LONG‐TERM CHANGES IN THE MACROALGAL VEGETATION OF THE INNER GULLMAR FJORD, SWEDISH SKAGERRAK COAST¹

Abstract

We examined long‐term changes in the macroalgal vegetation at Stora Bornö Island in the inner Gullmar Fjord on the Swedish Skagerrak coast. This was made possible by access to a 1941 diving investigation. The same sites were reinvestigated in 1998. Community composition and depth distributions of species were compared and changes were analyzed with focus on functional groups (size, thallus shape, and life‐history traits). We discovered a significant decrease in the depth extension of macroalgal species and a dramatic decline of species richness in the lower littoral (below 16 m of depth) compared with 57 years earlier. Ordination analysis revealed that there was a significant difference in the community composition between the two study periods. In general, small (<10 cm), thin, filamentous, and aseasonal ephemerals increased in relative abundance, whereas larger (>10 cm), coarsely branched, and perennial algae decreased. Calibrations of individual species to local sediment cover, using canonical correspondence analysis, indicated that part of the change in species composition was related to sediment load. Furthermore, large‐scale climate differences (NAO Winter Index) between the study periods indicated a higher impact of Baltic Sea and Kattegat water in the nutrient dynamics of the fjord in the 1998 study. We concluded that the observed long‐term changes in the macroalgal community at Stora Bornö Island were consistent with an increased nutrient availability.

Long-term changes in sublittoral macroalgal assemblages related to water quality improvement

“…The effects of pollution on macroalgal assemblages have been reported in previous studies (Bellan-Santini 1968, Munda 1974, Anger 1975, Littler and Murray 1975, Murray and Littler 1978, Belsher 1979, Kautsky et al 1986, Hardy et al 1993, Soltan et al 2001, and several works have examined long-term changes following the onset of sewage discharge , Gorostiaga and Díez 1996, Underwood and Chapman 1996, Díez et al 1999, Bishop et al 2002, Eriksson et al 2002, Echevarri-Erasun et al 2007. However, only a few studies have focused on the recovery of macroalgal assemblages following clean-up measures (Hardy et al 1993, Bokn et al 1996, Archambault et al 2001, Díez et al 2009), and only two have addressed Mediterranean communities (Soltan et al 2001, Tsiamis et al 2013.…”

Recovery stages over long-term monitoring of the intertidal vegetation in the ‘Abra de Bilbao’ area and on the adjacent coast (N. Spain)

“…These authors also point out that there are questions such as nutrient uptake efficiency where these models would be useful. In this way, Eriksson et al (2002) suggest that small, thin, filamentous species were favoured at the expense of large, complex algae on the Swedish Skagerrak coast as result of an eutrophication process. There is also considerable documentation (Munda, 1993;Rodrı´guez-Prieto & Polo, 1996;Are´valo et al, 2007;Pinedo et al, 2007) and experimental support (Benedetti-Cecchi et al, 2001;Gorgula & Connell, 2004) for the loss of large canopy-forming algae in favour of turf-forming algae as a consequence of anthropogenic disturbances.…”

“…Shallow enclosed or semi-enclosed water bodies exhibit worldwide an increased algal growth due to eutrophication (Schramm & Nienhuis, 1996); in these environments, pollution abatement could give rise to a reduction in algal cover (Schernewski & Neumann, 2002). However, eutrophication results in a generally lower light regime and in increased organic sedimentation, factors that seem to entail algal cover decline below the first few metres in depth (Eriksson et al, 2002). Similarly, Krause-Jensen et al (2007) found that total macroalgal cover responds to differences in water quality and salinity between Danish coastal areas, increasing in clear waters and with salinity.…”

“…The decline of large perennial algae under the effect of pollution has been extensively reported, e.g. for several species of kelps (Burrows & Pybus, 1971;Borowitzka, 1972;Littler & Murray, 1975), Cystoseira (Golubic, 1970;Munda, 1980Munda, , 1993Sfriso, 1987;Rodrı´guez-Prieto & Polo, 1996;Cormaci & Furnari, 1999;Benedetti-Cecchi et al, 2001;Thibaut et al, 2005;Pinedo et al, 2007), Fucus (Russell, 1974;Vogt & Schramm, 1991;Bonk et al, 1992;Kautsky, H. et al, 1992;Eriksson et al, 2002), Sargassum (Hirose, 1978;Munda, 1993;Thibaut et al, 2005), Ascophyllum (Rueness, 1973;Bonk & Lein, 1978), Hormosira (Brown et al, 1990) or Gelidium sesquipedale (Gorostiaga & Dı´ez, 1996;Dı´ez et al, 2003). These species are good competitors in habitats with low stress and disturbance, but are progressively replaced by stress-tolerant species when pollutants are introduced into the environment.…”

“…In general, studies on phytobenthic communities subject to pollution have documented a reduction in species richness (Brown et al, 1990;Munda, 1993;Dı´ez et al, 1999), a decline in large perennial algae (Eriksson et al, 2002;Thibaut et al, 2005), and an increase in turf-forming algae (Gorgula & Connell, 2004) and ephemeral species Eriksson et al, 2002). It might be expected that all these responses in community structure would reverse as pollution decreases, but the recovery processes of benthic assemblages are poorly documented (Hardy et al, 1993;Bonk et al, 1996;Gorostiaga & Dı´ez, 1996;Archambault et al, 2001;Soltan et al, 2001).…”