Globally, reef-building corals are the most prolific producers of dimethylsulphoniopropionate (DMSP) 1,2 , a central molecule in the marine sulphur cycle and precursor of the climate-active gas dimethylsulphide 3,4 . At present, DMSP production by corals is attributed entirely to their algal endosymbiont, Symbiodinium 2 . Combining chemical, genomic and molecular approaches, we show that coral juveniles produce DMSP in the absence of algal symbionts. DMSP levels increased up to 54% over time in newly settled coral juveniles lacking algal endosymbionts, and further increases, up to 76%, were recorded when juveniles were subjected to thermal stress. We uncovered coral orthologues of two algal genes recently identified in DMSP biosynthesis, strongly indicating that corals possess the enzymatic machinery necessary for DMSP production. Our results overturn the paradigm that photosynthetic organisms are the sole biological source of DMSP, and highlight the double jeopardy represented by worldwide declining coral cover, as the potential to alleviate thermal stress through coral-produced DMSP declines correspondingly.It is widely accepted that the production of dimethylsulphoniopropionate (DMSP), a central molecule in the marine sulphur cycle, is restricted to marine algae and a few species of intertidal plants 5. Marine bacteria subsequently use DMSP as a source of sulphur and carbon and can metabolize this compound into the volatile gas dimethylsulphide (DMS) 6 , by which the largest natural flux of sulphur enters the atmosphere where it exerts considerable influence on atmospheric chemistry 7 . Despite recent controversy regarding the impact of DMS emissions on global climate 8 , DMS is probably involved in local climate regulation through its oxidation into aerosol particles that induce the formation of clouds and increase their reflectivity, thereby reducing light levels and water temperatures in the marine environment 3,4 . Concentrations of DMSP and DMS found in reef-building corals are among the highest recorded in the environment 1,2 , but it has been assumed that DMSP production derives solely from the coral's endosymbiotic microalgae Symbiodinium. Evidence that the total amounts of DMSP recorded in corals are consistently higher than levels present in Symbiodinium cells alone 9,10 raises the possibility of a cryptic source of DMSP in reef-building corals. A clear understanding of the sources of DMSP on reefs and the possible effects that global warming may have on DMSP production is paramount, given the influence that coralreef-derived sulphur emissions may have on local climates 11 . Corals in the genus Acropora are the most abundant reef-building organisms in the Indo-Pacific region 12 and, as broadcast spawners, they acquire Symbiodinium from their surrounding environment after larval development. The Symbiodinium-free larvae of this genus provide a unique opportunity to investigate Symbiodinium-independent production of DMSP in corals. Results presented here demonstrate that coral hosts (kingdom: Ani...

The waters surrounding coral reef ecosystems are generally poor in nutrients, yet their levels of primary production are comparable with those reported from tropical rain forests. One explanation of this paradox is the efficient cycling of nutrients between the coral host, its endosymbiotic alga Symbiodinium and a wide array of microorganisms. Despite their importance for the animals' fitness, the cycling of nutrients in early coral life stages and the initial establishment of partnerships with the microbes involved in these processes has received little scrutiny to date. Nitrogen is an essential but limited nutrient in coral reef ecosystems. In order to assess the early nutrient exchange between bacteria and corals, coral larvae of the species Pocillopora damicornis were incubated with two coral-associated bacteria (Alteromonas sp., or Vibrio alginolyticus), prelabeled with the stable nitrogen isotope 15 N. The incorporation and translocation of nitrogen from Vibrio-and Alteromonas bacteria into P. damicornis coral larvae and specifically into the coral-symbiotic Symbiodinium were detected by nanoscale secondary ion mass spectrometry (NanoSIMS). A significant increase in the amount of enriched 15 N (two to threefold compared to natural abundance) was observed in P. damicornis larvae within 8 h of incubation for both bacterial treatments (one-way ANOVA, F 5,53 = 18.03, P = 0.004 for Alteromonas sp. and F 5,53 = 18.03, P = 0.0001 for V. alginolyticus). These findings reveal that coral larvae acquire nutrients previously taken up from the environment by bacteria. The additional nitrogen may increase the survival rate and fitness of the developing coral and therefore contribute to the successful maintenance of coral reefs.

Diverse and abundant bacterial populations play important functional roles in the multi-partite association of the coral holobiont. The specificity of coral-associated assemblages remains unclear, and little is known about the inheritance of specific bacteria from the parent colony to their offspring. This study investigated if broadcast spawning and brooding corals release specific and potentially beneficial bacteria with their offspring to secure maintenance across generations. Two coral species, Acropora tenuis and Pocillopora damicornis, were maintained in 0.2 μm filtered seawater during the release of their gametes and planulae, respectively. Water samples, excluding gametes and planulae, were subsequently collected, and bacterial diversity was assessed through a pyrosequencing approach amplifying a 470-bp region of the 16S rRNA gene including the variable regions 1-3.Compared to the high bacterial diversity harboured by corals, only a few taxa of bacteria were released by adult corals. Both A. tenuis and P. damicornis released similar bacteria, and the genera Alteromonas and Roseobacter were abundant in large proportions in the seawater of both species after reproduction. This study suggests that adult corals may release bacteria with their offspring to benefit the fitness in early coral life stages.