Long-term decline and recent recovery of Fucus populations along the rocky shores of southeast Sweden, Baltic Sea

Abstract

The Fucus populations on rocky shores along 300 km of the coastal waters of southeast Sweden in the Baltic proper have been studied since 1984 at a number of fixed sites as part of monitoring programmes. This paper describes changes in distribution and abundance of F. vesiculosus and F. serratus during the period 1984-2001. Sheltered sites showed a consistent temporal and spatial pattern of Fucus spp. distribution over a coastline of 300 kilometres. The depth penetration and abundance of Fucus spp. increased during the 1980s. Around 1990 the development reversed as a consequence of grazing and in 1997 many sites were almost devoid of Fucus spp. Since 1998 both abundance and depth penetration have increased again, possibly as a result of local measures against eutrophication. Exposed sites, on the other hand, lost their Fucus populations at the beginning of the 1990s, and they have not recovered. Extended field studies lead us to deduce that the fixed sites referred to above were representative of the Fucus populations in the area investigated. Major declines, both at sheltered and exposed sites, are attributed to grazing by the isopod Idotea baltica. The populations of I. baltica may have been favoured by the continuing eutrophication of the Baltic, a series of mild winters in the 1990s, and a contemporary decline in some potential predators.

Effects of eutrophication, grazing, and algal blooms on rocky shores

“…Whether these alternative community states on rocky shores are stabilized by positive feedbacks and are therefore difficult to reverse is an important question that remains to be tested experimentally (Scheffer and Carpenter 2003). On the positive side, recent field surveys indicate the recovery of F. vesiculosus populations and associated fauna in the Baltic Sea following the reduction of nutrient loads (Nilsson et al 2004;Worm pers. comm.).…”

Effects of Pilayella littoralis on Fucus vesiculosus recruitment: implications for community composition

“…At the same time, the distribution of the perennial macroalga Fucus vesiculosus has become more restricted (Kangas et al 1982, Kautsky et al 1986, Schramm 1999, Middelboe & Sand-Jensen 2000, except for some local recovery in recent years (Kautsky 2000, Nilsson et al 2004.…”

Modeling the effects of abiotic and biotic factors on the depth distribution of Fucus vesiculosus in the Baltic Sea

“…The relatively small simulated impact of herbivory on growth rate originates mainly from its highly seasonal nature and the reduced palatability of light-limited plants. The importance of transitory outbursts in the number of consumers, arising from unusually favorable conditions, and their effect on F. vesiculosus (Nilsson et al 2004) might be underestimated by the model. It should, however, be taken into consideration that such observations have only been made with regard to belt width and algal cover and not the depth limit of single plants.…”

“…Kautsky et al 1986, Vogt & Schramm 1991, Eriksson et al 1998. Although partial recovery has been observed at some sites in recent years (Nilsson et al 2004), the general pattern of restricted depth penetration of F. vesiculosus in the Baltic Sea seems to persist (Torn et al 2006). Among other factors, such as direct habitat destruction or increased grazing due to overfishing of the mesograzers' predators, eutrophication is considered to play the most prominent role in this change (Kautsky et al 1986, Eriksson et al 1998, Torn et al 2006.…”

“…Therefore, the weak dispersal capacity of Fucus vesiculosus ) renders single plants at extreme depths irrelevant for the well-being of the ecologically more significant algal belts. Despite such putative limitations in dispersal, re-establishment of relatively isolated belts that had previously disappeared may happen rapidly (within 2 to 3 yr; Nilsson et al 2004). The observed patchiness may also be attributed to the significant reduction of suitable substrate due to stone fishing (the systematic removal of stones from the seabed), rather than stress-induced inability to form distinct belts (Schories et al 2009).…”