Plankton Summary• Plankton can’t control their location and are moved about by
wind, waves, currents and tides. Plankton are usually grouped by size, ranging from femtoplankton to megaplankton
• Diatoms are dominant phytoplankton in estuaries while dinoflagellates (some of which are harmful) and coccolithophores dominate surface waters offshore (i.e., nanoplankton are most abundant inshore and picoplankton most abundant offshore)
• Prochlorophytes are tiny, extremely abundant picoplankters that occur near the base of the sunlit layer in offshore waters
• Cyanobacteria (e.g., Trichodesmium) are nitrogen fixers and can be limited by iron
Plankton Summary• Half of all primary production occurs in shallow waters of the
continental shelf, while the other half is distributed over the rest of the entire ocean.
• Net primary production equals gross primary production (total production) minus respiration, which is the amount available for consumption by herbivores
• The euphotic zone is the depth to which light penetrates and photosynthesis can occur
• Four methods of measuring primary production are: oxygen evolution, 14C uptake, satellite sensing, and fluorometry
Plankton Summary• Light and nutrients are major factors controlling primary
production (p.p.). Photoinhibition occurs when there is too much light, and for this reason the max p.p. occurs below the surface
• Compensation depth is the depth where for a given algal cell, photosynthesis = respiration
• Ocean water has much less nitrogen than soil, which is why N is often limiting in the ocean
• Thermoclines prevent mixing of surface and bottom waters and prevents nutrients from re-entering surface waters
• High nutrient low chlorophyll (HNLC) zones are limited by iron
Plankton Summary• Critical Depth is the point at which Gross Photosynthesis = Total
Plant Respiration, and is a characteristic of the population
• Zooplankton regenerate nutrients by sloppy feeding and excretion, and can control phytoplankton abundance. The polar, temperate and tropical regions have characteristic seasonal patterns of phytoplankton and zooplankton abundance
• Bacterial cells are 5 orders of magnitude more abundant than algal cells and have been high growth rates. They use DOC as an energy source and can outcompete phytoplankton for nutrients.
• Original microbial loop concerned DOC, bacteria, flagellates and ciliates. The microbial web also includes the small phytoplankton that cannot be consumed by large zooplankton
Plankton Summary• Viruses are an order of magnitude more abundant than bacteria,
and cause them significant mortality. Virus also transmit genetic material to their hosts and can be imporant agents of evolutionary change for them.
• When bacterial consumption of DOC exceeds primary production this is NET HETEROTRPHY. When production exceeds bacterial consumption this is NET AUTOTROPHY
•
Planktos: “drifts” in greek
• Their distribution depends on currents and gyres
• Certain zooplankton can swim well, but their distribution is controlled by current patterns
• Zooplankton: all heterotrophic except bacteria and viruses; size range from 2 µm (heterotrophic flagellates, protists) up to several meters (jellyfish)
Nutritional modes in zooplankton
• Herbivores: feed primarily on phytoplankton
• Carnivores: feed primarily on other zooplankton (animals)
• Detrivores: feed primarily on dead organic matter (detritus)
• Omnivores: feed on mixed diet of plants and animals and detritus
Life cycles in Zooplankton
• Holoplankton: spend entire life in the water column (pelagic)
• Meroplankton: spend only part of their life in the pelagic environment, mostly larval forms of invertebrates and fish
Protists: Protozooplankton• Dinoflagellates: heterotrophic relatives to the phototrophic
Dinophyceae; naked and thecate forms. Noctiluca miliaris – up to 1 mm or bigger, bioluminescence, prey on fish egg & zooplankton
• Zooflagellates: heterotrophic nanoflagellates (HNF):
taxonomically mixed group of small, naked flagellates, feed on bacteria and small phytoplankton; choanoflagellates: collar around flagella
• Foraminifera: relatives of amoeba with calcareous shell, which is composed of a series of chambers; contribute to ooze sediments; 30 µm to 1-2 mm, bacteriovores; most abundant 40°N – 40°S
http://www.nsf.gov/pubs/1999/nsf98106/98106htm/ht-015.gif
Colonial choanoflagellatesBacteriofages (Ross Sea)
• Radiolaria: spherical, amoeboid cells with silica capsule; 50 µm to several mm; contribute to silica ooze sediments, feed on bacteria, small phyto- and zooplankton; cold water and deep-sea
• Ciliates: feed on bacteria, phytoplankton, HNF; naked forms more abundant but hard to study (delicate!); tintinnids: sub-group of ciliates with vase-like external shell made of protein; herbivores
Protists: Protozooplankton
• Cnidaria: primitive metazoans; some holoplanktonic, others have benthic stages; carnivorous (crustaceans, fish); long tentacles carry nematocysts used to inject venoms into prey
– Medusae: single organisms, few mm to several meters
– Siphonophores: colonies of animals with specialized polyps for feeding, reproduction and swimming; Physalia physalis (Portuguese man-of-war), common in tropical waters, GoM, drift with the wind and belong to the pleuston (live on top of water surface)
Invertebrate Holoplankton
• Ctenophores: separate phylum (not Cnidarians; transparent organisms, swim with fused cilia; no nematocysts; prey on zooplankton, fish eggs, sometimes small fish; important to fisheries due to grazing on fish eggs and competition for fish food
