Life savers, sea-sentinels and shapeshifting carnivores – Sea sponges

Sea sponges are almost description-defying. Spongy? Some are, but others are rock hard. But definitely filter-feeders? Mostly, but a few have evolved to be carnivorous and lucky for us, New Zealand is thought to be a global hotspot. OK, but it’s widely accepted that they are simple organisms, right? On one level, yes. But, on another, incredibly complex with cells that can change from one type to any other and possessing a treasure trove of compounds that have helped us develop life-saving drugs. It’s almost easier to say what they are not, rather than what they are – but let’s have a go anyway. Even better, we’ll guide you on where to find them in the Hauraki Gulf Marine Park/Ko te Pātaka kai o Tīkapa using NIWA’s Splendid Sponges e-guides.

Sponges are the most common marine invertebrates around New Zealand’s coastline. Some could be mistaken for colourful splashes of paint on rocks, while others have incredible structures more reminiscent of lace, seaweed, or fungi.

Sponges are found everywhere. From intertidal rock pools to subtidal rocky reefs; silty harbours to continental shelf seamounts; volcanic ridges and hydrothermal vents, to the south’s deep abyssal plains. Amazingly, some even live in freshwater, including our own endemic freshwater sponge called Heterorotula kakahuensis.

The majority of sponges are filter-feeders – they feed by straining food particles from water – like baleen whales and shellfish. But how is that achieved without a mouth? The name of their phylum, Porifera, provides the clue – ‘pore-bearer’. Essentially, cells called choanocytes, found within internal chambers connected to pores on the surface of the sponge, bear whip-like hairs that draw water in through the external pores (ostia). These cells capture the food and essentially ‘pass the parcel’ to other cells that deal with digestion, secretion, excretion, reproduction and defence. Meanwhile, the water continues on its way, being pumped through the choanocyte chamber and out through large exhalent holes called oscules.

Sponges perform an important role in the sea as environmental sentinels. If sedimentation is too high, or water too polluted, they disappear. Some also hold climate change information in their annular growth rings.

On learning how to identify sponges in NIWA’s guide, you learn that the surface of the sponge can be smooth, spiky, bumpy or hairy, while its texture may be fragile, crumbly, elastic, fleshy, stony, or even woody. Furthermore, its colour may be highly variable.

So, what gives sponges such varying shapes, textures and colours? Essentially, the singular or combined use (or lack) of two building materials they can manufacture: spongin and spicules. Spongin is a type of collagen that is used by the sponge to create a skeleton of fibre and is what gives some sponges that bounce-back elasticity (think bath sea sponges). Some sponges even use surrounding sand granules to give their spongin ‘skeleton’ more grit. But usually, sponges use spicules for stiffness and solidity.

Spicules are tiny inorganic mineral elements made of either silica or calcium carbonate. Under the microscope, spicules come in a mind-blowing array of shapes such as claws, hearts, dumbbells or even toothbrushes. Remember those carnivorous sponges? One found in the Kermadec Volcanic Arc has spicules the shape of a great white shark jaw! These spicules, found on its surface, helps the sponge snag the bristly exoskeletons of small crustaceans. Like something from a sci-fi movie, cells then migrate from around the sponge’s body and cluster over the trapped creature, slowly ingesting the prey.

Other sponges have no skeleton to speak of, instead using collagen to maintain their form.

Because sponges do not move around, they have evolved to produce chemicals to defend themselves from other organisms that want to eat or settle on them. The great news for humans is that many of these chemicals have potent anticancer, anti-inflammatory, antibacterial, antidepressant, antifouling and pesticide activity. For example, two drugs (the first anti-leukemia drug and breakthrough HIV-AIDS drug AZT) were developed from chemicals found in the Caribbean sponge Tectitethya crypta.

So, where can you easily find sponges in the Hauraki Gulf Marine Park? One look at iNaturalist reveals that they are everywhere along the Gulf’s coastline, from rockpools to intertidal platforms, and rocky, muddy and boulder-strewn shores. Even more are found under the water if you like to snorkel or dive. Let’s pick off a few.

