The Superpowers of Seagrasses

How many times have many of us, myself included, ignored a sign like this during our misspent adolescent years? Now that I am older (so say the majority!) and wiser (so say a small minority!), I realise the purpose of this type of sign is to protect and conserve nature. Nowadays I pay more attention because nature conservation is a subject close to my heart. Being a diver, I am particularly interested in sustainability of the coastal and marine environment.

This then begs the question why don’t we pay as much attention to seagrasses, and their protection, as we do to terrestrial grasses? I have always enjoyed diving over seagrass meadows because of the air of mystery … squinting through the suspended sediments in the hope of finding a dugong or turtle feeding, or a fascinating ‘creepy-crawly’. There has been many a time when I have become very excited about a shape appearing through the less than perfect visibility, only to find another buddy pair of divers or, more often than not, absolutely nothing! The eyes and the mind can definitely play tricks on you in this ‘atmospheric’ environment.

To my shame, I have paid little attention to the seagrass itself and more attention to the other creatures, which use or inhabit these special underwater meadows. Meadows … let me digress for just a minute or two or maybe longer … Seagrasses are in fact flowering plants, with roots, that live underwater and evolved from terrestrial plants, which returned to the sea millions of years ago. One of the ways they propagate is by underwater pollination and they generate energy in the same way that land plants do, by photosynthesis.

To stay healthy most seagrasses need:

Lots of sunlight.
Sediment in which to root.
Clear-ish water with some nutrients.
Low levels of physical disturbance.
Stable salinity and temperature.
Sufficient oxygen levels.

There are four main families of seagrass, making up the 60-70 species worldwide and they are found in many and diverse locations. In fact, the only continent where they are not present is Antarctica.

The most recently evolving of these families is Zosteraceae, which emerged in the form we know it today around 17 million years ago. It is from this family that the one species inhabiting the waters around New Zealand is coming, namely Zostera muelleri.

In the past, seagrasses were used as medicines, filling for mattresses, insulation for houses and as roof thatch to name a few of the weird and wonderful uses. The Maori reportedly used seagrasses for food and clothing decorations. However, they play far more important roles in our present lives and our future existence. In recent years, seagrasses are finally getting some of the recognition they deserve as one of the most productive and valuable ecosystems on earth. They are more valuable ecosystems than coral reefs and they help to keep coral reefs healthy in many places.

Seagrasses are often called ‘ecosystem engineers’ because they adapt their surroundings to create unique habitats. More importantly for us, they provide ecological functions and a variety of services for humans. So, we ask ourselves, what are these important and valuable services? What do seagrasses actually do?

Here are a couple of fun facts for you:

Seagrasses can store up to twice as much carbon as terrestrial forests per hectare.
Seagrasses cover less than 0.2% of ocean floor, but store about 10% of the carbon buried in the oceans each year.

In addition, seagrasses are also called the ‘sentinels of the oceans’ or ‘coastal canaries’ because they are the first to show signs of distress from disturbances in the oceans and provide an early warning system for ocean and, consequently, human health.

The diagram below highlights the services seagrasses provide for us.

To put it in a way the majority of us will understand, we have to put a monetary value on the ecosystems services seagrasses provide. This helps to hold people’s attention to the importance of their sustainable management. In the late 1990s, a calculation found that one hectare of seagrass (about two football fields) was estimated to be worth over $19,000 per year. However, adjustments to those calculations have put the current figure at about double. It may even be that these figures are still too low because it is still difficult to quantify some of the indirect services seagrasses provide for us.

Despite its importance for present and future generations, seagrass is declining worldwide, in many cases due to human activity. Estimates have put the global loss in the last 20-30 years at anywhere between 1.5 to 7% every year. Drawing upon the above analogy, that equates to around two football fields every hour. This decline has been described as one of the greatest threats to humans.

It is therefore crucially important that we take care of the lungs of our oceans, as seagrasses are commonly known. Already, there are local research and restoration projects taking place around the world. An interesting example in the United Kingdom is where a smart phone app has been developed by the Project Seagrass charity, called Seagrass Spotter. Any user is welcomed to add their sightings, observations and photos to the app. The aim is to gather a large dataset to learn more about the distribution, health and resilience of UK seagrasses.

Furthermore, a growing number of academics and scientists are working with governments and international organisations to try to counteract the decline. Academics in New Zealand have put forward that the IUCN Red List designation of Z. muelleri as of Least Concern is disturbing. They state that this does not reflect its true status around the coasts of New Zealand, where losses of more than half the population have occurred in some areas.

So, as divers what can we do to take care of ‘our sea-lungs’? Here are a few good practice basics to follow when diving over seagrasses: