Plankton - Lecture notes 15 PDF

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Prof. James Bron...

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PLANKTON Plankton, from the greek word πλανκτος (“planktos") meaning wanderer or drifter Individuals are termed “planktonts” or “plankters” Small(ish) animals (plants) and viruses spanning 7 orders of magnitude from 2m (jellyfish) floating, drifting or swimming in the water column. Zooplankton comprise >7000 species in 15 Phyla.

SIPHONOPHORES   

Largest planktonts are siphonophores, which belong to a class of colonial predatory invertebrates, sometimes resembling jellyfish, and can appear to be a single organism The best known example is the dangerous Portuguese Man o’War Physalia physalis which is a colony of four kinds of minute polyps Some siphonophores can reach up to 130 feet in length

More powerful swimmers are often termed “NEKTON”  

Nekton (larger organisms) are able to move independently of water currents as opposed to true plankton which are passive drifters or floaters. Oceanic nekton comprises animals largely in three main groups:  Vertebrates form the largest contribution i.e., animals which are supported by either bones or cartilage  Molluscs, e.g. squids  Crustaceans, e.g. lobsters and crabs.

Hard to define what is and what’s not plankton (e.g. fish larvae?) 

Copepods are the most numerous metazoan (multicellular organism) on the planet (more than insects and nematodes). Water covers 70% and copepods are the dominant group in most water bodies. Assuming just one copepod per litre (probably a gross underestimate) leads to a calculation that we share the planet with at least: 1,347,000,000,000,000,000,000 copepods (sextrillion, US or thousand trillion)

Can be defined as whatever you catch in a “plankton net” 

Plankton nets - fine meshed nets with collecting chambers at the end usually towed from boats. Phytoplankton nets have smaller mesh than zooplankton nets reflecting the sizes of target organisms

Why to study plankton? 

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Phytoplankton provide 50-90% (depending which figures you adopt) of the earth’s oxygen and mop up huge amounts of CO2 (30-50% of CO2 produced by burning fossil fuel), thus have an important part to play in global warming and climate change Some plankton produce toxins which may be passed by fish or molluscs to humans They may be actively or passively toxic to other organisms (including man) and may harbour parasites that pass ultimately to man

Ciguatera and Paralytic Shellfish Poisoning (PSP) 

Fish and shellfish consumption of a range of toxic plankton, particularly dinoflagellates (flagellate protists) and cyanobacteria, whose toxins accumulate in the flesh of finfish and shellfish, can give rise to a range of human poisonings including ciguatera and paralytic shellfish poisoning (PSP)

Few more reasons to study plankton 

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Phytoplankton are at the root of most of the key marine food chains, which ultimately provide a key resource for humans (e.g. wild and cultured marine fisheries depend ultimately on plankton). Plankton may act as indicators of the state of the marine environment including the effects of pollution and climate change. Products from plankton may be used in foods, drugs or cosmetics. Plankton affect the weather clouds and cyclones

Marine canaries    

Plankton show rapid responses to changes in their environment e.g., temperature or water quality. Changes in type of plankton dominant species, species composition. Changes in numbers of plankters. Can provide advance warning of major environmental shifts.

HOLOPLANKTON and MEROPLANKTON   

Holoplankton animals and plants that live their entire lives in the plankton. Meroplankton animals and plants that live in the plankton for only a part of their lives e.g., many marine larvae such as mussels, crabs, coral etc. Often the planktonic form will have a vastly different morphology, diet and life-style from the final (adult?) form.

Size matters

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Megaplankton Macroplankton Mesoplankton Microplankton Nanoplankton Picoplankton Femtoplankton

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Size determines (amongst other properties) the ability to absorb nutrients (smaller size gives larger surface area to volume ratio), the ability to avoid being eaten by (some) grazers/predators, the ability to sink quickly or float

>20 cm (jellyfish etc) 2-20 cm (krill, arrow-worms) 0.2-20 mm (copepods, cladocerans) 20-200 um (phytoplankton, nauplii) 2-20 um (diatoms, ciliates, radiolaria) 0.2-2 um (bacterioplankton) 0-2 um viruses

Marine viruses   

Viruses are the most numerous members of the plankton obligate intra cellular pathogens. 1L of seawater can contain 100 billion viruses Viruses infect all groups within the plankton including bacteria, phytoplankton, protists and larger zooplankton It is suggested that marine viruses have wide ranging effects on evolution of marine organisms and the marine carbon cycle

Vertical migration  

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Phytoplankton may migrate from the surface where they need sunlight to photosynthesise into deeper water during the night in order to obtain nutrients Many zooplankton on the other hand may migrate into surface waters to feed at night, the darkness helping to protect them from visual predators like fish This movement may be detected both by sonar imaging and through increased numbers of plankters caught by nets at night during plankton surveys. In this graph the y-axis is depth from surface and the x-axis is time (over 24hrs). Yellow / red shows highest plankton numbers.

