Repeated bleaching events may result in high tolerance and notable gametogenesis in stony corals: Oculina patagonica as a model

Abstract

Coral bleaching events (BEs) are occurring in coral reefs worldwide and are expected to become annual, triggered by seasonal changes in water temperature. The stony coral Oculina patagonica experiences repeated seasonal BEs along the Israeli Mediterranean coast. It thus constitutes a good model for assessing the potential effects of expected repeated BEs on coral physiology. Previous studies have shown that the overlap between bleaching and reproduction seasons in O. patagonica impedes gametogenesis. In the present study, we assessed the effect of bleaching on gametogenesis of populations commonly undergoing repeated seasonal BEs, and compared it with the effect of first and second summer BEs on gametogenesis of a population that has not experienced a summer BE in recent years. Interestingly, we found no differences between bleached and non-bleached colonies in most of the reproductive parameters tested in populations undergoing repeated seasonal BEs. We did find, however, that a population that experienced a summer BE for the first time presented significantly lower reproductive parameters in bleached colonies when compared to non-bleached colonies. Furthermore, in the following year, such bleached colonies showed an improvement in reproductive performance when compared to the previous year. The remarkable differences in gametogenesis between colonies experiencing first summer BE and those experiencing repeated seasonal BEs may be the result of improved utilization of alternative energy sources. This study provides the first evidence for notable gametogenesis in corals undergoing repeated bleaching, and suggests that adjustment processes may increase tolerance levels and may play a role in the ability of corals to overcome the expected repeated BEs.

Rapid Northward Spread of a Zooxanthellate Coral Enhanced by Artificial Structures and Sea Warming in the Western Mediterranean

“…The present study has characterized the rapid northward expansion of a coral species at high latitudes (40–42°N), a process that has been enhanced by artificial reef structures ahead of the migrating coral. Furthermore, O. patagonica is able to reproduce under the environmental conditions at these high latitudes (authors' unpublished data) and even adapt to the effects of repeated bleaching events [34]. Thus, a coral species with particular biological characteristics that allow it to withstand the temperature challenge that accompanies northward migration as well as the natural and anthropogenic side effects that this type of migration involves (i.e., competition with macroalgae, high sediment loads, turbidity, water chemistry) has accomplished a successful northward expansion and may be able to keep pace with the global warming prediction of ∼3°C over the next 100 years.…”

“…Both asexual dispersal in the form of polyp expulsion [33] and the release of gonads from colonies attached to ship hulls [29], which is favored because the species is capable of reproducing sexually when colonies are small [31], have been proposed as the primary vectors of invasive transport. Moreover, the species' ability to thrive and reproduce despite wide variations in temperature, salinity, UV radiation, turbidity and hydrodynamic conditions [31], [34] may have favored the species' spread throughout the Mediterranean.…”

Evidence for multiple stressor interactions and effects on coral reefs

“…However, there is considerable variety in species-specific responses (e.g., Abramovitch-Gottlib et al, 2003;Zhu et al, 2004;Abrego et al, 2008;Yee et al, 2008), as well as evidence for a possible mitigating effect of pre-exposure to irradiance on subsequent temperature exposure (Brown et al, 2002;Brown & Dunne, 2008), and acclimation to both temperature and irradiance (Robison & Warner, 2006;Visram & Douglas, 2007;Armoza-Zvuloni et al, 2011). Factors such as heating rate (Middlebrook et al, 2010) and preconditioning (Bellantuono et al, 2012) also introduce additional variation into the stress response.…”

Long-term reduced spawning in Orbicella coral species due to temperature stress

“…Although O. annularis appeared to be more stressed and was less likely to spawn during the 2010 event, this shallower species, which also showed signs of bleaching in 2005, exhibited a more rapid recovery over the subsequent 3 yr interval. Reefs with a history of frequent bleaching events are more resilient to these events (Armoza-Zvuloni et al 2011). The pattern noted among these Orbicella species indicates that this is also true within a reef among species.…”

“…Mendes & Woodley (2002) documented a 2 yr reduction in gonad development for mildly affected (bleached for 2 mo, pale for 5 mo) and more severely affected (bleached for 4 mo, pale for 7 mos) corals. Corals on reefs ex posed to frequent bleaching events appear to partially acclimate to the stress and reproduce at a greater rate compared to corals on reefs bleaching less frequently (Armoza-Zvuloni et al 2011).…”