Over the last decades, Fucus vesiculosus, an ecologically important macroalga in the German Baltic Sea, has shown a massive retreat from the deeper zones of its former distribution presumably due to low light co-acting with other potential stressors such as high temperature, fouling, and grazing. Global warming may increase abiotic as well as biotic pressures and exacerbate environmental conditions in coastal ecosystems. The present study focussed on the effects of single or subsequently combined stressors on survival and palatability of juvenile F. vesiculosus. Fucoid offspring were exposed to high temperature and/ or feeding pressure. Feeding preference of Idotea baltica was quantified in a pellet assay calculated as an odds ratio. High temperature significantly impaired the survival of juvenile fucoids. Neither single nor combined stress considerably influenced the feeding preference of I. baltica. Surprisingly I. baltica strictly avoided pellets with juvenile F. vesiculosus compared to adult F. vesiculosus. Avoidance tended to be less pronounced in juvenile fucoids previously stressed by high temperature. Obviously grazing does not induce anti-herbivore defence, but rather the young plants appeared constitutively well-protected against isopod feeding. These results contradict the prevailing opinion that juvenile F. vesiculosus is more susceptible to herbivore grazing than adult F. vesiculosus.
A reestablishment of Fucus vesiculosus where it is locally vanished would be an indicator for improved water quality. Thus the Agency for Agriculture, Environment and Rural Areas of Schleswig - Holstein (LLUR) is thinking about opportunities to resettle F. vesiculosus. On behalf of RADOST project, the tolerance of early fucoid life stages towards thermal stress was analysed and after four days of thermal treatment a high percentage of the treated fucoid offspring survived. It might be that inside species genotypes exist which are less sensitive against future environmental changes.
Over the last decades, Fucus vesiculosus, an ecologically important macroalga in the German Baltic Sea, has shown a massive retreat from the deeper zones of its former distribution presumably due to low light co-acting with other potential stressors such as high temperature, fouling, and grazing. In shallow water F. vesiculosus may be exposed to high water temperatures during summer seasons. Intensity and frequency of heat waves are expected to increase due to climate change which could potentially affect all fucoid life stages. Early life stage processes (fertilization, germination) are often considered particularly sensitive to stress. If the mortality caused by a first heat wave in a genetically diverse population selects for stress resistance, we would expect the survivors to be less sensitive to a second heat wave or possibly even to other stressors like feeding pressure.
In the present study, the mortality of early post-settlement stages of F. vesiculosus under thermal stress and the sensitivity of survived recruits against a proximate stressor (feeding pressure, second heat wave) were analysed by laboratory experiments. The mortality of early fucoid life stages at 25°C, compared to their mortality at 15°C was significantly higher. Regrettably, the ensuing assessment of feeding impact by Idotea baltica and Hydrobia ulvae on the surviving germlings could not be analysed since the two consumer species unexpectedly avoided feeding on the young stages of F. vesiculosus. During the second thermal stress experiment fucoid offspring which was genetically preselected by high temperature (first heat wave: 25°C) differed not significantly in sensitivity from fucoid offspring without prior stress.
Effects of sequential stressors on survival of young life stages of the bladder wrack Fucus vesiculosus L.
(2014)
