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Linking Pollution And Bacteria To Coral Reef Health

July 28, 2010 11:28 a.m.

San Diego State University professor Dr. Forest Rohwer's recent book "Coral Reefs In the Microbial Seas" gives evidence linking pollution and bacteria to coral reef health.

Related Story: Linking Pollution And Bacteria To Coral Reef Health


This is a rush transcript created by a contractor for KPBS to improve accessibility for the deaf and hard-of-hearing. Please refer to the media file as the formal record of this interview. Opinions expressed by guests during interviews reflect the guest’s individual views and do not necessarily represent those of KPBS staff, members or its sponsors.

MAUREEN CAVANAUGH (Host): I'm Maureen Cavanaugh, and you're listening to These Days on KPBS. We've been hearing for quite some time that the ocean's coral reefs are in trouble. Now a new book diagnoses the problems with the reefs down to the microbial level. It's a science book that not only explains the research being conducted, but tells stories about the way it was conducted. We meet the scientists, enjoy their camaraderie and adventures, all while learning to understand the precarious situation faced by the world's coral reefs. I’d like to introduce my guest, San Diego State University professor Dr. Forest Rohwer, author of the book, “Coral Reefs in the Microbial Seas.” And, Dr. Rohwer, thanks for being here.

DR. FOREST ROHWER (Microbial Ecologist, San Diego State University): Thank you for having me.

CAVANAUGH: Now, as I mentioned, the plight of the coral reefs has been talked about for quite some time. So what does your book add to our understanding of what’s happening to the reefs?

DR. ROHWER: Much of the things that happen to the ocean are actually taken on by the microbes. And people really haven’t spent much time thinking about microbial activity on coral reefs or understanding either how coral reefs are healthy with the right microbes or sick with the wrong microbes.

CAVANAUGH: How come they haven’t thought about this before?

DR. ROHWER: Actually, much of it’s technology driven. So up to about 20 years ago, we didn’t even have the techniques to look at them and up to 5 years ago we could have never actually seen what types of microbes are associated with the corals and asked what are they doing and how are they changing the health of the coral reef?

CAVANAUGH: I see. So, in other words, it’s basically science ability to actually study down to that level that is giving us good information now.

DR. ROHWER: Yes, it’s actually been mostly breakthroughs in DNA sequencing technology.

CAVANAUGH: Oh, I see. That’s interesting. Now, where did you conduct your research?

DR. ROHWER: Most of our research is done in the central Pacific. They’re called the Line Islands, which are about 800 miles below Hawaii, due south on the equator. But we also work all over the world, in essentially all reefs everywhere.

CAVANAUGH: Now how do you – Okay, do you actually do the DNA studies while you’re out on the ocean? I mean, do you collect samples and then bring them back and then do the research?

DR. ROHWER: Yeah, so my dream would be to do it on the ocean but actually no, we bring – We collect samples and we bring them back and do all the work here at SDSU.

CAVANAUGH: Now, you, in the book, you describe a sort of a vicious cycle that’s destroying the reefs. It revolves around over-fishing and algae and microbes. Can you explain that to us?

DR. ROHWER: Right. So this cycle is on a normal reef what you would have is you’d have a lot of grazing by fish and urchins and things and they would keep the algae at a very low level. It’s actually kind of hard to find big algae on a healthy reef. What happens, when we fish, the algae gets bigger and it releases essentially sugars that feed the microbes. And then the microbes, you get more microbes, about ten times as many microbes on a degraded reef, and they switch from what you would call open ocean microbes to pathogenic microbes. And we think then that is what kills the corals and that’s a positive feedback system which is what you don’t want because that clears up space for more algae, which then goes on and makes more microbes and kills the corals – more corals and more algae. Yeah.

CAVANAUGH: I see, so, as I say, it’s this vicious cycle.


CAVANAUGH: It just feeds on itself. And you also talk about the influence of nutrients being added to the environment.


CAVANAUGH: I think that’s something that people don’t recognize. Tell us what you mean by nutrients added to the environment.

