Seasonal patterns of toxicity in benthic invertebrates: The encrusting sponge Crambe crambe (Poecilosclerida).

Evidence is presented for an annual cycle of toxin production in the encrusting sponge Crambe crambe. Both sponge toxicity and the slope of the regression line between toxicity and extract concentration (which is taken to represent qualitative properties of the toxins) changed following a seasonal pattern, with maxima in summer and autumn. Within-colony variation was also detected. On average, the values of toxicity were higher at the periphery than in the centre. The reverse was true if the variable considered was the slope of the toxicity function. There was decoupling during particular seasons in the evolution of these variables in the central and the peripheral parts of the sponges, with a retardation of the maxima in the latter. It is suggested that the cycles are driven by internal, physiological factors (best represented in the central part of the sponges), although they can be modulated to a considerable extent by local environmental pressures, such as competition with neighbours (best seen in the evolution of the toxicity in the peripheral part of the sponge). The results are interpreted from the point of view of their biological and ecological implications, inducible defences, and optimal defence theory.