Plankton

Vertical divisions:  Pelagic = open water  Benthic = ocean bottom Horizontal divisions:  Coastal (neritic) = on/over shelf (shallow)  Oceanic = beyond continental shelf (deep) Ocean Zones

Plankton or Nekton? How fast can you swim?  Gulf Stream peak velocity = 5 knots = 2.5 m/sec  Surface currents more typically <0.5 knot = 0.25 m/sec (=0.56 mph)

Plankton or Nekton? Swim faster than 25 cm/sec? Yes → Nekton:  Dolphin = 170 cm/sec (up to 40 mph!)  Tuna = 75 cm/sec (higher burst speeds) No → Plankton:  Shrimp = 5 cm/sec  Bacteria = cm/sec

Slow, but not necessarily small Portuguese man-of-war float = 12 inches wide tentacles = over 150 ft. long (ouch!)

Net Plankton

Phytoplankton  Cyanobacteria  Unicellular microalgae  Diatoms  Dinoflagellates  Coccolithophorids c2004 Pearson Education, Inc., publishing as Benjamin Cummings

Zooplankton  Protozoans (unicellular):  Foraminiferans  Radiolarians  Ciliates

Zooplankton  Gelatinous:  Jellyfish (medusa)  Siphonophores NOAA

Zooplankton  Gelatinous:  Comb jellies (ctenophores)

Zooplankton  Gelatinous:  Salps  Larvaceans (invertebrate chordates) NOAA

Zooplankton  Molluscs:  Pteropods (gastropods), with and without shell

Zooplankton  Crustaceans:  Copepods  Amphipods  Ostracods  Isopods  Krill, shrimp

Zooplankton  “Arrow worms” (Phylum Chaetognatha)

Zooplankton  Mollusc larvae:  Trochophore  Veliger

Zooplankton  Crustacean larvae:  Crab zoea  Shrimp, barnacle nauplius  Lobster phyllosoma NOAA

Zooplankton  Other larvae:  Starfish (bipinnaria)  Brittle stars, urchins (pluteus) NOAA

Zooplankton  More larvae:  Polychaete worms (trochophore)

Zooplankton  Fish larvae

Zooplankton  Not all zooplankton are larvae  Those that are larvae, grow up to be nekton or benthic = meroplankton

Zooplankton  Not all zooplankton are larvae  Those that live whole lives as plankton = holoplankton

That Sinking Feeling  It’s a long way down – average ocean depth around 4000 m  Phytoplankton – need to stay in the light surface layer (0-200 m)  Zooplankton – eat the phytoplankton and/or other zooplankton, so need to be where the food is

That Sinking Feeling  Why am I sinking? Denser than water  Densities (in g/cm 3 ):  Seawater =  Air =  Lipids = 0.9  Proteins = 1.3  Carbohydrates = 1.5  Cellulose = 1.5  Silica shell = 2.6  Calcareous shell = 2.8

That Sinking Feeling  How not to sink:  Float –  Lipids (less dense than water)  Gas vacuoles, sacs, bubbles

That Sinking Feeling  How not to sink:  Stay neutral  High water content (gelatinous)  Reduced or no shell NOAA

That Sinking Feeling  How not to sink:  Drag (high surface area) –  Small size  Flat shape  Spines, long structures Isopod

That Sinking Feeling  How not to sink:  Upwelling (also good for nutrients) Southern Hemisphere – Ekman transport to the left

That Sinking Feeling  How not to sink:  Actively swim – cilia, flagella, muscles, appendages

Nowhere to Hide  Active predators can’t eat what they can’t see – so be invisible

Nowhere to Hide  Active predators can’t eat what they can’t see – so hide where it is dark

Somewhere to Hide  Floating mats of macroalgae and seagrasses form pelagic communities - camouflage NOAA Sargassum

Food Webs