In situ Pumping Rate of 20 Marine Demosponges Is a Function of Osculum Area

Abstract

Sponges play a key role in the transfer of energy and nutrients into many benthic ecosystems, and the volume of water they process is an important regulator of these fluxes. Theoretical scaling relationships between sponge volume, osculum cross-sectional area, and pumping rates were recently proposed and confirmed for small sponge specimens in the lab. To examine how these relationships apply to field populations we measured, in situ, the pumping rate (PR) of 20 species representative of different morphologies and host types (high- and low-microbial-abundance, HMA and LMA) from temperate and tropical regions. The total oscula area (∑OSA) increased allometrically with sponge volume (V) exhibiting similar exponents (∑OSA=aVb, b ranging 0.6–0.7) for all species, except for tropical HMAs (b = 0.99). Osculum flow rate (OFR) also increased allometrically with OSA and oscula of the same size pumped at the same rate irrespective of sponge volume. As a result, and in contrast to former reports, the PR of most of the sponges increased allometrically (PR=a∑OSAb) with scaling exponent b≈0.75, whereas PR of tropical HMAs increased isometrically. Osculum jet speed declined with the increase in the OSA for most species. The number of oscula and their OSA were the best predictors of the PR in sponges, explaining 75–94% of the in situ variation in PR throughout the natural range of sponge size. The pumping rate of a sponge population can be estimated by measuring the osculum density and cross-sectional area distribution once the relationships between the OSA and OFR are established for each species.

Adaptive strategies of sponges to deoxygenated oceans

“…However, the successive decrease in pumping rate (after 2 days) and the gradual production of a membrane to close the oscula remain unclear but could represent a trade‐off between increasing ventilation and keeping the energetic coast of pumping reasonable. In S. australiensis , body expansion is correlated with an increase in osculum area, and osculum area is the main determinant of pumping rate in this and many other species (Goldstein et al, 2019; Morganti et al, 2021). Perhaps the increase in pumping rate only represents a physiological consequence of the body expansion and is then quickly brought back to normal, decreasing the osculum size by producing an oscular membrane.…”

“…In sponges, pumping rate is correlated with OSA (e.g. Goldstein et al, 2019; Morganti et al, 2021). In the case of S. australiensis , this relationship was calculated on 20 sponges (following Yahel et al, 2005) and was found as PR = 6.55 OSA 1.43 (Figure S6).…”

Pumping Rate and Size of Demosponges—Towards an Understanding Using Modeling

“…Suggesting a constant density of pumping units (choanocytes) throughout any given sponge size, and assuming simple geometric (isometric) scaling V~OSA 3/2 , [17] suggested a theoretical scaling of Q~OSA 3/2 , which has been experimentally supported and confirmed in other studies, see Table 4 in [15]. However, [6,7] found in recent in situ studies on 20 demosponges that Q on average increased allometrically Q = a 1 OSA b1 with scaling exponent b 1 ≈ 0.75, 1.07 and 0.67 (instead of the theoretical value of b 1 = 3/2), thus suggesting that the choanocyte density may not be constant but on the contrary decreases with sponge size.…”

“…Data on sponge size and pumping rates (filtration rates) are important for ecological studies in determining the grazing impact, matter transport and nutrient cycling of observed populations of sponges [2][3][4][5][6]. While sponge volume (V) may be more difficult to measure or estimate in situ than the osculum cross-sectional area (OSA), the latter has also been used as a correlation parameter [7], who used the following allometric relationships to characterize sponges:…”

“…This is supported by [13] and see Figure 5 in [15], but not by Table 5 in [6] that give negative b values ranging from −0.2 to −0.7. Further, [7] recently reported b = −0.52 for seven Red Sea sponge species and b = −0.43 for eight Caribbean species and therefore suggested that the theoretical considerations that explained the relationships observed by [15,17] for relatively small sponge explants may not be "expected to hold for much larger and more static sponges". Thus, the scaling b < 1 of power-law exponents may, according to [7], be explained by different aquiferous system structures and by choanocyte chamber densities, which may vary among species and with sponge size, and that the distribution of choanocyte chambers may vary in different parts of the sponge body.…”