The one world ocean

1. The one world ocean The world’s oceans are connected in one vast water body.

2. Ocean water composition The oceans consist of (by mass): • 96.5% water • 3.0% sodium and chloride ions (table salt, Na+ and Cl–) • 0.5% other salts • Average salinity 35 %o (35 parts per thousand)

3. Vertical movement of ocean water Ocean water can move up or down due to wind, heating, or density differences. Upwelling = cold deep water comes to surface • Occurs where currents diverge • Brings nutrients to surface; promotes fisheries Downwelling = warm surface water moves downward • Occurs where currents converge • Brings dissolved oxygen to deep-water life

4. Upwelling Water along the California coast moves away from shore, allowing upwelling that nourishes biodiversity in surface waters.

5. Marine zones • Pelagic zone = open water between surface and seafloor • Benthic zone = ocean floor

6. Marine ecosystems: Open ocean - Surface waters of the pelagic zone are variable. • Many areas are scarce in life, but areas like nutrient-rich upwellings teem with life. • Plankton (photo) are the base of the food web.

7. Plankton Diversity: • Phytoplankton - diverse single-celled algae (e.g. diatoms) that drift passively • - the main photosynthesizers in aquatic biomes • - the first trophic level of aquatic food chains • Zooplankton - tiny animals (e.g. copepods and crustacean larvae) that drift passively • - the second trophic level of aquatic food chains

8. Marine ecosystems: Deep ocean Deep waters are devoid of sunlight, so ecosystems cannot rely on plant growth. Animals here (few and far between) scavenge detritus from above, or prey on each other, or have symbiotic microbes that produce food for them. Angler fish

9. Marine ecosystems: • Kelpforests consist of kelp (large brown algae or seaweed) that grow up to 60 meters (200 feet) tall from the continental shelves. • They create “forests” that harbor and feed many other organisms. • Coral reefs are the aquatic equivalent of the tropical rain forests and are being rapidly destroyed. • The intertidal zone is where the ocean meets the land. • These rocky or sandy regions are home to a surprising number of organisms adapted to the variable conditions

10. Marine ecosystems: Kelp forests

11. Marine ecosystems: Coral reefs – a treasure trove of biodiversity Different coral species provide habitat for moray eels and many others.

12. Coral An individual coral polyp living on a reef has stinging tentacles to gather food. It also houses photosynthetic zooxanthellae, symbiotic algae that produce food inside specialized cells.

13. Coral reefs are in worldwide decline “Coral bleaching” = occurs when zooxanthellae leave the coral or die Corals lose their color and die, leaving white patches From climate change, pollution, or unknown natural causes Nutrient pollution causes algal growth Which smothers coral Divers damage reefs by using cyanide to capture fish Acidification of oceans deprives corals of carbonate ions for their structural parts

14. Marine ecosystems: Intertidal zones

15. Threats to Marine Ecosystems • Marine pollution – nets, plastic debris, excess nutrients, trash from ships, oil spills, etc. • http://www.unep.org/regionalseas/marinelitter/ • Excess nutrients create eutrophication of aquatic systems and can cause “dead zones” and harmful algal blooms • e.g. Gulf of Mexico dead zone • Overfishing – probably the most severe impact • http://www.pewoceans.org/ • http://www.wsg.washington.edu/

16. Oil pollution comes from spills of all sizes

17. Ocean pollution: Algal bloomsNOAA's National Ocean Service: Harmful Algal Blooms Excess nutrient runoff (as from fertilizers) can spur out-of-control growth of algae that kill fish and other organisms. These harmful algal blooms are also called red tides because some types color water red.

18. Emptying the oceans • As bad as some pollution problems may be, the oceans today suffer most from overfishing. • http://overfishing.org • Oceans are vulnerable to the “tragedy of the commons.” • Depletion is not a new problem: For centuries people have taken more than is replenished • Fishing had already taken a toll on marine ecosystems many decades before ecologists began studying them.

19. Total global fisheries catch -Although stocks are being depleted, the global catch has increased as new technologies made it easier to find fish. -But the increase has stalled, and many fear a decline if drastic conservation measures are not taken soon.

20. Fishing has industrialized • Modern industrialized fishing fleets can deplete an area of large predatory fish and sharks surprisingly fast. • Recent analysis of old fishing records revealed: • As industrial fishing fleets reached a new part of the ocean, capture rates of large predatory fish were at first high, then crashed within a decade. • 90% of large species were gone in 10 years, and then numbers stabilized, so… • Today’s oceans hold just one-tenth the number of large fish they once did.

21. Fishing down the food chain • As fishing increases, the size and age of fish caught decline. • As some species become too rare to fish profitably, fleets target more abundant species, which tend to be smaller and less desirable.

22. Fishing practices • Driftnetting catches and drowns seals, dolphins, birds, turtles. • Longline fishing kills seabirds, turtles and sharks. • Bottom-trawling destroys whole ecosystems. Nets and bars dragged across the bottom flatten benthic structure, devastating habitat for marine organisms.

23. Fishing practices • Many marine fishing practices are not specifically targeted to the species fishermen want to catch. • Instead, they catch lots of nontarget species. • This is the by-catch. • By-catch accounts for deaths of many thousands of sharks, seals, dolphins, turtles, and birds each year.

24. Consumer choice can influence fishing practices • When eating seafood, purchase fish and seafood that • are caught or raised sustainably. • Use seafood guides • e.g. A Consumer's Guide to Sustainable Seafood | Monterey Bay Aquarium

25. Traditional fisheries management • Based on maximum sustainable yield (MSY): Allow maximal harvests of particular populations while keeping fish available for the future. • Managers regulate catch with limits or restrict the type of gear fishers could use. • Many marine scientists and managers feel it is time to rethink fisheries management. • Instead of single-species MSY, we need to manage for entire ecosystems, taking an ecosystem-based approach.

26. We can protect areas in the ocean Marine protected areas (MPAs) = most are along the coastlines of developed countries They still allow fishing or other extractive activities Marine reserves = areas where fishing is prohibited Leave ecosystems intact, without human interference Improve fisheries, because young fish will disperse into surrounding areas Many commercial, recreation fishers, and businesses do not support reserves Many change their minds once they see the effects

27. Reserves work for both fish and fisheries Marine reserves: Increased densities of organisms by 91% Increased biomass by 192% Increased organism size by 31% Increased species diversity by 23% Benefits inside reserve boundaries include: Rapid and long-term increases in abundance, diversity, and productivity of marine organisms Decreased mortality and habitat destruction Decreased likelihood of extirpation of species

28. Areas outside reserves also benefit A “spillover effect” occurs when individuals of protected species spread outside reserves Larvae of species protected within reserves “seed the seas” outside reserves Once commercial trawling was stopped on Georges Bank: Populations of organisms began to recover Fishing in adjacent waters increased