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

Poul S. Larsen,Hans Ulrik Riisgård

doi:10.3390/jmse9111308

Abstract

Filter-feeding sponges pump large amounts of water and contribute significantly to grazing impact, matter transport and nutrient cycling in many marine benthic communities. For ecological studies it is therefore of interest to be able to estimate the pumping rate of different species from their volume size or osculum cross-sectional area by means of experimentally determined allometric correlations. To help understand allometric data correlations and observed large variations of volume-specific pumping rate among species we developed a model that determines the pumping rate as a function of the size (volume) of a tubular-type demosponge described by 4 geometric length scales. The model relies on a choanocyte-pump model and standard pressure loss relations for flow through the aquiferous system, and density and pumping rate per choanocyte is assumed to be constant. By selecting different possibilities for increase of the length scales, which may also simulate different growth forms, we demonstrate that the model can imitate the experimental allometric correlations. It is concluded that the observed dependence of pumping rate on size is primarily governed by the hydraulics of pump performance and pressure losses of the aquiferous system rather than, e.g., decreasing density of choanocytes with increasing sponge size.

Highlights

Filter-feeding sponges are one of the major components of marine benthic communities with a worldwide distribution [1]
In the search of scaling relations for volume-specific pumping rate versus volume of a tubular sponge (Figure 3) we note that V~DO 2 H and Q~(DO 2 − Da 2 )H provided the pumping rate and density of choanocytes were constant in the structural annular volume
This scaling leads to the expression Q/V~1 − (Da /DO )2, which for increasing V implies a decrease, an increase, or no change depending on how Da /DO changes with increasing

Summary

Introduction

Filter-feeding sponges are one of the major components of marine benthic communities with a worldwide distribution [1]. May be more difficult to measure or estimate in situ than the osculum cross-sectional area (OSA), the latter has been used as a correlation parameter [7], who used the following allometric relationships to characterize sponges: Q/V = aV b ; Q = a1 OSAb1 ; Q = a2 V b2 ; U = a3 V b3 ; OSA = a4 Vb4 (1) iations. Where Q/V denotes the volume-specific pumping rate, Q the pumping rate, V the sponge volume, OSA the osculum cross-sectional area, and U the exhalant jet speed at osculum. An aquiferous module is a functional unit that draws ambient water through numerous inhalant openings (ostia) into an incurrent canal system by means of pumping units (choanocyte chambers, CC) that filter the water for nutrition and eject it via an excurrent canal system to an atrial cavity and through a single exhalant opening (osculum) as a jet to the surrounding water

Methods

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Discussion

Conclusion