Siliceous sponges as a silicon sink: An overlooked aspect of benthopelagic coupling in the marine silicon cycle

Abstract

Our current understanding of the silicon (Si) cycle in the ocean assumes that diatoms dominate not only the uptake of silicic acid, but also the production and recycling of biogenic silica (BSi), and that other organisms with siliceous skeletons, including sponges, radiolarians, and silicoflagellates, play a negligible role. In this study, we reexamine some aspects of the potential contribution by sponges and present in vitro evidence that BSi in the form of sponge spicules redissolves into silicic acid at far slower rates than those known for diatom frustules. We also show that the retention of Si by siliceous sponges in some sublittoral and bathyal environments is substantial and that sponge populations function as Si sinks. Additionally, by reanalyzing published information on sponge growth and BSi content, we estimate that BSi production rates by sublittoral sponges in Si-poor and Si-rich marine areas fall quite close to values known for diatom assemblages. Therefore, sponges may affect Si cycling dynamics and Si availability for diatoms, particularly in Si-depleted environments. Altogether, our data strongly suggest that the role of sponges in the benthopelagic coupling of the Si cycle is significant.

Identification of a silicatein(-related) protease in the giant spicules of the deep-sea hexactinellidMonorhaphis chuni

“…chuni and M. intermedia are deep-sea sponges, which live in a milieu highly under-saturated in silicon (see Maldonado et al, 2005). Therefore, it is very surprising that in this habitat these two hexactinellid sponges synthesize the largest bio-silica structures existing on earth (see Introduction).…”

Experimental silicon demand by the sponge Hymeniacidon perlevis reveals chronic limitation in field populations

“…Recent studies have suggested the idea that siliceous sponges are relevant DSi users at a large ecological scale, a role traditionally neglected by nutrient ecologists and biogeochemists and that is biasing the advance toward a realistic understanding of silicon cycling in marine systems, and particularly on continental margins (Reincke & Barthel, 1997;Maldonado et al, 2005Maldonado et al, , 2010aMaldonado et al, , 2011Chu et al, 2011).…”

High concentrations of amorphous, biogenic Si (BSi) in the sediment of a small high-latitude lake: implications for biogeochemical Si cycling and for the use of BSi as a paleoproxy

“…Hecky et al 1973), some chrysophytes (Chrysophyceae), silicoflagellates (Dictyochales, cf. Adjou et al 2011), sponges (Porifera: Demospongiae and Hexactinellida, cf Maldonado et al 2005), or as structural support for many land plants, where BSi is precipitated in amorphous form as phytoliths (see Epstein 2001;Piperno 2006). As BSi remains are preserved relatively well in soils and sediments, and as many species produce species-specific, original structures, BSi remains are commonly used paleo-indicators in both aquatic and terrestrial environments (cf.…”