||Organisms that have Biogenic silica (BSi) skeletons include diatoms, silicoflagellates, radiolarians and sponges. BSi in marine sediments is an important indicator of siliceous organism distributions and paleoproductivities, but the estimation were based on diatom frustule amounts. The sponges and radiolarians were excluded from the marine siliceous biogeochemical cycle estimation in the past. However, sponges had became a role in the cycle in recent years. The siliceous demosponges and the glass sponge reefs were suggested as a sink in local silica cycles. While the glass sponges and demosponges have been investigated, more results to support the importance of sponges in silica cycle was expected. This study will focus on the sponge spicules in sediments and the keratose sponges (Order: Dictyoceratida). There are three main parts in this study: 1. The Spatial distribution of spicules in sediments around Taiwan and the Sunda Shelf. 2. An efficient wet-chemical method to determine biogenic silica content in sponges. 3. Distribution of foreign particles in the bath sponge, Spongia sp..|
Thirty-one surface sediment samples were collected in South China Sea. Only sponge spicules were found in the depth from intertidal to depths of 1128 m, and the abundance of sponge spicules correlated positively and negatively with water depth and sediment grain size when coral reef sites were excluded, respectively. The low spicule abundance in shallow waters may have resulted by current conditions and the dilution effect through riverine input of terrestrial sediment. The highest spicule amount were found in coral reef sites, especially Site DBS, where the spicule number reached 7910 spicule n• g-1 sediment and 2293 spicule n• g-1 sediment in Site SK in Penghu area. The correlation of spicule in sediments and sponge biomass indicated the sponge biomass was not significantly related to spicules in sediments in Penghu intertidals, which may be influenced by local water currents and unrecorded sponge species. However, the large amount of keratose sponges could also increase the spicule amount in sediments by preserving those particles in sediment upper layers.
To measure the BSi in sponges, the wet-chemical method was employed to understand if this method is efficient for determing the BSi amounts in sponges. The wet-chemical method, that was used to measure the BSi in marine sediments studies, included alkaline solution digestion and molybdosilicate yellow determination as two steps. In addition to the wet-chemical method tests, the BSi amounts in five sponge species were compared after the methodology was fixed. The results indicated stable digestion of sponge BSi can be obtained by 2M KOH with 8.5-9 hours digestion time. As for molybdosilicate yellow method, the suppressive regent was suggested to remove from experiment. Samples can obtain the stable yellow color in 50°C water bath for 1 hour. The obtained BSi is about 80-90% of the original particle weight. Among the five sponge species, bath sponge Spongia sp. was with the lowest BSi amounts. BSi measurements in Tedania sp. were found to have a more stable results than previous studies. This method can be applied for obtaining BSi amounts from sponges, thus the BSi amount and distributions in those sponges can be better understood.
The bath ponge Spongia sp. were collected from 6 intertidal areas in Penghu. The sponges were defined as Outer and Interior layers to understand the BSi distribution and contents. The results indicated the BSi contents were concentrated in Outer layer, which was 2-3 times as the Interior parts. The BSi contents were not related to seasons or sites. The amounts of BSi in Spongia sp. may be controlled by the sponges itself. On the other hand, the non-BSi particle contents may relate to water currents since the amounts were higher at stronger water current location. However, the non-BSi particles may be transported passively by water currents instead of engulfing by sponges actively.
The BSi amounts in shallow water sediments and bath sponges were not high enough to influence the silica cycle. However, the biodiversity and abundances of the keratose sponges should be considered in further studies, especially the preservation of foreign spicules may delay the sparticles back into the siliceous biogeochemical cycle.