Octocorals

The title of this week’s DKHQ Marine Fact sounds like a sci-fi animal; the visual being half coral, half octopus. Although not a sci-fi creature, this animal is a coral.

When I use the word coral in conversation it often elicits responses such as, “Oh, you mean the coral in the Great Barrier Reef?” Yes, the Great Barrier Reef does have a diversity of beautiful corals, but you don’t have to travel to the tropics to see corals. The corals I am discussing today are found in the cooler temperate waters of Southern Australia. You may need to put on a thicker wetsuit to view them, but they are just as beautiful and colourful as their tropical cousins.

Here are some incredibly interesting facts about octocorals:

Fact 1: The ‘octo’ in octocoral represents the eight feathery tentacles found on each polyp that form the coral. The feathery tentacles are attached to the stomach.

Octocorals are beautifully colourful.
Octocorals are beautifully colourful.

Fact 2: Octocorals are filter feeders, meaning they eat microscopic organisms floating in the water column. The feathery tentacles, as described above, act like fingers swaying in the water current, capturing organisms such as plankton (microscopic animals) and phytoplankton (microscopic algae). Each tentacle is hollow, allowing the organisms to travel from the feathery tips down to the stomach.

Fact 3: Octocorals form colonies that are attached to the seabed or other hard structures such as large rocks.

Fact 4: To see octocorals you will need to SCUBA as they prefer to live at depths between 4-50m.

Fact 5: Octocorals are in the scientific Order Alcyonacea and consist of soft corals, gorgonians and sea whips.

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Cuttlefish

Most people associate cuttlefish with domesticated budgies (the bird, not the male swimsuit). This is because budgies are given cuttlebone, a long ovulated white structure, to sharpen their beaks. This beautiful cuttlebone is an important feature of the cuttlefish; it controls their buoyancy while swimming in the ocean at various depths.

Cuttlefish can be found across the globe. They belong to a group of animals termed cephalopods, which also includes the octopus, squid, chambered nautilus and argonauts. Scientifically, cuttlefish belong to the Class Cephalopoda in the Phylum Mollusca. This means cuttlefish are invertebrates and have no backbone.

Cephalopods are considered amongst scientists to be the most intelligent out of all invertebrates; they learn quickly, are able to solve problems, communicate via complex visual communication and can quickly adapt to their local environment. Like chameleons on land, cuttlefish are experts at adapting to the colour and patterns of the environment around them.

Cuttlefish, as well as the octopus, contain special organs in their skin termed chromatophores which are little elastic bags filled with colour pigment. By expanding and contracting, chromatophores display a particular colour. They can be turned on and off which allows the cuttlefish to create a particular set of colours and patterns with its skin. Additionally, skin flaps, termed papillae, can be pushed or shaped to mimic their surroundings, for example, seaweed or coral. These colour and pattern changes are used for: mating and courting rituals, mate-guarding and camouflage to hide from predators.

Here are some more fascinating facts about cuttlefish:

Fact 1: Cuttlefish have very well developed eyes and acute vision. They are colour blind but respond to differences in light intensity rather than differences in wave length (which vertebrates, like humans, use to determine colour).

Fact 2: Cuttlefish are carnivores, that is, they eat meat. They are active nighttime predators feeding on fish, crustaceans, shellfish and worms.

Fact 3:  During mating, the male passes packets of sperm to the female using its modified arm termed the hectocotylus. The females can immediately fertilise their eggs or are able to store the sperm in special receptacles inside their body for periods of time until they want to fertilise their eggs.

Fact 4:  Females attach the fertilised eggs to the seafloor either on or under hard surfaces such as rocks. Young cuttlefish develop with no parental assistance and many hatchings are carried around in surface ocean currents over long distances.

Fact 5:  Cuttlefish have 8 arms and 2 feeding tentacles. All arms have suckers along the length of the arm except for the feeding tentacles which have suckers only on the tip, termed clubs. The feeding tentacles can be pulled back into the mouth.

