Saba Bank Expedition: Physical physics

Janine Nauw
Wednesday 28 October 2015

I’m Janine Nauw, physical oceanographer at the Royal NIOZ. In early May, I was invited to join the cruise on the Caribbean Explorer II (CE II) doing the physics part of the CoralCarib project, which looks into the calcification or erosion of the corals on the Saba Bank. The Caribbean Explorer II is not a research vessel, but a liveaboard. For non-divers, a liveaboad is a vessel for divers to take their holiday on. You can spend your whole holiday in the water, only going out when your dive-computer tells you to breath out some nitrogen, before going back in again. Meanwhile, the cook is preparing wonderful meals in the galley and your bed is being made and your room cleaned; it’s like an all-inclusive resort on the water. 

Me and my buddy

Doing research on a vessel like this is very much possible, I can say now after spending a week on the CE II. I was responsible for investigating the physics, or hydrodynamics, in the area surrounding the experimental site. The experiment involved placing a tent on the reef, closing it up and looking at the changing chemistry in the tent. Yes, you read it correctly, fellow scientists with help of the crew put up a decent size tent on the reef at 15 and 20 m below sea level! Putting pins in the reef is not really possible, so the tent was held in place by putting heavy chains and weights on the flaps that in normal circumstances keep the rain out, but in this case keep the water in. As with every tent, it cannot not be completely closed off from the environment, but always some exchange exists, e.g. the tent leaks. To determine the leakage, we measure the salinity inside and outside of the tent; add a certain amount of salt water in the tent and wait until the salinity in the tent is equal again the one outside of the tent. In practice, this involved actually diving down to the tent and adding a highly saline solution into the tent with a 500 ml syringe (or two). 

The Acoustic Doppler Current Profiler (ADCP) on the camping site 

Besides this, we also took an Acoustic Doppler Current Profiler (ADCP) down, which measures the currents and turbulence structure in the entire water column using sound pulses and recording the Doppler shift of the returned signal. This is a measure for the current speed, just as the change in frequency in an approaching or a parting ambulance is a reference for its speed. On the Saba Bank, it was on the hard reef, but near Saba in Ladders Labyrinth we had a sandy bottom, so we dug The ADCP in, keeping only its “head” above the seafloor giving us an extra 20 cm of data near the seafloor. 

Besides diving and digging, operating the CTD was also quite strenuous. A CTD measures salinity, temperature and depth throughout the water column by lowering it to the seafloor and hauling it again using a winch. I, a spoiled scientist who has worked only on proper research vessels, am used to the CTD being operated by an electrical powered winch by the crew, while I’m sitting inside watching a computer screen seeing the data coming in. Here, we don’t have that luxury, as there is no electrical powered which. However, we brought a manual one – I and many others of the scientific crew, got plenty exercise from that, especially on one of the three deeper cast that were more than 100 meters deep.

Hence it took quite some physical work, including lots of diving, some digging and exercising on the CTD-winch, to collect a very nice dataset about the physics of the experimental site. Meanwhile, we were being pampered by the crew, just like any other guest on the CE II would. And all of this in one of the most beautiful places in the world.

Saba Bank expedition: Camping under water!

Erik Meesters
27 October 2015

This picture could have been the start of a new hype. Romantic camping for divers. However, it is our little coral world, a so called mesocosm, in which we measure everything that is going on (see blog Fleur van Duyl).

Scientists from the Royal Netherlands Institute for Sea Research have worked night and day to get everything ready and working. Now we are here on the Saba Bank hoping for suitable weather. As it is we had to go to Saba Where we are trying our different mesocosms out. We have one big tent and two small ones and by measuring the chemistry of the water we can deduce how the little world under the tent is functioning. This will give us data that will help to understand how coral reefs function and how we can better protect them from pollution and the negative effects of climate change.

Expedition Saba Bank: First week done. Highlights.

24 October 2015
Erik Meesters Expedition leader first week

Divers hanging on line and waiting to be picked up
while being watched by sharks

Well the first week is behind us. Part of the team has now left and we have a couple of new people on board to help with the next part.The expedition went very well. We were able to do everything we had planned and more. The Dutch navy was able to put in the two new moorings, so we now we can stay the night over on the Bank without anchoring. This is very good, because that way we will not cause any damage to the reef.

