We speak with the legendary Di Tracey about deep water corals, a lifetime working offshore and pioneering the marine field for women researchers.
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Dianne “Di” tracey
Deep-sea researcher - NIWA
I'm lucky enough to be joined by Diane “Di” Tracy for a chat about deep sea corals.
Great to be here. And it’s great to chat about deep-sea corals actually, because you keep thinking ‘oh everyone knows about deep-sea corals now, we've been looking at them since 2008 in this region’. But actually, they don't! They're just familiar with the Great Barrier Reef corals. So thanks for the chance!
I wanted to start with a bit of a foundation because a lot of people are sort of aware of corals but not their structure as an animal. So can you talk through just what a coral is? How this colonial organism functions?
It's right, they are animals. And the little polyp is a bit like an anemone. So each polyp is an individual animal but they have an exoskeleton which they build (in a tree-like way, often) a skeleton with branches. And it's on those branches that the polyp lives, often embedded in the skeleton, so you can't see it. But then it protrudes with the tentacles when it's feeding and breathing. They’re animals like anemones and jellyfish are in the same group of cnidaria. The skeletons are formed often using calcium carbonate, which they get from diet but also from just the natural minerals in the ocean.
Is there a continuous tissue? Are the polyps connected to each other?
In some, yes there is. The coenenchyme (or some people call it the coenosarc), that's the tissue that is covering the skeleton and connecting the polyps as well. There's not loads known about how that connection exists, but if the coenenchyme disappears, the coral is not doing very well as an animal. So yeah, within each polyp there's this pink tissue, and in some corals, this connects along the branches to the next polyp. That's all external. Internally, there's also stuff happening as well.
Is it one cloned organism? Is a single colony genetically uniform?
Yes we think so. That's correct yeah. And there are male and female colonies also.
Oh right at the colony level rather than the polyp level? Oh that's interesting!
Image courtesy of Ocean Exploration Trust
Yes that's what we believe. Certainly for the scleractinia (the stony corals). So one clump will be a male clump, and the other one will be female. The female will produce the oocytes and then the spermatophores come from the adjacent clump. Yeah but that kind of connection is quite tricky.
Yeah, I bet!
And then some breed the animal inside the mouth of the polyp too, so you've got that going on as well.
They're quite tricky in their simplicity, so there's just there's just one entrance/exit. Sothey eat and they expel eggs and sperm, and about the sounds of it expel even juveniles just through this single opening in the middle!
That's right, yeah. The ones that brood in the larvae, that would be in what we call the mouth of the polyp. So they’re just sitting in there amongst all the rest of the organs of the coral, and then yeah, it just pops them out when they're ready. And off they swim, which is amazing!
Yeah and they must have to halt all digestion and a lot of other processes in order to do that.
…to focus on the breeding. Yeah that's right.
Is a single colony functionally immortal? Or because it's a clone, is it building up genetic damage so is it important to have that sexual reproduction as well, to get some variety in there?
Oh, you would have to have that. You also would have to have the animal being far enough apart, so that the genetic material is more variable.
Yeah.
I'm just going to butt in here and say I'm not a taxonomist and I'm not a geneticist, I'm not a molecular person. My career began with us not even knowing about these animals. We didn't know where they were, we didn't know what they were.
Started on day one
Yeah! The focus was on single species stock assessment when my career began. So we were looking at how many fish are in the ocean, how many orange roughy were on these seamounts or in this area. And then focusing more on the bycatch. What we were also getting in the trawls, the other fishes as well as the invertebrates, led us to do a lot more work on invertebrate species in our region. And that's when we started with the coral research, the spatial distribution knowledge, you know… where are the hotspots?
This came from a fisheries element, because it's important for the fish. It's important as a habitat. These are not just animals in their own right, they shape the habitat around them.
Exactly, yeah. So they are very important. You'll hear that word ‘importance of habitat’ throughout anyone who talks about corals. They will mention habitat and importance and their associates: what lives on the corals? What species use them for shelter and refuge? Or what species really rely on them for platforms to get into the water column to feed? So, all that kind of information and knowledge has grown for me since we did the fisheries work. Of course, the were taxonomists in the museums in New Zealand looking at the corals around our coast. And that work was going on when they put the cable between the North and South island and lifted it for maintenance, they found corals on that cable. So there was work going on in the early days in the '60s and '70s. But that was more coastal. The deep sea knowledge really just started with the growth of the deep sea fisheries and knowledge of what was on the seamounts.
Image courtesy of Ocean Exploration Trust
Yeah things were just coming up in the in the bycatch that we’d never seen before. And some of the images from those early days of huge corals coming up with the the trawls!
