Historical ecology and coral reefs

Written By Carla Elliff

I am a big fan of interdisciplinarity. For me, there is no way we can talk about an ecosystem like a coral reef and not end up leaning on different subjects and combining approaches from various fields to build a stronger foundation of knowledge about them. So, when I saw National Geographic’s Explorer Classroom series had a lesson on the historical ecology of corals, they had me hooked! And this is saying something considering the massive tsunami of online classes and presentations we are currently going through!

The lesson was given by Jonathan Cybulski, a Ph.D candidate at the University of Hong Kong. He gives a hilarious and dynamic presentation (diving mask and snorkel included). However, if you do not have 50 min to spare just now, I’ll give you the basics right here.

Historical ecology is the study of past human interactions with plants and animals. It can be considered a close relative to Archeology and Paleontology, for example. 

Cybulski studies the history of human interactions with corals. In his Ph.D., he is investigating the influences that have led to the clear west-to-east gradient of coral diversity found in Hong Kong – with high diversity in the east and low diversity in the west. There are natural conditions that could be driving this distribution, but how much do humans influence this occurrence?

He begins showing this famous set of photographs spanning from 1975 to 2014 depicting increasing degradation in Carysfort Reef, USA. 

Carysfort Reef: A Full Restoration | Coral reef, Restoration, News ...
Fig. 1 Increasing coral reef degradation in Carysfort Reef (Florida Keys National Marine Sanctuary, USA) over time (Source: Science Friday)

Cybulski uses these pictures to explain the concept of the shifting-baselines syndrome. This recurring theme in historical ecology was coined by Dr Daniel Pauly. Pauly is a renowned fish biologist and, as quoted by Cybulski, said 

With each new generation, the expectation of various ecological conditions shifts. The results are that standards are lowered almost imperceptibly”.

Ok, so what does this mean to coral reefs? Suppose we did not have the older pictures of Carysfort Reef. If we saw the reef for the first time in 2014, we would only see the degraded landscape and most likely we would have lower expectations as to what it would look like if restored to its former glory. 

One big problem that allows this to happen is that it is rare to have actual records showing the progression of environmental degradation. We have these pictures for the past few decades of the Carysfort Reef, but what about other places? Also, humans have been around for a few thousand years, how long have we been modifying our environment? What can we do? Who you gonna call? Historical ecologists!

To answer some of these questions, Cybulski has collected sediment push cores from the area he studies. These cores are essentially big pipes pushed into the seafloor to pull out a record of all the layers of current living corals on top, followed by older dead coral, sediments, even older dead things, and so on. This profile of newer to older layers can then be read as a record of what that environment looked like years and years ago. Including what corals were present in the area long ago, allowing a comparison with what corals are present today.

Fig. 2 Example of a marine sediment core, a sort of “time capsule” of our environment (Source: Wikimedia Commons)

So, what has changed with the coral community of Hong Kong?

The data collected showed that the coral community has shifted from mainly branching coral species to massive coral species. Branching corals are faster growing and create a more complex habitat, which makes them important for maintaining diverse and thriving reefs. Loss of high numbers of branching corals shifts the whole community structure of reefs and has happened in many locations around the globe.

However, as put by Cybulski, the story does not end on this sad note. These results are being used to inform conservation practices looking forward. For example, by knowing which species of corals used to be present in a given area before humans, restoration efforts can aim to reproduce these organisms and place them in the best available places.

NOAA's Atlantic Oceanographic and Meteorological Laboratory ...
Fig. 3 Example of coral restoration in a laboratory. Small colonies are grown under controlled conditions before they can be transplanted into the environment. (Source: NOAA)

This is to me one of the key aspects of all disciplines that look to the past. Why do we want to know what corals looked like hundreds or thousands of years ago? Why do people study the politics of wars fought so long ago? Why is it important to think about where we came from? The answer to all these questions is that we look to the past to understand our present and predict our future.

Don’t miss Jonathan Cybulski’s amazing full presentation on YouTube: https://www.youtube.com/watch?v=qX0tjs71gvU

Big thanks to Jonathan Cybulski for his assistance with this article!

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