The Giant cuttle, Sepia apama, is found in southern temperate Australia extending from Western Australia to New South Wales. This species of cuttlefish can be identified by the three flat skin folds behind the eye and adults are often very curious.
The Giant cuttle, Sepia apama, is found in southern temperate Australia extending from Western Australia to New South Wales. This species of cuttlefish can be identified by the three flat skin folds behind the eye and adults are often very curious.

Fact 6: A cuttlefish’s mouth contains a hard beak, similar to a parrot’s beak. The beak is used to kill and paralyse the prey by injecting a poisonous saliva. The beak also breaks the prey into pieces and then it is further broken down with a row of very small sharp teeth.

Fact 7: When scared or irritated, cuttlefish squirt ink into the water column which can be shaped to be the same size as its body. This ink sac sits inside the body near the anus. Cuttlefish are also able to bury themselves under sand, with only the eyes remaining visible, when they want to hide.

Fact 8: Cuttlefish use their funnel and fins to swim. The fins extend out from its mantle (the back part of its body) enabling rapid or slow propulsion.

Many larger marine animals such as seals, whales and large fish eat cuttlefish, however, they are rarely caught in fisher nets. Perhaps this is indicative of their intelligence and being able to problem solve in difficult situations?

Seaweeds

Seaweeds are the plants of our oceans. Similar to land plants, seaweeds play an important role in absorbing large amounts of carbon dioxide and turning it into oxygen we all need in order to live.

Most of us view seaweed as that smelly stuff that washes up on the shore, frequently thrown around by rowdy kids and teenagers. A storm or human extractive activities are the root cause for seaweeds to be washed up on the shore. When washed up, seaweeds are dead and decomposing which is why you crinkle your nose to that funny smell.

Dalton Koss HQ Partner, Rebecca Koss, doing underwater monitoring and surrounded by the brown seaweed Cystophora subfarcinata.
Dalton Koss HQ Partner, Rebecca Koss, doing underwater monitoring and surrounded by the brown seaweed Cystophora subfarcinata.

Seaweeds are beautiful and come in a range of colours, shapes and sizes. They provide homes and protection for many ocean animals. Some seaweeds provide food for animals and are the basis for many food webs. Even humans harvest seaweed for food and other products. Here are some more interesting facts about seaweeds.

Fact 1: Seaweeds are plants, scientifically termed macro(large) algae. They are simple plants without roots, stems, leaves or flowers.

Fact 2: Seaweeds grow on the intertidal shore and in subtidal areas. Like land-based plants, seaweeds harvest sunlight for photosynthesis and will only grow at depths where sunlight can penetrate the water column.

Fact 3: There are three major seaweed groups and they are based on their colour: red seaweeds (Rhodophyta), brown seaweeds (Phaeophyta) and green seaweeds (Chlorophyta).

Fact 4: There is a fourth group of seaweed that is often contested to being a true seaweed amongst marine algae biologists (scientists who study seaweeds). This is the blue-green algae (Cyanophyta).

Fact 5: Some seaweeds are very small and grow on other seaweeds when environmental conditions are opportune. These seaweeds are known as epiphytes.

Fact 6: Some seaweeds have long fronds and can grow up to 10 meters in height creating underwater forests, for example, the large brown kelp Macrocystis angustifolia that grows in southern Australia. Other seaweeds are small, encrust hard structures and often look like lichen.

Red seaweed encrusting a snail's shell.
In the above picture, there are different growth formations of red seaweed. One growth form encrusts the snail’s shell (middle of the photo) while another growth form has fronds (top of the picture).

Fact 7: Seaweeds attach themselves to solid structures such as rock and wood pylons using their holdfasts. Holdfasts are like a whole bunch of fingers tightly gripping onto a solid item. However, seaweeds  are smart and go one step further. Holdfasts secrete a chemical that is similar to superglue to ensure the seaweed is permanently stuck to that structure. This allows the seaweed to withstand strong currents, tides, swells and stormy conditions. This super glue like chemical is being researched by chemists as a natural product to be used in human products, e.g. glues that can be used for building houses.

Fact 8: Some seaweeds are harvested globally as food, medicine and as a product for other applications such as toothpaste, ice-cream, soil fertiliser and shampoo.

