Seahorses were first identified at Studland Bay about 10 years ago
The UK's largest known colony of seahorses is threatened by boat-owners mooring vessels on the animals' natural habitat, Dorset campaigners have said.
The Seahorse Trust has tracked the animals for 10 years and believes the anchoring of boats at Studland Bay is risking the animals' existence.
Last year seahorses were registered as a protected species for the first time.
A scientific survey of the area has been commissioned to assess the impact of moorings on their habitat.
SeaStar Survey has been appointed by The Crown Estate and Natural England to undertake an independent scientific study of the region.
Protected by law
Last year spiny and short-snouted seahorses were added to Natural England's list of protected species which states the animals would be protected against "killing, injuring or taking".
The listing also seeks to protect them against the "damage or destruction of its places of shelter, or disturbance while such animals are occupying places of shelter".
The Seahorse Trust has seen 40 animals in Studland Bay
But Steve Trewhella, of the Seahorse Trust, said: "These animals are protected by law but so far very little has been done to protect them."
The estimated population of the Studland Bay colony is about 40 seahorses and Mr Trewhella has begun tagging the animals in an effort to track and monitor their existence.
Seahorses are unusual for the fact the male carries the young during impregnation, and The Seahorse Trust has been tracking pregnant seahorses.
A spokesman for Natural England said: "The seahorses were discovered in the bay about 10 years ago.
"Evidence shows the eelgrass bed is expanding and we think that the seahorse population is expanding as well.
"As yet there is no evidence that boat activity is affecting the seahorse population, which is why we have commissioned the study to investigate."
The Crown Estate, which owns the seabed, said on its website it is unable to take action on anchoring as it has no legal right to do so.
The seabed study is expected to take two years to complete.