UNSEEN DANGERS – Habitat restoration vs habitat creation


These days we have all become accustomed to headlines about habitat destruction and species extinction. The endangered species list grows annually as they suffer the effects of increased competition for resources accompanied by loss of habitat and, almost universally, there is one common factor; humans. Globally, our species hit around 7.4 billion in 2015 with an increase to 9.2 billion by 2040. In context, the 1900 had around 1.65 billion people globally.

As a species, we continue to be the root cause of most of the environmental problems on our planet today and in response, there has been a growing community of ‘green’ ambassadors who try and dampen our impacts.

As laudable as these acts are, there are often some unspoken truths about the impacts that these actions can have. First though, it’s important to define a few things.

Habitat restoration is the process by which an ecosystem that still exists, but might be verging on extinction, is aided through to recovery. By contrast, habitat creation is the transplanting of a new ecosystem over an existing one. The key here is that just because it looks like nothing is there doesn’t mean that is necessarily the case. In the marine environment, sandy shores often look like the least diverse as we search for life whilst snorkelling. The truth, however, is that the majority of life is within the sediments and we just don’t see it.

When implementing habitat restoration one needs to carefully consider the environmental context before one can decide how effective the strategy may be. If the loss of habitat is due to conditions which still exist then obviously, any restoration effort is likely to end in failure. In fact, it is because of these environmental conditions that the ecosystem has moved on to the new stable state even though a lack of species diversity has been the cost.

A good example of this in Gibraltar has been the seagrass beds which were found throughout the bay. These seagrasses were fertile fish nurseries and home to our two species of sea horses, Hippocampus hippocampus (the short snouted seahorse) and Hippocampus guttulatus (the long snouted seahorse). The latter is very rare in our waters and in no small part due to the destruction of our seagrasses. What has caused it?

Gibraltar has always had a strong naval history and has always been a natural harbour for sail ships of all kinds. Whilst in port, these ships have dropped anchors which have slowly ripped up the seagrass beds below. At first, the levels of damage was sustainable through natural growth but then, things changed.

The industrial revolution added a new complication, steam ships; some of which are still resting on our sea bed today in the form of the SS Rosslyn and the SS Excellent. These ships were larger and required a more substantial anchor to keep them in place. This had the knock on effect of ripping up a larger area of the seagrass beds each time. Further, the volume of ships also increased as extended ranges made it easier for them to arrive from further afield.

Steam gave way to oil and now we have a pollutant to the environment which has never been there. The anchor drags combined with the oil pollution would have had a pronounced effect on the seagrass beds, slowing down the growth rate in the exposed areas. Further, oil in the sediments would lower the viability of the seagrasses in that area. Over time, the oil would have built up in the sediments and the seagrass beds would have retreated, taking the seahorses with them.

Today, we have very few seagrasses left; albeit for some restoration work being done by Clive Crisp at the Department for Heritage and Climate Change. Mr Crisp has identified the exact species we have locally, Cymodecea nodosa (little Neptune grass), and attempting to re-seed the beds with some success. This is a great local example of an attempt at habitat restoration.

Habitat creation, on the other hand is a very dangerous game indeed. If I could indulge you in a thought experiment; imagine for a moment that instead of the appropriate locations identified by Mr Crisp, where there have historically been seagrasses, the re-seeding is done on the east side of the Rock with another species of grass which is known to be hardier and faster growing. At first, due to lack of competition, the grass takes root and begins to grow, successfully establishing itself off our beaches. The first obvious issue is that we have now introduced an invasive species to our marine ecosystem. At this stage however, the benefits outweigh the cons, for now.

Within a decade, the new species has firmly established itself in the environment covering almost the full extent of the eastern coastline. The beds are acting as nurseries and fish numbers are increasing and the project is hailed as a success. But, the proportion of fish species in that area has changed. Now the grazers which feed on the grass seeds rather than algae are dominating. Not only has that, but the water flow in the area slowed due to the sea grass presence. This slowing of water has also allowed Scyphozoans like the Mauve jellyfish to establish polyps in the area. As we have altered the fish feeding dynamic towards the grasses, the jellyfish numbers are quickly on the rise.

Within another five years, grasses are now constantly washing up on the sea shore and the jelly fish are almost permanently locked up close to the beaches due to the seagrasses blocking their passage away from it. You see where this is going.

The issue is not that my example is what is going to happen, but rather, that creating a new ecosystem, by adding invasive species or native species to areas where they don’t belong, can have catastrophic cascading effects on the rest of the ecosystem and should be avoided at all costs.

In the end, it is important that one is not tempted to do what they think is right but rather do the right thing with respect to environmental issues. Preventing the prime causes of habitat destruction is almost always better than to find substitute species to fill a niche. Otherwise, the next ecological disaster news story you read about might well be of our own making; again!

words | Lewis Stagnetto, The Nautilus Project