Research Article: Reproductive output of a non-zooxanthellate temperate coral is unaffected by temperature along an extended latitudinal gradient

Date Published: February 3, 2017

Publisher: Public Library of Science

Author(s): Valentina Airi, Selena Prantoni, Marco Calegari, Veronica Lisini Baldi, Francesca Gizzi, Chiara Marchini, Oren Levy, Giuseppe Falini, Zvy Dubinsky, Stefano Goffredo, Christina A. Kellogg.

http://doi.org/10.1371/journal.pone.0171051

Abstract

Global environmental change, in marine ecosystems, is associated with concurrent shifts in water temperature, circulation, stratification, and nutrient input, with potentially wide-ranging biological effects. Variations in seawater temperature might alter physiological functioning, reproductive efficiency, and demographic traits of marine organisms, leading to shifts in population size and abundance. Differences in temperature tolerances between organisms can identify individual and ecological characteristics, which make corals able to persist and adapt in a climate change context. Here we investigated the possible effect of temperature on the reproductive output of the solitary non-zooxanthellate temperate coral Leptopsammia pruvoti, along an 8° latitudinal gradient. Samples have been collected in six populations along the gradient and each polyp was examined using histological and cyto-histometric analyses. We coupled our results with previous studies on the growth, demography, and calcification of L. pruvoti along the same temperature gradient, and compared them with those of another sympatric zooxanthellate coral Balanophyllia europaea to understand which trophic strategy makes the coral more tolerant to increasing temperature. The non-zooxanthellate species seemed to be quite tolerant to temperature increases, probably due to the lack of the symbiosis with zooxanthellae. To our knowledge, this is the first field investigation of the relationship between reproductive output and temperature increase of a temperate asymbiotic coral, providing novel insights into the poorly studied non-zooxanthellate scleractinians.

Partial Text

Anthropogenic-derived climate change is the main source of environmental perturbation on a global scale, with an accelerated rate of increasing temperature that exceeds many pessimistic projections [1]. Combined with rising sea levels and shifting weather patterns, warming will have significant impacts on global biodiversity and ecological functioning [1, 2]. Given the substantial impact of climate change on ecological communities [3], studying how environmental parameters affect population persistence, community structure and the sustainable delivery of ecosystem services is a major challenge for conservation biology and ecosystem management [4].

Mean annual DT (°C) and mean annual SR (W/m2) were significantly different among sites (monthly DT, χ2 = 13.16, df = 5 and p-value < 0.05 in Kruskal-Wallis test; monthly SR, F = 84.36, df = 5 and p-value < 0.001 in ANOVA test; Table 1). All populations along the gradient were characterized by a gonochoric sexuality with male and female polyps. However, the Elba Isle population showed only females, not allowing the analysis of spermatogenesis for this site. L. pruvoti seems to be quite tolerant to the natural temperature range experienced in the field, since its organismal performance, such as population abundance, skeletal architecture and density, calcification rate [21, 23, 26], population dynamics [25], and reproductive output (present study), does not vary with temperature along the latitudinal gradient examined. However, the temperature threshold that this species will be able to tolerate is still unknown. Testing other environmental parameters not considered in this study, such as nutrients, zooplankton availability and turbidity, is crucial in order to verify the hypothesis that different responses between non-zooxanthellate (L. pruvoti) and zooxanthellate (B. europaea) species might depend on their different trophic systems. Further investigations are needed to better understand the environmental control on the ecology of these species, which may shed light on their potential resistance in the progressively warming Mediterranean Sea.   Source: http://doi.org/10.1371/journal.pone.0171051