They can live anywhere light and moisture are available - even the catacombs of Rome after artificial light was brought in for tourists
They bind 20-25% of organic carbon, despite being <1% of biomass
Oldest diatom found dates to Jurassic, but according to genetic research they may have emerged in the Permian or Triassic
Ecological preferences
Many species have very specific physical, chemical and biological factors
Since variables are correlated with each other it's sometimes hard to determine which has the strongest effect
Salinity
One of the most important variables controlling their occurence
Most of the known species live in saline waters, but they struggle in hypersaline waters (although some salt lake species are more tolerant)
The Kolbe and Husted classification for salinity is used to assign them into groups
pH
Very important for freshwater diatom community structure
They can live anywhere from 2.5 to 9 pH (very extreme), almost nothing else lives at these conditions
Diatom biodiversity (species richness) is highest in pH7 neutral water, this is common in northern Finnish lakes
Below 5.5 pH the planktonic component (free floating photosynthesising diatoms) slowly dissapear. Periphytic (adhering to surfaces like rocks or submerged logs) diatoms outcompete planktonic diatoms at this pH
In lakes with lower nutrients and higher water clarity, periphytic diatoms also outcompete diatoms
Higher pH means more plankton and less periphytic taxa
Nutrients
Nitrogen and phosphorous are most important
Limiting nutrient in oceans - usually nitrogen
In lakes - phosphorous
Increasing nutrient loading increases primary production, eutrophication and unfavorable conditions for benthic algae and other species
Primary production in eutrophied lakes is mostly controlled by planktonic algae. In oligotrophic lakes its benthic algae
Other factors (less important but still)
Other chemical (nutrient) factors like dissolved carbon, dissolved oxygen, silica, calcium, K, Mg, Fe...
Physical factors like water depth, turbulence, light, water temp
Bio factors like zooplankton abundance and parasites (parasites can infect the diatoms!)
Why are they good bioindicators?
Their shells preserve well in sediments
High concentration of sediments (abundant)
Easily identifiable to species or sub-species level
Large number of species (very diverse)
React quickly to environmental changes
Short, seasonal life span (spring and autumn blooms)
Many species have a very narrow tolerance to certain variables
Applications
Use in environmental research
Can use a qualitative (descriptive) or quantitative (statistical analysis, training set) approach.
Comparing time periods or different lakes
e.g. relative abundance of acid vs alkaline species
fresh water species vs saline species to study ocean transgressions or tsunamis, or changes in salinity in endorheic basins
plankton vs littoral species
Vegetation history can be indirectly studied by looking at total carbon and dissolved organic carbon reconstruction - certain species are diven by carbon content of the lakes
Hydrological changes - ocean sediments showing higher levels of freshwater species can be used to measure river flow
Other applications
Archaeology - reconstructing past landscapes at archaeological sites
Clay-pot origin (?)
Oil and gas -can be used for dating sediment layers for oil and gas search
Forensic science
Can find out if someone found dead in a lake drowned by seeing if there are diatoms in their lungs (meaning they inhaled water)
Diatoms in clothes indicate the source location - Jan Weckström is the person who examines diatoms in clothes after drowning incidents
Diatomite
Porous structure with a good ability to absorb water, used as filter for beer and wine brewing, explosives, filtering drinking water, toothpaste, polishing
Conclusion
Diatoms are the most commonly used biotic indicator in palaeolimnological research
Chrysophyte cysts
Relatively new bioindicator-group for paleolimnology
There are some problems with identifying them - there can be a lot of variation in one species
Scanning electron microscope is often required
Many of the cysts not been assigned to a species, we just give them "morphotype" names with numbers and such
Shape can be described as round to oval
Life cycle
Cysts are viable in sediments for decades, even in anoxic environments
Essential part of the light cycle
Environmental factors
Many factors affect them, and it's difficult to determine which one is the most dominant
Further challenges (undefined research)
We need to determine which cysts are produced by which taxa
We need to study cysts living in extreme envionments
Tropical and wetland taxa are not well studied as well
Conclusion
These are good to use as an additional piece of data along with other things
A bit bigger than diatoms in general, form a large part of zooplankton for fish
Known since the Permian period and have not changed much in the last 11,000 years
Primarily freshwater, but also in marine, wetlands, puddles, caves and tree depressions
General
Most feed on microalgae, bacteria and detritus
Different taxa have different habitat preferences (planktic (like Daphnia) vs littoral)
Structure
Egg-carrying like structures (Epippium) are a useful ID feature
headshield shape
order, shape and number of head pores
Habitats
Diverse genera live in different habitats (littoral to planktonic to benthic)
Factors affecting species occurence
Biogeography - how likely is it that a species will colonize a basin?
Physical/chemical properties
Eutrophy/oligotrophy
Predators
Competition
Use as bioindicators
They have a fast resposne to env change, there is a relatively low number of species and occur widely and are well preserved (their subfossils are anyways)
Can be used to identify acidification, nutrient level chanes, catchment area disturbance, changes in water level....
Also can identify fish abundance
Chironomids
A water insect family that lays eggs in lake then flies to new ones
Imporant group of benthic fauna, very important part of the food web
Especially in the north for fish
Recycle nutrients from sediment by burrowing
Environmental factors affecting their distribution
Food, quality of bottom substrata
water quality (pH, salinity, O2)
water depth
Air temperature - although this method is disbuted
Use as bioindicator
very numerous
High number of species, can often be IDd to species
Their heads (chitin) can be well preserved
Diverse ecological preferences
Pollen and spores
General
very common microfossils since the Palaeozoic
Size varies between 15-200µm (usually 20-50µm)
Basis for dispersion of plants and reproduction
We can reference current museum collections for identification
Basis of pollen analysis
Plants producing pollen/spores are common
Strong mechanical and chemical resistance
Fossils big enough to observe with the naked eye
Seeds, fruits, leaves, flowers, roots, bark
"megafossils" are things like cones or branches
Representativeness
Some plants e.g. Typha, Chara produce a large amount of macrofossils even if they are not actually very abundant
Other plants like Carex lasiocarpa, Potamogeton, Nuphar might be very abundant but don't produce many fossils
Important to consider dispersal, representativeness and preservation when considering plant macrofossils
Applications
past climate change
eutrophication history
dispersal history of plants
archaeology
AMS-dating of them - although you need to be careful about contamination from the rest of the carbon in the sediment
Plant Macrofossils vs Pollen
Macrofossils are for local vegetation, pollen can be local and regional
Macrofossils are usually low concentrations, pollen usually high
Need a large sample size for macrofossils, pollen needs a small sample size (labor intensive)
Some species only preserved as macrofossils, some species are only preserved as pollen
Summary
Palaeobioindicators are versatile and effective tools for environmental change reconstruction
Using many palaeobioindicators strengthens the outcome of the research