Fact 9: Port Phillip Bay located in Victoria, Australia has over 200 different types of seaweeds and is one of the most diverse seaweed locations in the world.

While seaweeds might be pretty stinky while decomposing on the shoreline, without them our oceans would be pretty dull and devoid of life.

The brown seaweed Hormosira banksii growing on the rocky intertidal shore.
The brown seaweed Hormosira banksii growing on the rocky intertidal shore.

What the devil……?

Every venture into our amazing marine world provides me with an opportunity to learn something new and to interact one-on-one with some wonderful creatures.

During one dive in Port Phillip Bay, located in Victoria, Australia, the Southern Blue Devil’s iridescent blue colours immediately caught my eye.  Scientifically known as Paraplesiops meleagris, this beautiful fish is endemic to southern Australia. The Southern Blue Devil can only be found in the beautiful waters between Perth in Western Australia to Port Phillip Bay in Victoria to a depth of up to 45m.

The Southern Blue Devil loves to live under ledges and in crevices and caves. They are fiercely protective of their territory, especially during breeding season. My first encounter with the Southern Blue Devil was during breeding season. The male of this species can be a little aggressive if you get too close to their territory, especially if you have any blue colours on your SCUBA kit or wetsuit. My SCUBA mask at the time was made of clear perspex and rubber lined with bright blue rims around the eyes. Thinking I was a competitor for it’s territory, this male Southern Blue Devil told my SCUBA mask in no uncertain terms that it wasn’t welcome.

Southern Blue Devil 1: Dalton Koss HQ SCUBA mask 0.

The Southern Blue Devil on the defensive mode due to my blue rimmed SCUBA mask coming across as a potential competitor.
The Southern Blue Devil on the defensive due to my blue rimmed SCUBA mask appearing to be a potential competitor.

Although quite a visually funny story, here are some other interesting facts about the Southern Blue Devil.

Fact 1. Similar to human finger prints, adult Southern Blue Devils can be individually identified and monitored due to their unique pattern of markings on the lower part of their gill cover.

Fact 2: Adult pairs will stay together during the breeding season, protecting their eggs that are usually laid on rock surfaces in narrow crevices.

Fact 3: The Southern Blue Devil is protected by law across Australia as they are endemic, that is, they are not found anywhere else in the world.

Fact 4: Known to be curious, the Southern Blue Devil will usually interact with SCUBA divers even during non-breeding season.

Fact 5: The Southern Blue Devil loves to eat small crustaceans, snails, worms and sometimes other small fishes.

If you ever have an opportunity to SCUBA across Australia’s southern oceans, look out for the Southern Blue Devil. In fact, it will probably find you first.

The Southern Blue Devil loves living in and around crevices, ledges and caves.
The Southern Blue Devil loves living in and around crevices, ledges and caves.

Estuaries

Taking inspiration from my paper that was published this week, this week’s Dalton Koss HQ Marine Fact takes a look at estuaries.

Estuaries are fascinating systems that are often forgotten natural spaces. This is because they are neither freshwater nor seawater, rather they are a mix of the two. One of Dalton Koss HQ’s favourite sayings is to be in a liminal state meaning that the subject is never in one state of being. This is true for estuaries where saltwater from the open sea mixes with freshwater that flows down from uprivers and streams. As the chemical makeup of saltwater is more dense compared to freshwater, the saltwater will sit under the freshwater layer. This saltwater layer usually decreases in depth as you move up the estuary away from the ocean. Additionally, sediments from both land and ocean meet and mix in the estuary.

Hawkesbury Estuary, New South Wales, Australia.
Hawkesbury Estuary, New South Wales, Australia.

Due to this unique combination of water and sediments, estuaries are incredibly naturally productive places that provide protection from the rough seas. Fish use estuaries for migrating and reproduction, birds feed and nest on the side of estuaries and there is even documented evidence that suggests larger mammals such as whales and larger fish species such as sharks use estuaries as reproductive areas.

