The Ria Formosa lagoon, Portugal
The Ria Formosa lagoon was once home to one of the densest population of seahorses in the world. Today that population has significantly decreased.
Iain Caldwell, Project Seahorse PhD candidate and his volunteer helper Blake McDonald
Iain Caldwell, a Ph.D. candidate with Project Seahorse, set out to learn how and why the populations of the two European seahorses have shifted.
Two seahorse species are found in the lagoon - the long-snouted seahorse and the short-snouted seahorse. Both are listed on the IUCN Red List.
Seahorses in the lagoon were thought to live mainly in seagrass and algae dominated habitats. Iain found something different....
Iain went looking for seahorses throughout the lagoon. When he found them he recorded their GPS locations, and measured temperature, water depth, pH, current speed and other environmental factors.
Capturing seahorses
Iain then captured a few seahorses and brought them to the surface to be measured and then tagged.
The seahorses were measured to make sure that they were large enough to wear a tag and to find out whether larger seahorses move more than smaller seahorses.
Acoustic tags where attached to the seahorse's neck and activated.
Iain then returned the tagged seahorses to a new location in the lagoon and then tracked where they moved from day to day using a hyrdophone and an acoustic receiver.
Iain discovered that within 5-10 days seahorses were found within a metre of another seahorse, even in sites where seahorses had not been found before.
Seahorse curled around an urchin
Seahorses were found in unexpected locations, using holdfasts such as urchins and tubeworms rather than seagrass. Water depth has changed throughout the Ria and could be a reason for the shift in population locations.
The information Iain collected from the tagged seahorses and their environment may also help us to understand why this particular species has declined by 93% in the lagoon in recent years. We are sharing our findings with Parque Natural da Ria Formosa to help them address the problem.