Stoneworts Overview and Conservation

Study Notes

Stoneworts

Stoneworts (also known as charophytes) are a family of algae that live in wetlands and freshwater or brackish habitats.
They are submerged species, preferring depths between 1-10 meters.
Their name comes from the stony texture they acquire due to calcium carbonate encrustation.
Stoneworts are closely related to land plants.
There are over 400 species globally and approximately 30 in the UK.
Their populations have significantly decreased since the mid-twentieth century due to habitat loss and pollution.
Seventeen species are listed as Threatened or Endangered in the UK.
There are five genera of stoneworts in the UK:
- Chara: alkaline waters, often calcium-encrusted.
- Lamprothamnium: coastal lagoons.
- Nitella: softer waters (pH 6.5 - 7.5), lacking encrustation, stem without cortex.
- Nitellopsis: mesotrophic lakes, lacking encrustation, stem without cortex.
- Tolypella: calcareous ditches and canals.
Threats to stoneworts include:
- Eutrophication
- Sedimentation
- Unmanaged succession, particularly of common reed (Phragmites australis)
- Avian grazing, particularly by geese
Stoneworts lack true leaves and roots.
They have branchlets arranged in whorls around the stem and fine rhizoids for anchorage.
Stonewort cells are very large (up to 20 cm in length).
They are sensitive to water quality, particularly metals.
They are also sensitive to competition from filamentous algae.
Stoneworts exhibit morphological plasticity based on their habitat and water quality.
They are pioneer species, often colonizing new water bodies.
Some stoneworts have spines (hispid), which may be for protection and ion uptake.
Nitella spp. and Nitellopsis spp. are ecorticate (lacking cortex), not hispid, and do not deposit calcium salts.
Stoneworts reproduce sexually through oospores.
Oospores are formed when eggs within the female oogonia are fertilized by male antherozoids.
Reproduction is stimulated by light and temperature increase.
Some species reproduce vegetatively through bulbils.
Stoneworts are highly sensitive to water quality, likely due to their algal structure.
They are particularly sensitive to heavy metals, nitrates, and phosphates.
Stoneworts can be used as indicators of water quality.
They play several important roles in aquatic ecosystems:
- Enhancing water clarity
- Sediment stabilization
- Providing habitat for microbes, zooplankton, molluscs, and invertebrates
- Acting as a nutrient sink
Conservation methods for stoneworts can be site-specific and include:
- Reducing nutrient input
- Removing surface sediments
- Removing competitive vegetation
Mechanical clearance can be used to restore stonewort habitats.

Desmids

Desmids are green algae considered to be among the earliest-evolved plants.
They have the same photosynthetic pigments (chlorophylls a and b) as other plants.
They have cell walls made of cellulose and store starch and chlorophyll in double membrane-bound chloroplasts.
Most desmids have two pronounced lobes connected by an isthmus.
Their name comes from the Greek word "desmos" meaning "bond".
They are freshwater algae, preferring nutrient-poor habitats like peat bogs and ponds.
Desmids secrete mucilaginous sheaths that host symbiotic bacteria.