The Intertidal Zone

Over the past few weeks, quite a number of the Dalton Koss HQ Marine Facts have referred to the intertidal zone. Many DKHQ readers have curiously responded with the questions:

  1. Where is the intertidal zone located?
  2. Exactly what is the intertidal zone?

At Dalton Koss HQ we are more than happy to answer these two questions.

The intertidal zone is located along our coastlines, specifically where the sea meets the land. This zone varies all across the globe. It can be made up of rocky shores with many fun rockpools, mudflats or sandflats, mangroves, salt marsh and seagrass beds, sandy beaches and coral reefs. The intertidal zone can be exposed to the rough and tumble of open oceans or located in sheltered places such as bays and inlets. Some scientists refer to the intertidal zone as the littoral zone.

An exposed intertidal rocky shore at low tide along Victoria's Great Ocean Road. Notice the prolific range of seaweeds adorning the rocks.
An exposed intertidal rocky shore at low tide along Victoria’s Great Ocean Road. Notice the prolific range of seaweeds and mussels adorning the rocks.

At Dalton Koss HQ we often refer to the intertidal zone being in a liminal state. This is because the intertidal zone is either covered with ocean waters or exposed to the sun and air due to the constant movement of tides. It is never in one state of being within a 24 hour period; rather it is in continuous flux.

Being exposed to two completely different types of conditions means that as an animal or plant living in this zone, one needs to have some incredibly amazing adaptations to survive. Intertidal plants and animals need to be resilient to wave wash, tides and currents, sun exposure, predators and drying out all while trying to photosynthesise/eat and reproduce.

An exposed intertidal sandy flat located along Cape Conran Coastal Park in eastern Victoria, Australia.
An exposed intertidal sandy flat located along Cape Conran Coastal Park in eastern Victoria, Australia.

This makes the intertidal zone a fascinating area to explore and discover the spectacular range of marine animals and plants. To conserve this amazing zone while you explore, please be careful where you tread/snorkel, place rocks back to their original positions when you examine what is beneath and keep all rockpool animals and plants fully immersed in water to reduce their stress.

An intertidal coral reef exposed at low tide located in Fiji's Coral Coast.
An intertidal coral reef exposed at low tide located in Fiji’s Coral Coast.
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Chitons

Visitors to coastal shores often come across unusual looking animals hidden in rock crevices. Here at Dalton Koss HQ we strive to help make sense of these unusual sea creatures by sharing our marine knowledge.

Chitons are one of these more unusual finds that many coastal visitors find on the rocky shoreline. With the Ch pronounced as a k sound, chitons have a fossilised appearance due to their numerous armoured plates. In fact, some people call Chitons the armadillos of the ocean as they are able to curl up into a ball using their armoured plates as protection.

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The armoured plates grow from the head to the foot of their body providing protection and camouflage from predators, hence why this animal is also commonly known as the coat-of-mail. The actual animal grows and lives under these armoured plates and its body is not segmented like its armour.

Here are a few interesting facts about chitons:

1. Chitons can only be found in the intertidal and upper subtidal zone of rocky shores.

2. The majority of chitons are vegetarian, grazing and eating seaweeds using their radula (see earlier What creates those circular holes on seashells? DKHQ Marine Fact to find out more about radulas).

3. Chitons can live from 1-20 years or more.

4. All chitons have a girdle around their body and plates.

5. Chitons prefer to move around during dusk and at night to reduce their chances of being prey to birds and other larger animals.

6. Sexual reproduction is often associated with a particular phase of the moon or with a tide, in some instances both.

The most fascinating and favourite Dalton Koss HQ Chiton fact is their homing ability. Chitons are able to have a night out crawling around rocks and feeding, but they are able to return to exactly the same spot before the sun comes up. Just amazing for a creature that has no eyes!

SEA SPIDERS

At Dalton Koss HQ we can already hear the arachnophobes fearfully exclaiming, “Sea Spiders! Will they bite me if I go for a swim? Are they poisonous?”

The answer to both questions is no. Sea Spiders are not interested in devouring humans.

Sea Spiders are scientifically known as pycnogonids. You can see in the image below, that sea spiders are not as chunky looking as their land dwelling cousins and are quite small in size (the Sea Spider in this image was no bigger than a $1 Australian coin).

This sea spider's scientific name is Pseudopallene ambigua and was found moving around a subtidal rocky reef inside Port Phillip Heads Marine National Parks, Victoria, Australia.
This sea spider’s scientific name is Pseudopallene ambigua and was found moving around a subtidal rocky reef inside Port Phillip Heads Marine National Parks, Victoria, Australia. The arrows point to several interesting body features.

This is because Sea Spiders have developed a number of really interesting body features over a long period of time. Here are just a few interesting feature facts:

Fact 1: The abdomen of the sea spider is very small and located towards the back of the body, while some of the gut is located in its legs. Their waste products are released directly into the seawater via a diffusion process across their cell walls.

Fact 2: Sea spiders use the same cell wall diffusion process to obtain oxygen, i.e. they have no lungs or respiratory system to breathe oxygen like many other animals.

Fact 3: Due to their very small body size, the sea spider’s reproductive system is found in their legs.

