7 The Water Column Plankton Notes for Marine Biology: Function, Biodiversity, Ecology by Jeffrey S. Levinton ©Jeffrey S. Levinton 2001

Plankton: Definitions Plankton: organisms living in the water column, too small to be able to swim counter to typical ocean currents

Plankton: Definitions 2 Phytoplankton are photosynthetic plankton (some ambiguity here, because some groups like dinoflagellates have non-photosynthesizing members) Zooplankton are animals living as plankton Mixoplankton are organisms that may function as animals but ingest phytoplankton and maintain the chloroplasts of their food organisms (phytoplankton), and the chloroplasts photosynthesize in their new hosts

Plankton: Definitions 3 Holoplankton - planktonic organisms that complete their entire life cycle in the plankton Meroplankton - spend only a part of their life cycle in plankton. Most common example: planktonic larvae of benthic animals Neuston - plankton associated with water surface, such as bacteria in surface film Pleuston - plankton that live at surface but protrude in air, such as Portuguese Man-of-war, which has a surface float

Plankton: Definitions 4 Size classes Ultraplankton < 2 m Nannoplankton 2-20 m Microplankton 20-200 m Macroplankton 200-2000 m Megaplankton > 2000 m

Vertical Position of Plankton - Factors Bulk density - regulated by ionic subsitution, gas secretion and release (cuttlefish, Nautilus) Swimming behavior Turbulence stirs plankton through the water column

Vertical Position of Plankton - Factors Size of plankton - smaller plankton live in world of low Reynolds number Low Re means there is a boundary layer around plankter’s body Smaller organisms denser than seawater sink with a constant velocity, proportional to organismal volume, although increases of spines etc. can slow sinking

Phytoplankton Diatoms Occur singly or form chains Size range of nanno to microplankton Encased in silica shell consisting of two valves Usually radially symmetrical Reproduce asexually by binary fission Also sexual reproduction Doubling once or twice per day usually

Diatoms Dinoflagellates Coccolithophore Flagellate Isochrysis

Asterionella japonica Thalassiosira Chaetoceros Asterionella japonica

Phytoplankton Dinoflagellates Secrete organic test and have two flagellae Size range of nanno and microplankton Asexual and sexual reproduction Often many life history stages Many species are heterotrophic Often abundant in tropics, mid-latitudes in summer A few species are the cause of red tides

Diatoms Dinoflagellates Coccolithophore Flagellate Isochrysis

Peridinium

Phytoplankton Other Groups Cyanobacteria - abundant in ocean, responsible for nitrogen fixation Coccolithophores - unicellular, nannoplankton, spherical and covered with calcium carbonate plates called coccoliths Silicoflagellates - unicellular, biflagellate, internal skeleton of silica scales, often in Antarctic, open ocean

Diatoms Dinoflagellates Coccolithophore Flagellate Isochrysis

Phytoplankton Other Groups Cyanobacteria - abundant in ocean, responsible for nitrogen fixation Coccolithophores - unicellular, nannoplankton, spherical and covered with calcium carbonate plates called coccoliths Silicoflagellates - unicellular, biflagellate, internal skeleton of silica scales, often in Antarctic, open ocean

Diatoms Dinoflagellates Coccolithophore Flagellate Isochrysis

Phytoplankton Other Groups Cyanobacteria - abundant in ocean, responsible for nitrogen fixation Coccolithophores - unicellular, nannoplankton, spherical and covered with calcium carbonate plates called coccoliths Silicoflagellates - unicellular, biflagellate, internal skeleton of silica scales, often in Antarctic, open ocean

Phytoplankton Other Groups Numerous other groups, including many flagellated types

Zooplankton Crustacean zooplankton (Arthropods) Crustaceans have an external chitin skeleton Some degree of segmentation Paired jointed appendages (e.g., legs, antennae) They possess antennae, mandivles and maxillae as head appendages Usually have compound eyes Include copepods, krill, amphipods (crabs, lobsters, sowbugs - not in plankton)

Zooplankton Crustaceans - Copepods Largest group of crustaceans in zooplankton Range from <1 - a few mm long Planktonic forms belong to the Calanoida Long pair of antennae Swim mainly with aid of 5 pairs of thoracid appendages Lack compound eyes, medial naupliar eye Feed on phytoplankton or smaller zooplankton, depending on the species

Zooplankton Copepod Feeding Low Reynolds number - viscosity dominates Feeding current (green) generated by thoracic appendages Maxilliped reaches out and grabs particles entrained in current

Zooplankton Copepods Females of different species with eggs

Zooplankton Crustaceans - Euphausids (Krill) Shrimplike, up to 5 cm long Abundant in Antarctic and in upwelling regions Main food of baleen whales in Antarctic Feed on phytoplankton and smaller zooplankton Feeding by means of group of appendages that form a basket - appendages have setae and smaller setules, hairs that capture particles

Zooplankton Crustaceans - Euphausids (Krill)

Zooplankton Gelatinous Zooplankton Jellies include a wide variety of distantly related groups, all have gelatinous material used for support (skeleton)

Zooplankton Gelatinous Zooplankton - Cnidaria Planktonic Cnidaria are mainly Scyphozoan jellyfish, but also include Hydrozoan jellyfish (some meroplanktonic jellyfish stages) and siphonophores, specialized colonial and polymorphic cnidarians such as Portuguese man-of-war Jellyfish are mainly carnivores, feeding with aid of nematocysts - stinging cells - on tentacles

Zooplankton Gelatinous Zooplankton - Cnidaria Note muscular bell and tentacles

Zooplankton Gelatinous Zooplankton - Cnidaria Siphonophores By-the-wind-sailor Velella Porpita (ca. 10 cm wide) Physophora (50 mm high) Siphonophores

Zooplankton Gelatinous Zooplankton - Ctenophores Known as comb jellies Microcarnivores - feed on smaller zooplankton, planktonic eggs, invertebrate larvae 8 rows of meridional plates, some have two long tentacles

Zooplankton Gelatinous Zooplankton - Ctenophores

Zooplankton Gelatinous Zooplankton - Salps Related to benthic sea squirts, but have incurrent and exit siphons on opposite ends of body Solitary or colonial (up to 2 m in length) Have a tail, typical of tunicate swimming larvae Small, only a few mm long Tail generates current through house, current is strained by fine fibers that trap food Gelatinous Zooplankton - Larvacea

Colonial Salp Pegea sp.

