Abstract
The demographic traits of the solitary azooxanthellate scleractinian Leptopsammia pruvoti were determined in six populations on a sea surface temperature (SST) gradient along the western Italian coasts. This is the first investigation of the growth and demography characteristics of an azooxanthellate scleractinian along a natural SST gradient. Growth rate was homogeneous across all populations, which spanned 7 degrees of latitude. Population age structures differed between populations, but none of the considered demographic parameters correlated with SST, indicating possible effects of local environmental conditions. Compared to another Mediterranean solitary scleractinian, Balanophyllia europaea, zooxanthellate and whose growth, demography and calcification have been studied in the same sites, L. pruvoti seems more tolerant to temperature increase. The higher tolerance of L. pruvoti, relative to B. europaea, may rely on the absence of symbionts, and thus the lack of an inhibition of host physiological processes by the heat-stressed zooxanthellae. However, the comparison between the two species must be taken cautiously, due to the likely temperature differences between the two sampling depths. Increasing research effort on determining the effects of temperature on the poorly studied azooxanthellate scleractinians may shed light on the possible species assemblage shifts that are likely to occur during the current century as a consequence of global climatic change.
Highlights
Climate change is the defining environmental, economic, and social issue of our time, and it is certain that the rapid increase in CO2 concentration in the atmosphere since the 19th century industrial revolution is driving significant changes in the physical and chemical environment of Earth [1]
The correlation between average daily sea surface temperature (SST) data from data banks and average daily temperature data collected by the digital thermometers at 16 m produced r2 values ranging from 0.784 to 0.935, indicating that 78–94% of the variance of seawater temperature at 16 m is explained by SST variations (Fig. S1)
All sites were characterized by a negative exponential relationship between mean growth rate and age, with age explaining 45– 74% of growth rate variance (Fig. 3)
Summary
Climate change is the defining environmental, economic, and social issue of our time, and it is certain that the rapid increase in CO2 concentration in the atmosphere since the 19th century industrial revolution is driving significant changes in the physical and chemical environment of Earth [1]. The rate of global climatic changes is accelerating, and the average surface temperature of the Earth is likely to increase by 1.1–6.4uC by the end of the 21st century [2]. Synergy among increased seawater temperature, enhanced ultraviolet-B (UVB) radiation, surface ocean acidification, and human anthropogenic stress is affecting all levels of ecological hierarchies in a broad array of marine ecosystems [4]. The Mediterranean basin is likely to be one of the regions most affected by the ongoing warming trend and by an increase in extreme events [5], representing a natural focus of interest for research. The enhancement of interactions between climate change and many other disturbances such as eutrophication caused by fertilizer runoff and the damming of rivers [7] all increase the stresses to which Mediterranean biota are exposed
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