Differences in the Structural Components Influence the Pumping Capacity of Marine Sponges

Azraj S Dahihande,Narsinh L Thakur

doi:10.3389/fmars.2021.671362

Abstract

Marine sponges are important sessile, benthic filter feeders with a body plan designed to pump water efficiently. The sponge body plan generally consists of mineral spicules, gelatinous mesohyl, and the pores and canals of the aquiferous system. These structural components have stark differences in compressibility, mass, and volume; therefore, their proportion and distribution are likely to affect sponge morphology, anatomy, contraction, and finally the pumping capacity. We examined seven demosponge species (from high spicule skeleton contents to no spicules) commonly found along the central west coast of India for structural components, such as total inorganic contents (spicule skeleton and foreign inclusions), body density, porosity, and mesohyl TEM for the high microbial abundance/low microbial abundance status. Additionally, we estimated the sponge pumping rate by measuring the excurrent velocity, the abundance of individual pumping units and cells, i.e., choanocyte chambers and choanocytes, and also carried out a morphometric analysis of aquiferous structures. The excurrent velocity and the oscular flow rates showed a positive relationship with the oscular crosssectional area for all the study species. The inorganic spicule contents by their weight as well as volume formed a major component of tissue density and higher proportions of spicules were associated with reduced aquiferous structures and lower pumping rate. The ash mass% and the ash free dry weight (AFDW %) in the sponge dry mass showed separate and distinct associations with aquiferous system variables. For example, the number of choanocytes per chamber showed a wide difference between the studied species ranging from 35.02 ± 2.44 (C. cf. cavernosa) to 120.35 ± 8.98 (I. fusca) and had a significant positive relationship with AFDW% and a negative relationship with ash mass%. This study indicates that the differences in the proportions of structural components are closely related to sponge gross morphology, anatomy, and probably body contractions, factors that influence the sponge pumping capacity.

Highlights

Poriferans are found in almost all benthic habitats and are capable of processing the volume of water several times their body volume per hour (Reiswig, 1971, 1981; Riisgaard and Larsen, 1995)
Variables related to the structural components such as tissue density, spicule volume, and inorganic contents were positioned along with the second component and their vectors were oriented toward species scoring high on these variables (C. cf. cavernosa and B. fortis)
The variables related to the filtration apparatus (CC mm3, choanocyte chambers (CC) diameter, and the number of choanocytes per chamber CC−1, and porosity%) showed a positive correlation with the pumping parameters and a negative correlation with structural components

Summary

Introduction

Poriferans (sponges) are found in almost all benthic habitats and are capable of processing the volume of water several times their body volume per hour (Reiswig, 1971, 1981; Riisgaard and Larsen, 1995). Considering the wide distribution range and exposure to different environmental regimes, different morphological adaptations are observed in sponges. These morphological differences can manifest on macro as well as microlevels i.e., gross morphology and spicule morphology, respectively (Bell et al, 2002). Sponges are sessile metazoans lacking muscular, nervous, and digestive systems Instead, they have a body full of pores and canals with a body plan designed to efficiently pump water. The sponge body plan generally consists of three major structural features, the aquiferous system, gelatinous mesohyl, and the spicule skeleton. The mesohyl and the spicule skeleton support the pores and the canals of the aquiferous system by forming a three-dimensional scaffold structure

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