Assessing the Potential of Sponges (Porifera) as Indicators of Ocean Dissolved Si Concentrations

Abstract

We explore the distribution of sponges along dissolved silica (dSi) concentration gradients to test whether sponge assemblages are related to dSi and to assess the validity of fossil sponges as a palaeoecological tool for inferring dSi concentrations of the past oceans. We extracted sponge records from the publically available Global Biodiversity Information Facility (GBIF) database and linked these records with ocean physiochemical data to evaluate if there is any correspondence between dSi concentrations of the waters sponges inhabit and their distribution. Over 320,000 records of Porifera were available, of which 62,360 met strict quality control criteria. Our analyses was limited to the taxonomic levels of family, order and class. Because dSi concentration is correlated with depth in the modern ocean, we also explored sponge taxa distributions as a function of depth. We observe that while some sponge taxa appear to have dSi preferences (e.g., class Hexactinellida occurs mostly at high dSi), the overall distribution of sponge orders and families along dSi gradients is not sufficiently differentiated to unambiguously relate dSi concentrations to sponge taxa assemblages. We also observe that sponge taxa tend to be similarly distributed along a depth gradient. In other words, both dSi and/or another variable that depth is a surrogate for, may play a role in controlling sponge spatial distribution and the challenge is to distinguish between the two. We conclude that inferences about palaeo-dSi concentrations drawn from the abundance of sponges in the stratigraphic records must be treated cautiously as these animals are adapted to a great range of dSi conditions and likely other underlying variables that are related to depth. Our analysis provides a quantification of the dSi ranges of common sponge taxa, expands on previous knowledge related to their bathymetry preferences and suggest that sponge taxa assemblages are not related to particular dSi conditions.

Rock sponges (lithistid Demospongiae) of the Northeast Atlantic seamounts, with description of ten new species

“…The amount of silica in the water does not seem to be related either since these two groups of seamounts have many lithistids, and they possibly require large amounts of silica to build their skeleton. Another explanation is that lithistids are very efficient at removing the silica from the water thus, not requiring large amounts of this element (Alvarez et al, 2017;Maldonado et al, 2015). Since there is no data regarding the biogeochemical parameters of the water column upon the time of collection of the material, it remains unclear if the cause of this variation are abiotic factors or intraspecific variation due to distinctive geographical area, as it was also observed in other astrophorins (Van Soest, Beglinger & de Voogd, 2010) including lithistids (Pisera & Vacelet, 2011).…”

Biosilicification Drives a Decline of Dissolved Si in the Oceans through Geologic Time

“…The link between sponge distributions and DSi stems from the implicit assumption that siliceous sponges are unable to thrive at low DSi (e.g., Maldonado et al, 1999;Ritterbush et al, 2015), although siliceous sponge reefs in the modern oceans are still forming in some areas despite the relatively low DSi concentrations (10-40 µM) (Uriz, 2006;Chu and Leys, 2010;Maldonado et al, 2015). The modern day global distribution of sponges suggests that sponges are adapted to a great range of DSi conditions and the presence of sponges in the stratigraphic record must be treated cautiously (Alvarez et al, 2017).…”

“…However, highly siliceous sponge reefs are still forming in selected areas of the modern oceans despite the relatively low DSi concentrations (Uriz, 2006;Chu and Leys, 2010;Maldonado et al, 2015). There are certainly other factors, such as food availability and ocean temperature (Kahn et al, 2012) that control the abundance and biosilicification of sponges (Alvarez et al, 2017).…”

Table 1: The number of records obtained through Google Scholar and PubMed using the search terms “sponge spicules”, “glass ramp”, “spiculite” and “spongillite”.

“…However, such actualistic approach needs to be applied with caution. Under certain favorable conditions (e.g., calm hydrodynamic setting and high water dissolved silica (DSi) concentrations (Alvarez et al, 2017)), modern sponges that are interpreted as indicators of cold deep waters may have inhabited warm and shallow settings in the past (Gammon, James & Pisera, 2000). Sponge distribution is closely associated with water nutrient level, including water DSi concentrations (for more details see Alvarez et al, 2017).…”

“…Under certain favorable conditions (e.g., calm hydrodynamic setting and high water dissolved silica (DSi) concentrations (Alvarez et al, 2017)), modern sponges that are interpreted as indicators of cold deep waters may have inhabited warm and shallow settings in the past (Gammon, James & Pisera, 2000). Sponge distribution is closely associated with water nutrient level, including water DSi concentrations (for more details see Alvarez et al, 2017). Sponge assemblages were studied to estimate the distributions of sponges along a DSi gradient and to assess the validity of fossil sponges as a paleoecological tool for inferring DSi concentrations in the past oceans (Alvarez et al, 2017).…”