Substrate as a driver of sponge distributions in mangrove ecosystems

Abstract

Caribbean mangrove-associated sponge communities are very distinct from sponge communities living on nearby reefs, but the mechanisms that underlie this distinction remain uncertain. This study aimed to elucidate the relative importance of substrate and habitat in determining the ability of sponges to persist in mangrove ecosystems, and to evaluate the role of bacterial symbiont composition and carbon uptake in sponge distribution. Two reef species (Aplysina archeri and Desmapsamma anchorata) were transplanted to mangrove roots and PVC tubes at a mangrove stand and a reef site. The mangrove species Mycale microsigmatosa was transplanted to both substrates in mangroves as control and showed complete survival. In contrast, lowest survival for D. anchorata was observed on roots in mangroves and intermediate survival on both PVC in mangroves and roots on the reef. Complete survival was observed on PVC on the reef. A. archeri had reduced survival in all treatments, but was most affected by the root substrate in mangroves. These results reveal that the inability of typical reef species to survive in mangrove ecosystems is related to habitat and substrate. The symbiotic bacterial communities were host specific and very similar before and after transplantation. The cluster analysis of metabolic diversity of bacterial communities in A. archeri, M. microstigmatosa and D. anchorata showed strong separation between host species and the surrounding water. It is speculated that compositional differences in dissolved organic matter (DOM) composition and symbiotic bacteria are potentially important in structuring sponge communities, explaining the exclusion of typical reef species and persistence of mangrove species in mangrove ecosystems.

Root-derived organic matter confines sponge community composition in mangrove ecosystems

“…In contrast, 60% of the specimens transplanted to substrates containing mangrove DOM showed substantial (40-100% of the tissue) necrosis (white lesions) after 1 week ( Figure 1D), suggesting that mangrove DOM significantly affected the performance of D. anchorata (two-sample z-test, z = 2.1, p = 0.0384). This response is in agreement with previous observations on reef sponges transplanted to mangrove roots Wulff 2004;Pawlik et al 2007;Hunting et al 2013). The mangrove sponge T. ignis did not reveal any sign of necrosis on substrates containing mangrove DOM or on the control substrates ( Figure 1B,D).…”

“…Mangrove DOM consists mainly of tannins and polyphenolic compounds (Maie and Jaffe 2006), which are structurally complex and recalcitrant to biodegradation (Field and Lettinga 1992;Koch et al 2005;Kristensen et al 2008), thereby reducing mangrove palatability and inhibiting growth of fouling organisms on mangrove roots (e.g., Schmitt et al 1998). A limited number of bacterial and fungal species are able to degrade complex polyphenols and tannins (Bhat et al 1998).…”

Significance of sunlight for organic matter degradation in aquatic systems

“…Sunlight is known to impair microorganisms through detrimental effects on DNA and extracellular enzymes (e.g. Santos et al 2013), in which indirect effects of sunlight can also affect OM-associated microbial communities via photo-oxidation of OM and its degradation into smaller palatable or harmful molecules depending on OM substrate (Mopper and Zhou 1990, Scully et al 1996, Obernosterer and Benner 2004, Albarino et al 2008, Hunting et al 2013b. Adverse effects of shorter wavelengths (e.g.…”

“…recalcitrant substrates nor specific substrates typical of the plant leaves used in this study. It is thus impossible to directly relate the carbon substrates utilization to actual microbial density and community structure, as well as their relative metabolic activity and how they would function under natural conditions, yet the number of utilized substrates offers a proxy of the metabolic or functional diversity of a microbial community (Hunting et al 2013b, Zhai et al 2016, or the resource breadth utilized by the bacterial community (Hunting et al 2015(Hunting et al , 2017. Plates were incubated for 96 h at 18°C and absorbance was measured at 590 nm using a BIO-RAD SmartSpec ™ Plus spectrophotometer.…”

UV radiation and organic matter composition shape bacterial functional diversity in sediments

“…It is therefore impossible to directly relate substrate utilization profiles to the actual functioning of the developed bacterial communities. Nonetheless, the number of substrates used can serve as a proxy of the metabolic diversity of the bacterial community, and differences in utilization profiles indicate that functionally distinct bacterial communities can develop depending on treatment (Garland, 1999; Hunting et al, 2013a). At the end of the experiment (day 5), 1 mL of the sediment top layer with minimal water was sampled with a pipette, diluted 30× with DSW and vortexed.…”