DR. ROHWER: Right, so any nutrients by – Most of the time, what we mean are things like phosphate and nitrogen, and these are things that you have in your fertilizers and also out of sewage. And what those do is algae is often limited by them, so if you get more of them than the algae will grow, and then you get the more microbes and the more coral disease again.

CAVANAUGH: And that’s something that comes off – basically runoff from fertilizer, as you say…


CAVANAUGH: …and things of that nature. You know, when we hear about the coral reefs and the problems that are making coral reefs be destroyed and decimated in some areas, we often hear about the larger climate change and the oceans warming and so forth. You make the distinction in this book between these larger global elements and the localized problems that – different areas that have coral reefs are actually experiencing.

DR. ROHWER: Right, so it’s really important to pull those two things apart. Really, the global changes, a lot of them are going to happen essentially no matter what we do right at this point. So we are going to see climate change and we are going to get acidification of the ocean because of the CO2. The hope and the – there’s data that supports this a little bit, that if the reefs are actually healthy they can actually survive some of those changes much better. And one of the key examples we’re looking at is in the same area of the ocean which experience very dramatic bleaching events because of extra water – I mean, extra hot water. And in those cases, the reef still had intact fish communities and it looks like coral recruits, so the baby corals are actually coming back to that reef. So that’s the hope, is that local – by keeping the reefs healthy in a local area, they’ll be able to survive better the global changes.

CAVANAUGH: And by keeping the reefs healthy locally, it means working on things like over-fishing and those kind of things…


CAVANAUGH: …in that particular area.

DR. ROHWER: Very much so, just over-fishing and not dumping a whole bunch of contaminants on the reef, mostly nutrients.

CAVANAUGH: I’m speaking with San Diego State University professor Dr. Forest Rohwer. He’s the author of the book, “Coral Reefs in the Microbial Seas.” You know, one of the great things about this book is in the beginning of each chapter you kind of share a story about conducting the reef search. They’re funny stories about the team trying to stay safe and avoid sharks and things of this nat – Why did you choose to include those stories in each of the episodes?

DR. ROHWER: Mostly so my parents would read it, right? No. No, I needed – You know, with – When you’re trying to convey science to a broader audience, one of the main things is to make it fun, and science is really fun, right? Everything we do. We get to travel around the world, dive on these beautiful places, and investigate all these new things. And that’s the hope, is that we – people understand how wonderful these places are and how much fun looking at them are, yeah. And it also gives you a feel of science is also done by people.

CAVANAUGH: Yeah, exactly. You really get the feeling of teamwork here. Now, tell us a little bit about some of the team are called Fish, some of the team are called Microbes. Who gets those distinctions?

DR. ROHWER: Right, so that the Fish are our favorite people to make fun of on the reef when we’re out doing the stuff. And they are – they actually have a very hard job. They swim transect lines, they’re called. You lay down a line on the reef and you swim up and down and you count the number of fish and how big they are. And it takes a lot of time underwater, so they work 14 hours a day doing just that. Then the Benthics are the people that actually look at the bottom and try to figure out how – what types of coral are there, how much coral versus algae and then whether the coral is healthy. So they do that in – both by taking pictures and surveys and so forth. And then the Microbial people, we basically only collect water underwater, which is people always make fun of us because we’re catching water while we’re underwater. But we’ll take all of those samples back and do all of our analysis on the boat. Yeah.

CAVANAUGH: You know what I think is very telling in these little vignettes that you put in front of the chapters is how really sort of makeshift and how all alone you are out there when you’re out on this – on the boat trying to do this research. I think – I don’t think that’s what people really understand. You know, we kind of think you’re out there with all your scientific equipment and your backup and so forth. Tell us a little bit about the kind of, you know, you have to make do with what you have.

DR. ROHWER: Yeah, there’s – You have to make everything. Anything that breaks, you have to fix it and rebuild it and that leads to many just jerry-rigged sort of items. Everything has to be very tough so almost all the equipment we build is really designed to just get beat up and, hopefully, survive the cruise.

