Sclerosponge Workshop





Miami March 21-23, 1998



A sclerosponge retrieved from the Bahamas weighing over 200 lbs and measuring 24" in diameter. Unfortunately this specimen was badly bioeroded. However, we estimate this specimen to be in excess of 1000 years old!!



Organizers

Peter K. Swart

Jim Rubenstone

Chris Charles

Joachim Reitner





Purpose

To discuss issues regarding the use of sclerosponges as paleoenvironmental proxies.



Background

It has been more the three decades since Goreau (1959) described the ecology of the deep Jamaican reefs and found them to contain large populations of the sponge Ceratoporella nicholsoni. These sponges were assigned to a new class of sponges- the Sclerospongiae (Hartman and Goreau, 1970).

The biology and ecology of the sponges has been well described by Lang et al. (1975), Dustan et al. (1975), Hartman and Goreau (1970), Scoffin and Hendry (1984), Wood (1990), while their growth has been studied by Dustan and Sacco (1982) and Benavides and Druffel (1986). Lang et al. (1975) found the sponges growing within the framework and under coral talus in the shallower portions of the reef (above 55m), while below 55m they are found on the steep surfaces of the deep fore-reef. They have been reported growing to depths of 145 m. Of the six sclerosponges described by Lang et al. (1975), the largest and most visible is Ceratoporella nicholsoni which in Jamaica was estimated to cover between 25 to 50% of the available space, attaining a size in excess of 1 m in diameter. During our recent collection trips in the Bahamas we retrieved one colony which we believe to be C. nicholsoni, 1 m in diameter (See Figure 1). Unfortunately its internal structure was completely obliterated by bioerosion. Based on our age estimates this sponge could have been 4,000 years old and therefore the ramifications for the use of sclerosponges as proxy indicators of climate obvious .Stromatospongia vermicola also grows to a reasonable size (40 cms in diameter) and can be locally more abundant than C. nicholsoni. The remaining species of sponges (Hispidopetra miniana, S. norae, Goreauiella auriculatra, and Merlia sp.) are relatively small but can be locally abundant.

Sclerosponges such as Ceratoporella nicholsoni show concentric growth bands apparently on a 4 to 5 year time scale. The significant of such banding is not known. These concentric growth patterns suggest that the growth is regular and that there is not significant diagenetic reactions affecting the sponge. In some instances we have found sponges in which the concentric rings are completely obliterated by bioerosion. The growth rate of Ceratoporella nicholsoni have been studied by both direct staining using Alizarin Red-S (Dustan and Sacco, 1982) and by using 14C and 210Pb (Benavides and Druffel, 1986). Both studies were conducted on sponges from Jamaica. In the staining study, specimens of sponges were stained and collected some six years later. Dustan and Succo (op cit.) estimated a growth rate of 0.1 to 0.2 mm/yr. The radiometric methods gave slightly higher growth rates (0.27 mm/yr using 14C and 0.22 mm/yr using 210Pb).

Sclerosponges have the ability to provide a valuable new geochemical proxy for the understanding of climate and ocean circulation. Their important attributes are

Long Lived- The relatively low growth rate of the sponges (0.25 mm/yr) means that a colony with a diameter of 10 cm may be 400 years old!

Wide Range of Depths- Sclerosponges live over a wide range of water depths and therefore unlike corals can provide information on different water masses.

Resistance to Diagenesis- The relatively dense skeleton of the sclerosponges means that they are resistant to diagenetic alteration.

Equilibrium with the Environment- Studies conducted to date suggest that the sclerosponges are in equilibrium with their environment with respect to both oxygen and carbon isotopes.



Questions which Need to be Addressed

What is the growth mechanism of sclerosponges?

What do the growth bands mean?

What is the extent of isotopic equilibrium of sclerosponges?



Meeting Attendance is open to everyone, but space is limited. In addition there are limited funds available for travel support.

For further details contact Peter Swart.