Pauly et al.: Growth and related traits of Hippospongia lachne 
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459 models as of December 2019, 84% of the models 
described marine ecosystems, but only 12 models included 
sponges. Moreover, in only 3 of those models were sponges 
a group of their own, not combined with corals or other 
benthic animals. 
Table 2 presents the food consumption and production 
per unit biomass estimated for sponges from a variety of 
sources by the authors of the 3 models in which sponges 
were not grouped with other organisms. Other stage-based 
or individual-based models depicting sponge population or 
community stability under fishing or environmental pres- 
sure also exist (Cropper and DiResta, 1999; Butler and 
Dolan, 2017), but they do not explicitly incorporate food 
consumption or respiration in relation to production. 
Discussion 
We hope that the relationships given in the “Results” sec- 
tion will be useful to colleagues involved in the comparative 
study of sponges, the assessment of the status of fisheries 
for the wool sponge and similar sponges, the modeling of 
the ecosystems in which such fisheries are embedded, and 
the potential mariculture of sponges. There is, however, 
another interesting aspect to the growth and related traits 
of wool sponges pertaining to the first author’s attempt to 
formulate, test, and illustrate a comprehensive theory of 
growth for WBE, the gill-oxygen limitation theory (Pauly 
and Cheung, 2017; Pauly, 2019a, 2021a). 
Sponges originated approximately 800 million years 
ago in the Pre-Cambrian (Reitner and Worheide, 2002; 
Turner, 2021); therefore, they had ample time to evolve 
sophisticated defenses in the form of spicules embedded in 
a tough matrix, which partly protects them against spon- 
givores (Wulff, 2006; to generate a list of spongivorous 
fishes, select sponges in the drop-down list of the food item 
search tool on FishBase, available from website), a strat- 
egy resembling that of thorny land plants. Also, similar 
to plants, sponges cannot evade predators and as a result 
have evolved an ability to synthesize a dazzling array of 
complex organic molecules to protect themselves against 
potential consumers and pathogens (Pawlik, 2011; Loh 
and Pawlik, 2014; Rohde et al., 2015), and that array is 
the reason they are sought after as a source of potentially 
useful medical compounds (Blunt et al., 2003). 
On the other hand, sponges did not evolve the many dif- 
ferentiated cells, tissues, organs, and appendages that are 
characteristic of other phyla, such as mollusks, arthro- 
pods, and chordates. Therefore, we can more easily detect 
in sponges the constraints that have shaped the transition 
to multicellularity in the first animals and the emergence 
of the first body plans. In particular, we agree with Ward 
(2006), who believes that “respiration was perhaps the most 
important driver of animal body plans.” Indeed, the appear- 
ance of sponges on earth, predating oxygen-producing mul- 
ticellular plants by 300 million years (Brocks et al., 2017), 
occurred during a period when dissolved oxygen was at a 
premium. At that time, a day on earth was 21 h long and 
atmospheric oxygen levels were only about 50% of what they 
are today (Klatt et al., 2021). Although global oxygen stores 
later increased rapidly with the evolution of multicellular 
plants, for 500 million years sponges evolved in a world 
depauperate in oxygen. In the absence of tissues or organs 
specialized for oxygen acquisition, sponge morphology was 
likely strongly constrained by physiological oxygen demand. 
The notion that oxygen constrains sponge energetics 
and morphology is contrary to the suggestion in Storr 
(1964) that the supply of nutrients (i.e., food) is the lim- 
iting factor to the survival and multiplication of the cells 
in the interior of a cell mass. In their review of food com- 
petition and limitation for coral-reef-dwelling sponges, 
Pawlik et al. (2015) found no evidence for food limitation 
of sponge growth. However, the reef sponge community is 
dominated by low-microbial-abundance sponges with high 
filtration rates and large canal volumes, and they dwell in 
an oxygen-enriched environment. The opposite is true for 
shallow-water-dwelling coastal sponges for which growth 
appears to be limited at high densities of sponges because 
of limitation of either food or oxygen (Valentine, 2019). 
Herein we show that oxygen supply could indeed be a pri- 
mary constraint on sponge growth, at least for spherical 
high-microbial-abundance sponges. 
The effects of a limited capacity to deliver oxygen to tis- 
sues is evidenced across many animal phyla (Heim et al., 
2020). For Homo sapiens, effects are manifested in heart 
insufficiencies and attacks (Weber and Janicki, 1979) 
and in ischemic strokes (Janardhan and Qureshi, 2004). 
This phenomenon also applies to cancerous tumors whose 
cells shift to glycolytic metabolism when their interior is 
deprived of oxygen or when a temperature increase drives 
their oxygen demand beyond the capacity of the blood 
supply that they have commandeered (Warburg, 1930; Al 
Tameemi et al., 2019). 
The fundamental reason for a limiting role of oxygen 
is that, because of its toxicity, molecular oxygen cannot 
be stored in living animal tissue (Lane, 2002); the oxy- 
gen that is stored in the mesoglea of jellyfish (Thuesen 
et al., 2005) is no exception because the mesoglea is not 
living tissue. The only way oxygen can be stored is through 
chemical bonding as in blood (Lenfant et al., 1970; Noren 
et al., 2002), and oxygen storage requires an internal cir- 
culatory system that is absent in many phyla (Heim et al., 
2020), including the Porifera. 
As a result, the growth of poriferans, and especially 
those with a spherical shape, is constrained by the afore- 
mentioned dimensional tension (Pauly and Cheung, 2017) 
inherent in having to supply a growing (3-D) body with 
oxygen in water whose flow is determined by the cumu- 
lative (2-D) cross section of the inhalant ostia (inhalant 
pores). This constraint remains even if a sponge’s pumping 
rate increases with body size. 
If they are limited by oxygen, we can predict that 
sponges, especially sphere-shaped demosponges when 
fully grown, will experience hypoxia and even anoxia in 
the central part of their bodies, as is commonly observed. 
Yet, this oxygen limitation also permits the presence 
of anaerobic bacteria and archea within the commensal 
community dwelling inside sponges, not too dissimilar to 
