broadcast spawning | The Marine Detective

Posts tagged ‘broadcast spawning’

Underwater Smoking Log and the Worm That is Not a Worm?

Submerging into the dark, you never know what you are going to see.

It is a large part of what is so intoxicating about diving in cold, dark waters – all the mystery; all the wonder; all the opportunity for learning and sharing.

So what was it today?

This – a smoking log at about 6 m depth!

Teredo navalis spawning. March 8, 2015 ©Jackie Hildering.

Northwest Shipworms spawning. March 8, 2015 ©Jackie Hildering.

The “smoke” was brief but intense and of course it was not smoke at all. It was the spawn of some animal. Many marine invertebrates are broadcast spawners where all individuals in an area release their sex cells at the same time to enhance the chances of fertilization.

I knew the source of the “smoke” had to be a shipworm species since it was coming from a rotting log with lots of tunnels bored into it. I then had to do a bit of reading to be sure of whether it was the invasive Naval Shipworm (Teredo navalis), or the indigenous Northwest Shipworm (Bankia setacea).

Either way, shipworms are not worms at all!

Northwest Shipworm Source: MARINE WOOD BORERS IN BRITISH COLUMBIA; D. B. Quayle; 1992

Shipworms are saltwater clams. They look like a worm in a calcareous tube but have two small shells at the front of their bodies that are specialized to bore through wood, much to our dismay! The clams also have symbiotic bacteria that release an enzyme to help break down the cellulose in the wood.

I believe in this case it was the Northwest Shipworm that was spawning and the initial cue for the synchronous release of sex cells in this species is believed to be a sudden change in temperature or salinity. Once the spawn begins, it is believed that neighbouring Northwest Shipworms drawing water into their siphons detect the spawn and that this further triggers them to release their sex cells.

The Northwest Shipworm it is more common in BC than the Naval Shipworm; the tunnels in the wood looked like those caused by this species; but also relevant in my knowing it was this species is that I saw eggs being released as well as sperm.

With the oh-so-successful Naval Shipworm that originated in the Atlantic but is now boring through wood in all the world’s oceans, only the males release sex cells. Sperm are then drawn into females’ inhalant siphons; the eggs are fertilized and develop in the female’s gills in huge numbers to be released as free-swimming larvae.

Northwest Shipworms spawning. The white material on the logs is known as “frass”- waste discharged through the clams’ excurrent siphons. March 8, 2015 ©Jackie Hildering.

The Northwest Shipworm does not have this reproductive strategy. With both genders broadcast spawning, you can imagine how many sex cells need to be released for successful reproduction.

After about 3 weeks (at 12 – 15°C), the Northwest Shipworm larvae appear to be able to detect wood. They attach themselves, soften the wood, bore into it, develop into adults and cause economic discontent in we humans. This is especially the case in the logging industry which depends on transporting and storing wood in the Ocean.

Apparently the Northwest Shipworm can burrow 10 cm per month at temperatures greater than 10°C. See here for examples of the damage to wood by this species. If you are a Northern Vancouver Islander, you can see how this wood has been used as a decorative wall covering in the Whale Interpretive Centre.

For me, there was no discontent today. It was a wonder to be swimming by at the exact time this species was spawning. Providing me with a further opportunity to . . . smoke out facts about our marine life and share them with you!

Sea of Love – Broadcast Spawning!

Most often, divers prefer good visibility. But oh to have the good fortune to happen to be in the water when marine invertebrates are spawning!

I’ll never forget the first time the seas suddenly turned white and these green packets drifted by my mask.

Orange sea cucumber egg pellet — *Egg pellet from an Orange Sea Cucumber*.

I was euphoric that I happened to be in the water when Orange Sea Cucumbers (Cucumaria miniata) and Giant Plumose Anemones (Metridium farcimen) were broadcast spawning. Witnessing the magnitude of this great force that ensures these species will survive is as awe-inspiring as witnessing the annual spawn of herring or salmon.

Female orange sea cucumber about to release an egg pellet. Click to enlarge. © 2014 Jackie Hildering; www.themarinedetective.ca — *Female Orange Sea Cucumber about to release an egg pellet.*

The same female orange sea cucumber 1 minute later, releasing the egg pellet. Click to enlarge. © 2014 Jackie Hildering; www.themarinedetective.ca — *The same female Orange Sea Cucumber 1 minute later, releasing the egg pellet.*

Another spawning male. Orange sea cucumbers can also be this darker colour. Click to enlarge. © 2014 Jackie Hildering; www.themarinedetective.ca — *Spawning male Orange Sea Cucumber. Species can also be this darker, brownish colour.*

During broadcast spawning, invertebrate males and females each release their sex cells into the water column – in astoundingly copious amounts.

You can imagine how many gametes must be released for there to be a chance of fertilization and for enough of the resulting larvae to survive and not to be eaten by the many filter feeders such as barnacles, anemones and sea cucumbers!

Not only was it the male Orange Sea Cucumbers that were making the cloudy with their astounding numbers of gametes. The Giant Plumose Anemones were broadcast spawning too. Males releasing slow, white jets of their sperm and females then releasing their pinker egg masses. (Note that Giant Plumose Anemones can reproduce asexually as well by pedal laceration but broadcast spawning allows for diversity through sexual reproduction).

Spawning giant plumose anemone. Click to enlarge. © 2014 Jackie Hildering; www.themarinedetective.ca — *Spawning male Giant Plumose Anemone.*

*Giant Plumose Anemones spawning. Males release the whiter masses of gametes while the females’ masses of eggs have a pinkish colour. See them here?*

Giant plumose anemone releasing gametes. Click to enlarge. © 2014 Jackie Hildering; www.themarinedetective.ca — *Close-up of a male Plumose Anemone spawning.*

It is of course a good strategy to have males and females living in close proximity and that timing is everything! The spawn must be synchronized. To release sex cells when others of your kind are not doing so, would be a very failed reproductive strategy indeed. Probable cues for spawning are ocean temperature; the number of days/hours of sunlight (cumulative temperature); and/or the presence of a plankton bloom.

Apparently for both Orange Sea Cucumbers and Giant Plumose Anemones, the males are the first to release their gametes, triggering the females to spawn.

Research has also found that, in the case of Orange Sea Cucumbers, females release around 130,000 eggs packaged in buoyant egg pellets. The egg pellets drift to the surface and dissociate into the individual eggs after about 20 minutes. Spawning in Orange Sea Cucumbers most often happens within 1.5 hours after slack low tide which adds to the success by allowing for a greater concentration of sex cells, maximizing the chances of fertilization.

Through these images, I hope I have been able to relay the awe I felt at witnessing this biological marvel that has allowed these species to survive on Earth for thousands of times longer than we humans have walked upright.