Welcome back! Today (Wednesday 16 December 2915) was the last day of our expedition through north-west Australia’s remote Kimberly coastal waters. Our study area covered part of the Bonaparte Archipelago. The last stage of the journey is to steam back to port in Darwin which will take about 40 hours.

And, though it started with a thunderstorm, today turned out to be the best day yet. In this blog, I’ll show you some highlights from a reef walk we did on West Montalivet Island, show you a a video of the most stunning undersea sponge gardens we’ve seen so far on this trip, and introduce you to the sounds of snapping shrimp and whistling dolphins that we recorded in the waters near Cape Chateaurenaud (northern tip of Bigge Island).

At long last- time for a reef walk!

Because most of the places where the water was deep enough for us to visit with the RV Solander was covered with soft sand or mud, we saw very few hard corals during our trip.  Baby hard corals must anchor themselves to a hard surface (like a rock) in order to survive. So, even a morning thunderstorm couldn’t dampen our enthusiasm to get up close and personal with a coral reef!
We split into two teams: a beach team and a reef flat team. I was in the beach team. Solander crew Scotty took us out in the zodiac (small inflatible boat) as close as he could get to the island.  Once we hit lots of coral Bonnie’s in shallow water, we jumped out of the zodiac and our reef walk began!  As it turns out, steel capped boots are not only perfect for working on deck, but they also work a treat for walking on sharp dead corals and climbing slippery sea cliffs!

 

 

First up was an exploration of the sea cliffs that framed each of the two beaches we walked along.  The rocks provided evidence of the extent of high tide- rocks typically underwater at high tide were darker in colour, covered with algae, and very slippery (see above). Rocks not typically underwater were an artist’s palette of red ochres, yellows, and greys (see below). Tide pools were formed in the cracks between the rocks even stop the higher cliffs.

 

 

Of course we had to explore the fringing reef just off the beach! It was chock full of partially submerged hard corals that we saw are branching corals (see below) and brain corals (see next set of photos). Branching corals do just as their name suggests- they grow in a series of branches made up of thousands of individual, tiny coral polyps (look closely in the right-hand image to see them).

 

 

Brain corals also look just like you’d expect from their name. In the picture below,you can see how the individual polyps combine to form structures that look just like the twisting and turning folds inside a human brain!

 

Meanwhile, the reef flat team headed over towards an extensive reef flat further to the north. They had great fun searching for critters to capture in their white buckets.

 

 

All too soon, it was time to return to the Solander to complete our last towed video transect and last sled for the trip.

Who will find the best sponge gardens?

Yesterday, we completed our last planned towed video transect and could start using results from Nick and Iain’s multibeam sonar data to try to find ideal spots for corals and sponges to live. As I said earlier, much of the sea floor in our study area deep enough for the Solander to visit has been made of soft sand and mud. But sponges and corals need something hard (like a rock) to anchor themselves against the raging tidal currents in this part of the world. The difference between high and low tide can be as much S 4 to 6 metres!!

Yesterday, I posted a video on You Tube that showed lovely sponge gardens at a spot between South Maret Island and Berthier Island that Marcus picked. We called this ‘Marcus’ Sponge Wonderland’.  Today we ran the towed video over a rock that Nick detected using the multibeam data. The spot we named ‘Nick’s Rock’ was absolutely stunning- colorful fish were zipping through dense undersea gardens of sponge and soft corals. If you watch closely, you can see brittle stars and feather stars crawling on top of sponges, sea fans, sea whips, and of course lots of different types and colors of sponges.

Watch the video of sponge gardens at Nick’s Rock.

See if you think that Nick’s Rock is best by comparing it to the also gorgeous video from Marcus’ Sponge Wonderland.

Yesterday, Iain took a great photo of two green sea turtles near the Maret Islands (see below). We also saw a white tipped reef shark and a school of Giant Trevally.

 

What does a coral reef sound like?

Speaking of Iain, at the start of our trip, he put an instrument in the water on the north side of Bigge Island to record underwater sounds. After two weeks, we picked tge instrument back up and he has started sifting through the data it recorded.
The picture below is a spectrogram. It shows you on a picture when sounds occurred, how high or low pitched they were (the frequency), and how loud they were (colors; blue=quiet, red=loud). Click on the picture to hear the sounds recorded over one 4.5 second time window. In that time, you can hear two dolphin whistles (circled in yellow on the picture) and lots and lots of the clicking noise made by snapping shrimp.  It is because of that clicking sound that I think diving or snorkeling on a reef sounds like marbles bouncing on a tiled floor.

Above the white line on the picture are sounds that human ears can’t hear. If we we could, we’d hear dolphin clicks. Dolphins use their own version of sonar to navigate and find food. They make sound (the clicks) and the time it takes for the sounds to return to them (and how loud the returning sound is) creates a map in their minds of their surroundings. Learn more about underwater animal sounds.

Farewell from the RV Solander

The crew of the Solander, as always, did an amazing job. And my fellow scientists were a pleasure to work with- spending every waking moment together for nearly three weeks.  Thanks to all!!

 

One of the benefits of working on a ship is a panoramic view of the sunset every night. On the NE Atlas channel on You Tube is a video showing my favorites from each day of the trip.  Below are three of them.

 

 

I hope you enjoyed this blog! Thanks for reading 🐠🐠🐠