By Fiona Hodge

Some places are definitely more stressful then others; traffic jams, crowded spaces, or hospital emergency rooms for example. How do we humans cope with stress? Generally by predicting and avoiding it; by listening to the radio traffic report, getting to the ticket booth early, or being cautious on our bicycles.

Plants do not have the luxury of planning ahead and avoiding stressful situations. Instead those that live in stressful places accept stress as part of their lives, and are built to cope. One of the most stressful habitats around is the intertidal. Here plants spend half their time in the air drying out and heating up, and the other half being submerged and pummelled by cold waves. Despite the stress it’s a densely populated place, filled with barnacles, mussels, and of course seaweeds.

Standing up to stresses: all of the pink on the rocks is coralline seaweed. Dr Martone provides an idea of scale.

It was the finely branched pink coralline seaweeds that caught Dr Martone’s eye nine years ago. He was intrigued that these delicate and beautiful corallines seaweeds could “resist forces [from the waves] far greater than those imposed by hurricane winds... and this every 12 seconds or so”.

These coralline seaweeds secrete hard calcium carbonate segments which are joined together to form the plants, much like beads forming intricate necklaces. What joins the segments or beads together are thousands of long fibrous cells, acting like individual strands to form a strong rope. It’s these rope-y joints that Dr Martone studies to determine how corallines cope with wave stress.

Two coralline seaweeds in the hand... (Calliarthron tuberculosum)

Dr Martone measures the force corallines’ rope-y joints can withstand using a tensometer: a device based on the principles of the torture rack. Specimens are inserted, the rack is wound, specimens are stretched, specimens break. All the while Dr Martone is measuring the force on the specimens. The average Calliarthron specimen can resist 20 N before breaking: roughly the force of holding 20 kg! Why? The cells that make up the strands of this rope are mainly cell wall, and have a range of compounds embedded in their cell walls that increase their strength.

Having a bead necklace like structure also allows corallines to go with the flow, which minimises the impacts of waves. Corallines also have an insurance plan: the fronds grow from a crust. This crust is almost indestructible, and can grow more fronds as required.

So to sum up corallines live with stress by going with the flow (reducing stress impact), being strong (coping with stress), and having a backup plan (accepting stress). They should be an example to us all.

A magnified view of the insides of the rope-y joints of a coralline algae (C. tuberculosum).

Disclaimer: Fiona Hodge is currently working in Dr Martone’s lab group.