SEALINK Cruise

9 January 2024 - Introduction

Coral reefs are among the most biologically diverse and productive ecosystems on earth, providing island communities with important services for tourism, recreation, employment, fisheries production, shoreline protection, beach creation, and cultural heritage. Relevant for the corals, sponges, and algae, that live in the shallow waters surrounding the island are 1) activities on land, including runoff, urban development and sewage discharge and 2) processes taking place in the ocean such as hydrodynamics and mixing.

The coral reefs that we study are influenced by these two categories of processes which both influence the water quality and biogeochemistry: the former is studied by field work conducted from land (e.g. by scuba diving), while the second processes are analyzed using the research vessel Pelagia. More specifically, we will use this expedition to analyze the ocean currents around the island and define the biological and geochemical characteristics of the different water layers by collecting water samples. Water turbulence and mixing in combination with the bottom topography will determine how chemical and biological substances are distributed along the island and what potential influence they can have on coral reef health and biodiversity.

21 January 2024 - What we cannot see with the naked eye

By Lisa Schellenberg

Coral reefs are important for shoreline protection and biodiversity, but are also just fascinating to look at and explore, as all tourists know. Furthermore, there is lots to explore scientifically. Besides fish there are these unicellular organisms called microbes. They are highly important for primary production, recycling and ecosystem functioning. There is so much happening on reef systems that we can’t see with the naked eye. In just one milliliter of seawater there are over hundred thousand unicellular primary producers (phytoplankton), one million bacteria and over ten million viruses. These organisms take up substances, but also excrete substances (chemical molecules). With so much activity in every drop of seawater, it is important to consider the microbial and molecular dynamics around the reef. We want to understand more about the effect of natural and human influenced processes on these microbes and (their) chemical compounds (for example natural toxins and antibiotics). Not only in and around the reef, but also the substances that come from land to the reef such as pesticides, cosmetics and pharmaceuticals.

On the chemical side of things we are exploring the world of dissolved organic matter (DOM = biological molecules from organisms) from the reef to the open ocean. We take samples for metabolomics (the study of metabolites/chemical molecules), which are preserved for later analysis using a liquid chromatography tandem mass spectrometry, a state of the art method to measure compounds, at NIOZ on Texel. This is a new field for marine sciences and brings exciting new insights from the highly active reefs. From our earlier research expedition in 2022, we see some interesting results already, but since I am in the midst of analyzing the over 40 thousands compounds that are in these samples, it needs a bit more time before I can tell you the conclusions. We also determine what proportion of the dissolved organic matter that is readily available for uptake by the reef system and its marine microbes and the share that cannot be easily absorbed.

Now, let’s talk about the activity of the microbes. We want to know how fast they grow, if they are eaten, or if they die by viral infection. Our team starts typically at 7 AM, preparing and getting ready to collect up to 50 liters of water for the different measurements and experiments. Most of the water we use comes from the general CTD that all teams use for water samples, but we also collect water directly above the nearby reef in a small boat. We count the phytoplankton directly using a flow cytometer and we preserve some to count bacteria and viruses back at NIOZ. In parallel, others of our team set up the experiments. Since there is not enough time in one day to do it all, we have to divide the work into two days; one day for bacterial work and a second day to focus on phytoplankton.

We count the phytoplankton and its population directly after sampling and after an 24h incubation time at the actual light and temperature the samples were coming from. Once we are ready to give the samples a break for their 24h incubation, two team members make their way from the lab container to the sample incubator with light proof backpacks with 48 x 1 liter bottles of sample bottles. It looks like we are going on an adventure! We are nearing the end of the cruise and the adventure of analyzing the hundreds of samples just starts.

By connecting all forces of our various disciplines within SEALINK, we hope to elucidate the missing link of how natural processes and human influence have an impact on marine reef systems and specifically on the invisible realm of microbes.

17 January 2024 - Living on the edge

 By Furu Mienis

While the highest mountain on the island of Curacao is 372 m high, the island is also an underwater mountain with majestic slopes that reach down to more than 1200 m water depth. With the camera system that we have on board of the Pelagia we can explore these deep slopes that are beyond scuba diving depths. A tethered camera system is used, consisting of a downward- and a forward-looking camera that are fitted in a frame with a lot of light, since the light slowly fades away below 200 m water depth.

The camera frame is attached to a Kevlar cable and is dragged behind the ship with a constant speed and at a constant height above the seafloor. Via optical fibres in this cable we have a live view of what we see on the seafloor. Only a very small part of the deep sea (7%) has been looked at by humans, so we continuously explore new territory. The videos give us an idea about the topography underwater, the type of substrate and all the megafuana that are living there.

The geology of the slopes is very variable, changing between steep cliffs of hard substrate and soft sediment plains. In these different environments we also observe very different species. On soft sediment we often encounter sea urchins, squat lobsters and sea cucumbers. On hard substrate we see more abundant and diverse life, including deep-sea corals, sponges and crinoids. These species need a hard substrate to settle on, but also need strong currents to provide them with food particles that they filter from the water column.

