Bryozoan biofouling and how to control it
Furry looking, blob-like, and slimy ‘moss-animals’ called bryozoans have found a home in many municipal and industrial water systems. These invasive creatures can cause severe economic headaches. They are especially damaging when their large sticky colonies clog and become tangled within equipment. Physically removing them from essential screens, filters, pipelines, intakes, and valves requires costly labor and maintenance.
Bryozoans latch onto substrates located within flowing waters that bring them sustenance, such as intakes, screens, filters, heat exchangers, and cooling systems. Growing colonies can progressively decrease waterflow and eventually cause equipment failure. Often, bryozoan biofouling co-occurs with other invasive species such as zebra or quagga mussels, exacerbating the stress placed on operators to clear and maintain blocked equipment.
What are Bryozoans?
Bryozoans are an invertebrate animal that thrives in flowing, nutrient-rich water. They range in size from a few inches to over two feet and have diverse forms, including tubular, spherical or branch-like structures. They live in fresh or saltwater environments depending on class and species.
In freshwater, bryozoans have different shapes and may appear as large gelatinous spheres or intricate woven networks. These networks can easily be mistaken for a single organism, but they are actually colonies of smaller organisms called zooids. Each zooid measures only 1–2 mm in length and contains a primitive digestive tract. Collectively, zooids stack and nest on each other to form a net-like structure that comprises a single bryozoan.
Why are Bryozoans difficult to kill?
Bryozoans are highly adapted to withstand suboptimal conditions. In unfavorable conditions such as freezing weather or chemical stress the colony retreats within itself and may appear dead, only to revive when water conditions improve. Freshwater bryozoans also have a unique ability to expel tiny seedlike survival pods known as statoblasts.
A statoblast is a self-contained dormant mass of cells protected by a tough outer shell. Statoblasts grow in the guts of zooids, where they form hard shells made of chitin, a protective material also found in insect exoskeletons. The production of statoblasts allows bryozoans to reproduce asexually in harsh and unpredictable conditions.
Statoblasts can take one of three forms: sessoblasts, floatoblasts or piptoblasts. Sessoblasts typically adhere firmly to substrates but they can also hitch rides to new locations with migrating waterfowl, either in their digestive systems or on their bodies. Floatoblasts are the most difficult to control because they float freely with currents until they settle and germinate. Piptoblasts simply fall around existing colonies and germinate in place.
How can Bryozoan infestations be controlled?
Once bryozoans establish themselves in a body of water, they can be difficult to eradicate. Reduction and control are possible, however. Here are some common treatment options to manage bryozoan infestations:
- Physical Removal: Scouring and manual scrubbing can remove live colonies from their substrates but is labor intensive and time consuming. Manual removal also carries a risk that young bryozoans may remain unseen and continue to reproduce. Statoblasts are even more difficult to detect and remove manually because of their tiny size.
- Changes in Aquatic Environment: Methods such as heating, desiccation, sonication, and ultraviolet light can help reduce bryozoan populations, but statoblasts will likely remain unaffected. These treatments are also difficult to implement in larger water sources such as lakes and ponds and may produce inconsistent results.
- Sodium Hypochlorite: Sodium hypochlorite has been administered as a chemical treatment to decrease bryozoans. However, sodium hypochlorite presents various drawbacks in that it is not EPA-registered for this use, is dangerous to non-target organisms at high dose rates, and produces halogenated byproducts that are carcinogenic to humans.
- Granular Copper Sulfate: Granular copper sulfate has been shown to reduce bryozoans, but may require copper concentrations high enough to be impractical or uneconomical due to low solubility and inefficient formulation. Improper dosage can cause copper build-up in the sediment leading to lasting damage within the ecosystem and harm to aquatic organisms.
The EPA requires compliance with National Pollutant Discharge Elimination System (NPDES) permits to protect water quality and public health. NPDES regulations limit the amount of added chemicals or pollutants, such as copper, discharged from water-cooled power plants and industrial facilities. High levels of copper sulfate can bring facilities into non-compliance and harm the environment.
Controlling bryozoan biofouling with EarthTec QZ
Fortunately, not all forms of copper are created equal. Advanced liquid formulations use acid stabilization to maintain the copper in the cupric ion form (Cu2+) and eliminate the disadvantages associated with copper sulfate crystals. Ionic copper is more bioavailable and in turn allows effective performance at unprecedentedly low dose rates.
EarthTec QZ is an EPA-labeled liquid ionic copper formulation that can reduce bryozoan populations in pipelines and open waters while remaining within NPDES permitted copper discharge limits. EarthTec QZ is also NSF certified to ANSI Standard 60 for drinking water and effectively reduces invasive species populations at copper concentrations far below the EPA maximum limit of 1.3 ppm mandated by the Lead and Copper Rule.
EarthTec QZ’s unique formula is stable, requires no mixing, and disperses easily throughout the target treatment area. It does not settle into sediment, which allows organisms to ingest copper at a pace suitable for the nutrient cycle. With fewer adverse impacts on non-target organisms, EarthTec QZ’s low dose copper is effective and functions within EPA safety regulations. EarthTec QZ is also a certified molluscicide and can be used to control zebra and quagga mussels in addition to bryozoans.