I. I.Phytoplankton Over 4000 described species A. A.Bacillariophyceae (Diatoms) Dominant in temperate and high-latitude waters Prefer well-mixed, nutrient-rich conditions Pelagic and benthic forms Pelagic forms generally non-motile Unicellular, though some may form chains, which then may form mats Test composed of two silica valves Tests are important components of marine sediments in some areas - diatomaceous oozes An ooze is any sediment that contains more than 30% tests, the rest typically terrigenous

Fig. 2.1

I.Phytoplankton A.Bacillariophyceae (Diatoms) Two basic body shapesTwo basic body shapes Pennate – EPennate – Elongate, typically motile, mostly benthic (Exception – Nitzschia) Centric – Mostly planktonic (Ex –Centric – Mostly planktonic (Ex – Coscinodiscus, Chaetoceros)

I. I.Phytoplankton A. A.Bacillariophyceae (Diatoms) Planktonic forms typically non-motile with anti-sinking mechanisms 1) 1)Reduced body size 2) 2)Structural elaborations – increase drag 3) 3)Formation of chains 4) 4)Reduction of internal ion concentration 5) 5)Sequestration of low-density ions, e.g. NH 4 + 6) 6)Production and storage of oils Many of these mechanisms are generally applicable to planktonic organisms Living cells typically sink 0-30 m d -1, while dead cells may sink twice as rapidly Senescent or near-senescent cells may 1) 1)Lose ability to regulate ion content or sequester low-density ions 2) 2)Lose ability to produce and store oils 3) 3)Release a chemical (e.g. a polysaccharide) that lowers viscosity of water immediately surrounding cell

I.Phytoplankton B.Dinophyceae (Dinoflagellates) Motile forms possess two flagellaMotile forms possess two flagella Not all dinoflagellates are motile and not all are autotrophic Some lack flagella Some heterotrophic (~50%) Some mixotrophic (auto- and heterotrophic) Some symbiotic (e.g. zooxanthellae) Two basic formsTwo basic forms Thecate – Covered with theca made of cellulose platesThecate – Covered with theca made of cellulose plates Theca may have spinesTheca may have spines Athecate – Less commonAthecate – Less common

Fig. 2.3

I.Phytoplankton B.Dinophyceae (Dinoflagellates) Important open-water primary producers, especially in tropical regionsImportant open-water primary producers, especially in tropical regions More tolerant of low nutrients and low light than diatoms Advantage for thriving under post-diatom-bloom conditions Often abundant in summer/autumn following spring and summer blooms of diatoms Motility allows individuals to maintain position in water column under low-turbulence conditions Motility also allows individuals to spend daylight hours in surface waters (light for photosynthesis) and night hours in deeper waters (nutrients more plentiful) Most abundant phytoplankton in stratified, nutrient-poor tropical and subtropical waters

Thecate species of heterotrophic dinoflagellates use pallium feeding idinium/ProtoperidiniumSEM02.jpg Feed on other plankton with a pallium (sac) extruded from a microtubular basket. Siana and Montrasor (Eur. J. Phycol. 2005) reported ingestion rates up to 36 diatoms/ Protoperidinium vorax /hr Other reports are lower

Protoperidinum feeding on Ceratium furca Arrow shows pallium Arrowheads show multiple Protoperidinium feeding on the same prey Olseng, et al Mar Ecol Prog Series Other species of dinoflagellates use a tube inserted into prey to consume the cytoplasm Only naked dinoflagellate species engulf prey Olseng, et al. (2002) Mar Ecol Prog Series

Swimming with bioluminescent dinoflagellates Campbell and Reece Figure 28.12x2

Dinoflagellates often cause Harmful Algal Blooms

I.Phytoplankton C.Haptophyceae (Coccolithophorids) Very small (typically less than 20 μm) Covered by calcium carbonate coccolithsCovered by calcium carbonate coccoliths Coccoliths may be important components of sedimentsCoccoliths may be important components of sediments Typically motile at some life stage (have flagella) Most species occur in warm water at relatively low light intensities Most abundant at depths of ca. 100 m in clear, tropical, oceanic water Blooms may cover extensive areas Ex – Bloom covering 1000 x 500 km of sea surface in North Atlantic (area roughly equivalent in size to Great Britain)