And those huge corals still come up with the trawls because you know people are always going to new areas to look for more fisheries or more stocks, and they're bringing up corals still. We're continuously doing work for the protection of corals for the Department of Conservation. We're monitoring bycatch on fishing vessels and we're still seeing those really large corals coming up from the deep. For example, the bubblegum coral. You know that charismatic Paragorgia that's still being bought up in trawls as we speak.
And what would the age of a colony like that be? We know they're incredibly slow-growing.
Well, the bubblegum corals don't seem to be as slow-growing as some of the other coral groups. So we get black corals living to over 2,000 years, but the bubblegums seem to live… to be honest we've only radiocarbon dated one specimen, 300 to 500 years. So yes, all old, but not 2,000 years. They seem to have quite a fast growth rate, it might be because they're not calcium carbonate structures, they're more chitinous.
If they're well-fed, they can lay it down pretty quick.
Yeah.
Should we talk about the two main structural groups? How they make their skeletons impact the flavour of the coral quite a lot. If they're slow growing and hard, or if they’re proteinaceous and a bit flexible.
Right. So there's the scleractinian (stony corals) the protected reef-like coral that we have in our region. They’re made of calcium carbonate and so they are very slow growing. It could take about 2,000 years for one meter of that colony to grow. So that's that's one key group: the calcium carbonate structures of scleractinian stony corals. Then there's the bamboo corals, which are a mixture of calcium carbonate and gorgonian. They are also very slow-growing but not as slow as the stony corals. And then we look at the black corals. They’re made up of a different material, kind of more chitinous. They can be quite fast growing in the Fiordland region and can live to about 300 years. But in the deep sea, they're very slow growing and we've aged them to over 2,000 years as well.
Even the very youngest of the ones you mentioned are older than our ability to impact them. We've only been able to bump into these things for the last 100 or so, at the very most. It's only really the last 30 years, maybe last 40 if you're pushing it, where we've really been impacting these very very slow-growing animals. So they've not really had a chance to rally or adjust.
No, not at all. I mean, we've carried out recovery experiments, we've been out to the seamounts and looked at where there's been damage to the colonies. We've looked for signs of recovery… are the corals growing back along those tracks that have been heavily trawled? And we're not really seeing any signs of the growth. What seems to happen with the stony corals (which my colleague Jennifer Bowmont has been studying the reproduction work) was that we've seen the larvae brooding inside one of the species, garella and we've seen those larvae come out and settle really quickly and start laying down a skeleton. To get some kind of base, get some hold on something hard and on a suitable substrate, and then the growth would slow. So it's initially: let's get set and start growing a skeleton so that we're safe, and we can start growing. That seems to be a reasonably fast phase of growth, that initial one. And you see that in a lot of animals, but then it slows.
Let's talk about the corals as habitat engineers. So say an empty seamount or a seamount that's been impacted by industry. How do they change the habitat?
So a lot of the seamounts we've studied on the Chatham Rise, a few are protected. So we can look at those pristine environments and see how the corals are behaving there and see what they provide, as far as habitat for many other invertebrates. Not just the live matrix, but the dead matrix as well. So we can observe side-by-side an impacted seamount and what importance the corals have. They don't just provide habitat for other invertebrates, they're also important for other fisheries. You know, the fish either feed on the animals that feed on the corals, or feed on the animals within the corals. Or they use that coral matrix for refuge and shelter as well. So quite an important role.
It's beyond the immediate habitat, they actually engineer and influence quite a halo around themselves, because they change fluid dynamics as well. And they bring more nutrients into the area, by changing the fluid flow and the productivity in the area. So they seem to enrich quite far beyond their colonies.
I mean, that's been hugely studied in the Great Barrier Reef area where you're seeing a coral and the coral dinoflagellate symbiotic animals, you're seeing them maintaining, at an individual level, that kind of environment. We really don't know how much that is happening in the deep sea. That's kind of a huge area. But you're right, those corals, that halo of corals that are draped over the flanks of the seamounts, are also changing the whole environment at a local level. Upwellings that occur with the oceanography around seamounts is a huge thing, and that's where you'll get a lot more food. But that's beneficial to the corals and the animals that live within the corals
Image courtesy of MBARI
I realise we've missed something quite fundamental when we're talking about deep corals versus shallower, which is the lack of the symbiotic algae
That's right. All of the corals that we look at in the deep sea, they are azooxanthellate; they don't have these dinoflagellates. So they do their own breathing and feeding. Whereas in the shallows and in the Great Barrier Reef, they're helping the coral survive by doing the breathing and providing the food. And also, by maintaining the ocean environment around the corals, keeping that pH at a level that the corals like. But they're battling climate change at the same time, so that's when you get the bleaching events and those dinoflagellates die. They bring the colour to the coral and so you just see bleaching and pale corals. We're not seeing that in New Zealand because our corals are doing their own breathing and maintaining their environment, but they still get stressed because the ocean chemistry is changing as well as the temperature in our oceans. So when that changes, you can't form the skeletons. So they are suffering in a different way, but just as serious as the shallow water corals.
