Growth and energetics of the sponge Halichondria panicea

The filtration rate (F, ml min(-1) measured as clearance of algal cells) and maintenance respiration rate (R(m), ml O-2 h(-1) measured as starvation respiration rate) as a function of Halichondria panicea colony size (dry weight DW, g) were described by: F = 28.35DW(0.914) and R(m) = 0.632DW(0.927), respectively. At the maximum specific growth rate of 4% d(-1) the net growth efficiency was about 30%. The specific respiration rate (R(s)) as a function of the specific growth rate (mu) was described by the equation: R(s) = n mu + a where n is the energy cost per unit of growth and a is R(s) at zero growth rate. It was found that the energy cost of growth constituted 139% of the biomass increase. This showed that sponges apparently have a higher energy demand for growth than other invertebrates. When sponge colonies were transferred to filtered sea water, a near linear decrease of chlorophyll a (chl a) was seen during the first 24 h. A similar decrease was observed in sponges transferred directly from the field to filtered sea water. The reduction constants (r) in the 2 cases were 3.3 and 2.8% h(-1), respectively. The estimated filtration rates, using the equation F-est = (r x S)/chl a, where S is the steady-slate chl a content, were almost identical to filtration rates measured as clearance. It is stressed that sponges have a low water pumping capacity compared with other filter-feeding invertebrates, but compensate for this by a high retention efficiency for small particles >0.1 mu m.