Pelagic Flashcards
Neritic zone?
Continental shelf. Adjacent to shore. 8% ocean surface.
High terrigenous input = high primary production.
Oceanic zones?
Neustic zone (0m) = UV vulnerability = floating organisms often blue (protective pigments). High interchange between air + water.
Epipelagic: Photic zone up to 200m. Primary production.
Mesopelagic zone: Enough light for visual predators.
Primary production in pelagic system?
Rely on upwellings, coastal runoff, + seasonal cycles.
Floating seaweed rafts.
North Atlantic plankton productivity cycles?
Solar radiation high in summer, low in winter.
Surface nutrients high in winter - lots of storms + flooding rivers.
Spring diatom bloom (use nutrients from winter upwellings).
Eaten by zooplankton + thermocline (no upwellings) = diatoms decrease.
Autumn storms = second bloom.
Holopelagic seaweeds?
2 main raft species: Sargassum natans + fluitans.
Dominant primary producers in Gulf of Mexico. Support dolphinfish, tuna, + mackerel.
Sargassum isn’t primary producer though - phytoplankton on sargassum grazed by herbivorous species (stable isotope analysis).
Forage fish?
Eg: Herring + anchovies.
Migratory fish?
Eels: Larvae move from Caribbean to Europe, + return to Caribbean to spawn.
Great white sharks: Females migrate between male pops = maintains diversity.
Whalesharks.
Whaleshark ecology?
Largest fish. Filter feeder. Eat Euphasiid krill.
Long-distance seasonal migrations (eg: 19 tagged off Ningaloo Reef, Australia, 2003-4).
Daily vertical migrations: Surface for navigation, dive to 1000m to feed. Thermoregulate by warming on surface.
Risks vs benefits of planktonic life stage?
Most meroplankton consumed by holoplankton blooms.
But some advantages:
- Colonise new areas = long-term survival (eg: survive mass extinctions).
- Dispersal decreases inbreeding depression.
- Can exploit seasonal phytoplankton blooms in different locations (if synchronised w/ primary productivity).
- Eggs + larvae cheap (don’t need parental care).
Cushing’s match-mismatch hypothesis?
Synchrony not achieved = larvae die.
Spawning changes from climate change = temp cues disrupted.
Top-down vs bottom-up effects?
Top-down: Predation + fishing.
Bottom-up: Daily/seasonal cycle changes + climate change.
Beaugrand et al (2002).
Changes in calanoid copepod biogeography in N. Atlantic + European shelf seas.
Continuous Plankton Recorder Survey: Warm water species shifted 10 degrees north, cold water species declined in number + diversity.
Caused by increase in N hemisphere temp + North Atlantic Oscillation.
Consequences for resources in N Sea (eg: fisheries - collapse of cod stocks).
Gennner et al (2010).
Spring-spawning pelagic larval fish appeared earlier in cooler years (adults migrate to overwintering grounds earlier).
Summer-spawning pelagic larval fish appeared earlier in warmer years (faster gonad maturation).
Mismatched timing of spawning - climate change (0.5-4c SST rise in next 50yrs).
Could affect other ecosystems (eg: seabird breeding success relies on prey abundance).
More studies needed on reasons for timing change.
Myers + Worm (2003).
Continental shelf + open ocean communities contribute 50% global primary production.
UN resolved to restore fisheries + marine ecosystems.
Industrialised fisheries reduced large, predatory fish biomass by 80% within 15yrs.
Current large, predatory fish biomass = 10% of pre-industrial levels.
Need to return to unexploited levels to ensure future restoration.
More research needed on top-down effects of large predator removal.
Local extinctions can go unnoticed in open ocean.
Wilson et al (2006).
Whale sharks gather to feed off Ningaloo Reef (March-June), then travel to Indian Ocean.
Whale sharks declining in intensive fishing areas (eg: Indonesia) - information on their movements used to supply markets.
Need more research on movements in unprotected areas.