As estuaries are directly linked with the ocean they are often influenced by tides. Some estuaries are devoid of water at low tide making it very easy to walk across from one side to the other. Estuaries provide humans with a number of services that contribute to our health and wellbeing. In the field of environmental economics this is called ecosystem services as the natural system (ecosystem) is providing us (humans) some type of service that contributes to our health and wellbeing. Here are some examples of estuary ecosystem services:

1. Humans take out fish and shellfish from estuaries as food to eat.

2. Many of the mangroves, coastal shrub and salt marsh that grow along estuary shores remove pollutants from the air providing us cleaner air to breathe. These same plants can trap sediments amongst their roots which decreases erosion and soil run off into the water. This in turn provides stability to houses and human made infrastructure built along the estuary.

3. For those who visit or live along an estuary, looking and experiencing beautiful natural landscapes can create feelings of relaxation, pleasure, peace and enjoyment.

4. Estuaries contribute to the traditions and cultures of Indigenous peoples across the globe.

Within Australia, there are over 1000 estuaries of different forms and types. In fact, over 60% of Australia’s population live along estuaries, for example, Melbourne and Port Phillip Bay, Hobart and the Derwent River Estuary and Fremantle and the Swan River Estuary.  Globally, there are thousands more. As human populations continue to grow, greater pressure will be placed on our estuaries. How to balance population growth, city planning and impacts on our natural environment needs in depth consideration by governments and citizens across the globe.

Whale Rock, Tidal River Estuary, Wilsons Promontory National Park, Victoria, Australia.
Whale Rock, Tidal River Estuary, Wilsons Promontory National Park, Victoria, Australia.

SEA CUCUMBERS

Very different to cucumbers that we eat in our salads, sea cucumbers are animals that live in our oceans. They look like a cucumber due to their shape and appearance (see pictures above and below), even if they are not always green in colour. Sea cucumbers have an incredibly important role in maintaining a healthy ocean.

Dalton Koss HQ often hear marine scientists refer to sea cucumbers as being the worms of our oceans. Sea cucumbers clean and fertilise the sand like worms clean and enrich our soils. When a sea cucumber eats sand from the ocean floor, it moves through its gut where it takes out very small pieces of food. Everything else, for example the sand, is excreted. This excreted sand is clean and contains healthy bacteria.

Sea cucumbers go about their business eating and cleaning the ocean's floor. Quite often the body of a  sea cucumber is covered with sand allowing it to camouflage with the ocean floor. This image was taken along the Coral Coast, Fiji.
Sea cucumbers go about their business eating and cleaning the ocean’s floor. Quite often the body of a sea cucumber is covered with sand allowing it to camouflage with the ocean floor. This image was taken along the Coral Coast, Fiji.

Apart from the amazing role sea cucumbers play in keeping our oceans clean, here are some other INCREDIBLE facts about these animals.

FACT 1: Sea cucumbers are soft to touch because their spiny skeleton has been reduced and absorbed into its leathery flesh.

The exoskeleton of this sea cucumber can be found within its soft leathery body wall. When handling sea cucumbers it is important to hold them gently underwater to minimise stress to the animal. Do not squeeze or pull them.
The exoskeleton of this sea cucumber can be found within its soft leathery body wall. When handling sea cucumbers it is important to hold them gently underwater to minimise stress to the animal. Do not squeeze or pull them.

FACT 2: Sea cucumbers are also called holothurians. This is because they are scientifically classified as Holothuroidea. In fact, the Class Holothuroidea belongs within the Phylum Echinodermata, which means the sea cucumbers are close relatives to sea stars, sea urchins, feather stars and brittle stars.

FACT 3: Sea cucumbers can be found in tropical and temperate oceans across the globe. They prefer to live in the subtidal zone so they are not exposed to the sun and air at low tide.

FACT 4: Sea cucumbers have two openings; a mouth at one end and an anus at the other.

FACT 5: A sea cucumber’s mouth is very different to other animals. The mouth is surrounded by tentacles. Each tentacle is made up of little tube feet that move sand up to the mouth opening, similar in function to a conveyer belt. Some sea cucumbers use their tentacles to filter feed, meaning they catch plankton and other particles drifting in the water column.

