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NEYEDC improve and inform environmental decision making, conservation, land management and sustainable development in North and East Yorkshire through the collation, management, analysis and dissemination of biodiversity information.

The Natural History of Yorkshire in 100 Species

Explore the rich and diverse natural history of our region through the stories of 100 species, told by the people who know them best.

#87 Bladder Wrack by Jackson Sage

Meet Jackson Sage, Project Manager at Humber Nature Partnership!

Jackson is the Project Manager for the Humber Management Scheme at Humber Nature Partnership. With the number environmental designations that the Humber Estuary holds, it is Jackson’s role to pull together all of the relevant authorities from across the region to manage the Humber as one holistic system. Jackson’s background is in Marine Biology and spent 4 years of postgraduate study looking at the interactions between marine microorganisms and fluid mechanics. 

Bladder Wrack Fucus vesiculosus might not be the flashiest marine organism. It’s usually only noticed when it pops under our feet when we stepped on, or brushed aside in a rockpool when looking for more “interesting” species; but Bladder Wrack plays a vital role in coastal ecosystems, traditional medicine, and even modern sustainability efforts.

Bladder Wrack (c) Tom Goskar, Flickr CC-BY-NC

Appearing on rocky shores across Yorkshire and the rest of the United Kingdom, Bladder Wrack is a large brown alga found across the mid-shore growing up to 1.5m in length, though its size and shape can vary depending on wave exposure. Bladder Wrack gets its name from the air-filled bladders found on the midrib of the plant (usually found in pairs), with vesiculosus coming from the Latin vesicula, meaning “blisters”. These bladders help the plant float upright underwater, allowing for increased nutrient and gas exchange.

Seaweed reproduction is something that Jackson did not anticipate would be interesting to him (or that he’d have to admit to) … however some 20 years on after learning about how Bladder Wrack reproduces, he is still amazed by it. Bladder Wrack plants are either male or female. At the tips of the plant is a warty-like structure about the length of a grape – these are the receptacles. Each receptacle contains many cone-shaped sub-surface chambers called conceptacles which open to the surface via a pore. Male conceptacles contain antheridia, which is a structure containing 64 sperm cells; whereas the female conceptacle contain oogonia, a structure containing 8 eggs.

Often on a calm night just prior to a full moon, the antheridia and oogonia are ejected from male and female plants, with both of these structures quickly breaking down to release the sperm and eggs. Studies have found that egg production per gram of frond mass can be as high as 210,000 eggs!

The sperm follow a pheromone released by the negatively buoyant and now sinking eggs; however, they have a surprising tool to help them find the egg. Each sperm cell has a rudimentary eye… yes, you read that correctly… very basic in structure, but an eyespot that is able to detect light; or in this example, able to differentiate between the bright moonlit waters of the surface, and the darkness of the bottom of the water column where the eggs are. Fertilised zygotes adhere to the seabed in hours and germlings are visible to the naked eye within a few weeks.

On the rocky shore, very young germlings of Bladder Wrack provide a tender food source for herbivorous animals, however once the plant becomes established it has very few predators, owing to the chemical deterrents it releases such as phlorotannins, phytotannins and galactolipids. The beds of Bladder Wrack themselves provide a dense habitat for species such as the polychaete worm Spirorbis spirorbis and shelter for a myriad of marine invertebrates and juvenile fish.

Bladder Wrack has many uses including as fertiliser for agriculture, body care products such as shower gels, body creams and toothpastes or health supplements where it is labelled as “Kelp Tablets” (Morrissey et al. 2001). Bernard Courtois' accidental discovery of iodine from Bladder Wrack and Kelp in 1811 was a game-changer for both chemistry and medicine. Iodine quickly became essential for thyroid health, leading to its widespread use in dietary supplements and medical treatments. Even today, Bladder Wrack is valued as a natural source of iodine.

Antheridia at 400x magnification (c) Jackson Sage

Bladder Wrack also plays a significant role in wave attenuation, particularly in high-energy coastal environments where it forms dense seaweed beds. These beds help dissipate wave energy, reducing the impact of waves on shorelines, preventing scouring of the seabed and contributing to coastal protection.

Bladder Wrack is a prime example of how seemingly ordinary marine species play extraordinary roles in both ecological systems and human innovation. From its contributions to shoreline protection and biodiversity to its historical significance in iodine discovery, this resilient seaweed underscores the intricate connections between nature and science. Next time you step on one and hear that satisfying “Pop!”, maybe take a second to appreciate all the incredible things it’s doing—it’s earned it!

Recording and monitoring

Records of marine and intertidal species can be submitted to your local LERC, Natural History Society (where they have a marine or other relevant section), or recorded via iRecord. You can also get involved with marine and intertidal recording via The Wildlife Trust’s Shoresearch citizen science project.

Further information and acknowledgements

NEYEDC would like to thank Jackson for his time and expertise in helping to create this blog.

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