Orange golf balls with polygon-shaped warts

Found on the shadowy overhangs in the intertidal zone of all types of the Gulf’s coastline and harbour environments is the bright orange Tethya burtoni, known colloquially as the orange golf ball sponge. As its name suggests, it is a spherical sponge up to 6 cm in diameter, with a surface that is irregularly bumpy with polygon-shaped warts. Its texture is inflated and soft, which can change to corky and rough when contracted. If you find a pink golf ball sponge, you’ve found Tethya bergquistae.

The velvety stalagmites of the shore

You’ll only see the 6 cm high yellow turrets or ‘fistules’ of the candle sponge, Ciocalypta cf. penicillus, as its lumpy base is usually buried under sand at the base of crevices on rocky reefs and channels. The straight or slightly twisted turrets are longitudinally grooved. The texture of the base is firm and slightly compressible, while the fistules are velvety to the touch, but also stiff and easily broken. A similar sponge, Ciocalypta polymastia, is found in the muddy sandy areas of our harbours and sheltered bays. Its yellow turrets are smaller, 1-3 cm high, with a texture that is fleshy, firm and compressible, and a surface that is smooth, felty and grooved.

Just add water: From spiky to smooth

A sponge that frequents iNaturalist is Aaptos tenta, a dull pinkish brown sponge found on the rock platforms of sheltered coasts and harbours of the Gulf. Its shape is irregularly globular, and it is typically up to 8 cm in diameter and 6 cm high. When submerged its surface is smooth with rounded bumps which become spiky when exposed, behaving a bit like a puffer fish. Wiggle it side-to-side and you’ll find that it is slightly elastic, with a surface that is fleshy and slightly granular to the touch. And surprise, while dull on the outside, internally it is mustard-coloured! You might find it with large buds attached to it – these are asexually-produced baby sponges that remain attached to the parent before expanding into adults.

Multi-coloured splashes of paint

Encrusting boulders and rock ledges or found between cracks or around the edges of pools, you can find encrusting sponges. Hymeniacidon cf. perlevis is a yellowish sponge that can look different depending on where you find it. In exposed intertidal locations the sponge may be spreading and smooth, while in more sheltered locations the sponge thickens with pimple-like projections. Search for tubeworms in rockpools, and you’re likely to find this lovely sponge as well.

On the darker side is Tetrapocillon novaezealandiae, an olive green to black sponge that is ‘dirty gold’ on the inside. This sponge is velvety to the touch with moderately densely scattered oscules throughout. When handled, this sponge emits a dark-olive fluid. On the lighter side is Haliclona brøndstedi, a fawn-coloured sponge studded with a large number of oscules. To the touch it is generally smooth and slightly fuzzy from projecting spicules, with a soft, crumbly texture.

On the lighter side is Haliclona brøndstedi, a fawn-coloured sponge studded with many oscules. To the touch it is generally smooth and slightly fuzzy from projecting spicules, with a soft, crumbly texture.

The crockery of the sea: flasks, cups, bowls and plate-shaped sponges

Deeper in the sea, sponges take on more complex forms. If you like to snorkel or dive in the Gulf you might find the white flask sponge, Leucettusa lancifera. Just 2–3 cm in diameter, these bulbous sponges have a smooth creamy-coloured surface with a flared opening at their tip. They have no elasticity to speak of and are easily crushed.

If you find a massive bright orange sponge about 30 cm diameter and up to 20 cm high, shaped like a shallow bowl or a tall thick cup, you’ve actually found two sponges: Stelletta crater, which is the main bulk of the sponge, and is actually white, and the encrusting sponge, Desmacella dendyi, which gives it its orange colour.

These are just a few of the stunning sponges you can find in the Hauraki Gulf Marine Park. To see more, check out NIWA’s Splendid Sponges e-guides – grouped into general and intertidal.

Love it, Restore it, Protect it