Although this sea cucumber is bent in a funny position, it is clearly displaying its anus, mouth opening and tentacles. This image was taken at low tide along the Coral Coast, Fiji.
Although this sea cucumber is bent in a funny position, it is clearly displaying its anus, mouth opening and tentacles. This image was taken at low tide along the Coral Coast, Fiji.

FACT 6: The respiratory system, that allows the sea cucumber to breathe, is located in its gut towards the back part of its body.

Dalton Koss HQ’s most favourite sea cucumber fact is their ability to throw out their respiratory system through their anus as a defence mechanism when they think they are being attacked. By throwing out their internal organs it distracts the predator into thinking the sea cucumber is dead. What is more amazing is that the sea cucumber can then regrow its respiratory system and continue to live.

As an animal that comes across as simple and unobtrusive, the sea cucumber plays an important role in maintaining beautiful oceans for us to enjoy.

The simple and unobtrusive sea cucumber going about its business of cleaning the ocean floor.
The simple and unobtrusive sea cucumber going about its business of cleaning the ocean floor.

SEA SQUIRTS

Visits to the coastline are often filled with feelings of enjoyment, relaxation and excitement through discovery and exploration. At Dalton Koss HQ we often see young children and teenagers having fun exploring the beach, especially when they find sea squirts exposed at low tide. The name giveaway here is the squirt of seawater that comes out of this animal when lightly squeezed.

Sea squirts live on the lower areas of intertidal zone (see this link), from rock platforms to human made structures such as groynes and seawalls.

Sea squirts attached to a pylon and sea wall on Hampton Beach, Victoria, Australia. Notice that each individual sea squirt has two siphons for intake and outtake of water and gases.
Sea squirts attached to a pylon and sea wall on Hampton Beach, Victoria, Australia. Notice that each individual sea squirt has two siphons for intake and outtake of water and gases.

Aside from the amusement they provide when squeezed, here are some interesting facts about sea squirts:

FACT 1: Sea squirts, in the adult form, are individual animals that permanently attach themselves to hard structures, such as rock platforms, groynes and sea walls.

FACT 2: Sea squirts are filter feeders meaning they filter their food and oxygen out of the water column. To do this sea squirts have two siphons, one for bringing in the water and one for getting rid of the water. The walls of the siphons are lined with cilia (think of cilia as microscopic arms that wave and move together) that grab plankton and absorb oxygen as the water passes through the intake siphons. Any unwanted matter and carbon dioxide is released from the outtake siphon

FACT 3: Sea squirts along Australia’s southern shoreline have a brown outer colour and a beautiful orange/red inner colour. This brown outer colour allows them to blend in with the seaweeds and hard structures they are attached to.

FACT 4: At low tide sea squirts close their siphons so water cannot escape while providing protection against predators and the elements (e.g. sun and air).

FACT 5: Sea squirts are also referred to as cunjevoi or ascidians (as they belong in the scientific class Ascidiacea).

FACT 6: Sea squirts are mostly hermaphrodites meaning they possess both male and female reproduction organs.

FACT 7: The larvae of sea squirts look like small tadpoles that can swim around in the water. They only stay in this form for a few hours before settling on a hard surface, which signals the start of its transformation into the adult form.

Perhaps one of the most interesting facts about sea squirts is their evolutionary link between animals without a backbone (think sea stars, sea jellies, sea snails) to animals with a backbone (such as fish, birds, humans). In the larval stage sea squirts have a notochord, which looks like a rod. The notochord eventually forms into the backbone. However, sea squirts do not form a backbone. When the sea squirt larvae settle onto hard structures, the notochord disappears. This is an interesting phenomenon for evolutionary scientists who study how animals and plants evolve over time.

Sea squirts have a few predators including humans who cut up the sea squirt and use the red part of its body as fish bait. Although we often see how much fun everyone has from squeezing and squirting each other with water from sea squirts, it does cause them a lot of stress while they are exposed to the sun and air at low tide. So while it is tempting to squeeze sea squirts, it is best to leave them in peace as they wait out the turn in tides.