Nasrolahi, Ali (2012) Stress ecology: interactive effect of temperature and salinity on early life stages of the barnacle, Amphibalanus improvisus. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, Germany, 142 pp.

Preview

Text Nasrolahi_Diss.pdf - Published Version Available under License German copyright act UrhG. Download (2MB) | Preview

Abstract

It is well accepted by now that in the course of global change, several potential stressors will appear and intensify simultaneously and may exhibit antagonistic, additive, or synergistic effects, which make predictions based on the assessment of single stressors unreliable. Intertidal barnacles, as conspicuous, widely distributed, and ecologically important species have served to study the effects of environmental factors for decades. The interactive effect of putative stresses such as supra- or suboptimal temperature and salinity on early stage performance and survival of barnacles has, however, been subject of only a few studies. Early life stages seem to be particularly sensitive to environmental changes and alteration of their fitness might drastically affect subsequent life stages and subsequently the whole population. Responses toward multiple stressors of Amphibalanus improvisus, the dominant barnacle species within the Western Baltic Sea, have not been investigated so far, neither in larval stages nor in juveniles. In this study, I first focused on the combined effects of temperature (12, 20 and 28°C) and salinity (5, 15 and 30 psu) on pelagic phase (naupliar and cypris stages) of A. improvisus. Also, there is an urgent need for comparative assessment of separate populations from one species to enhance our ability to extrapolate local results to regional or global scale. Therefore, I evaluated the performance of early stages of two different populations of the Baltic Sea (one at Kiel Fjord, Germany and another one at Tjärnö, Sweden) under different temperature and salinity combinations. Afterwards, I concentrated on early benthic phase (juvenile) of this species and had a closer look on the critical and relatively neglected transitional period between the cyprid and the adult stage (settlement and early juvenile). Because of the exteremly important function of biofilms in attachment processes of barnacles and the potential interaction with their macroalgal host, I furthermore, investigated the effect of biofilms composed of macroalgal epbiotic bacteria, on the number of attached cyprids in field assays. Naupliar duration of A. improvisus from Kiel population increased with decreasing temperature) and, nauplii survival decreased with increasing salinity. Cyprid metamorphosis success, in contrast, was interactively impacted by temperature and salinity. Highest settlement rates occurred at the intermediate temperature and salinity combination, i.e., 20°C and 15 psu. Settlement success of “naive” cyprids, i.e., when nauplii were raised at 20°C/15 psu, was less impacted by stressful temperature/salinity combinations than that of cyprids with a stress history. The proportion of nauplii that transformed to attached juveniles was highest under “home” conditions (local conditions during peak settlement i.e., 20°C/15 psu). In contrast to Kiel population that performed relatively better at home conditions of temperature and salinity, barnacles from Tjärnö population showed a better performance at lower salinities and higher temperatures than that of typical for Sweden west coast during the season of peak settlement. Juvenile mortality was high (42 - 63%) during the first week following attachment under all temperature and salinity treatments. Highest mortality and lowest growth of juveniles occurred at lowest temperature (12°C) and salinity (5 psu). Juvenile barnacles constructed more shell material compared to soft body mass at low temperature and low salinity while the reverse was observed at high temperature and high salinity. Barnacle attachment is reduced by monospecies bacterial biofilms and natural microbial assemblages (originally isolated from Fucus) by 20% to 67%. However, the repellent effects of bacterial bifilms were no longer observed when settlement pressure was high. The composition and abundance of biofilms on macroalga (Fucus vesiculosus), a potential host for barnacles, were affected by temperature which led to a reduction of their repellent effects by 60% at high temperature. In summary this thesis shows that stressors may enhance the high natural mortality when occurring at crucial ontogenetic phases (larval and early juvenile stages). The responses of different populations to these stresses may differ as observed for Kiel and Tjärnö population of A. improvisus. Low performance of Tjärnö barnacle larvae at its local conditions implies that this population is apparently maladapted to its habitat. For the juveniles, environmental changes can alter patterns of survivorship and growth. Warming and desalination as predicted for the Baltic Sea in the course of climate change may, however, act antagonistically and compensate each other’s isolated effect on juvenile barnacles. Indirectly, barnacle settlement may be impacted by stress-driven shifts in epibiotic biofilms. However, high settlement pressure may outrun any effects of biofilm.

Actions (login required)

View Item