* looked at first fossil occurrences of members of a genus in the fossil record. First occurrences occur much more frequently in tropics than at high latitude Conclude: Center of Origin hypothesis is supported *D. Jablonski et al., Science 314, 102 -106 (2006)

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

Shifting Baselines Diversity, ecosystem structure today may be strongly altered relative to a few human generations ago We might mistakenly take today’s situation as the baseline for conservation But the baseline for a natural community has shifted over generations because we have forgotten the original natural state

Conserving Marine Biodiversity Value 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 More diverse ecosystems may be more resilient, extinction of one species results in expansion of ecological function by another species

Conservation Strategies Individual species - preserve abundance of target species, such as large carnivores, marine mammals Conserve total biodiversity of a region - one might focus on hotspots of high diversity. Conserve ecosystem function - here concern is focused on species that are important in ecosystem processes, such as primary production, nutrient cycling, decomposition; higher biodiversity might enhance some functions, such as total productivity Establish economic value of ecosystem by evaluating its ecosystem services; ecosystems have human value that can be quantified in money (resources, water supply, recreation, etc.)

Conservation Strategies Marine Protected Areas (Marine Reserves). Set aside a fraction of ecosystem area/volume to allow populations to thrive and spill over into remaining unprotected sites Population density, body size, biomass, biodiversity all found to be higher within marine reserves

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

Legislation and Programs Protecting Biodiversity Objectives National Marine Sanctuaries Program Identifies sites for protection, provides management programs National Estuarine Research Reserve System Identifies estuarine sites for long-term observation National Wildlife Refuge System Identifies areas where wildlife is especially valuable, migratory birds Endangered Species Act Identifies species in danger of extinction Marine Mammal Protection Act Maintain healthy marine mammal populations Fisheries Conservation and Management Act Intended to prevent decline of fisheries within 200 miles of U.S. coast U.S. Presidential Executive Order, 2000 Declares system of marine protected areas, managed on an ecosystem basis

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 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 suitability of target habitat - 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 Some invaders become common inhabitants of the target area

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

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