Staying in the water column  

Being too buoyant leaves plankton floating at the surface where they are vulnerable to predators, physical damage and UV damage. Swimming to keep position takes energy. Small size, hairs or lipid droplets allow them to stay at a particular depth (“neutrally buoyant”) or sink very slowly

On being small…

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For very small organisms, water behaves differently  It is thick and viscous like treacle or tar  There is little inertia if you stop swimming you stop (you don’t keep going for a bit...).  It is sticky tends to hold on...  It holds trails e.g. odours Thus small animals (and plants) must burrow or dig / scoop their way through water and can not feed by filtering food from the water but must guide it into their mouths / feeding apparatus by changing water flow patterns.

Plankton forms the basis of the majority of marine food webs particularly in oceanic waters 

10% energy transfer between trophic levels:  10,000 kilos of phytoplankton in needed to feed 1,000 kilos of small zooplankton, which I turn supports100 kilos pounds of larger zooplankton, which supports 10 kilos of small fish species (like herring or anchovies), which support 1 kilo of a larger fish species such as those harvested for human consumption.”

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No plankton = no fish

PHYTOPLANKTON    

Phytoplankton, tiny marine plants and cyanobacteria (bacteria that photosynthesise), are the primary producers that drive many food webs Can be thought of as “the grasses of the sea” and are the basis of marine productivity Majority of chlorophyll is in small cells the size of bacteria small size gives greater surface area to volume ratio to absorb nutrients Because of this small size and rapid growth rates, phytoplankton numbers respond rapidly to changing conditions e.g. temperature / nutrient availability

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Diversity of phytoplankton: Euglenophytes, Chlorophytes, Haptophytes, Glaucophytes, Pyrrophytes, Bacillariophytes + a vast range of cyanobacteria (bacterioplankton)

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Chlorophyll can be observed by satellite and changes observed from year to year, this being informative for studies of global warming / climatic change.

Phytoplankton and weather patterns 

Phytoplankton are believed to have major effects on weather patterns

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In 2004 it was observed that under conditions of high UV, phytoplankton produced high levels of dimethylsulfoniopropionate (which in turn reacted to produce cloud forming compounds hence affecting weather conditions (and shielding the plankton from damaging UV radiation) More recently 2010 it has been suggested that the amount of phytoplankton in the water (determining water colour and hence local surface heating by sunlight) may affect the incidence and strength of tropical cyclones

DOM = Dissolved Organic Matter 

 marine snow

Sinking of “marine snow”, mostly produced from plankton (=dead stuff, bacteria and poo...) and deposition in the deep oceans is a key mechanism for removal and storage of carbon from the atmosphere, helping to reduce or retard global warming

OCEAN ACIDIFICATION

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Chalk cliffs are composed of coccolithophores whose tests are made of calcium carbonate (CaCO3): one way that carbon is stored for geological periods

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Diatomaceous earth similarly comprises siliceous fossilised diatom frustules used for filtering, abrasives, bug killer etc., but these DO NOT contain carbon.

PLANKTON BLOOMS 

Plankton blooms reflect local temperature / light / nutrient / wind conditions

ZOOPLANKTON    

Zooplankton may reach very high densities, particularly when migrating to surface waters to feed. The Antarctic krill, Euphausia superba, has an estimated biomass of over 500 million tonnes, roughly twice that of humans. Swarms of krill may reach a density of 10,000 to 60,000 individuals per cubic metre with a single swarm covering over 1km with a depth of over 30m. “Some swarms estimated to contain more than 2 million tonnes of krill spreading over more than 450 km2 have been observed. This is the equivalent of 28.5 million people, 4 times the population of Greater London.”

Whales and plankton    

Whales, and in particular the blue whale, are the largest animals known to have lived on the planet. A blue whale may measure up to 29 metres in length and weigh up to 158 tonnes. Small crustaceans, copepods and euphausids (“krill”), filtered out of the water using baleen plates, make up the vast majority of the diet. One whale can consume up to 4.1 tonnes of krill per day

Plankton as Indicators of Climate Change 

10 degree isotherm (a line linking points of equal temperature) has moved northward over time with changing climate

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With increasing sea temperatures, northern species are moving out of the North Sea and southern species are moving North. Long-term records from the continuous plankton recorder survey (CPR) show this clearly. Each column of graphs shows a group of species with particular temperature preferences and its spatial distribution through time (red = high numbers, blue = low numbers)

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Numerical abundance data for commonly recorded plankton in the central North Sea (red = high, blue = low). Each row is a single species, each column is a single year. Species having similar environmental preferences are grouped next to each other on the y-axis (Species). Moving along the x-axis (Years) for given species or groups of species, sudden major shifts can be seen e.g. late 70’s

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The ratio of the warmwater copepod species (Calanus helgolandicus) to the the cold-water species (Calanus finmarchicus) is increasing, with total Calanus from both species decreasing over the study period.

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Inter-annual variability in the peak seasonal development of echinoderm larvae (an indicator of plankton phenology) in the North Sea. Warmer temperatures = earlier seasonal appearance, colder temperatures = later seasonal appearance. The general trend through time is towards an earlier seasonal cycle.

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Some species are disappearing completely from particular areas in response to environmental changes

INVASIVE SPECIES 

Arctic ice melt is allowing some species (in this case Pacific diatom, Neodenticula seminae, in the Labrador Sea) to move from the Pacific to the North Atlantic. Such invasions may have catastrophic effects on marine ecology, e.g. changing food webs with the possibility of pestspecies prospering and human food species declining....