Funky Creatures

When I discovered that a one-inch-square piece of kelp frond is a microcosm of creatures, (once more) the enormity of the ocean and what we don’t yet know about it, dawned on me.

Our trainees were ashore on a rainy afternoon, no doubt raiding the shops for sweets, when I decided to sample some seaweeds off a rocky shore and return them to the sail training tall ship Pelican of London for identification and a look what lives within the fronds. We found tiny brittle stars, a sea spider, snails and crustaceans and then … a nudibranch stole the whole show!

This tiny sea snail was just about the most flamboyant, funky creature I’ve ever encountered. Just about 3 mm long, it had golden ‘horns’ (gills) and its white, translucent body was covered in numerous iridescent fingerlike projections (cerrata) in colours of orange, red, blue, purple and white.

The nudibranch moved onto a section of a kelp frond that was covered in bryozoans, geometric looking colonies of tiny animals. I decided to cut a section of bryozoan-covered kelp frond to place under the microscope in a dish with seawater.

The bryozoan colony looked dead at first, but soon we saw subtle movements. Then something that looked like a tiny upside-down jellyfish popped out of its little ‘cage’ and started feeding. A sea mite wandered into view, followed by some translucent wormy lookalike….and of course sections of the mesmerising nudibranch moving in and out of view.

We had half an ecosystem in that petri dish!

• Kelp are large brown algae (macrophytes) that grow rapidly¹ in dense ‘forests’ in nutrient-rich, clear, shallow, cool coastal waters in temperate to high latitudes. Along with coral reefs, kelp forests have are rich in biodiversity, and are spawning and nursery grounds for many invertebrate and fish species². Kelp forests are also important hunting grounds for predators, shelter for marine mammals and seabirds during storms, contribute to ‘blue’ carbon sequestration and are harvested for use in chemical and food industries³.
• Bryozoans are invertebrates that have a planktonic early life stage originating from sexual reproduction. When ready to become sessile, an individual sticks itself to a solid substrate, such as a rock or kelp blade, and undergoes metamorphosis⁴. The adult individual zooid is less than a millimeter in size and lives in a box-shaped compartment. By cloning, a colony of thousands is formed over time. Bryozoans feed on unicellular algae, bacteria and organic matter drifting by, capturing particles with a crown of tentacles (lophophore) on a stalk that extends from the compartment and is retracted in danger or resting time. Bryozoans are preyed on by sea urchins, fish and nudibranchs and compete with sponges, algae and sea squirts (tunicates) for space.
• Halacarid mites have for pairs of legs, but unlike their close relatives, the marine spiders, they don’t have to come up for air. Different species dwell on specific substrates and some are predators, others parasites, some graze on algae and others scavenge dead organic matter. ⁵
• Nudibranchs are mollusks with external gills and no shell. They are predators and many feed on hydroids, bryozoans, small sea anemones and sponges that live on and around the kelp. Nudibranchs also eat each other – part of a diet that includes many creatures with toxic, foul tasting or stinging properties. Nudibranchs are able to use these ‘chemical weapons’ to deter predators. They also fulfil an important role in their ecosystem by controlling the spread of their prey, and that’s not all: nudibranchs are sensitive to rising sea water temperatures and their shift in habitat to cooler waters is a climate change indicator.⁶

If you can bear a video that is less than pin-sharp in places (perhaps view it on a small screen) and you haven’t seen kelp under the microscope before, watch this:

Let us protect the ocean we know and the many things we don’t know about it from bottom trawling, deep sea mining, chemical pollution, overfishing and temperature rise…too much to ask? Not once we realise that we all and our future depend on a healthy, functioning and thriving ocean system.

References:

1. NOAA. What is a Kelp Forest? National Ocean Service. National Oceanic and Atmospheric Administration. https://oceanservice.noaa.gov/facts/kelp.html#:~:text=They%20grow%20in%20dense%20groupings,almost%20any%20other%20ocean%20community. ↩︎
2. Mission Blue. 15-05-2025. Kelp101: What are kelp forests, and why do they Matter? https://missionblue.org/2025/05/kelp-101-what-are-kelp-forests-and-why-do-they-matter/?mc_cid=d82f8dea10&mc_eid=5f49b2b685 ↩︎
3. Oceana. Kelp Forests. Marine Life Encyclopedia. Marine Science and Ecosystems. Oceana – Protecting the World’s Oceans. https://oceana.org/marine-life/kelp-forest/ ↩︎
4. Buchsbaum, R., Buchsbaum, M., Pearse, J., and Pearse, V. 1987. Animals Without Backbones. 3rd edition. University of Chicago Press, Chicago. Accessible at: Bryozoa: Life History and Ecology https://ucmp.berkeley.edu/bryozoa/bryozoalh.html ↩︎
5. Halacaridae. Wikipedia. https://en.wikipedia.org/wiki/Halacaridae ↩︎
6. Lubbe, Tyrone. 2024. Nudibranchs: The Ocean’s Colourful Climate Indicators. https://www.linkedin.com/pulse/nudibranchs-oceans-colourful-climate-indicators-tyrone-lubbe-0wvgc/ ↩︎