Many species of marine sponges on tropical reefs host abundant and diverse symbiont communities capable of varied metabolic pathways. While such communities may confer a nutritional benefit to some hosts (termed High Microbial Abundance (HMA) sponges), other sympatric species host only sparse symbiont communities (termed Low Microbial Abundance (LMA) sponges) and obtain a majority of their C and N from local sources. Sponge communities are widespread across large latitudinal gradients, however, and recent evidence suggests that these symbioses may also extend beyond the tropics. We investigated the role that symbionts play in the ecology of sponges from the temperate, hard-bottom reefs of Gray's Reef National Marine Sanctuary by calculating the niche size (as standard ellipse area (SEAc)) and assessing the relative placement of five HMA and four LMA sponge species within bivariate (δ13C and δ15N) isotopic space. Although photosymbiont abundance was low across most of these species, sponges were widespread across isotopic niche space, implying that microbial metabolism confers an ecological benefit to temperate sponges by expanding host metabolic capability. To examine how these associations vary across a latitudinal gradient, we also compared the relative placement of temperate and tropical conspecifics within isotopic space. Surprisingly, shifts in sponge δ13C and δ15N values between these regions suggest a reduced reliance on symbiont-derived nutrients in temperate sponges compared with their tropical conspecifics. Despite this, symbiotic sponges in temperate systems likely have a competitive advantage, allowing them to grow and compete for space within these habitats.

This study investigated the effects of disodium fumarate (DF) on methane emission, ruminal fermentation and microbial abundance in goats under different forage (F) : concentrate (C) ratios and fed according to maintenance requirements. Four ruminally fistulated, castrated male goats were used in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments and the main factors being the F : C ratios (41 : 59 or 58 : 42) and DF supplementation (0 or 10 g/day). DF reduced methane production (P < 0.05) on average by 11.9%, irrespective of the F : C ratio. The concentrations of total volatile fatty acids, acetate and propionate were greater in the rumen of goats supplemented with DF (P < 0.05), whereas the abundance of methanogens was lower (P < 0.05). In high-forage diets, the abundance of Selenomonas ruminantium, a fumarate-reducing bacterium, was greater in the rumen of goats supplemented with DF. The abundance of fungi, protozoa, Ruminococus flavefaciens and Fibrobacter succinogenes were not affected by the addition of DF. Variable F : C ratios affected the abundance of methanogens, fungi and R. flavefaciens (P < 0.05), but did not affect methane emission. The result implied that DF had a beneficial effect on the in vivo rumen fermentation of the goats fed diets with different F : C ratios and that this effect were not a direct action on anaerobic fungi, protozoa and fibrolytic bacteria, the generally recognized fiber-degrading and hydrogen-producing microorganisms, but due to the stimulation of fumarate-reducing bacteria and the depression of methanogens.