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Home › Ocean Creatures › Marine Biology › Invertebrates › Sponges

Interesting Facts about Sea Sponges

[Sea Sponge Phylum: Porifera] [Class: Demospongiae] [Order: Verongiida] [Family: Spongiidae]

There are more than eight thousand (8,000) living sea sponges belonging to the phylum Porifera and they occupy a wide range of marine habitats throughout a broad global distribution.

This section contains a collection of sea sponge facts with detailed information about where they are found, what they eat, and how these fascinating marine invertebrate animals reproduce.

Where Do Marine Sponges Live in the Sea?

The global distribution of demosponges (e.g. the common sea sponge) ranges from the polar regions to the tropics.

You will find sponges living in areas where the oceans meet the land (intertidal zones) and even in some deep sea environments at depths greater than 8,000 metres.

Even so, the greatest diversity occurs around the coral reef formations in the warm waters of tropical and subtropical regions.

Around 240 freshwater sponges live in freshwater systems. Still, 98% of all sea sponge species inhabit some kind of marine ecosystem.

Most of the phylum Porifera thrives best in locations where natural conditions support their filter-feeding lifestyle, such as:

• A steady supply of clear, clean, flowing water that supplies them with food particles (e.g., bacteria, organic debris, and planktonic organisms).
• Solid substrates that adults can firmly attach themselves to, like reef structures, corallites (coral skeleton), rocks, and shells.
• Stable water temperatures and environmental conditions that create little (or no) sedimentation because it can clog their sensitive pores, such as overhangs or deep-water zones.

Facts about Sponges: Some marine sponges prefer to live in dark, shaded habitats. Whereas, others need light-exposed regions for harbouring photosynthetic symbionts, such as algae and cyanobacteria.

Sea Sponge Characteristics and Traits

A number of key biological features help to distinguish the ocean sponge from other marine animals. For example, there are no organs or true tissues.

Sponge sea creatures also lack a heart, a stomach, and they do not have any lungs. There is no nervous system, circulatory system, or excretory system.

With only a complex network of canals and chambers, these simple filter-feeding invertebrates rank among some of the most primitive of multicellular animals.

But wait - there's more:

The skeleton is made of spongin (calcium protein spicules) and the body is porous, hence the sea sponge scientific name Porifera (meaning 'pore-bearer'), but they're full of ostia (tiny incurrent pores).

Whereas, the internal canal system contains an osculum (large 'mouth-like' excurrent opening). This means water is able to flow continuously throughout their body and it also creates microhabitats for shrimps, brittle stars, and hydrozoans.

Marine Sponge Size and Colours

Different kinds of sponges create a wide variety of sizes, shapes, and colours that are often linked to their habitats and available water flow.

Typical morphologies are barrel shaped, encrusting, tubular, vase shaped, branching, and boring.

The most common colours of sponges are red, blue, yellow, brown, and grey. Others may have shades of green on their body, usually as a result of excessive algae growth.

The orange pipe sponge (genus Leucosolenia) is one of the smallest, measuring around three (3) centimetres tall.

However, the giant barrel sponges rank among the largest, with some specimens growing to two (2) metres in diameter.

Chemical Defences

One surprising fact about the sea sponge animal is their ability to generate 'bioactive compounds' that can deter predation from some species, such as fish and sea turtles, and even prevent organisms from settling on them.

Some species in the sea sponge classification are used in medical research, mainly for their invaluable sources of antibiotic drugs and cancer-restraining properties.

What Do Sea Sponges Eat?

Most of the sea sponge species are filter feeders with a diet based on the tiny particles that get carried to them by the water that surrounds them, such as:

• Bacteria
• Dissolved organic matter (e.g., dissolved carbon, nitrogen compounds)
• Fecal pellets
• Phytoplankton (including microalgae)
• Tiny organic debris (detritus)
• Zooplankton

In addition, nutrients created from photosynthesis can supply close to 80% of a sponge's energy requirements in some species.

Types of Sea Sponges

How Do Sea Sponges Reproduce?

Marine sponge reproduction occurs through two modes, asexual and sexual. Asexual reproduction methods refer to the way sponges are able to grow, repair themselves, and colonise new areas.

The process starts with 'budding' where a small 'bud' forms and begins to grow on the parent sponge. Eventually, it will break off and develop into a completely new sponge.

Fragmentation is another method where a part breaks off (maybe due to storms or predators) and attaches itself somewhere else to grow into a full sponge.

Here's the thing:

In freshwater sponges, internal buds known as gemmules are special survival pods made of tough cells. They are usually produced as a result of stress (e.g., severe cold, pollution).

During this kind of extreme duress, the gemmules can remain dormant for months. But they are able to hatch into new sponges when the conditions improve.

Sexual Reproduction in Sponges

The majority of sea sponge species are hermaphrodites that use sexual reproductive strategies at least part of the year. Each individual is able to produce sperm and eggs, albeit at different times to avoid self-fertilisation.

They expel sperm through the osculum into the water column (a method known as "broadcast spawning") so that the water currents will carry them to mix with other sponges.

When a neighbouring sea sponge draws in the sperm through their filtering current, the eggs will remain inside the body. Thus, fertilisation will occur internally.

As each tiny planula larva is released into the open water currents, it may be free-swimming for several days until it finds a suitable habitat to settle and transform into a juvenile sponge.

Sponge Facts: The sea sponge phylum Porifera doesn't have typical reproductive organs (gonads). Instead, they use regular cells to produce the gametes used in reproduction.

Sea Sponge Predators and Threats

In spite of some strong defence mechanisms that help them survive, sea sponges face multiple natural predators and some modern human-driven threats as well. Natural predation in ocean sponges is most common from:

• Angelfish (Pomacanthidae) (especially queen angelfish, French angelfish, and gray angelfish)
• Butterflyfish (Chaetodontidae)
• Filefish (Monacanthidae)
• Hawksbill sea turtle (Eretmochelys imbricata)
• Nudibranchs (sea slugs)
• Parrotfish (less common)
• Sea stars (especially Echinaster)

Some of the environmental threats that are also threatening the long term survival of some species of sponges in vulnerable locations, include:

• Destruction of their natural habitat (mostly due to dredging, coastal development, and trawling)
• Plastics pollution (including chemicals, heavy metals, and sewage)
• Ocean acidification (climate change and warming seas weaken bivalve shells due to a reduction in the availability of calcium carbonate)

Important: The IUCN Red List of Threatened Species does not see any specific risk for the general population of marine sponges (classification Demospongiae).

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