Maybe less visually striking. The bleaching events are quite immediate, but it’s more subtle with the deep ones. It's hard to see when they're stressed.
It is. Deep ones are very colourful when they're healthy, actually. They're very pink and red and yellow and purple. They're pretty stunning. So you would see changes because of temperature and that coenenchyme that we talked about earlier (the tissue that surrounds it), that pink tissue would disappear. But yeah, it’s more subtle. We're seeing those massive bleaching events that are very dramatic. Seen from space!
It's going to be more gradual and it's hard to ‘right the ship’ in the deep sea. Maybe it's always been there and we just haven't recorded it, but we've been seeing more and more high temperatures rolling through the deep sea. And because of the crazy current regimes where it's often detached from the surface, the surface could be fine, but a pulse of warm water has has gone through the deep sea and stressed a load of things in a way they haven't done before
That's right, we're seeing those hot spots in New Zealand already. So yeah it is serious for the shallow and the deep sea corals.
When you're growing over hundreds of years, they can't dodge out the way like fish finding a new optimum.
Well, we mentioned earlier that this transplanting at sea that's going on, it's not just going on in shallow water corals but in the deep sea as well. They're taking up colonies and growing them in an aquarium and then settling them back into those deep sea environments.
I did not know that! I know that in NIWA, you've kept them alive in the labs there
Yeah, we maintained them in our aquarium and they they lived for well over a year in a cold dark environment that mimicked their natural environment. The first work we did was on ocean acidification impacts; looking at changes in pH and how they would affect the corals. So that was one experiment we did. And over a long period, we certainly saw impacts. Dead polyps and the coenenchyme, that pink tissue disappearing from the skeletons. Then the second study was looking at sedimentation. How did elevated levels of sedimentation impact the corals. Again, we saw pretty robust results. The corals were doing okay for a short period of time, but as the sedimentation accumulated over time, we could see stress on the corals. The tentacles weren't able to flick out the sediment adequately and they would die. Or the coenenchyme tissue would just be disappearing over time.
They can cope to a point, but then it's quite an abrupt point where it's just too much and the colony is struggling
I mean they often live in quite a high sediment environment. Some corals live on seamounts where it's hard bottom rocks and not much sand or sediment. Then other corals will live on small stony structures on flat sediment. So to a certain extent, they can maintain themselves and stay alive in those environments. But when you add additional stress, that's when they struggle. So yeah, they're not all found on hard rocky outcrops or on the sides of canyons. They are also found in soft sediment. We have the stony corals, the cup form not the reef form I've talked about a lot, those corals can be on hard structures like other corals or on rocks. You have the reef-forming corals that attach to rocky substrate and seamounts and drape themselves down seamounts, but you also have the cup corals and they can live on hard substrate or just in sediment. They have a different structure.
Are they the ones that tend to be solitary? They look like an armoured sea anemone, they make these cool tooth-like plugs.
Yeah, cup corals yeah.
I know it's present in a lot of the stony corals, but because they're so much bigger, you really get to see how beautiful that structure is. How much the flesh of the animal is quite small and there are these beautiful ridges to the the cup itself.
Yeah, the septa. They have these different patterns. Yeah, they're amazing and then the column can be long and elongate, or flat and like a bowl. Yeah they're really beautiful, you're right.
Image courtesy of Ocean Exploration Trust
Is there any sharing of resources through the connecting membrane? Or is each polyp on its own?
I think there's sharing of resources, but I have no real understanding of it. They seem to be able to survive on their own, when we've taken the samples back. They haven't seemed to be dependent on the polyp next door, but there must be connections. There's often hollow tubes between some of the corals. Not all, but the stony branching form, the branches have a hollow connection running through them.
I always thought of the nerves of a tooth, you know, there's a little core of flesh that goes through.
But the other corals, the bubble gum and the black corals, that skeleton's solid and you can't really see that they would share. It's a hard structure, so perhaps it's the external tissue that shares between polyps and not the internal.
Oh that's interesting! What are the common commensal organisms? Who are the friends of the corals? and I suppose there's going to be predators and things that graze on them as well.
