What Makes the Difference?—Sea Sturgeon on Both Sides of the Atlantic Ocean
Arne Ludwig and Jörn Gessner
Abstract. – Sea sturgeons are closely related anadromous fishes inhabiting both shores of the North Atlantic Ocean. They are classified in two species: the European sturgeon Acipenser sturio in Europe and the Atlantic sturgeon A. oxyrinchus in North America. The Atlantic sturgeon is further separated into two subspecies: Atlantic sturgeon (North American East Coast populations) A. o. oxyrinchus and Gulf sturgeon A. o. desotoi. Most recent studies of morphology and genetics support these classifications. Furthermore, they produced evidence for a trans-Atlantic colonization event during the early Middle Ages. Atlantic sturgeon colonized Baltic waters, founding a self-reproducing population before they became extinct due to anthropogenic reasons. Today, populations of Atlantic sturgeon are found along the Atlantic Coast from the St. Johns River, Florida to the St. Lawrence River, Quebec, whereas only one relict spawning population of European sturgeon still exists in the Gironde River, France. The evidence of a population of Atlantic sturgeon in Baltic waters requires a detailed comparison of both sea sturgeon species, describing differences and similarities, which may influence the ongoing restoration projects in Europe as well as concerning conservation efforts in North America. This article reviews similarities and differences in the fields of genetics, morphology, and ecological adaptation of European sturgeon and Atlantic sturgeon, concluding that, besides morphological and genetic differences, a wider range of spawning temperatures in Atlantic sturgeon is evident. This wider temperature adaptation may be a selective advantage under fast-changing climatic conditions, possibly the mechanism that enabled the species shift in the Baltic Sea during the Middle Ages.