Field impression: Diving into the clear, cool waters off the Ningaloo Coast, my eye is immediately drawn to the intricate, almost microscopic tapestry clinging to the underside of an overhang. It's not coral, nor sponge, but a delicate, velvety carpet of pastel pinks and purples, interspersed with tiny, frilly white plumes that retract with the slightest disturbance. The water hums with the distant murmur of the reef, but these silent architects of the shallows offer a different kind of beauty, a living lacework constantly filtering the passing currents.
How to Identify Marine invertebrate biodiversity australia bryozoa
Bryozoans, often called 'moss animals' or 'lace corals', are colonial invertebrates made up of thousands of microscopic individuals called zooids. Identifying them in the field often requires a keen eye and sometimes a hand lens or even underwater macro photography to discern their intricate structures. Colonies can range from a few millimetres to several decimetres across.
| Feature | What to Look For |
|---|---|
| Body shape | Highly variable: encrusting sheets (e.g., Celleporaria spp.), delicate branching forms (e.g., Bugula spp.), rigid fan-like structures (e.g., Reteporellina spp., often called 'lace corals'), globular masses, or even free-living forms. Look for the distinct, often organised arrangement of individual zooids. |
| Colouration | Extremely diverse. Many species are white, grey, or translucent, taking on the colour of their substrate or symbionts. Others display vibrant hues: bright orange, fiery red, deep purple, or emerald green, often due to pigments, diet, or symbiotic algae. Bugula neritina is often a distinctive deep purple-brown. |
| Size compared to common object | Individual zooids are typically 0.2-1 mm long, about the size of a grain of sand or a pinprick. Entire colonies can range from a thumbnail-sized patch (a few square centimetres) to large, dinner-plate sized encrustations or branching structures reaching 20-30 cm in diameter or height. |
| Voice / sound | Completely silent. Bryozoans lack vocal structures and produce no audible sounds. Their presence is detected purely visually and ecologically. |
| Tracks / signs | Bryozoans do not leave tracks. However, some species, particularly those with calcareous skeletons, contribute significantly to marine bioerosion. They can leave tell-tale etching marks on shells or corals as they encrust and potentially dissolve substrate. Conversely, their calcareous skeletons contribute to the formation of marine sediments and even reef structures upon death. |
Under magnification, the individual zooids of most species are typically box-like or oval, each with a retractable crown of ciliated tentacles (a lophophore) used for filter-feeding. Some zooids are modified for defence (avicularia, resembling tiny bird heads with snapping jaws) or reproduction (ovicells, brood chambers).
Where and When to Find It
Bryozoans are ubiquitous in Australian marine environments, from the intertidal zone to the abyssal plains. They are found year-round, with peak growth often occurring during warmer months when plankton productivity is higher. Look for them on:
- Rocky Reefs and Coral Reefs: Encrusting species like Celleporaria sp. are common on the undersides of rocks, coral rubble, and dead coral skeletons. Delicate 'lace corals' (Reteporellina spp.) thrive in areas with moderate current, often on deeper reef slopes or cave entrances in places like the Great Barrier Reef (e.g., Lizard Island, Heron Island) and Western Australia's Ningaloo Reef.
- Seagrass Beds and Algae: Many species, such as Membranipora membranacea, specialise in encrusting seagrass blades (e.g., in Shark Bay, Western Australia, or Port Phillip Bay, Victoria) and large macroalgae.
- Mangrove Roots and Estuaries: Species tolerant of fluctuating salinity, including some Bugula species, can be found encrusting the prop roots of mangroves (e.g., in the tropical estuaries of Queensland and the Northern Territory) and jetty pilings in brackish waters.
- Artificial Structures: Docks, jetties, boat hulls, and aquaculture infrastructure provide abundant substrate. Bugula neritina is a common fouling organism in harbours like Sydney Harbour and Fremantle.
- Temperate Waters: Off the coast of Tasmania and southern Victoria, extensive bryozoan gardens can form, contributing significantly to biodiversity and forming important habitats alongside sponges and gorgonians, particularly in areas like the Bass Strait.
Behaviour Worth Watching
- Unique behaviour 1: Coordinated Mucus Net Formation: While individual zooids filter feed with their lophophores, some encrusting bryozoan colonies, particularly species of Conopeum or Electra common on seagrass and mangrove roots, exhibit a fascinating colony-wide feeding strategy in turbid waters. When particulate load is high, instead of relying solely on individual lophophores, the entire colony can collectively secrete a delicate, ephemeral mucus net across its surface. This net acts like a large, communal sieve, efficiently trapping detrital particles and microalgae that might otherwise pass through individual lophophores. Once laden, the net is gradually drawn inwards and consumed by the coordinated retraction and ingestion actions of adjacent zooids. Observing this requires patience and very clear,