Marine Lessons from Piha


What can be learnt about our marine environment from a quick trip to the beach? What does that shell belong to? What is seafoam made of? What are 'blue-bottle jellyfish'?

A beautiful (but windy) winters day blew my friends and I on a spontaneous trip to Piha beach and as a group of science students it didn’t take long before we were applying knowledge from the classroom to our surroundings.

Making our way up the beach, we noticed several blue bottle jellyfish washed ashore and I stepped in to give a marine science lesson. Also known as Portuguese man o' war, this jellyfish is in fact, not a jellyfish but a siphonophore. Multiple animals make up this one organism and work together to function as one. They are each specialised to do different jobs- feeding, reproduction, transport or defence and are so interdependent they can’t survive on their own. The gas bladder floats at the top with a sail like membrane meaning its transportation is at the mercy of the winds. Tentacles are suspended below which sting, paralyse and kill squid and fish with some tentacles containing chemicals to liquify the prey so it can be drunk like a smoothie. Even after the blue bottles have died and washed ashore, the stinging nematocysts can still injure you so it’s important to take great care when having a closer look. If you encounter any of these while diving or in the water, they are often in groups (due to the passive nature of their transportation) so take care, and ensure you have gloves and a nice thick wetsuit if you want to continue your swim. In the case of a blue bottle sting, as it’s not technically a jellyfish vinegar doesn’t help and can actually activate more stinging cells. The best thing to do is immediately rinse in seawater and then soak in warm water to speed up the break-down of toxins.

dead blue bottle portugeese man of war

Reaching the southern-most end of the beach there was so much seafoam it looked like piles of snow. On some beaches, the pounding waves are so strong they break up single cell phytoplankton called diatoms which then release their internal nutrients. Diatoms are a major group of microalgae, easily distinguished by their hard and decorative cell wall made of silica that can group together in pretty ribbons, zig-zags or stars. The surf then forces bubbles into the nutrient-algae soup like a SodaStream machine to make the foam. In New Zealand this phenomenon is common on high energy, west coast beaches particularly in winter and although it may be mistaken for a sign of pollution, is really evidence of a thriving, productive ecosystem.


Higher up in the sand along with many other shells were a large array of dainty, white spiralled shells- a common site on various east and west coast beaches in New Zealand. Someone asked me if I knew what they were and I realised I had never stopped to think about the critter it belonged to. A quick google search took me to NIWA’s website and I was very surprised at the response.

spirula spirula

The shells are scientifically known as Spirula spirula but commonly known as belonging to the ‘Ram’s horn squid’! The shell is a buoyancy organ for the squid to help orient it in the water column where it lives 500-1000m deep in the day and migrates to 300m to feed at night. The chambers inside the shell are gas filled which means the squid can control the amount in each compartment to allow it to ascend or descend through the water. The Ram’s horn squid only live for a year and a half and are rarely seen but the shells that float ashore once the squid dies are much more frequently observed.

Our little Piha excursion was a great reminder the classroom is everywhere if you pay enough attention. Science is all around us and there are plenty of lessons to be learnt!

Georgia Third

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