The Life of a Sponge in a Sandy Lagoon

Area of Science:

• Marine Biology
• Invertebrate Zoology
• Ecology

Background:

• Sponges typically inhabit hard substrates, but Biemna ehrenbergi is an exception, found exclusively in soft-bottom lagoons of the Red Sea.
• This unique habitat is characterized by high particulate organic matter deposition, with most of the sponge body buried in sediment.

Purpose of the Study:

• To investigate the feeding and water-filtration mechanisms of Biemna ehrenbergi in its unusual soft-bottom environment.
• To understand how this sponge avoids clogging its aquiferous system despite being partially buried.

Main Methods:

• Dye tracing experiments to visualize water flow through sediment and into the sponge's aquiferous system.
• Analysis of plastic replicas of the aquiferous system and electron microscopy of sponge tissues.
• Examination of the location and structure of ostia and oscula.

Main Results:

• Biemna ehrenbergi actively pumps interstitial water, rich in particles and nutrients, from the sediment into its aquiferous system.
• Transcellular ostia, primarily on the buried surface, facilitate water intake, while elevated, closable oscula on siphons prevent outflow clogging.
• The sponge harbors a diverse bacterial population within its bacteriocytes, some of which are consumed by the sponge.

Conclusions:

• Biemna ehrenbergi has evolved specialized adaptations to exploit soft-sediment environments, including unique water-filtration strategies.
• Cellular mobility in ostia and the strategic placement and function of oscula are key to its survival and feeding in this niche habitat.
• The sponge likely benefits from symbiotic bacteria, supplementing its nutrition through their consumption.