New research finds that “marine reserves” – tracts of ocean where fishing is banned – are protecting fish, the coral reefs where they live and vast undersea "gardens," a lot more than once thought.

Large-scale commercial fishing has, for years, been depleting fish-stocks in many places around the world - especially in coral reefs in the tropics. In response, several countries have designated certain areas of the sea as "marine reserves," where neither fishing nor other development is allowed. Now, a team of scientists from US and Australian universities has produced compelling new evidence. It shows these reserves have not only been helping stocks rebound, but are also protecting massive coral "food webs" - beds of sea-grasses and algae - important reservoirs for carbon storage. 

by Larry Powell

In this satellite photo, "halos" appear as pale blue circular bands 
surrounding tiny dark spots.The spots are likely small patch reefs 
or other shelter for small fish and invertebrates that protect them 
from predators. Each halo is probably about 10 meters wide. 
The more there are, the healthier marine life there is likely to be.

Using hi-rez images from both satellites and underwater cameras, the researchers studied hundreds of small, tropical reefs in the huge Great Barrier Reef complex off Australia. 

Those images detected about two-&-a-half times more halos within the reserves than elsewhere. The more halos, the healthier the reef is considered to be as a home for both fish and invertebrates. 

These pale blue, circular bands surrounding the small dark spots, are where herbivorous, or plant-eating fish and some marine mammals, venture out to graze on surrounding vegetation such as algae or seagrass. Then, they dart back in, using the reefs as protection from the predators. 

The scientists refer to the halos as "seascape-scale footprints" of healthy, increased activity in aquatic life.

Elizabeth M.P. Madin, Ph.D.

Assistant Research Professor
Hawaii Institute of Marin Biology

University of Hawaii at Manoa, USA.

The spokesperson for the study, Dr. Elizabeth Madin (above), tells PinP, "What the halos are telling us is that marine reserves - especially older ones - where predator and herbivore populations have had sufficient time to recover from previous fishing - are protecting key species and their resulting interactions.

"Specifically," she adds, "we’re more likely to see halos in especially older reserves (40 years old or so), which suggests that predators and prey are in sufficient numbers there to interact and cause these halo patterns." 

Since halos can also be found in some ares unprotected from fishing, the team calls for more research to further confirm the connection.

Among groups funding the research were the World Wildlife Fund and the US National Science Foundation.

The findings were published recently in the proceedings of The Royal Society in the UK and in Frontiers in Ecology and Evolution.  

But the benefits of marine reserves, don't stop here.

"Importantly," Dr. Madin goes on, "we know from another of our studies, that halos affect carbon storage. So, not only are marine reserves re-shaping coral reef landscapes on very large scales in ways we didn’t know about before, but they’re also affecting a key ecosystem service - carbon storage."

She's referring to a truly fascinating undersea scenario in which predator fish actually play a beneficial - albeit indirect - role in carbon sequestration. A healthy habitat means more predators. Their prey, often herbivorous fish or marine mammals, cling to the relative safety of their home reefs and don't venture too far afield to find plants to eat. 

Dugongs, a type of marine mammal, are
known to be capable of decimating sea-grass beds
as they graze. Photo taken in an oceanarium in Jakarta.

This spares massive sea-scapes of algae and sea-grasses nearby, which would otherwise be stripped by the plant-eaters. Instead, the vegetation grows taller and denser, greatly increasing its capacity to store carbon, thus providing a significant buffer against climate change.

Not only are the number of marine reserves growing, worldwide, they're getting bigger, too (some more than 100 thousand km2). Nineteen of these "mega-reserves" have been established since 2009. And happily for the sea-life living there, the research finds, the bigger the reserves, the more protection they offer!

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