title: Cell turnover and detritus production in marine sponges from tropical and temperate benthic ecosystems.
abstract: This study describes in vivo cell turnover (the balance between cell proliferation and cell loss) in eight marine sponge species from tropical coral reef, mangrove and temperate Mediterranean reef ecosystems. Cell proliferation was determined through the incorporation of 5-bromo-2'-deoxyuridine (BrdU) and measuring the percentage of BrdU-positive cells after 6 h of continuous labeling (10 h for Chondrosia reniformis). Apoptosis was identified using an antibody against active caspase-3. Cell loss through shedding was studied quantitatively by collecting and weighing sponge-expelled detritus and qualitatively by light microscopy of sponge tissue and detritus. All species investigated displayed substantial cell proliferation, predominantly in the choanoderm, but also in the mesohyl. The majority of coral reef species (five) showed between 16.1±15.9% and 19.0±2.0% choanocyte proliferation (mean±SD) after 6 h and the Mediterranean species, C. reniformis, showed 16.6±3.2% after 10 h BrdU-labeling. Monanchora arbuscula showed lower choanocyte proliferation (8.1±3.7%), whereas the mangrove species Mycale microsigmatosa showed relatively higher levels of choanocyte proliferation (70.5±6.6%). Choanocyte proliferation in Haliclona vansoesti was variable (2.8-73.1%). Apoptosis was negligible and not the primary mechanism of cell loss involved in cell turnover. All species investigated produced significant amounts of detritus (2.5-18% detritus bodyweight(-1)·d(-1)) and cell shedding was observed in seven out of eight species. The amount of shed cells observed in histological sections may be related to differences in residence time of detritus within canals. Detritus production could not be directly linked to cell shedding due to the degraded nature of expelled cellular debris. We have demonstrated that under steady-state conditions, cell turnover through cell proliferation and cell shedding are common processes to maintain tissue homeostasis in a variety of sponge species from different ecosystems. Cell turnover is hypothesized to be the main underlying mechanism producing sponge-derived detritus, a major trophic resource transferred through sponges in benthic ecosystems, such as coral reefs.
authors.affiliation: Department of Aquatic Ecology and Ecotoxicology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands; Porifarma B.V. Poelbos 3, Ede, The Netherlands.
authors.forename: Brittany E
authors.initials: BE
authors.lastname: Alexander
authors.affiliation: Department of Aquatic Ecology and Ecotoxicology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Kevin
authors.initials: K
authors.lastname: Liebrand
authors.affiliation: Porifarma B.V. Poelbos 3, Ede, The Netherlands.
authors.forename: Ronald
authors.initials: R
authors.lastname: Osinga
authors.affiliation: Department of Aquatic Ecology and Ecotoxicology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Harm G
authors.initials: HG
authors.lastname: van der Geest
authors.affiliation: Department of Aquatic Ecology and Ecotoxicology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Wim
authors.initials: W
authors.lastname: Admiraal
authors.affiliation: Department of Pathology, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands.
authors.forename: Jack P M
authors.initials: JP
authors.lastname: Cleutjens
authors.affiliation: Department of Molecular Cell Biology, Research Institute Growth and Development, Maastricht University, Maastricht, The Netherlands.
authors.forename: Bert
authors.initials: B
authors.lastname: Schutte
authors.affiliation: Electron Microscopy Unit, CRISP, Maastricht, The Netherlands.
authors.forename: Fons
authors.initials: F
authors.lastname: Verheyen
authors.affiliation: Institut de Ciències del Mar-Consejo Superior de Investigaciones Científicas (ICM-CSIC), Barcelona, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Ribes
authors.affiliation: Department of Computational Geo-Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Emiel
authors.initials: E
authors.lastname: van Loon
authors.affiliation: Department of Aquatic Ecology and Ecotoxicology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands; Porifarma B.V. Poelbos 3, Ede, The Netherlands.
authors.forename: Jasper M
authors.initials: JM
authors.lastname: de Goeij
mesh_terms: D000818:Animals; D017209:Apoptosis; D001973:Bromodeoxyuridine / Q000737:chemistry; D053148:Caspase 3 / Q000378:metabolism; D049109:Cell Proliferation; D057894:Coral Reefs; D017753:Ecosystem; D008522:Mediterranean Sea; D011161:Porifera / Q000145:classification / Q000378:metabolism* / Q000648:ultrastructure*; D013045:Species Specificity; D014329:Tropical Climate
chemical_list: D053148:Caspase 3; D001973:Bromodeoxyuridine