Revisiting silicon budgets at a tropical continental shelf: Silica standing stocks in sponges surpass those in diatoms

Abstract

Most of the silicon (Si) in marine coastal systems is thought to recirculate under the biological control of planktonic diatoms. We challenge this view after comparing the biogenic silica (bSi) standing stocks contributed by communities of planktonic diatoms and benthic sponges in five habitats of an extensive continental shelf area of the Mesoamerican Caribbean. In most habitats (outer reefs, patch reefs, sea grass beds, and mangroves), the sponge bSi stocks surpassed those of diatoms. Collectively, bSi in sponge communities was about 88.6% of the total Si pool. Diatoms represented 4.2% and ambient silicate about 7.2%. Consequently, when constructing future regional Si budgets in coastal areas, the Si standing stocks in sponge populations should be empirically examined before deciding that their contribution to the total is negligible. In order to understand Si fluxes in coastal areas where sponges are relevant, we need additional empirical approaches to set the timescale of sponge bSi turnover, which appears to be substantially slower than that of diatom bSi.Silicate, a dissolved form of silicon (Si), is a major ocean nutrient. It fuels primary production by enhancing growth of diatoms, which require silicate to construct their skeletons of biogenic silica (bSi). Therefore, there is enormous interest in predicting the interplay between silicate and bSi budgets. Ever since the earliest models attempting to establish a general balance for Si in the ocean (Harriss

A Proposal for the Evolution of Cathepsin and Silicatein in Sponges

“…However, there are several subclades within demosponges unable to produce silica (e.g., orders Dendroceratida, Dictyoceratida, and most members of Verongimorpha), suggesting that the ability to produce silica may have been lost secondarily. Such loss would agree with claims that siliceous sponges suffer a chronic limitation by dissolved silicon in the modern ocean, outcompeted by diatoms (Maldonado et al 1999(Maldonado et al , 2010Maldonado 2009). On the other hand, we have not identified here any silicatein gene in hexactinellids, homoscleromorphs, or in the demosponge Chondrilla nucula, which produce siliceous spicules.…”

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

“…Hourly uptake rates measured for each sponge individual were then normalized by its volume (ml) and AFDW weight (g). We have given uptake rates preferentially normalized by the volume (ml) of living sponge, as such an approach will allow subsequent inference of field DSi demands following non-destructive measurements of sponge volume through photography (Shortis et al, 2009), rulers (Maldonado et al, 2010a) or any other method avoiding specimen collection. Nevertheless, one of the two available studies to date provided DSi uptake kinetics as AFDW normalized values.…”

“…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).…”

Protistan Skeletons: A Geologic History of Evolution and Constraint

“…Siliceous sponges can be locally important in coastal ecosystems (Maldonado et al 2010), but the fossil record indicates that they have progressively declined in ecological importance among shelf communites through the late Mesozoic and Cenozoic eras (Maliva et al, 1989). Indeed, when grown at silica concentrations similar to those inferred for a pre-diatom world, some modern sponges produce spicule morphologies not seen in the geologic record since the Jurassic Period (Maldonado et al 1999).…”