Absence of genetic differentiation in the coral Pocillopora verrucosa along environmental gradients of the Saudi Arabian Red Sea

Abstract

The Red Sea is the world's northernmost tropical sea. The 2000 km long, but narrow basin creates distinct environmental conditions along its latitudinal spread. The Red Sea displays a pronounced salinity gradient from 41 to 37 PSU (north to south) with an opposing temperature gradient from 21 to 27 • C in the north to 27-33.8 • C in the south. The Red Sea further displays a decreasing nutrient gradient from south to north that can also influence underwater light fields due to higher phytoplankton content and turbidity. Despite this strong variation in temperature, salinity, nutrients, and light conditions, the Red Sea supports large and diverse coral reef ecosystems along its nearly entire coastline. Only few studies have targeted whether these prevailing gradients affect genetic connectivity of reef organisms in the Red Sea. In this study, we sampled the abundant reef-building coral Pocillopora verrucosa from 10 reefs along a latitudinal gradient in the Red Sea covering an area of more than 850 km. We used nine Pocillopora microsatellite markers to assess the underlying population genetic structure and effective population size. To assure the exclusion of cryptic species, all analyzed specimens were chosen from a single mitochondrial lineage. Despite large distances between sampled regions covering pronounced, but smooth temperature and salinity gradients, no significant genetic population structure was found. Rather, our data indicate panmixia and considerable gene flow among regions. The absence of population subdivision driven by environmental factors and over large geographic distances suggests efficient larval dispersal and successful settlement of recruits from a wide range of reef sites. It also advocates, broadcast spawning as the main reproductive strategy of Pocillopora verrucosa in the Red Sea as reflected by the absence of clones in sampled colonies. These factors might explain the success of Pocillopora species throughout the Indo-Pacific and Arabian Seas.

Niche acclimatization in Red Sea corals is dependent on flexibility of host-symbiont association

“…However, Symbiodi nium identity was not determined in these studies and it remains uncertain as to whether the here-proposed mechanism of symbiont flexibility in P. lutea can be generalized. Overall, coral populations along reefs in the Red Sea seem to be connected (Robitzch et al 2015), but host genotypic divergence may have played a role in the observed host-symbiont pattern in P. lutea as has been shown for Seriatopora hystrix in the Great Barrier Reef (Bongaerts et al 2010). …”

Extensive phenotypic plasticity of a Red Sea coral over a strong latitudinal temperature gradient suggests limited acclimatization potential to warming

“…Although the sample size of our study preclude an exhaustive analyses of inter- and intra-population variation, other studies have also shown small or no regional differentiation for this species along the strong environmental gradients in the Red Sea. Robitzch, et al51 investigated the population structure of P. verrucosa based on 360 samples collected between Al-Wajh (2-WAJ) and Doga (5-DOG) with the same mitochondrial marker as used in this study, and with nine additional microsatellite markers. They did not find any differentiation of the coral populations over a distance of 850 km.…”

Physical Mechanisms Routing Nutrients in the Central Red Sea

“…Numerical simulations presented by Zhan et al () indicated that that eddies may considerably impact coastal current variability and cause substantial vertical transport at the coastal boundary due to the interaction with the boundary. The impact of eddies on coral reef communities has been proposed by Robitzch et al (), who infer that eddies may substantially contribute to the dispersal of coral larvae, and by Kürten et al (), who showed that coral reef biota assimilate macronutrients from the oceanic catchment in the Red Sea. As has been observed in the open ocean (Gaube et al, ; McGillicuddy et al, ; Rodríguez et al, ), eddies may appreciably impact primary productivity of the Red Sea.…”