That is why these species tend to form reefs at ridges and cliffs. Since they create 3D structures that protrude from the seafloor they also attract a lot of other species such as fish, resulting in hotspots of biodiversity in the deep. During our video surveys we unfortunately observe that also the deep sea is influenced by human activity. We have found a lot of anthropogenic waste, mainly plastics, bottles and cans. At the same time, we also visit places where we encounter beautiful and surprising moments when for example a dumbo octopus or shark appears out of the dark or when we observe ancient water bottles from a long time ago.

15 January 2024 - From shallow to deep

By Lennart de Nooijer

The overarching goal of our Sealink project is to understand the influence of pollution and other influences from land on the shallow, tropical reefs around Curaçao. Not only do we need to quantify what and how much is transported from land into the coastal waters, but also do we need to know how long pollutants and nutrients are staying near the shallow coral reefs. Coral reefs may not ‘see’ a heavy pollution, if there are strong currents that carry away the harmful substances and replace it with fresh open ocean-water.

To understand the influence of the open ocean on the coral reefs, we are using the RV Pelagia to map biological, physical and chemical parameters of the seawater (see previous and next blogs). From land, we have performed various sampling campaigns by scuba diving. However, there is a gap between what we can cover from land and from sea. Therefore, we use a zodiac to go halfway the Pelagia and coast to sample the missing water depths. This requires a small team to jump (not literally) in the boat every morning and head towards the edge of the reef and lower portable devices to measure the temperature, oxygen and water depth above these reefs. The water itself is also sampled to determine amount and type of anthropogenic substances, the geochemistry and biological productivity in these waters.

The boat is manned by two of the ship’s crew to take care of the sailing and two scientists: one samples the water for chemical parameters (nutrients, carbon content) and one samples for biological parameters including typical markers for human activity (pesticides, pharmaceuticals, cosmetics). To analyze whether the reef is actually taking up or releasing any of these chemicals, we sample at different depths, which is also what we do when taking samples with the CTD rosette from the Pelagia at all the deeper stations. With the RV Pelagia we can reach the deeper depths to determine the background water characteristics of the open ocean uninfluenced by land and the strength of the currents. In this way we sample a full transect from 10 m water depth to over 1000 m water depth. One limitation of this sampling strategy is the rough conditions at the northern side of the Island. With predominant winds from the east in this region, the coast facing south-east is relatively well-sheltered, while the northern shore of Curaçao is always bombarded by breaking waves. This makes it impossible to sample with the small boat, but then the shallow coral reefs that we study are mostly found in the south…

10 January 2024 - It's alive!

By Vesna Bertoncelj & Floran Brinkman

On the 4^th of January we departed from the harbor of Willemstad. The days preceding that, we have been busy with preparing our equipment, bringing in the final instruments and organizing our working stations on board. This ship will be our home, office and laboratory for almost three weeks, with no chance of buying something that we break or forgot to pack. Liquid nitrogen? Check. Sufficient batteries for the frames that we’ll deploy? Check. 20 different types of tubes, 10,000 vials and 35 pencils? Check. 

The famous floating bridge of Willemstad that allows pedestrians go from one half of the city center to the other, opened for our 70 meter-research vessel and off we went into the Caribbean Sea. Under a pleasant afternoon sun and surrounded by flying fish, we set off to our first sampling station. This is done by a so-called CTD device, that measures the Conductivity (from which you can derive the salt content), Temperature and Density of the seawater. It also measures oxygen, chlorophyll content and light, by the way and can be lowered from a cable and measure all these parameters as the device goes down towards the seafloor. It is also equipped with 24 bottles that can be closed at chosen depths so that we can collect seawater at specific depths. We will do so all around Curaçao to map chemical and biological characteristics (and perhaps see the influence of the urban development on the island). After a round of testing all equipment and instruments, we are finally ready for our sampling campaign!

Different teams within the scientific crew are focusing on their own aspect of the marine environment. Our task specifically, is to measure the currents around the island. This is important as the open ocean-water movement may carry nutrients from afar to the coast of Curaçao and at the same time may remove (polluted) waters from the near-shore zone. To accurately map these currents (speed as well as direction), we use the so-called ADCP that is mounted to the bottom of the ship. This instrument sends out acoustic waves and records the returned waves: the Doppler effect that modulates the returned waves allows calculating the flow velocities and directions underneath the boat.

The first few days we have been busy analyzing the data and optimizing the settings of the profiler to get the best results. Gladly, we found out that the signal of the ship-mounted multibeam caused interference on our ADCP-readings. The multibeam sends out high-frequency sounds to determine the distance to the bottom of the seafloor. Now we have a better signal and started to record the current speed and directions over night at a few locations south of the island. This means we have to be up overnight sometimes to check up on the instrument. In between checking we can enjoy the stars and the night at sea. Later in this expedition we will cover the northern half of Curaçao to get a full picture of the interaction between the open ocean and the coastal environment and thereby the coral reefs, of the island.

However interesting and important, this requires that we spend quite a bit of time behind our laptops and sometimes miss out on some of the more ‘cinematic’ activities. Another team spends time analyzing video recordings of the seafloor. Sometimes if we are waiting for our data we can help doing taxonomy on the recordings.

The rare moments that we are not busy it is incredible to go outside, enjoy the warmth, the sun and the breeze. Standing outside seeing instruments being deployed with a beautiful sunset in the background is a view to remember. It is a great experience to be part of this expedition and we are looking very much forward to the days to come to see what beautiful sea creatures and currents it will bring us.