Bryozoans vs. Corals

What's the Difference?

Bryozoans and corals are both marine invertebrates that belong to the phylum Bryozoa. However, they differ in their physical characteristics and ecological roles. Bryozoans are colonial animals that form intricate, branching colonies composed of individual zooids. These zooids have a soft, gelatinous body and a crown of tentacles used for filter-feeding. On the other hand, corals are also colonial organisms, but they are characterized by the presence of a hard exoskeleton made of calcium carbonate. Corals have a symbiotic relationship with photosynthetic algae called zooxanthellae, which provide them with energy through photosynthesis. While both bryozoans and corals play important roles in marine ecosystems, corals are particularly known for their ability to build massive reef structures that provide habitats for a diverse range of marine life.


ClassificationPhylum BryozoaPhylum Cnidaria
Colonial StructureColonialColonial
SizeVaries, typically smallVaries, can be small or large
Body SymmetryAsymmetricalRadial Symmetry
Polyp StructureU-shapedTubular or Cup-shaped
Calcium Carbonate SkeletonPresentPresent
Feeding MethodFilter FeederFilter Feeder
HabitatMarine and freshwaterMarine
ReproductionSexual and asexualSexual and asexual
Ecological ImportanceProvide habitat and food for other organismsBuild coral reefs, provide habitat for marine life

Further Detail


Bryozoans and corals are fascinating marine organisms that belong to the phylum Cnidaria. While they share some similarities, they also have distinct attributes that set them apart. In this article, we will explore the characteristics of bryozoans and corals, highlighting their unique features and ecological roles.

Anatomy and Structure

Bryozoans, also known as moss animals, are colonial organisms that form intricate colonies of interconnected individuals called zooids. Each zooid is a tiny, filter-feeding organism enclosed in a hard exoskeleton. The exoskeletons of bryozoans are typically composed of calcium carbonate, which gives them a rigid and often branching structure.

On the other hand, corals are also colonial organisms, but they are characterized by the presence of a calcium carbonate skeleton secreted by individual polyps. These polyps are soft-bodied and have tentacles surrounding a central mouth. The coral polyps secrete a cup-shaped skeleton, which provides support and protection to the colony.

Both bryozoans and corals have specialized cells called polyps that play a crucial role in their survival. However, their structural differences give rise to distinct colony formations and growth patterns.

Ecological Roles

Bryozoans and corals are essential components of marine ecosystems, providing habitats and food sources for a wide range of organisms. Bryozoan colonies create complex three-dimensional structures that offer shelter and attachment sites for various marine invertebrates, such as small crustaceans and mollusks. They also serve as a food source for filter-feeding organisms, including sea squirts and certain fish species.

Similarly, corals form extensive reef systems that support a diverse array of marine life. Coral reefs are often referred to as the "rainforests of the sea" due to their high biodiversity. They provide shelter, breeding grounds, and feeding areas for countless species, including fish, crustaceans, and mollusks. Additionally, coral reefs protect coastlines from erosion and act as natural barriers against storms and waves.

Both bryozoans and corals contribute significantly to the overall health and stability of marine ecosystems, making them crucial players in maintaining biodiversity and ecological balance.

Reproduction and Growth

Bryozoans reproduce both sexually and asexually. Asexual reproduction occurs through budding, where new zooids develop from the parent zooid. This process allows bryozoan colonies to expand rapidly and cover large areas. Sexual reproduction involves the release of sperm and eggs into the water, where fertilization occurs externally. The resulting larvae are then dispersed by ocean currents, allowing for the colonization of new areas.

Corals also reproduce both sexually and asexually. Asexual reproduction in corals occurs through a process called budding, where new polyps develop from the parent polyp. This budding can lead to the formation of new branches or the growth of the existing colony. Sexual reproduction in corals involves the release of eggs and sperm into the water, followed by fertilization and the development of free-swimming larvae. These larvae eventually settle on suitable substrates and develop into new coral colonies.

Both bryozoans and corals have remarkable reproductive strategies that allow them to colonize new areas and ensure the survival of their species. Their ability to reproduce both sexually and asexually contributes to their resilience and adaptability in various marine environments.

Environmental Sensitivity

Bryozoans and corals are highly sensitive to changes in their environment, particularly water temperature and quality. Bryozoans are generally more tolerant of environmental fluctuations and can thrive in a wide range of conditions. However, they are still susceptible to pollution, sedimentation, and habitat destruction, which can negatively impact their growth and survival.

Corals, on the other hand, are extremely sensitive to environmental changes, especially increases in water temperature. This sensitivity is due to a phenomenon known as coral bleaching, where corals expel the symbiotic algae living within their tissues, causing them to turn white. Coral bleaching is often a result of prolonged exposure to high water temperatures, which disrupts the symbiotic relationship between corals and algae. If the stressors persist, corals can die, leading to the degradation of entire reef ecosystems.

Given their sensitivity to environmental conditions, both bryozoans and corals are considered important indicators of ecosystem health. Monitoring their populations and studying their responses to environmental changes can provide valuable insights into the overall well-being of marine ecosystems.


Bryozoans and corals are remarkable organisms that contribute significantly to marine ecosystems. While they share similarities as colonial filter feeders, their structural differences, reproductive strategies, and environmental sensitivities set them apart. Bryozoans form branching colonies of interconnected zooids, while corals create reef systems through the secretion of calcium carbonate skeletons. Both organisms provide habitats, food sources, and ecological services, but corals are particularly known for their role in supporting diverse and fragile reef ecosystems. Understanding the attributes of bryozoans and corals is crucial for their conservation and the preservation of marine biodiversity as a whole.

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