We also explored a new part of the bank that appeared very rich in terms of coral cover and fish density. In many places we found large groupers and together with the large number of sharks this seems to indicate that the bank is in a relatively good condition.

Yellowfin Groupers closely followed by a trumpet fish on the
Saba Bank

We had very calm weather which helped enormously to get things done. Normally, wave are easily 2-3m high, but this year there only was a little rippling over the bank. Maybe this is related to the El Nino event  which is causing strange and unpredictable weather patterns all over the world. For the marine life it can be devastating. Some animals travel half way across the globe to rich waters and an El Nino may change current patterns and upwelling areas may not turn into the highly productive systems that animals expect or just turn into the opposite.

For corals an el nino may lead to warm water and to bleaching, the loss of the unicellular symbiotic algae from the tissue of the corals. As a consequence the coral appears white because the underlying white skeleton is shining through. The animal is not yet dead, but this is likely to happen if the warm water temperatures last for more than a week.

A coral (Porites astreoides)  that is partly bleached.

What exactly will happen is difficult to predict. Sea currents are among the most difficult things to predict. Let's hope sea water temperatures will quickly return to normal and that the damage to the Saba Bank coral ecosystem will be minimal. Since corals generally are very slow growing, an intense bleaching episode may need a few decades of recovery. There are indications that healthy corals bleach less, and reports from Gouadeloupe are already speaking of severe bleaching while here on the Saba Bank we only saw a few bleached corals. This seems to indicate that corals in general are healthy on the Saba Bank and may be some reasons for optimism for the Saba Bank coral reef ecosystem.

Expeditie Sababank: A Bank of Sponges?

Aiolochroia crassa. Photo by Oscar Bos.

By Lisa Becking

During the Saba Bank 2015 expedition, I am studying the sponge diversity. My partner in crime is Oscar Bos, who is making brilliant pictures of the colorful species. Here I’ll give a little background to the study and in a coming blogpost I’ll fill you in on our actual day-to-day activities.

The Saba Bank houses an expansive coral reef ecosystem with a rich diversity of marine species. Not only a high diversity of corals, but also a great diversity of sponge species. Sponges are little recognized yet vital components of reef systems. They are giant vacuum cleaners, which filter out all sorts of bacteria and fungi from the water column.

Sponges are able to provide food for other reef organisms by converting dissolved organic carbon into detritus. Besides food, they also offer shelter to a variety of creatures who live among the internal channels of the sponges. What is more, sponges are beautiful!

Sponges on the Saba Bank. Photo by Franck Mazeas

Hard surface is a valuable asset in the reef. Sponges and corals are in a constant rivalry for space. It may seem silent and peaceful down there, but all the while warfare is raging in the reefs as sponges and corals smother each other or exude their toxic chemicals to claim and maintain space. This competition is a natural state, yet in recent years there has been some concern that sponges are getting the upper hand and that the Caribbean reefs are turning into so called ‘sponge reefs’. The reason for this is that corals are becoming weaker and their cover is generally declining due to a variety of causes such as climate change, disease and local disturbances. A high abundance and diversity of sponges is not necessarily a bad thing, but a coral reef does need corals after all!

Callyspongia plicifera. Photo by Oscar Bos.

Due to its offshore location and upper-mesophotic reef system (20-50 m deep), Saba Bank coral reefs appear to have suffered relatively little anthropogenic disturbance compared to the reefs of the surrounding islands. Yet the Saba Bank reefs are still vulnerable to global stresses from climate change. With the current research we aim to see if the Saba Bank is becoming a ‘sponge reef’.

During the IMARES Saba Bank expeditions in the years 2011, 2013 and now in 2015, thirty-three 50m long transects were laid out in over the reefs and photographed. We will analyze these photographs of the benthos to see what the composition was of the community of sponge species in each year and to see how the cover and abundance of these sponges have changed through time. Identifying sponges based only on overview pictures is tough. To make certain we identify the sponges correctly, we’re setting up an identification database of sponge species, by collecting tissue and pictures of each species of sponge. When we get back home we’ll be identifying the pieces of sponge with molecular (DNA) techniques and morphological characters. In addition, we’ll compare our data with the historic collection of sponges from the Saba Bank from the 1970s that is now stored at Naturalis Biodiversity Center, Leiden.