I.Phytoplankton D.Chrysophyceae (Silicoflagellates) Silica test, usually with spinesSilica test, usually with spines Single flagellumSingle flagellum Relatively rare but more common in colder water than tropicsRelatively rare but more common in colder water than tropics E.Cyanobacteria (Blue-Green Bacteria) Most relatively minor primary producers Certain species may be important in particular areas for limited periods of time Some can fix nitrogen (e.g. mats of Oscillatoria) Attribute may explain relatively high abundances of Oscillatoria in tropical waters which often have low concentrations of nitrogen sources generally used by algae (e.g. ammonia, nitrite, nitrate)

Cyanophyceae (Cyanobacteria) Phycoerythrin and phycobilin accesory pigments. Nitrogen Fixation Some symbiotic Some filamentous or colonial A.Katagnymene spiralis B.Two colonies of Trichodesmium C.Aphanizomenon sp. colony [note heterocyst (H)] D.Benthic Rivularia atra E.Lichen Lichina confinis F.Diatom with cyanobacterial symbiont Richelia intracellularis (R) G.Dinoflagellate with a "collar" specialised for Synechococcus (S) cyanobionts.

I.Phytoplankton F.Prochlorophytes Very small ( μm diameter) Components of nanoplankton and picoplankton Resemble bacteria in some respects and algae in others Structurally, resemble large chloroplasts with internal membranes that facilitate photosynthesis Appear to be closely related to cyanobacteria and may be ancestors of modern algae In some areas, e.g. oceanic equatorial Pacific, production by prochlorophytes may constitute a substantial fraction of total phytoplankton chlorophyll (up to 60%) and primary production Cell densities may be comparable to those for bacteria (ca ml -1 ) Phytoplankton community in some areas may change from diatom- or dinoflagellate-dominated assemblages to prochlorophyte-dominated assemblages Shift has profound consequences for entire food web

I.Phytoplankton F.Prochlorophytes Very small ( μm diameter) Components of nanoplankton and picoplankton Resemble bacteria in some respects and algae in others Structurally, resemble large chloroplasts with internal membranes that facilitate photosynthesis Appear to be closely related to cyanobacteria and may be ancestors of modern algae In some areas, e.g. oceanic equatorial Pacific, production by prochlorophytes may constitute a substantial fraction of total phytoplankton chlorophyll (up to 60%) and primary production Cell densities may be comparable to those for bacteria (ca ml -1 ) Phytoplankton community in some areas may change from diatom- or dinoflagellate-dominated assemblages to prochlorophyte-dominated assemblages Shift has profound consequences for entire food web

I.Phytoplankton G.Blooms Occur when conditions become favorable for one species or group of phytoplankton Population of that species or group increases rapidly and suddenly If bloom species is a dinoflagellate, densities sometimes increase so rapidly and reach such high levels that reddish-brown pigment they produce may color the water and cause a red tide

I.Phytoplankton G.Blooms Red tides typically become visibly apparent when cell concentrations reach 2-8 x 10 6 cells l -1 Cell concentrations may exceed 10 8 cells l -1 As nutrients are depleted and bloom begins to break down, bacteria begin to decompose the remaining organic material If material is sufficiently abundant, bacterial decomposition may deplete oxygen in surface waters, negatively impacting local fauna Phenomenon applies to any large phytoplankton bloom, not just red tides Red tides may involve species that produce pigments but are not toxic or may involve species that produce compounds that are toxic to marine life

I.Phytoplankton G.Blooms Toxin (Saxitoxin) may be 1) 1)Released into water, where it may be consumed directly by organisms that graze on phytoplankton (e.g. zooplankton) and indirectly at higher trophic levels 2) 2)Transmitted from dinoflagellates directly to higher organisms, e.g. clams, mussels, scallops, oysters, which then may be food for larger animals Result of consuming tainted fish or bivalves is Paralytic Shellfish Poisoning (PSP) - may be fatal Some forms can be extremely toxicSome forms can be extremely toxic Ex – PfiesteriaEx – Pfiesteria Blooms triggered by coastal pollutionBlooms triggered by coastal pollution Causes extensive fish killsCauses extensive fish kills Toxin can cause memory loss in humansToxin can cause memory loss in humans