Heart of glass: spicule armament and physical defense in temperate reef sponges

Abstract

Siliceous inclusions play an important role in deterring terrestrial herbivores, but their role in marine systems remains controversial. Sponges are ubiquitous members of marine benthic communities and represent a potentially valuable food source for many predatory species, yet they have few natural predators. An in situ method was used to assess the deterrent effects of siliceous spicules or whole sponge skeleton, which were hypothesised to act as a physical defense in temperate reef sponges. Natural concentrations of spicules from 5 species of sponge and the spongin skeleton from a sixth species were incorporated into artificial diets, which were similar in nutritional quality to the sponge tissues. These were offered to the sea urchin Centrostephanus rodgersii in feeding choice experiments including control discs containing no spicules or spongin skeleton. Spicules from 4 species, Tedania anhelans, Clathria pyramida, Chondrilla australiensis and Chondrilla sp., deterred feeding by C. rodgersii. Spicules from a fifth species, Callyspongia sp., and intact skeleton isolated from Cacospongia sp., failed to deter C. rodgersii. This is the first demonstration of antifeedant activity associated with skeletal elements against sea urchins. Importantly, unlike previous work in the tropics, very small spicules (microscleres) measuring <100 µm were effective feeding deterrents.

Chemical defense against predators and bacterial fouling in the Mediterranean sponges Axinella polypoides and A. verrucosa

“…These spicules are not very abundant and difficult to detect in the tissue of A. polypoides (Alvarez & Hooper 2002), which might prevent their effectiveness. However, they are generally located near the surface (which can elevate their ability to deter a predator), and no correlation between spicule density and deterrence was found by Ferguson & Davis (2008). Clearly, further experiments are necessary to establish whether A. polypoides has a physical defense against predators.…”

“…These 2 species are known to contain bromopyrrole compounds including feeding-deterrent ones (Fedoreyev et al 1986, Assmann et al 2001b, Assmann & Köck 2002, Ortlepp et al 2007, and thus might rely on chemical anti-predator defense alone. Ferguson & Davis (2008) indicated the possibility that spicules of a size smaller than 100 µm deter the generalist sea urchin Centrostephanus rodgersii. The third spicule type of A. polypoides, the microscleres of the trichodragmata type, is shorter than 30 µm.…”

“…Most sponges have high nutritional values, eliminating the possibility of predator avoidance due to low nutritional value (Kubanek et al 2002). While there is evidence for feeding deterrence based solely on physical defense by spicules or sponge skeleton elements in some sponges , Hill et al 2005, Ferguson & Davis 2008, the synergistic effects of physical and chemical defenses (Jones et al 2005) along with feeding deterrence by means of organic extracts and purified compounds have been reported more often than physical defense alone for sponges from diverse geographical regions (e.g. Pawlik et al 1995, Sokolover & Ilan 2007.…”

Establishment and persistence of species-rich patches in a species-poor landscape: role of a structure-forming subtidal barnacle

“…Urchins can have dramatic impacts on sessile invertebrates (Vance 1979, Himmelman et al 1983, Sebens 1986), but we suspect that chemical or physical defenses deterred urchins from feeding on sponges once barnacles were removed. Antifeedant activity has been demonstrated for a number of the major space-occupying sponges in urchin barrens of our region (Wright et al 1997, Ferguson & Davis 2008.…”

“…Urchins can have dramatic impacts on sessile invertebrates (Vance 1979, Himmelman et al 1983, Sebens 1986), but we suspect that chemical or physical defenses deterred urchins from feeding on sponges once barnacles were removed. Antifeedant activity has been demonstrated for a number of the major space-occupying sponges in urchin barrens of our region (Wright et al 1997, Ferguson & Davis 2008.A growing body of literature attests to the importance of habitat complexity in the structure and function of assemblages (MacArthur & MacArthur 1961, Hixon & Menge 1991, Talman et al 2004. In marine systems, structural complexity has been linked to enhanced diversity (Castilla et al 2004, Eriksson et al 2006, Hauser et al 2006, but usually this is inferred from snapshots of data collected over short time frames rather than following a time course of several years.…”