23 November 2018 | Category: Saba Bank

Falling chickens and the complexity of coral reefs

By Marin Van Regteren

In my PhD project I look at processes that influence vegetat...

Day 3. Counting fish

We are ready to start diving with our group of eight scientists plus dive instructor Kirstin. At the diving deck we are queuing up with our regulators and fins in hand. Then the captain gives a sign and we jump into the water at a rapid pace, one by one from the side of the boat. As soon as I’m in the water I swim towards the buoy on my back and I take a bottle out of my net. After rinsing it a few times, I fill it with surface water, of which I will determine the nutrients later on board. Then I find my buddy Ayumi and we can descend with the rest of the group. On the reef, I swim behind my buddy who counts the fish, with fifty meters of measuring tape. When you roll out the reel you sometimes get surprised, I look up and … I’m face to face with a mega Caribbean lobster!

Falling chickens and the complexity of coral reefs

Caribbean lobster on the Saba Bank (photo: Oscar Bos)

The complexity of the reef

On the way back I measure the relief of the reef, by noting down the height of the coral every five meters. This way we get ten height measurements per transect of fifty meters. This is a measure of the complexity of the reef, or the number of hiding places for fish and other marine animals, or even for the nurse shark we encountered this morning. After this is done I take the second water sample at the seafloor.

Falling chickens and the complexity of coral reefs

Altitude measurements of the reef by Marin (photo: Oscar Bos)

Falling chickens

Falling chickens and the complexity of coral reefs

Filtering water for nutrients (photo: Oscar Bos)

Once out of the water, I process the water samples on deck. All our stuff is in a box that is tied to the boat. The wind and waves create an extra challenge: we have to be careful that no bags, caps and filters will be blown away. Fortunately, the box also protects us against the wind. We filter the water from the litre bottles, and transfer them into small tubes, which are further processed in the Netherlands. They have to fly back home frozen, so I join cook Julian in the galley and ask him if he can make room in the freezer full of food for our samples. You have to watch out that there is no frozen chicken falling on your head while you stow the sample tubes (upright) neatly. Then I quickly close the freezer again. Soon afterwards a big wave comes, and while the chopping boards and bowls are flying out of the kitchen cabinets, Julian catches the frying pan with hot oil in a reflex. This is next level cooking! Yet he ensures that every day a delicious meal is ready for us. And tonight’s desert: a warm brownie with chocolate ice cream!

Disco algae

In the dark we are anchored in the lee of the mountains of Saba, what a rest! In the light of the boat the tarpons – large silver fish with laser eyes – hunt for flying fish: strike! With a well-filled stomach we are back on the dive deck to get into those wet suits again for (possibly the only) fun dive of the week. The water bottles, slate and measuring tape now remain on board. During this night dive we are also treated with beautiful corals, sponges and all kinds of small animals. A giant basket star appears: a kind of starfish with thousands of curled tentacles. We turn our lamp the other way, away from the animal. In the dark, the flow between the tentacles creates a light show of disco algae!

Falling chickens and the complexity of coral reefs

Fishes and their shelters on the Saba Bank (photo: Oscar Bos)

Leadphoto: Basket star (type of starfish) (Photo: Erik Meesters)

By Marin Van Regteren

In my PhD project I look at processes that influence vegetation establishment on salt marshes. This research is embedded within the Mud Motor project, that looks at opportunity to re-use harbour dredge disposal beneficially to enlarge salt marsh areas and both its ecological and physical consequences. Salt marshes protect the coastline by their wave attenuation, a nature-based flood protection, in addition to being a vital area for many unique floral and faunal species. The potential for marsh expansion lies at the outer edges of the marsh, the transition zone from marsh to intertidal flats. This is a dynamic area affected by (among other variables) salt stress and occasionally extreme dry conditions, frequent tidal submergence, and deposition and erosion of sediment.

Specifically, I look at the interactions between bioturbating soil fauna, vegetation establishment and sediment dynamics, using lab and mostly field experiments. Bioturbation by worms can bury seeds and cause freshly sprouted seedlings to tumble, thereby reducing vegetation establishment. Erosion may deplete the seedbank and transport viable seeds away from the transition zone. Sedimentation can lead to seed retention but also has the potential smother seedlings or bury seeds too deep for surfacing once germinated. Spatial and temporal patterns of seed availability, weather conditions and sediment dynamics are in constant interplay that determines salt marsh reduction or expansion.

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