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, 14 C uptake, satellite sensing, and fluorometry Predation can cause: changes in size distribution; both decreases and increases in diversity; morphological modifications (spines, mimicry, crypsis)

Plankton Summary Light and nutrients are major factors controlling primary production (p.p.). Light inhibition 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

Zooplankton

Planktos: “drifts” in greek Their distribution depends on currents and gyres Certain zooplankton can swim well, but distribution controlled by current patterns Zooplankton: all heterotrophic plankton except bacteria and viruses; size range from 2 µm (heterotrophic flagellates, protists) up to several meters (jellyfish)

Herbivorous zooplankton: Grazers

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

Feeding modes in Zooplankton Filter feeders Predators – catch individual particles

Filter Feeder Copepod

Filter Feeder Ctenophore

Predator Chaetognath Arrow Worm

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

Holoplankton Copepods Planktonic crustaceans

Meroplankton Nauplius larva

Meroplankton Cypris larva

Cypris larva and metamorphosed juveniles

Barnacle population regulation

Gadidae Gadus morhua Ichthyoplankton

Gadidae Gadus morhua Ichthyoplankton

Gadidae Atlantic cod Gadus morhua Demersal Adult

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

Dinoflagellates Noctiluca miliaris

Colonial choanoflagellates Bacteriofages (Ross Sea)

Foraminifera (calcareous – all latitudes)

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

Figure 3.21b Radiolarians (siliceous – low latitudes)

Live Radiolarian

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 specialization: feeding polyps, reproductive polyps, swimming polyps; Physalia physalis (Portuguese man-of-war), common in tropical waters, Gulf of Mexico, drifted by the wind and belong to the pleuston (live on top of water surface) Invertebrate Holoplankton

Cnidarian (medusae)

Cnidaria (medusae)

Cnidaria (siphonophora)

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

Ctenophora (comb jellies)

Invertebrate Holoplankton Mollusca: –Heteropods: small group of pelagic relatives of snails, snail foot developed into a single “fin”; good eyes, visual predators –Pteropods: snail foot developed into paired “wings”; suspension feeder – produce large mucous nets to capture prey; carbonate shells produce pteropod ooze on sea floor

Heteropod (Preys on Ctenophores)

Pteropod

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

Appendicularian

Pelagic Salps

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; 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)

Amphipoda

Amphipoda (parasites of gelatinous plankton)

Euphasids (krill)

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)

Copepods

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

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

Molluscs: Meroplankonic Veliger larvae PLANKTOTROPHIC

Diel Vertical Migration DAILY (diel) vertical migrations over distances of 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

Three explanations for the existence of vertical migrations

Horizontal distribution: patchiness

Exotic Planktonic species New England Ctenophore  Black Sea

Water Tank Ballast Holoplankton Meroplankton

Black Sea Ballast Invasions Mnemiopsis

Black Sea Ballast Invasions Mnemiopsis Beroe ovata

European Green Crab – Carcinus maenas

Barnacles: benthic sessile crustacean

Gadidae Gadus morhua Ichthyoplankton

Vertical Distribution Epipelagic: upper m water column; high diversity, mostly small and transparent organisms; many herbivores Mesopelagic = 300 – 1000 m; larger than epipelagic relatives; large forms of gelatinous zooplankton (jellyfish, appendicularians) due to lack of wave action; some larger species (krill) partly herbivorous with nightly migration into epipelagic regimes Oxygen Minimum Zone: 400 – 800 m depth, accumulation of fecal material due to density gradient, attract high bacterial growth, which in turn attracts many bacterial and larger grazers; strong respiration reduces O2 content from 4-6 mg l-1 to < 2 mg l-1 Bathypelagic: 1000 – 3000 m depth, many dark red colored, smaller eyes Abyssopelagic: > 3000 m depth, low diversity and low abundance Demersal or epibenthic: live near or temporarily on the seafloor; mostly crustaceans (shrimp and mysids) and fish

Scattering Layer