• Chaetognaths: arrow worms, carnivorous, <4 cm Polychaets: Tomopteris spp. only important planktonic genus
Invertebrate Holoplankton
Invertebrate Holoplankton• Mollusca:
– Heteropods: small group of pelagic relatives of snails, snail foot developed into a single “fin”; good eyes, visual predators
– Pteropods: snail with foot developed into paired “wings”; suspension feeders – produce large mucous nets to capture prey; carbonate shells produce pteropod ooze on sea floor
Protochordate Holoplankton
• Appendicularia: group of Chordata, live in gelatinous balloons (house) that are periodically abandoned; empty houses provide valuable carbon source for bacteria and help to form marine snow; filter feeders of nanoplankton
• Salps or Tunicates: group of Chordata, mostly warm water; typically barrel-form, filter feeders; occur in swarms, which can wipe the water clean of nanoplankton; large fecal bands, transport of nano- and picoplankton to deep-sea; single or colonies
Arthropoda: crustacean zooplankton
• Cladocera (water fleas): six marine species (Podon spp., Evadne spp.), one brackish water species in the Baltic Sea; fast reproduction by parthenogenesis (without males and egg fertilization) and pedogenesis (young embryos initiate parthenogenetic reproduction before hatching)
• Amphipoda: less abundant in pelagic environment, common genus Themisto; frequently found on siphonophores, medusae, ctenophores, salps
• Euphausiida: krill; 15-100 mm, pronounced vertical migration; not plankton sensu strictu; visual predators, fast swimmers, often undersampled because they escape plankton nets; important as prey for commercial fish (herring, mackerel, salmon, tuna) and whales (Antarctica)
Arthropoda: crustacean zooplankton• Copepoda: most abundant zooplankton in the oceans, “insects
of the sea“; herbivorous, carnivorous and omnivorous species
– Calanoida: most of marine planktonic species – Cyclopoida: most of freshwater planktonic species – Harpacticoida: mostly benthic/near-bottom species
• Copepod development: first six larval stages = nauplius (pl. nauplii), followed by six copepodit stages (CI to CVI)
• Tropical species distinct by their long antennae and setae on antennae and legs (podi)
• Mollusca: clams and snails produce shelled veliger larvae; ciliated velum serves for locomotion and food collection
• Cirripedia: barnacles produce nauplii, which turn to cypris
• Echinodermata: sea urchins, starfish and sea cucumber produce pluteus larvae of different shapes, which turn into brachiolaria larvae (starfish); metamorphosis to adult is very complex
• Polychaeta: brittle worms and other worms produce
trochophora larvae, mostly barrel- shaped with several bands of cilia
Common Meroplankton
• Decapoda: shrimps and crabs produce zoëa larvae; they turn into megalopa larvae in crabs before settling to the sea floor
• Pisces: fish eggs and larvae referred to as ichthyoplankton; fish larvae retain part of the egg yolk in a sack below their body until mouth and stomach are fully developed
Common Meroplankton
Meroplanktonic Larvae• Planktotrophic
– Feeding larvae– Longer Planktonic Duration Times– High dispersal potential
• Lecithotrophic (non-feeding) – Non-feeding larvae– Shorter planktonic Duration Times– Low dispersal potential
http://www.pbs.org/wgbh/nova/sharks/island/images/veliger.jpeg
Molluscs: Meroplankonic Veliger larvaePLANKTOTROPHIC
Diel Vertical Migration
• DAILY (diel) vertical migrations over distances of <100 to >800 m
– Nocturnal: single daily ascent beginning at
sunset, and single daily descent beginning at sunrise
– Twilight: two ascents and descents per day (one each assoc. with each twilight period)
– Reversed: single ascent to surface during day, and descent to max. depth during night
Black Sea Ballast InvasionsMnemiopsis
Black Sea Ballast InvasionsMnemiopsis
Beroe ovata
European Green Crab – Carcinus maenas
• http://web.me.com/russellkelley/rk/The_plankton.html
• http://www.youtube.com/watch?v=HSPxXCq9krU&feature=list_related&playnext=1&list=SP3A32768200CED51C
Composition of Marine Snow
Once living material (detrital) that is large enough to be seen by the unaided eye.
Described first by Suzuki and Kato (1955)
High C:N makes for poor food quality.
• Senescent phytoplankton • Feeding webs (e.g., pteropods,
larvaceans)• Fecal pellets• Zooplankton molts
Formation of Marine Snow
Type A: Mucous feeding webs are discarded individually.
Type B: Smaller particles aggregate into larger, faster sinking particles.
Aggregates
Marine Snow Particles
Contribution of Marine Snow to Vertical Flux
Narrow window of particle sizes which are large enough to sink but numerous enough to be widely distributed.
2 200 20,000 (um)
Snow
Bodies
Cells
cell chainplanktonfeces
aggregates Willie
X
1-10 m
50 m
100 m
2000 m
Available towater columnprocesses
Reduction in Vertical Flux over Depth
1 2 3The Martin Curve
Martin and Knauer 1981
50% losses by 300 m75% losses by 500 m90% losses by 1500 m
Extreme Deposition: Food Falls
• Rare events (not recorded in traps)• Deposit large amounts of high quality organic
materials to sea floor (low C:N)• Rapid sinking, reach 1000s of meters in few days• Large bodies that remain intact (whales, fish,
macroalgae, etc)
Amount of nutrients at different depths is controlled by photosynthesis, respiration, and the sinking of organic particles.
Nutrients are recycled but sink!
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