The echinoids graze on them, so I'm not a fan of them. There are also deep sea urchins, they'll move across the seamount and start nibbling on the coral polyps. The little squat lobsters also use them as a platform, but they're not really in a symbiotic or commensal relationship, they just use it as a structure to get into the water column to feed. If you're looking at those Gorgonian octocorals, they seem to have these ophuroids that are always on them and they just seem to live in more of a commensal way. They're not being eaten, they're just those snake stars that are just twisted all around the branches.
I know a lot of fish, particularly the elasmos, there's some skates and some small dogfish, that seem to really target the corals to lay their eggs. And the egg cases actually seem to be structured so that they coil and and wrap around the coral and get secured that way.
That's exactly right. In fact, my colleague Brit Finucci, whom you've interviewed I believe, always says look out for the skate cases on the coral matrix. So they are very important structures.
Did you want to talk a little bit about your career progression because you were on the front line of getting to sea, and I know you've done a lot of work for improving the offshore environment, particularly for women in science. You've seen the industry change and you've driven a change in that area. Even in the 20 years I've been going to sea, the attitude has really changed. But we still get fisheries observers writing in saying ‘I keep finding garlic under my pillow because they think I'm a witch’...
Well that's pretty sad isn't it? You think things have changed… Yeah I started in the 70s, so it was a long time ago. I was four years working in the fisheries research division, it was called the marine department dep. and then it became Ministry of Agriculture and Fisheries. And women had just started to go to sea on the James Cook. I think the first woman Anne Brunt who went on that vessel, the director had signed off the voyage program without reading the names. And that's how we got a woman onto that trip! And then for those four years that I was working, yeah there were always two or three women going on that research boat. And that was a pretty good equitable experience, to be honest. You know, the young technician that I was learning about the job and learning how it was to be on Research vessels. It was all a good experience. You often come to awareness about equity when you're a little bit older and you go: ‘hold on a minute, they're doing the same job as me and I've been doing this for years and they're paid more than me.’ So that kind of awareness came when I got back from overseas, when the exclusive economic zone had just been declared, (the EEZ) and suddenly there was 200 miles of waters to research.
So you were part of that transition? Because it's so galvanized now the EEZ, but it's a really new thing! There was a time when it was 12 miles.
We didn't have a research vessel that could really perform in that whole region, it was huge. So we relied on initially foreign vessels that were in the region. But yeah, I was often the only woman on those trips and I kind of relied on the support of my male colleagues to make sure everything went okay. It was very unusual for women to go on those voyages. Then we spent 10 years going on the New Zealand research commercial vessels before we got our research vessel the Tangaroa. So we used commercial boats to do research for quota or research for surveys on all the new stocks that were being discovered. This was mainly a deep sea focus. If I was leading the voyage, I always made sure I had women on my team. You know, we're 50% of the population and of course we bring value to the job and we do things slightly differently sometimes and add a huge dimension, and sometimes that was hard to get women on the trips. And sometimes it was a struggle in those environments because you did have sexism and pornography in the workplace.
“And now, we seem to have a lot of women going to sea, and they’re leading voyages. And they sometimes have an all-woman team, but that still gets questioned which I find really intriguing. So we still get that bias. And it’s a bit more underground, you could say, that unconscious bias. ”
Even during my career, that's really changed. Just the atmosphere offshore has changed.
Yeah, well good! I think that was a time of making sure people heard women. We showed that we were capable of leading voyages and several women that I worked with led voyages in the 70s and 80s. In the '80s, some women would say maybe it was a bit easier then. We had equal employment opportunities and there was a big focus on equity and fairness and women's rights. So that was a bit of a stick that the men had to comply with. But then over time, sometimes it was hard for women who had families to keep going to sea, so I didn't have children. So even in the '90s, I was still often the only woman at sea. But yeah, as you say, the environment is loads better. We addressed the issues of pornography in the workplace, we had rules and sexist behaviour wasn't as common. And now, we seem to have a lot of women going to sea, and they're leading voyages. And they sometimes have an all-woman team, but that still gets questioned which I find really intriguing. So we still get that bias. And it's a bit more underground, you could say, that unconscious bias.
But yeah, throughout my whole career I've tried to support women because it has been a very non-traditional role. And you know, two women at sea was much easier than one. And then, just as I pass on the baton of coral research, I'm probably a bit biased myself and made sure that I've passed it on to a lot of great women researchers. So here's a shout out to woman researchers, thanks for the question.
Yeah I wanted to talk about that because just in my time, I've seen a a huge change and I just think the more different your team is, the better you work. you can have the smartest most capable people. But if they're all the same type of smart and capable, they only have the same ideas. I really like mixed diverse teams, because someone at the back of the room will have this totally different experience or this different way of thinking.
Exactly.
Thanks so much for your time today.
Thanks Thom!