Zooplankton Arrow worms Torpedo shaped, a few cm in length Rapid swimmers, carnivorous

Zooplankton Pteropods Holoplanktonic snails Swim by means of lateral projections from foot Suspension feed or are carnivorous, depending upon species

Zooplankton Planktonic polychaetes Have very well developed parapodia

Zooplankton Protistan zooplankton - Foraminifera Secrete skeleton of calcium carbonate, sometimes with great ornamentation Common in plankton Range from ca. 1 mm to a few mm in size Contractile pseudopodia stream from body wall, trap food particles Form sediment in deep sea from skeletons

Zooplankton Protistan zooplankton - Radiolaria Secrete skeleton of silica, sometimes with great ornamentation, occurs singly and as colonies, depending on species Common in plankton Range from ca. 50 m to a few mm A membrane separates interior cell from exterior cytoplasm, which streams out something like foraminifera Form sediment in deep sea from skeletons

Zooplankton Protistan zooplankton - Ciliates Common in plankton, feed on bacteria, smaller phytoplankton, some mixotrophic Elongate, ranging from size from about 50 m to over 1 mm in length, covered with rows of cilia Strombidium sp. under ultraviolet light, showing ingested chloroplasts in red Strombidium, 80m long

Patchiness of the Plankton Plankton rarely distributed homogeneously in the water column Plankton occur in spatially discontinuous patches, sometimes distinct aggregations, sometimes concentrated at interfaces between water bodies

Patchiness of the Plankton 2 Spatial changes in physical conditions (light, temperature, salinity) - behavioral responses and population growth/mortality responses Water turbulence and current transport Spatially discontinuous levels of grazing Localized reproduction Social behavior

Patchiness of the Plankton 3 Phytoplankton - patchiness a function of population growth versus rate at which turbulence spreads out the population If turbulence is limited,and if growth conditions are optimal, plankton grow fast, producing a bloom

10m 100m 4h 4h 2h 2h 1h 1h Current No current Example of spread of plankton with general turbulence (left) Or in a current (right)

Diurnal Vertical Migration of Zooplankton Zooplankton rise to shallow water at night, sink to deeper water during the day Found in many different groups of zooplankton Zooplankters usually start to sink before dawn, and start to rise before dusk Cycle is probably an internal biological clock that must be reinforced by day-night light changes

Diurnal Vertical Migration of Zooplankton 2 Zooplankton rise to shallow water at night, sink to deeper water during the day Found in many different groups of zooplankton Zooplankters usually start to sink before dawn, and start to rise before dusk Cycle is probably an internal biological clock that must be reinforced by day-night light changes

Diurnal Vertical Migration of Zooplankton 3 Zooplankton rise to shallow water at night, sink to deeper water during the day Found in many different groups of zooplankton Zooplankters usually start to sink before dawn, and start to rise before dusk Cycle is probably an internal biological clock that must be reinforced by day-night light changes

Night 100 Depth (m) 200 Day 300 Twilight 400 0 1 2 3 Distance (km) Vertical migration of planktonic shrimp Sergia lucens

Diurnal Vertical Migration of Zooplankton 4 Zooplankton rise to shallow water at night, sink to deeper water during the day Found in many different groups of zooplankton Zooplankters usually start to sink before dawn, and start to rise before dusk Cycle is probably an internal biological clock that must be reinforced by day-night light changes

Diurnal Vertical Migration of Zooplankton 5 Cause of Vertical Migration? 1. Strong light hypothesis - plankton migrate away from strong light Problem: plankton migrate to great depths, below those where light damage is likely

Diurnal Vertical Migration of Zooplankton 6 Cause of Vertical Migration? 2. Phytoplankton recovery hypothesis - zooplankton migrate downward for a time to allow phytoplankton to recover Problem: Why not cheaters who would stay up to feed on phytoplankton. Hypothesis requires cooperation, even among many species

Diurnal Vertical Migration of Zooplankton 7 Cause of Vertical Migration? 3. Predation hypothesis - zooplankton migrate downward to avoid visual predation during day This idea is consistent with avoidance of predation. Many visual predators feeding on zooplankton. Site in Washington where copepods have a reverse migration, moving up during the day, apparently in response to arrow worm predators, which themselves carry a more typical diurnal vertical migration

Diurnal Vertical Migration of Zooplankton 8 Cause of Vertical Migration? 4. Energy conservation hypothesis - zooplankton migrate downward to avoid higher surface temperatures during the day, which saves energy Consistent with calculations of energy budget of a planktonic copepod, which would benefit from the vertical migration, relative to the cost of swimming and loss of feeding in the surface for part of the day Consistent with fact that copepods tend to sink beneath the surface after spring phytoplankton increase, suggesting an adaptation to save energy in the lower temperature deeper waters

Diurnal Vertical Migration of Zooplankton 9 Cause of Vertical Migration? 5. Surface mixing hypothesis -

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