REPRODUCTIVE SUCCESS OF FUCUS VESICULOSUS (PHAEOPHYCEAE) IN THE BALTIC SEA

Abstract

Marine organisms colonizing brackish habitats such as the Baltic Sea must cope with the negative effects of low salinities on reproductive success because these may reduce gamete viability and/or increase polyspermy. Reproductive characteristics of the marine seaweed Fucus vesiculosus L. were studied in several brackish habitats, particularly in the northern Baltic Sea, to understand its ability to reproduce where few other marine species survive. Polyspermy and fertilization success were variable at the boundary of the continuous distribution of F. vesiculosus in the Baltic Sea, and polyspermy was high (10%–30%) when fertilization was successful. A strong female bias (80%–86%, ca. 5.5:1) was found at the northernmost limit of Baltic F. vesiculosus. Electrophysiological studies showed that many eggs have a high input resistance (519 ± 150 MΩ[mean ± SE, n = 14] at Drivan, 1995), which may be helpful in preventing polyspermy in this brackish habitat. The polyspermy block remains sodium‐dependent in the northern Baltic. Sperm bound quickly to northern Baltic eggs in natural water, but fertilization was delayed compared to marine F. vesiculosus. A subset of northern Baltic eggs studied during an optimal reproductive period (7–11 July 1995) had a membrane potential (Em) of ca. −100 mV and an effective fertilization potential (FP) of ca. 2 min with a plateau of −25 mV, but repolarized too rapidly for the FP to be protective. Pronuclear migration and cell wall secretion occurred more slowly in Baltic than in marine zygotes. The reproductive success of theseboundary populations may be dependent upon windows of opportunity when there are favorable combinations of the levels of salinity, water motion, population density, and sex ratio. These factors and the short duration of the reproductive season in the northern Baltic Sea may result in reproductive failure in some years.

Functional divergence in heat shock response following rapid speciation of Fucus spp. in the Baltic Sea

“…2a-d). The results reveal divergence between these species at a functional genomic level, even where they occur in mixed stands in the Central Baltic Sea, reinforcing current evidence for species differentiation (reproductive isolation, clonality, divergent morphology, and reproductive success; (Serrão et al 1996(Serrão et al , 1999Bergström et al 2005;Tatarenkov et al 2005;Pereyra et al 2009). …”

“…South of the Central Baltic sympatric site at Ö regrund typical mean annual SST is fairly constant at 9-10°C (Siegel et al 2006). The HSR of F. radicans suggests that thermal stress and/or growth temperature requirements could play a role in excluding this species from more southerly parts of the Baltic, restricting it to marginal habitats, where sexual reproduction (particularly male function) is compromised by low salinity conditions (Serrão et al 1996(Serrão et al , 1999, and clonal reproduction is an advantage .…”

“…Decreasing sea surface temperature (SST) from the western to the northern Baltic (Siegel et al 2006) has received less attention than salinity clines, despite the important role of thermal stress in marine biogeography (Somero 2005). While it has been established that extreme low salinity (3-4 PSU in the Gulf of Bothnia) has negative effects on fucoid reproductive ecology (Serrão et al 1996;Serrão et al 1999), gradients of both salinity and SST may affect broader distributional patterns of Fucus spp. in the Baltic.…”

Spatial and temporal variability in dispersal and population genetic structure of a rockpool alga

“…Thus, even if pools are isolated from bulk seawater on the high tide immediately following release, dispersal of zygotes is still possible on subsequent high tides when there may be exchange of water among pools. Both the low sperm:egg ratio of monecious fucoids and gamete longevity favor the higher than expected dispersal of F. distichus occurring mainly through continued dispersal of unattached zygotes versus from gametes (Brawley 1991, Serrão et al 1999a).…”

Seasonal variations of Fucus vesiculosus fertility under ocean acidification and warming in the western Baltic Sea

“…Increase in temperature and/or exceeding temperature thresholds, either alone or in combination with irradiance, stimulate receptacle and gamete maturation in fucoids (Mathieson et al 1976, Pearson and Brawley 1996, Kraufvelin et al 2012. Finally, gamete release seems to be governed by endogenous free-running circadian or circalunar cycles (Pearson and Serrão 2006), which may be synchronized by environmental factors such as tidal height, wave action, salinity (Serrão et al 1999, Ladah et al 2008, time of day and lunar phase (Andersson et al 1994). The endogenous cycles, however, have not been unequivocally identified in fucoids.…”