Previous work of ours from 2013 has shown that Saba Bank is a store house of marine diversity for the nearby islands. With the current expedition we will document the sponge diversity that is thriving on the Bank.

Expeditie Sababank: het verhaal achter de foto's

Donderdag 22 oktober
Door: David Stevens

Ik ben David Stevens, huisarts in Voorburg en onderwaterfotograaf. Na 1 jaar biologie ben ik geneeskunde gaan doen. Biologie is echter wel altijd een passie gebleven. Boven water ben ik excursies blijven doen met oud studiegenoten en onderwater ben ik actief gebleven bij de Leidse studentenduikvereniging. De nadruk ligt bij deze vereniging op mariene biologie. Na 10 jaar duikervaring kreeg ik de behoefte de levende wereld onderwater vast te gaan leggen. Mijn passie onderwaterfotografie was geboren.

Het is begin juni 2015 toen ik van Ingvild Harkes de vraag kreeg om als onderwaterfotograaf mee te gaan op expeditie naar Sababank. Ingvild is bij het Wereldnatuurfonds (WNF) manager van het Kusten- en Oceanenprogramma in Caribisch Nederland. WNF is medefinancierder van deze expeditie. Mijn rol als onderwaterfotograaf is zo veel mogelijk van het onderzoek vastleggen in een beeld-verhaal. Met als extra opdracht ook foto's te maken die het grote publiek aanspreken. Dit is een aardige klus aangezien het onderzoek erg specialistisch is.

We komen aan en het is al meteen duidelijk dat ik niet de enige ben met een camera. Het zag er indrukwekkend uit. Eerlijkheidshalve moet ik zeggen dat ik me even afvroeg waarom ik was meegegaan, want ik was niet de enige fotograaf. Maar al snel realiseerde ik me dat Ingvild en ik de enigen aan boord zouden zijn die alle teams aan het werk zouden zien. Daar waar iedereen in zijn eigen onderzoek bezig is bewegen wij ons vrij tussen alle teams en krijgen alles te zien. Een heerlijke ervaringsrijkdom en ik voel me dan ook bevoorrecht dat ik dit allemaal mag vastleggen.

Er zijn meerdere teams aan boord:

• Team vissen: Tadzio Bervoets, Steve Piontek, Ingrid van Beek, met hulp van de crewleden Brett en Polly
• Team koralen en sponzen (benthos): Franck Mazeas, Jean-Philippe Maréchal, Ewan Trégarrot, Erik Meesters, Lisa Becking, Oscar Bos.
• Team NIOZ: Fleur van Duyl, Steven van Heuven, Xuewu Liu, Didier de Bakker, Alice Webb.

We doen in de 6 dagen 11 duikstekken aan. Om ervoor te zorgen dat de verschillende duikers geen last van elkaar hebben worden de teams verdeeld in 2 groepen. Als het vissenteam zijn werk heeft gedaan op een duikstek gaan de andere teams op dezelfde lokatie hun gegevens verzamelen. Ik begeef me afwisselend tussen groep 1 en 2 om alles te kunnen vastleggen.

Er volgden veel interessante gesprekken met de verschillende onderzoekers. Allen even aardig en even gemotiveerd om mij uit te leggen waarom ze bepaalde gegevens gingen verzamelen. Ik kreeg een kijkje in de keuken maar ik leerde ook meteen de teamleden kennen.

Het fotograferen en de gesprekken hebben me veel gebracht. Het was een rijke en leerzame ervaring waarbij ik op een nieuwe manier beeldmateriaal kon verzamelen.

Bedankt allemaal.

