spongy kelp with a thick cushioned body on wave-swept rock

Size
Height: 10–30 cm
Lifespan
2–5 years
Diet
Photosynthetic. Grows on rocky reefs in low intertidal and shallow subtidal zones. Requires clean water, stable rock surfaces, and good water flow. Forms spongy, soft fronds that are dark brown to olive-green.
Habitat
Grows on rocky shores in southern New Zealand, from Cook Strait down to Stewart Island. Forms soft, inflated, golden-brown sacs in the low intertidal zone.
Range
Found throughout the North and South Islands on rocky reefs in low intertidal and shallow subtidal zones. Most common in clear, sheltered waters with good water flow. Also found in temperate regions worldwide.
Endemism
Native
Main Threats
None significant. This species is common and widespread. Localised threats include coastal development, pollution, and climate change affecting water temperature. Classified as Not Threatened, with healthy populations in most exposed rocky shore habitats of southern New Zealand.
Population
Not Threatened. Spongy kelp is common on exposed rocky shores in southern New Zealand, particularly in the South Island and Stewart Island. It often grows in the lower intertidal zone, where it is submerged for most of the tide.
Conservation Status
Not Threatened
The squishy one has fronds that are soft, inflated sacs, like small, golden-brown pillows or water balloons. They are filled with a gelatinous, jelly-like substance, not air. When you touch them, they feel soft and squishy, yielding to your fingers. They look like they might burst, but they are tougher than they seem. It is the alga of the soft touch, the one that gives when you press it. What makes it special is the texture. The spongy kelp is soft and gelatinous, unlike the tough, leathery fronds of other kelps. The jelly inside the sacs is a mixture of water and polysaccharides, which helps the plant retain moisture at low tide. It also makes the plant less appealing to grazing animals, snails and sea urchins prefer tougher, more substantial fare. It is the alga of the clever defence, the one that protects itself by being unappetising. The fronds are club-shaped or pear-shaped, tapering to a narrow stem. They are usually 5 to 15 centimetres long, pale golden-brown to olive-green. They grow in clusters, attached to the rock by a small, disc-like holdfast. Under a hand lens, the surface is smooth and shiny, with a gelatinous sheen. Biologically, the spongy kelp is a brown alga. It reproduces by releasing spores from specialised structures on its fronds. The spores are released into the water, carried by the currents, and settle on nearby rocks to grow into new plants. To find spongy kelp is to find a patch of soft, squishy pillows on the rock. They look like they might pop if you poke them, but they do not. They are soft, yielding, almost friendly. It is the squishy one, the gelatinous one, the one that looks like it might burst but never does, the one that proves that softness can be a form of strength.