Fact 4: Female sea spiders deposit their fertilised eggs, which are then picked up and looked after by the male sea spider.

Fact 5: Most sea spider legs end in very small claws.

Fact 6: At each growth stage, starting from the larval phase, the sea spider develops a new set of legs until it reaches adulthood.

Fact 7. Sea spiders have a proboscis (think of it as their mouth and tongue rolled into one) so that they can suck out the fluids of animals they eat, for example, anemones, hydroids and bryozoans, but NOT humans.

Fact 8: Sea Spiders live in cool and warm water oceans at all depths.

How can I spot a Sea Spider?

Dalton Koss HQ’s tip for spotting a sea spider is to use a snorkel and mask and slowly drift over rocky reefs at high tide (for safety, always snorkel with a buddy). Sea Spiders are quite small so you need to look closely between seaweed tufts, anemones and other hydroids that grow on the rock.

Slugs in the nud’

At Dalton Koss HQ we come up with some creative names to describe some of the more interesting creatures that can be found in our marine front yards.

Slugs in the nud’  are nudibranchs. Nudi what? Nudibranchs.

Nudibranchs are oceanic snails, do not possess a shell and are mostly brightly coloured.

To break it down, Nudi = nude and branchs = gills. As these snails do not have shells for protection, their gills are nude and exposed (see image below).

Without a shell covering, the nudibranch's gills can be found on the top part of its body and exposed to the water.
Without a shell covering, the nudibranch’s gills can be found on the top part of its body and exposed to the water.

Nudibranch Facts

1. The bright colours of nudibranchs are used as defence mechanisms to avoid predators.

2. Many are able to camouflage with their surrounding environment, such as corals and sponges.

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3. Nudibranchs do not make a tasty meal. In fact, they are toxic and poisonous to eat. This is because nudibranchs feed on the stinging cells of sea jellies, anemones and corals.

4. Nudibranchs can be found at different depths in both warm and cool ocean waters.

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Although not in the same size category of many other sea creatures, they do create a level of excitement for DKHQ when spotted under water.

Seahorses & Seadragons

Amongst Dalton Koss HQ’s favourite animals and plants are the enigmatic seahorses and seadragons.

Are they real? Do they really exist?”, DKHQ is often asked.

 Yes, they are real and live in both tropical and cooler oceans across the globe.

Regarded by most as resembling half horse half fish, these gentle oceanic creatures spend their time slowly cruising amongst seagrass meadows, seaweed gardens and coral looking for small shrimp to eat.

Both seahorses and seadragons belong to the bony fish family, Syngnathidae, which also includes pipefish and pipehorses (a DKHQ marine fact for another day) .

Seahorses tend to have an upright vertical position while stationary or moving,  while seadragons tend to have a horizontal stationary and moving position. Although seahorses and seadragons look different, they are closely related.

There are some AMAZING facts about seahorses and seadragons.

FACT 1: The seahorse and the seadragon are the only animals in the world where the male gives birth to the babies. Yes, you read correctly! The only animals in the world where the male gives birth. Female seahorses deposit their eggs into the male seahorse pouch where they are then fertilised. The male seahorse will carry the growing babies in the pouch until they are born, which is why some male seahorses look like they have a very big belly. This reproduction approach is very similar for seadragons, however,  the male seadragon will carry the babies in pouches that are attached to their tail rather than in their belly.

FACT 2: Seadragons can only be found in the cooler waters across southern Australia and no where else in the world. The Weedy seadragon is Victoria’s marine state emblem, while the Leafy seadragon is South Australia’s marine state emblem.

FACT 3: If you have an opportunity to dive amongst the tropical reefs of South East Asia, keep your eye out for the pygmy seahorse. No bigger than an average sized thumb, pygmy seahorses will only live on specific types of coral.

A pygmy seahorse attached to coral in the beautiful reefs of Malaysia. Image by Dr Elizabeth Strain.
Spot the pygmy seahorse attached to coral located in the beautiful reefs of Malaysia. Image by Dr Elizabeth Strain.

The next time you are snorkelling or diving amongst seaweed gardens, seagrass meadows or coral reefs, keep your eyes open for a beautiful seahorse or seadragon.

OUR GRASSY OCEAN MEADOWS

“Grass that grows in seawater?”, Dalton Koss HQ is often asked. Yes, grass that can grow in and withstand seawater. But how?

Seagrass is similar to land-based grass, having leaves, veins and roots. The leaves grow from the base of the leave and reproduce with flowers and seeds. Many individual seagrass plants found growing together is termed a seagrass bed or seagrass meadow. Seagrass meadows can be found across the globe, usually in coastal areas close to shore where sunlight can penetrate the water column. Like all plants, seagrass needs sunlight to grow.

The different parts of the seagrass, Amphibolis antarctica, or commonly known as the sea nymph.
The different parts of the seagrass, Amphibolis antarctica, or commonly known as the sea nymph.

Although seagrass meadows may not look like much to the casual observer, they play an incredibly important role in supporting not only the health of our coasts and oceans, but also to humans. There are so many incredible facts about seagrass that DKHQ would like to share with you.