Saba Bank Expeditie: Erosie op de bank / Erosion on the Bank

Woensdag 21 oktober
Alice Webb

Alice en Didier aan het werk tijdens de meting (foto: David Stevens)

Mijn werk op de Saba bank is echt leuk. Mijn begeleider Didier Bakker (IMARES) en ik willen weten of de koraalriffen hier gezond zijn. Met de hulp van Steven van Heuven (NIOZ) duiken we in water vol met haaien en meten sponzen die in het koraal boren. Je vraagt je af waarom wij geïnteresseerd zijn in deze dingen? Nou, de moeders en neefjes van Oscar, Lisa en Steven lezen mee. Voor jullie, een beetje context, omdat jullie het anders misschien niet snappen.

Boorspons (Foto: Didier de Bakker)

Coral reef systems worldwide exist in a dynamic balance moderated by various processes resulting either in carbonate production or in the breakdown of previously deposited skeletal carbonate. Corals represent the primary constructional components on many reefs whilst bioeroding agents such as sponges, bivalves and worms directly degrade the reef’s framework increasing their susceptibility to physical and chemical erosion. Ongoing ocean acidification causes major shifts in species composition generally assumed to result in a shift in the growth/erosion balance.  Determining the relative role of these different processes is therefore crucial to conceptualise and quantify reef geomorphic performances.

By joining the Saba bank cruise, we aim to find out if the reefs of this gigantic submerged atoll are shifting towards net erosion instead of net growth. Using the ReefBudget method, we record calcifying and bioeroding species along fixe transects while diving.

Three days into the cruise, we have already dived 7 sites and recorded data along 21 transects. Each site very distinct from the other. Some reefs present high densities of bioeroding sponges while others harbour healthy coral populations. Many sites still await us and we look forward to analysing our data and determining the state of Saba Bank coral reefs.

Nou, ik ben klaar met mijn verhaal; ik hoop dat jullie het leuk vinden. Morgen is er iemand anders aan de beurt, ik denk jouw moeder, Roose. Je vous souhaite à tous et à toute une merveilleuse lecture. La vie à bord nous sourit et nous mangeons comme des rois.

Bon vent!

Saba Bank Expeditie: Hamerhaai in de vissurvey!

Ingrid van Beek
Dinsdag 20 oktober

Het vissurvey team bestaat uit 6 personen, die als eerste te water gaan om de visgemeenschappen op de Sababank te inventariseren: 3 duikers leggen ieder een transectlijn uit, achter de onderzoekers aan zwemmend om de vissen niet te verstoren; 3 onderzoekers noteren aantal en lengte van 100 vissoorten in een zogenaamd ‘belt transect’ van 50 meter lang en 5 meter breed. Het is belangrijk dat de transectlijnen recht en op de juiste plek liggen, want het benthos team gebruikt ze daarna om koralen en andere soorten bodembedekking onder de lijn te fotograferen.

Op de eerste duikdagen werd het vissurvey team onder aan de ankerlijn steeds verrast door een verpleegsterhaai die nieuwsgierig om de duikers heen zwom. Mogelijk verwachtten ze een lekker hapje, want op dit deel van de Saba Bank plaatsen vissers regelmatig lobster traps (kreeftenkooien) voorzien van aas. Het is opvallend dat er tijdens deze expeditie meer haaien gezien worden dan bij eerdere expedities. Bij praktisch ieder duikstation wel een of meer soorten, van verpleegsterhaaien en Caribische rif haaien tot een 3 meter lange hamerhaai! Scalloped en Great Hammerheads zijn pelagische haaien, die soms het rif opzoeken en soms ook duikers benaderen. Aan het eind van het transect kwam de hamerhaai op ons af en boog af toen hij op ongeveer 5 meter afstand was. Van opzij was de bijzondere kop goed zichtbaar, waarna hij helaas uit het zicht verdween voor we een foto konden maken.

Veel voorkomende vissoorten in de transecten zijn parrotfish (papegaaivissen), groupers (zeebaarsen, waaronder ook de grotere soorten zoals de Nassau Grouper en Yellowfin Grouper) en andere roofvissen zoals jacks (horsmakrelen) en barracuda.

Na afloop van de expeditie zullen de visdata vergeleken worden met die van voorgaande jaren om te bepalen of er een significant verschil is in de tijd en per station en of er een relatie is met de benthos en complexiteit van het rif.