Bryozoans are small aquatic invertebrates that inhabit a wide range of water environments across the globe. Often referred to as “moss animals” or “sea mats,” these creatures are typically found in colonies, though a few solitary species exist. Individual zooids are generally microscopic, measuring about 0.5 millimeters long. Their colonies, however, can vary significantly in size and form, ranging from a few millimeters to over a meter across. These diverse organisms play a role in both freshwater and marine ecosystems.
How Bryozoans Capture Food
Bryozoans possess a specialized feeding structure called a lophophore, which is central to their ability to obtain sustenance. This lophophore is a crown-like arrangement of hollow tentacles lined with microscopic cilia. The coordinated beating of these cilia generates water currents, effectively drawing microscopic particles from the surrounding water towards the bryozoan’s mouth. The lophophore’s shape can vary, appearing either circular or horseshoe-shaped depending on the species.
Each zooid can extend its lophophore outward to feed, or rapidly retract it for protection when disturbed. The tentacles are often coated with mucus, which aids in trapping the food particles as they are swept in by the water currents. While the general mechanism of current generation is understood, the precise method by which particles are ultimately captured and transferred to the mouth is an area of ongoing study. This filtering system efficiently gathers food.
What Bryozoans Consume
Bryozoans are filter feeders, meaning they sieve small, suspended particles directly from the water column. Their diet consists primarily of microscopic organisms and organic debris. They consume various types of phytoplankton, including diatoms, dinoflagellates, green algae, and cyanobacteria.
In addition to phytoplankton, bryozoans also feed on bacteria and protozoa, which are single-celled organisms abundant in aquatic environments. Small organic detritus also contributes to their diet. Some freshwater bryozoan species have a broader diet, including even smaller invertebrates like rotifers, nematodes, and microscopic crustaceans. This diverse diet of suspended particulate matter supports their growth and allows them to thrive in various aquatic habitats.
Bryozoans’ Impact on Their Environment
As active filter feeders, bryozoans significantly influence their aquatic environments. By consuming microscopic particles, they contribute to the clarity of the water, removing suspended sediments. This purification helps maintain healthier water. The presence of thriving bryozoan colonies often serves as an indicator of good water quality, as they are sensitive to environmental changes and pollution.
Bryozoans also play a role in nutrient cycling within ecosystems. Their feeding activities help to process and redistribute nutrients, with studies showing their growth rates increase in waters with higher nutrient concentrations, particularly phosphorus. Furthermore, bryozoans act as a link in the aquatic food web, transferring energy from consumed microorganisms to other animals. They serve as a food source for a variety of larger organisms, including snails, aquatic insects, and certain fish.