Morphological and genetic variation ofFucusin the eastern Gulf of Bothnia, northern Baltic Sea

Abstract

Fucus vesiculosus and F. radicans (Phaeophyceae) are important habitat-formers on rocky shores in the Bothnian Sea. While both species occur sympatrically along the entire western Bothnian Sea coast, F. radicans has been found only in the northern part of the eastern coast. According to previous studies, the two species can be distinguished based on morphology, F. radicans having narrower thalli and a bushier appearance. However, marine mapping in the eastern Bothnian Sea has revealed that high morphological variation in Fucus, partly caused by gradients in salinity and exposure, makes differentiation between the two species difficult. We studied morphological and genetic variation to find out whether the two Fucus species can be differentiated in the southeastern Bothnian Sea, and if F. radicans occurs in the area. The study was carried out in six subareas including 350 km of coast, with a salinity gradient of 3.5-6.5 PSU, and varying wave exposure. We found a gradual change towards smaller and narrower thalli and a higher number of holdfasts in Fucus populations when moving northwards to lower salinities. Distinct Fucus morphs were often found within the study sites but the morphs were genetically differentiated only at one study site in the Skaftung subarea, suggesting the occurrence of both species. However, in the Vasa subarea the sample size for analysing genetic differentiation was low due to high clonality. In the Luvia subarea south of Skaftung, Fucus morphology corresponded to that of F. radicans in earlier studies but the population was genetically more similar to F. vesiculosus in the southern subareas. We conclude that by using only morphological characteristics it is not possible to differentiate between the two species in central and northern parts of the eastern Bothnian Sea. Based on genetic analyses, the southernmost known occurrence of F. radicans in the eastern Bothnian Sea is in Skaftung.

Clonality, polyploidy and spatial population structure in Baltic Sea Fucus vesiculosus

“…Previous results on spatial genetic structuring of the Baltic Sea F. vesiculosus population have been somewhat mixed. Our work is in line with previous results showing strong structure among spatially closely located populations along the Swedish east coast (Pereyra et al, 2009 ; Tatarenkov et al, 2007 ), the Finnish west coast (Rinne et al, 2018 ), and also at larger scales (Ardehed et al, 2016 ; Johannesson et al, 2011 ). Contrary to this, a wide‐scale study only found significant genetic structuring among local attached F. vesiculosus populations in the Gulfs of Bothnia and Riga, but not among the regions (Pereyra et al, 2013 ).…”

“…Polyploidy has not been found in previous genetic studies of Baltic Sea F. vesiculosus (Ardehed et al, 2016 ; Johannesson et al, 2011 ; Pereyra et al, 2009 ; Rinne et al, 2018 ; Tatarenkov et al, 2005 , 2007 ), but has infrequently been reported elsewhere in Fucus spp. (Coyer, Hoarau, Pearson, et al, 2006 ; Gómez Garreta et al, 2010 ; Sjøtun et al, 2017 ).…”

“…To our knowledge, however, polyploidy has not been documented in the Baltic Sea F. vesiculosus and all previous genetic studies have assumed a diploid genetic system (e.g. Ardehed et al, 2016;Johannesson et al, 2011;Rinne et al, 2018).…”

Geographic variation in fitness‐related traits of the bladderwrack Fucus vesiculosus along the Baltic Sea‐North Sea salinity gradient

“…Morphology is (within genetic limits) an integrative response of F. vesiculosus to environmental drivers such as irradiance, nutrients, temperature, salinity, and/or hydrology (see Rinne, Björkman, Sjöqvist, Salovius-Laurén, & Mattila, 2018 and citations therein). The frond length, frond width, and stipe width were directly measured in the field for every individual collected in 17 of the 24 stations, covering the overall salinity gradient (see Figure 2).…”

The status of brown macroalgae Fucus spp. and its relation to environmental variation in the Finnish marine area, northern Baltic Sea

“…F. vesiculosus is widely distributed extending to approximately 3.5 PSU salinity in the north (Bergström and Bergström 1999; Schagerström 2013) and to even lower salinities in the eastern Gulf of Finland (Lehvo and Bäck 2000; Ardehed et al 2016). Fucus radicans, endemic to the Baltic Sea (Pereyra et al 2009), occurs mainly in the Gulf of Bothnia (Johannesson et al 2011; Rinne et al 2018) but also along the west coast of Estonia and in the eastern Gulf of Finland (Pereyra et al 2013; Schagerström 2013; Ardehed et al 2016). The Fucus of the northern Baltic Sea show high genetic and morphological variation both on large and more local scales (Tatarenkov et al 2007; Ardehed et al 2016; Rinne et al 2018), complicating their distinction to two species.…”