Upper-mesophotic and shallow reef corals exhibit similar thermal tolerance, sensitivity and optima

The physiology of ectotherms living in marine environments is strongly influenced by their local thermal experience. Scleractinian corals living near their thermal optimums are increasingly vulnerable to bleaching and mortality as oceanic heat waves increase globally. Mesophotic coral ecosystems (MCEs) below 30 m depths are characteristically cooler than adjacent shallow water reefs, which according to theory should result in differential metabolic responses to temperature between depths. How local temperatures influence physiological responses in mesophotic corals is poorly understood. We compared thermal sensitivities of four coral species between a shallow (5–10 m) and upper-mesophotic (30−35 m) reef in Bermuda. Thermal performance curves (TPC) were measured in laboratory mesocosms for four common coral species (Diploria labyrinthiformis, Orbicella franksi, Montastraea cavernosa andPorites astreoides) across a wide range of temperatures (19−36). Our results indicate that the maximum rate of gross photosynthetic (GP) performance (GP-Pmax) and the mean overall photosynthetic rates (GP-lnc) varied significantly among species. In contrast, thermal sensitivity (Pmax, Topt, lnc, E, Eh, or Th) did not vary between depths for conspecifics except for deactivation energy (GP-Eh) in D. labyrinthiformis. Additionally, gross respiration (R) did not differ among species or between depths for any thermal metric. Similar metabolic responses between depths suggest that local adaptation and/or acclimatization to different thermal conditions is likely not occurring. Instead, upper-mesophotic corals in Bermuda do not have lower bleaching thresholds than shallow water conspecifics, but similar thermal sensitivities supporting the potential for MCEs to function as a thermal refuge

Self-fertilization as a mechanism for population maintenance in a changing environment

The scientific aim of this study is to examine genetic diversity and parentage of B. europaea in the Mediterranean to determine the relative importance of self-fertilization for population maintenance and if the degree of self-fertilization varies with population demography, which can then be extrapolated to estimate the effects of changing seawater temperature. This goal will be achieved by conducting direct comparisons of progeny and parental genotypes using six previously developed B. europaea specific microsatellite loci. Levels of self- fertilization will be estimated using larvae collected from populations of varying density and results used to estimate the effects of environmental degradation and increasing seawater temperature

Population structure of Montastrea cavernosa on shallow versus mesophotic reefs in Bermuda

Mesophotic coral reef ecosystems remain largely unexplored with only limited information available on taxonomic composition, abundance and distribution. Yet, mesophotic reefs may serve as potential refugia for shallow-water species and thus understanding biodiversity, ecology and connectivity of deep reef communities is integral for resource management and conservation. The Caribbean coral, Montastraea cavernosa, is considered a depth generalist and is commonly found at mesophotic depths. We surveyed abundance and size-frequency of M. cavernosa populations at six shallow (10m) and six upper mesophotic (45m) sites in Bermuda and found population structure was depth dependent. The mean surface area of colonies at mesophotic sites was significantly smaller than at shallow sites, suggesting that growth rates and maximum colony surface area are limited on mesophotic reefs. Colony density was significantly higher at mesophotic sites, however, resulting in equal contributions to overall percent cover. Size-frequency distributions between shallow and mesophotic sites were also significantly different with populations at mesophotic reefs skewed towards smaller individuals. Overall, the results of this study provide valuable baseline data on population structure, which indicate that the mesophotic reefs of Bermuda support an established population of M. cavernosa

Do the shuffle: Changes in <i>Symbiodinium</i> consortia throughout juvenile coral development - Fig 4

<p><b><i>Symbiodinium</i> phylotype composition in various <i>Porites astreoides</i> life stages reared <i>in situ</i> (A) and <i>ex situ</i> (B).</b> (A) <i>Symbiodinium</i> phylotype composition of shallow <i>P</i>. <i>astreoides</i> adults, their brooded planulae, and newly settled juveniles reared <i>in situ</i> on shallow (10 m) and upper mesophotic (30 m) reefs. <i>Symbiodinium</i> phylotype frequencies differed significantly between (1) adults and planulae, (2) planulae and juveniles transplanted to the shallow reef, (3) planulae and juveniles transplanted to the upper mesophotic reef, and (4) between juveniles transplanted to the different depths. There was no difference in <i>Symbiodinium</i> phylotype frequencies between adults and juveniles transplanted to different depths. (B) <i>Symbiodinium</i> phylotype composition of planulae and <i>ex situ</i>, reared juvenile <i>P</i>. <i>astreoides</i>. No difference was found in <i>Symbiodinium</i> phylotype frequency of (1) planulae or juveniles from different parental depths or (2) between planulae and juvenile.</p

Map of shallow (10 m) and upper mesophotic (30 m) sampling sites in Bermuda.

<p>Sites were used for adult <i>Porites astreoides</i> colony collection and juvenile transplantation.</p

Tukey-type multiple comparison of proportions of <i>Symbiodinium</i> phylotype frequencies in <i>P</i>. <i>astreoides</i> life stages.

<p>Tukey-type multiple comparison of proportions of <i>Symbiodinium</i> phylotype frequencies in <i>P</i>. <i>astreoides</i> life stages.</p

Specific growth of <i>in situ</i> and <i>ex situ</i> reared <i>Porites astreoides</i>.

<p>Specific growth of juvenile <i>P</i>. <i>astreoides</i> reared on shallow (10 m) and upper mesophotic (30 m) reefs (<i>in situ</i>) did not differ using transplant depth and <i>Symbiodinium</i> phylotype combinations as factors (left). Specific growth of shallow and upper mesophotic juvenile <i>P</i>. <i>astreoides</i> reared in outdoor aquaria (<i>ex situ</i>) also did not differ (right). Both treatments of <i>in situ</i> reared juveniles (left) had significantly higher growth rates than both treatments of <i>ex situ</i> reared juveniles (right). Shaded bars represent mean specific growth (% growth d^-1) ± SE.</p

<i>Symbiodinium</i> phylotype composition of field-collected shallow and upper mesophotic adult <i>Porites astreoides</i>.

<p>There was no significant difference in <i>Symbiodinium</i> phylotype frequency between depths.</p