Development of a new protocol for testing bath sponge quality

Abstract

Due to the diverse morphological variation that occurs in sponges between and within species, protocols for quantitative quality testing are required to select sponges and optimise conditions for the aquaculture of high quality bath sponges. A protocol was developed to assess the quality of sponges using mechanical engineering techniques. It quantified the physical properties of sponges (density, fibre width, fibre length, absorbency, and water retention efficiency) and their mechanical properties (firmness, compression modulus, compressive strength, tensile strength, elastic limit, elastic strain, modulus of elasticity, and modulus of resilience). To demonstrate these methods and provide a relative comparison, quality was measured for Rhopaloeides odorabile and Coscinoderma sp. and three commercial species, Hippospongia lachne, Spongia 1, and Spongia 2. There were significant differences between species for all quality parameters creating a unique profile for each species. R. odorabile was the firmest (37.8 ± 4.3 kPa), strongest (157.4 ± 17.3 kPa), and most rigid (838.7 ± 53.5 kPa) species tested, while Coscinoderma sp. was one of the softest sponges (7.3 ± 1.1 kPa) and had the highest elastic energy (30.5 ± 3.5 kJ/m³) and water retention efficiency (40.1 ± 1.4%) of all the species. Of the commercial species, H. lachne was the softest (3.2 ± 0.3 kPa), weakest (36.3 ± 3.1 kPa), and most absorbent sponge (31.0 ± 1.1), while Spongia 1 and Spongia 2 had intermediate quality characteristics for all measured parameters. These tests enable scientifically rigorous comparisons of quality between and within species regardless of origin or post-harvest treatment. Comparisons between species may be used to select species for aquaculture and as a marketing tool to promote aquaculture products for specific applications. Within species testing will allow quantification of differences in quality caused by genetic or environmental factors.

Introduction

Bath sponges have been used for more than 3000 years (de Laubenfels and Storr, 1958) for bathing, painting, cleaning, medical uses, padding for battle armour, and as a vessel for drinking water (Cresswell, 1922). Today they still have many applications despite the introduction of synthetic products. In countries such as Australia, where sponge aquaculture is under research and development, new dictyoceratid sponge species are being investigated for their potential as commercial species. At present, industry and scientists alike rely on the experienced hand of sponge traders to determine the quality and value of bath sponges. This subjective method prevents the comparative assessment of species or individuals using quantitative indices. To date, information regarding what constitutes a high quality sponge or the various quality characteristics needed for specific applications is scarce.

Development of quantitative quality testing protocols will enable direct comparisons between new aquaculture candidates and known commercial sponges and provide guidelines for species selection. Sponge quality varies between species, and may also vary within a single species according to its original habitat (Cresswell, 1922). Although there is an abundance of literature describing the morphological plasticity of sponges according to their environment (Storr, 1976, Palumbi, 1986, Maldonado and Young, 1998, Krasko et al., 2000, Mercurio et al., 2000, Bell et al., 2002, Hill and Hill, 2002), this plasticity has not been quantified with regard to sponge quality. Understanding the environment necessary for producing sponges of optimal quality will aid in aquaculture site selection and the success of the industry. In addition to natural variation, post-harvest treatment protocols applied to the sponge also influence quality. With the development of quality testing protocols these treatments can be optimised for each species and tailored for specific applications and markets.

In this study, quantitative measures were developed to describe the physical properties of density, fibre width, fibre length, absorbency, and water retention efficiency, and the mechanical properties of firmness, compression modulus, compressive strength, tensile strength, elastic limit, elastic strain, modulus of elasticity, and modulus of resilience. These were applied to Rhopaloeides odorabile and Coscinoderma sp. and three commercial bath sponges: a sponge considered to be Spongia graminea which will be referred to as Spongia 1, a sponge considered to be Spongia zimocca which will be referred to as Spongia 2, and Hippospongia lachne. R. odorabile and Coscinoderma sp. are two dictyoceratid sponges with promising potential for commercial aquaculture in Australia (Louden et al., in press). Values of quality, including absorbency, water retention efficiency, and all mechanical properties, were then correlated with each other and with the physical properties of density, fiber width, and fiber length to determine the most critical parameters. It was not the aim to compare the commercial quality of test species, nor to make systematic implications, but rather to use commercial specimens as a means to develop quantitative quality testing procedures using sponges with diverging skeletal features and post-harvest treatments.