CAVANAUGH: And another thing is about the fact that you – your diet was kind of sparse when you were on your research ship, Holly.


CAVANAUGH: Tell us a little bit about that.

DR. ROHWER: Yeah, that was a – There were many mistakes made there, so… We ran out of money and so we – The cook in charge bought all the food he could have afforded but one of the things we thought we would be doing is fishing and that, in theory, would’ve been great except very few people actually remembered to bring fishing gear so we didn’t have the best diet on that. And, in fact, everybody lost a fairly significant amount of weight. And…

CAVANAUGH: No fear of over-fishing then, huh?

DR. ROHWER: No, not at…

CAVANAUGH: Tell us a little bit about the artwork that you use in the “Coral Reefs in the Microbial Seas,” your new book.

DR. ROHWER: Yeah, it’s – all of the art is really fun. It’s done by a tattoo artist from San Diego named Derek Vosten and he has an incredible ability to sit down with the scientists and he’ll spend, literally, you know, a week trying to actually learn the science and then draw a picture that conveys that and so he’s wonderful to work with.

CAVANAUGH: Well, you know, I think on first hearing, it might be strange for someone to hear that your book was illustrated by a tattoo artist. Why did you choose him?

DR. ROHWER: Yeah, because compositionally he’s incredible. He can render what a shark looks like as it twists through the water in just a way that it is amazing. And it’s very – So he can be incredibly precise and still have an artistic feel to it.

CAVANAUGH: And one of the things, too, one of the themes as you go through the chapters in your book, you have this lovely sort of scrollwork that is in – begins each chapter and we see the coral build up on this scrollwork and then kind of go – basically disappear.

DR. ROHWER: Right.

CAVANAUGH: And tell us why.

DR. ROHWER: Yeah, so that was actually Derek’s idea. And so after he read the book, he came up with this idea of building the – He thought of them as columns and then actually imagine a column underwater and over time it gets colonized by all of the different organisms and you would get this beautiful looking column and then as you go through the story and you learn about coral reefs dying, then he actually did the degradation of the coral reefs and they’re actually pretty precise. They kind of follow the same theme of the whole book.

CAVANAUGH: Now, San Diego’s a long way from the coral reefs that you were studying. Is there anything that we can do here to help preserve coral reefs?

DR. ROHWER: There are a lot of things. Much of what we do, even associated with the fishing, is the main thing. You should never give any business to – that uses not – uses sharks or anything about in their food. There’s actually a – if you go to like the Monterey Aquarium website, you can actually find out what fish are sustainable. That’s a great thing to do. The other thing is, is actually money that goes into good ecotourism is actually one of the main drivers that’s helping protect coral reefs so, honestly, if you want to see the most beautiful places on the planet, go to a coral reef and do it with somebody that does it in an ecologically friendly way and that can actually help and it’ll be really fun.

CAVANAUGH: Yeah, that’s a wonderful way to help. I’m wondering, what other expeditions are you planning? What’s in the works for you?

DR. ROHWER: So there are two big ones right at the moment. One is going to Moorea in about a month, and that will be to do a whole bunch of lab studies on the reef that’s there. And…

CAVANAUGH: Where is Moorea?

DR. ROHWER: French Tahiti.

CAVANAUGH: Oh, okay. Not familiar with it.

DR. ROHWER: Yeah, sorry. Yeah, it’s the same area of the ocean, Pacific. And then we are actually going back to the northern Line Islands for seven weeks this fall, and in that case we’re actually working out more of the energy, how energy moves through the food webs and – on these reefs.

CAVANAUGH: This is fascinating stuff. Thank you so much for coming in and telling us about it.

DR. ROHWER: Thank you for having me.

CAVANAUGH: I’ve been speaking with Dr. Forest Rohwer, San Diego State University professor and author of the new book, “Coral Reefs in the Microbial Seas.” If you’d like to comment, please go online, And stay with us for hour two, coming up in just a few minutes here on KPBS.