‘Green gravel’ paves way to save kelp forests


Credit: NOAA's National Ocean Service, CC BY

Kelp forest

Underwater kelp forests are in serious trouble worldwide.

Kelp consists of several seaweed species varying from less than a metre to over 40
metres in length. Seaweed can reproduce rapidly and grow fast. Similar to rainforests,
kelp forests sustain a large diversity of marine species. They also provide protection
against coastal erosion and minimise our carbon footprint. These underwater wonders
can be found along all coastlines around the world, except in Antarctica.

But kelp forests are in serious peril due to the effects of climate change, pollution,
habitat destruction and the impact of invasive species. They are increasingly being
replaced by less productive habitats consisting of only one or a few species. More
worryingly, there has been almost no natural recovery of degraded kelp forests.

A recent study led by Stein Fredriksen from the University of Oslo in Norway
studied methods that are cheap and easy to implement to restore degraded kelp forests.

Fredriksen and his team were aware that previous attempts at kelp forest
restoration have been largely unsuccessful, expensive, and applied only at small
scales. Some of these approaches have included transplanting adult kelp from one
location to another, or building artificial kelp forests.

Fredriksen and his team wondered whether kelp spores (individual kelp cells that
develop into male or female individuals called sporophytes) would stick to small
rocks under laboratory conditions. If these spores could develop into sporophytes then
this ‘green gravel’ could simply be dunked into the ocean to ‘reseed’ degraded ocean
floors. As Fredriksen and his team notes, “restoring reefs using green gravel requires
little investment and provides potential … ways to …. ‘future proof’ vulnerable kelp

The process for making green gravel. (Source: Fredriksen et al., 2020).

They were successful in attaching and growing kelp sporophytes on rocks (now green
gravel) for up to two and a half months in the laboratory until the kelp was 2-3cm in
length. Seeding degraded kelp forest with this new green gavel showed promising
results. Green gravel tossed overboard from a boat grew kelp up to 54 cm tall in under
a year. The researchers discovered that 100% of green gravel deployed this way
retained kelp for at least 203 days.

Although further trials are required to understand the full benefits of this simple
approach, green gravel is already a promising alternative tool for kelp forest
restoration. It is cheap, easy to create, and can be scaled up to suit larger areas. These
are the exact results Fredriksen and his team were hoping for, noting that ‘green
gravel … overcomes some of the current major limitations of kelp restoration and
provides promising new defence against kelp forest decline’.

No single approach to restoration will be suitable for all kelp forests, but
understanding how techniques such as green gravel can be used to compliment more
traditional approaches could be the answer to sustain these valuable ecosystems for
future generations, and reap the environmental benefits they provide.