Chapter 7

1. Chapter 7 Long longlonglong Pelagic Ecosystems

2. Review • Pelagic? • Largely open, unbounded environment • Large range of freedom to move in three dimensions • Largest habitat on earth • Extremely variable in temperature, salinity, turbidity, biomass, etc. • Human effects • Global climate change • 90% of stocks of large pelagic fish (tuna) removed by fishing • Zooplankton communities shift in spatial distribution • Microscopic plastic fragments widespread and cause a variety of problems • Regime shifts—ecological step-changes

3. More Zone Review • Pelagic zone—sea surface to just above the seabed • 99.5% of the earth’s habitable space • Made up of the neritic and oceanic zones • Neritic • Makes up 8% of the earth’s total sea area • Limited by the 200m depth contour (isobath) • Oceanic • 92% total sea area • 65% earth’s surface • Characterized by ‘Case 1’ and ‘Case 2’ waters • Benthic zone

4. Case 1 and 2 waters • Case 1—ocean color is determined by algal pigments • Example of ocean coloring? • Case 2—ocean color is due to reflections from particulate matter • Difference in particulate loading can lead to differences in underwater light climate • Have led to varying photosynthetic processes in neritic and oceanic phytoplankton • European flying squid and diatoms • http://www.youtube.com/watch?v=dwYr1TJbue0

5. More zones yay • Neustic zone—upper surface of the ocean • Harsh envionment due to high levels of ultraviolet radiation • Organisms are typically blue because protective pigments in the color reflect the damage • Ozone hole in earth’s atmosphere may cause UV damage to multiple creatures, including Antarctic krill • Photic zone—upper layer of the water column into which light penetrates • top 200 meters • Epipelagic zone • Also upper 200 meters of the water column • Red light doesn’t penetrate far in this zone • Many organisms have some sort of red coloring to protect against predators

6. Changes with depth • Organisms are faced with increasing pressure • How much at 2 meters? • Oxygen minimal layers—due to bacteria breaking down marine snow • Total mass of biota per unite volume of seawater decreases • Because biological processes are fueled by photosyntetically generated organic matter from the surface • http://www.youtube.com/watch?v=vsLBOkYLLeI • Food availability decreases—more distance • Energy efficiency become more important • Biological pump - http://www.youtube.com/watch?v=nM4SjToMgkM

7. Pelagic inhabitants • Plankton can’t move horizontally, but they can move vertically • DVM—diel vertical migration • Driven primarily by escape from predators and search for food • Also known as…? • Holoplankton—spend their entire life as plankton • Meroplankton—only spend part of their life as plankton • Planktotrophic larvae—have an extended planktic phase • have a higher mortality rate than lecithotrophiclarvae • Will have a larger genetic dispersal though

8. Pelagic inhabitants cont. • Smaller organisms tend to be plankton, not nekton • Exception—lion’s mane jellyfish • Occurs usually because of the interaction between size and viscosity • More energy is required for them to keep moving • Microbial loop—fuels the pelagic food chain, especially in oligotrophic waters • http://www.youtube.com/watch?v=qybUFnY7Y8w - cascades

9. Temporal and spatial variability • Variability due to interactions between physical and biological processes • Graphed using the Stommel diagram • Shows variations between the interplay of these two factors • Space vs. time

10. Physical processes • What causes changes in… • Light? • Mixing? • Temperature? • Density? • Nutrient and gas concentration? • Langmuir circulation—small scale upwelling • http://faculty.gvsu.edu/videticp/langmuir.htm • Cause near-surface vortexes • Alternating lines of upward divergance and downward convergence develop • Can lead to the accumulation of zooplankton and flotsam

11. Ekman stuff • Coriolis effect—force of the earth spinning • causes water blown by the wind to move 90º to the wind • Right of the wind in northern hemisphere, left in southern hemisphere • Ekman transport—movement of the water pushed by the wind left or right depending on the hemisphere • Front—horizontal boundary between water masses with different physical propterties • “meanders in fronts” –core rings—important for transoceanic mixing

12. Umm…ocean stuff(How productivity is affected) • Mixed-layer depth—the depth to which water-column mixing occurs • Problematic for phytoplankton because they may be carried below the compensation depth, where they can’t get light • May eventually inhibit phytoplankton growth though if vertical stratification prevents mixing for too long • Upwelling regions • Nutrients not normally limited • annual primary production is high • Exception: El Nino • http://www.esrl.noaa.gov/psd/map/clim/sst_olr/sst_anim.shtml

13. Other regions and Sucky stuff • HNLC—high nutrient, low chlorophyll • Southern Ocean and equatorial Pacific • Due to grazing pressure and absence of trance elements, especially iron (Iron Hypothesis) • Since 1999, global ocean primary productivity has fallen 0.19 Pg C per year • Pg C=petagram=1015 grams=1 billion metric tons • Mostly occurring in low-latitude oceans (45ºN to 45ºS) • Due to strengthening stratification limiting nutrients • Increasing gin mixing and nutrient replenishment in the polar regions are unlikely to counteract middle-latitude production • Smetacek’s theory—that whales are keystone species in southern oceans • Krill capture iron • Whales eat krill, keeping iron from sinking below use • Whales return iron to the environment, and phytoplankton use it for the krill to eat

14. Biomes • Biome—the largest coherent community unit that is convenient to recognize (lazy scientists) • Categorized into four different groups characterized by the mechanisms driving their mixed layer depth • Westerlies biome—local winds and irradiance force the mixed layer depth • Trades biome—mixed layer depth is influenced by large-scale ocean circulation processes • Polar biome—buoyant fresh water from ice melt in spring constrains the layer • Coastal biome—diverse procecsses like upwelling (Provinces—allow regional differences in physical oceanography that help make predictions and gain understanding)

15. Primary production to nekton • GLOBEC—global research effort to understand interactions between primary consumers, higher trophic levels, and fisheries • Direct linear relationship between the magnitude of annual primary production and nekton production • Many zooplankton populations are bottom-up controlled • Zooplankton blooms can’t occur unless phytoplankton biomass and production is sufficient • Temperate waters—zooplankton spike in spring and autumn • High latitudes—limited to spring/summer peak and stay dormant in diapause • Spatial segregation allows higher overall biomass to be maintained, versus homogenous phytoplankton and grazers everywhere

16. Sampling the open ocean • Extreme horizontal, vertical, temporal patchiness, and huge siz-erange of organisms makes it difficult to get quantitative samples • Early studies used mostly fishing nets • Presently, nets have depth, temperature, salinity and other sensors that can convey where the area of interest is back to the ship • OPCs—used instead of nets to obtain espimates of zooplankton numerical density • Can also use echo-sounders to detect and quantify abundance zooplankton and fish • Larger organisms that come to the sea surface can be counted by observers

17. Other methods • Sampling platforms with moored instruments • AUVs • Gliders • Vertically-profiling floats • Earth-orbiting satellites • Give almost weekly information on sea surface temperature, chlorophyll concentration, and front position • Can also track the movements of larger animals • Can be used to reduce bycatch

18. Pelagic fisheries • Amount the most sustainable and least damaging to the environment • Rates of bycatch are minor compared to other kinds of fisheries • Mostly going after shoaling species • Atlantic mackerel • North Sea herring • Lantern fish (Myctophids) • …and planktivorous forage fish • Sardine and anchovy • Create wasp-waist ecosystems—one or a couple species of small planktivorous fish dominate their trophic level

19. Controversy over pelagic fishing • Analyses of long-line data suggests that 90% of large pelagic fish may have been removed before management procedures developed • People argue the limits for fisheries are incredibly low because they represent already-depleted stock levels • Makes restoration of stocks difficult • We don’t know what the pre-exploitation biomass was • Can’t calculate when restoration is completed • Long-line fishing is the major factor in substantial declines in albatross populations • Take the baited hooks when thrown from the ship and drown as they sink

21. Fishing squid • Also called “jigging” • Jig—hooked coloed lures with extremely bright lights • Lights can be so bright that satellites can detect them—may help to monitor and manage open-ocean squid fisheries • Why do we care? • Squid respond rapidly to changing oceanographic conditions • May help predict interannual variations in recruitment

22. Regime shift • Typically take less than one year to occur—may last for decades • Driven by: • Climatic changes • fishing pressure • Or both • Present major challenges for scientists attempting to manage fisheries • Can be measured using CPRs(Continuous Plankton Recorder) • Example of regime shift—influx in the population of plankton in the North Sea due to an increase in nutrient-rich Atlantic water

23. Suspected regime shifts • Increase in jellyfish population in many pelagic marine ecosystems • Possibly in response to climate and fishing effects • How could that be? • Hint: turtles • Correlation between abundance in jellyfish and NAOI (North Atlantic Oscillation) • Also compete with herring(overfished) for zooplankton food • Jelly-fish dominated pelagic communities may be one consequence of overexploitation of fish stocks • Scientists have detected more regime shifts since the 1990’s • Incidence of regime shifts may be increasing or… • We may just be able to detect more changes

24. Future of pelagic ecosystems • Down the food web—as traditional fish species are removed, fishing effort turns to smaller species • ever-increasing human population and demand for food protein • Fisheries have gradually been moving farther and farther from shore • We still suck: • Removing biomass through fishing • Incidence of waste is increasing and pushing species beyond their usual range • Alien species have devastating effects on pelagic ecosystems • Ex: ctenophore—native of eastern USA, led to the collapse of the Black Sea anchovy fishery because it preys on fish eggs

25. We suck so bad • Could dump CO2 out at sea to reduce further increasing in atmospheric concentrations • Ocean sound • Low-frequency noise from shipping oil-exploitation, and military activities • may significantly impact cetacean communication and foraging by masking their sounds • Killer Whales have increased the length of their calls by about 15%, probably attempting to overcome noise generated by boats • Sound underwater and ocean acidification • Propagation of underwater sound in the range of frequencies used for cetacean communications will increase as the ocean becomes more acidic • Changes in ocean acidity could enable sounds to travel up to 70% farther • Will increase the levels of background noise and may affect marine mammal behavior

26. Climate change • The likely state of aquatic ecosystems in 2025 will be due singularly to climate warming • Have already had impacts on sea-ice extent and zooplankton distribution • Could result in multiple extinctions before the end of the century • Largest threat: increased warming and consequent freshening of the Artic may switch off the North Atlantic Current (NAC) and damage global ocean circulation • Could reduce north Atlantic plankton biomass by more than half • Could reduce global export production by more than 20% • http://www.youtube.com/watch?v=kxPwbhFeZSw

27. YAY IT’S THE END!!! :D

28. Good (sort of) Videos to watch • http://www.youtube.com/watch?v=TgNeL7igtnw • http://www.youtube.com/watch?v=8101vCjM7nY • http://www.youtube.com/watch?v=5cqCvcX7buo&list=PLE5E6A5688B2CB642