Did you know that seagrass meadows are nurseries for baby sea animals, providing shelter and protection from bigger animals and food to help them grow? Most of the fish we buy to eat would have spent some of their younger years living and growing in seagrass meadows before swimming to the oceans as adults.

An eleven arm seastar (Coscinasterias muricate) and small mussels (Electroma georgiana) living in swan grass (Zoestera muelleri).
An eleven arm seastar (Coscinasterias muricate) and small mussels (Electroma georgiana) living in swan grass (Zoestera muelleri).

Due to the amazing root network of seagrass, they are able trap and stabilise soft sediments, sand and other very small items floating in seawater. This means seagrass plays an important role in protecting our shorelines from erosion and helps improves seawater clarity.

In areas of seagrass meadows there are less toxic algal blooms. Seagrass is amazing at absorbing a whole lot of different nutrients, that often contribute to algal blooms, and using it as food to grow.

The seagrass plant is like a small cosmos to itself. It provides a solid surface for other small seaweeds, sponges and animals to grow.

A meadow of Southern strapped (Posidonia australis) in Corner Inlet Marine National Park, Victoria.
A meadow of Southern strapped (Posidonia australis) in Corner Inlet Marine National Park, Victoria.

Worried about high carbon levels in the atmosphere? Seagrass is able to absorb and store large quantities of carbon in their leaves and roots. Let’s protect seagrass so it can be a wonderful and natural way to address our high carbon lifestyles.

If you ever have an opportunity to snorkel in a grassy ocean meadow, do not pass it up! You might just be surprised with what you find.

A beautiful and vibrant red sponge growing in the Southern strapweed.
A beautiful and vibrant red sponge growing amongst the Southern strapweed.

Sea Anemones of the Southern Ocean

At DKHQ we are constantly asked whether some of the facts portrayed on Finding Nemo are true, specifically the much difficult to pronounce Sea Anemone. Pixar did a wonderful job raising the profile of tropical reefs, although to the detriment of Clown Fish who, if the facts are correct, were being flushed down toilets by young children wanting to release ‘Nemo’ back into the ocean.

This aside, the often asked sea anemone questions at DKHQ are: a. can sea anemones sting, and b. can their poison kill humans? The answer to a. is yes and to b. is no. This public fascination with sea anemones inspired today’s DKHQ Marine Fact, with a focus on southern sea anemones.

Unlike the large sea anemones of our tropical reefs systems found across the globe’s equator line, the sea anemones of the southern ocean are comparatively smaller but just as beautiful and colourful. Here are some interesting facts:

1. Southern sea anemones always occur as solitary individuals usually in intertidal and subtidal areas.

2. All sea anemones have one opening, function both as its mouth and anus (this fact usually elicits some funny facial and noise reactions). Sea anemones are carnivores, on other animals.

3. The sea anemone body is supported by water pressure, which means when not in water their body and tentacles become floppy.

4. The tentacles of all sea anemones radiate from the mouth in one or many rows and are hollow. These tentacles contain stinging cells known in marine science as nematocysts. Each nematocyst contains a pressurised coil that can be pushed out to capture prey or used as self defence. The sea anemone use the nematocysts to stun, and in some cases, kill the prey.

5. Nearly all southern ocean sea anemones grow attached to a rock or some other type of hard structure. The exception to this rule (and when it comes to Mother Nature, there is usually one exception to the rule) is the Swimming anemone known by its scientific name as Phlyctenactis tubercles. (See image below). The Swimming anemone can move through the current or crawl along hard structures.

The Swimming anemone, Phlyctenactis tuberculosa.
The Swimming anemone, Phlyctenactis tuberculosa.

So why can’t sea anemones sting us? Our skin is too thick to be penetrated by its stinging cells, unlike many sea creatures with very thin skin. In the case of Clown fish, they have adapted over a long time for their skin to not be affected by the stinging cells and use the sea anemone as a place of protection from enemies.

DKHQ hopes you enjoyed these sea anemone facts and will leave you to enjoy the beautiful colours of some of the southern ocean’s sea anemones.

This beautiful sea anemone is known as Phlyctenanthus australis and can be found along Australia's intertidal shoreline that is exposed to ocean waves.
This beautiful sea anemone is known as Phlyctenanthus australis and can be found along Australia’s intertidal shoreline that is exposed to ocean waves.
This gorgeous red sea anemone is known as the Waratah Anemone and it's scientific name Actinia tenebrosa. This lovely Waratah Anemone can be found along the intertidal shoreline, often looking like a red blob at low tide.
This gorgeous red sea anemone is known as the Waratah Anemone and it’s scientific name Actinia tenebrosa. This lovely Waratah Anemone can be found along the intertidal shoreline, often looking like a red blob at low tide.
This fun orange and white stripped sea anemone is known as Anthothoe alboctinia and can be found under rocks or underhangs along Australia's intertidal shoreline that is exposed to ocean waves.
This fun orange and white stripped sea anemone is known as Anthothoe alboctinia and can be found under rocks or underhangs along Australia’s southern intertidal shoreline that is exposed to ocean waves. There are two variations to this sea anemone, white and orange stripes and brown and green stripes.