This seahorse, which doesn’t live in the sea, needs South Africa’s help to survive
At 3.30am on 25 May 2021, the big excavator rumbled into life, tearing open the last bit of sand separating Swartvlei estuary from the sea. Over the next few days water levels in the estuary on the doorstep of Sedgefield began to drop.
Seagrass and other aquatic plants became exposed in the shallows. By 28 May, citizen scientist volunteers were finding Knysna seahorses (Hippocampus capensis) lying motionless, their tails wrapped tightly around the plants. Without water, these creatures will dehydrate and die, so the rescue work continued well into the weekend.
These seahorses are classified as endangered and are found only within a 70km stretch of the southern Cape coast. They are the only seahorses that don’t live in the sea.
Swartvlei is typically closed to the sea for five to nine months a year.
But SANParks, which called in the excavator, must balance ecological and other needs. Sometimes this demands artificially breaching the estuary. By 25 May the Swartvlei’s waters had reached the threshold, 1cm shy of the authorised breaching height, 2m above mean sea level.
Compromise needed
Jonathan Britton, SANParks marine ranger, says intervention was unavoidable because the agency was managing a “compromised system”. “The development of low-lying properties on the floodplains has resulted in a situation in which a compromise is needed. The estuary needs to be mechanically breached to balance ecological, social and hydrological needs,” he says.
Natural system
The estuary is used by recreational and subsistence fishers from a variety of backgrounds – some well off, others less so; some live nearby, others are holidaymakers. Fishing, of course, depends on there being fish, and the natural functioning of the estuary system is key to maintaining healthy fish populations. Many fish species come into the estuary when the mouth is open, some to breed, because the estuary’s vegetation gives juvenile fish somewhere to hide. Closed, the estuary provides stable conditions that allow plants and the web of life that depends on them to flourish. “The closed period is actually very productive for the estuary, but often misunderstood for being stagnant and lifeless,” SANParks Scientific Services marine biologist Clement Arendse explains.
Citizen science
Arendse says previous estuary openings have resulted in between 10 and 1,000 seahorses stranding.
He praised his team of dedicated citizen scientists for their help with monitoring the number of seahorses stranded – and returning as many as possible to the water. Hearsay suggested to Arendse, a newly appointed SANParks marine biologist at the time, that the seahorse population was high in 2017. So before the estuary opened, Arendse revived the Seahorse Citizen Science Programme.
It was a good thing he did, because that year more than 1,000 stranded seahorses were found by his citizen scientists. Half were still alive and returned to submerged seagrass. The others were donated to science so their bodies could be used to un
derstand more about their populations.
Prohibited species
Seahorses are a prohibited species under the Marine Living Resources Act, which makes it illegal to handle or be in possession of them without a permit. This year with a temporary permit in hand I was one of the seahorse citizen scientists.
Led by SANParks honorary ranger Joan Musto, at one bank we began searching in the seagrass, picking out seahorses and putting them in our buckets filled with water. For lack of anything else to hold on to, two of the seahorses in my bucket linked tails and held on to each other for a time. Wading out to a deep patch of seagrass, I released each of them, watching them flutter down until they disappeared into the grass.
This Ocean Watch story is part of Roving Reporters’ biodiversity writing project, supported by Youth4MPAs and the Earth Journalism Network. Rio Button is a conservation biologist and freelance environmental writer. Follow her @biologistbutton on Instagram and Twitter