Pauly et al.: Growth and related traits of Hippospongia lachne 
103 
Note that Z, in fisheries science, is commonly thought to 
consist of fishing mortality (F) and natural mortality (M), 
in the form of Z=F+M. 
Equation 8 was derived to estimate Z from ¢,,,, but can 
also be inverted (i.e., used to obtain rough estimates of 
longevity, given estimates of Z). Such estimates are avail- 
able from ecosystem models, in which the ratio of produc- 
tion to biomass (p/b) of sponges was computed under the 
assumptions that the VBGF described individual growth 
and that population numbers decayed exponentially. 
Given these 2 assumptions, p/b=Z (Allen, 1971), an equa- 
tion that makes it easier to estimate ratios of production 
to biomass than the complicated approach proposed by 
Winberg (1971). 
Reproduction 
The predictability and relative fixity of the ratio between 
L,, and mean length at first maturity (L,,) of different 
groups of fish (Beverton and Holt, 1959) has led to the con- 
cept of “a reproductive load” (Cushing, 1981), whose val- 
ues tend to range from 0.4—0.5 in large fish species, such 
as tuna, to 0.6—-0.7 in smaller fish species, such as sar- 
dines (Beverton and Holt, 1959; Beverton, 1963; Mitani, 
1970; Froese and Binohlan, 2000). This concept embodies 
the notion that fish and other WBE stop growing because 
their “energy,” once L,,, is reached, is channeled into repro- 
duction rather than somatic growth (van Oosten, 1923; 
Hubbs, 1926; Jones, 1976; Lagler et al., 1977; Charnov, 
2008; Quince et al., 2008). However, this notion is con- 
tradicted by the following facts: 1) in the majority of fish 
species, the females grow faster than males, even though 
they devote more energy to reproduction (Pauly, 2019b); 
2) in long-lived fish (Liang, 2021) and other long-lived 
WBE, maturity is reached while growth in weight is still 
accelerating (Pauly, 2021b); and 3) a number of WBE con- 
tinue to grow and reproduce throughout their lifetimes 
without suffering from senescence (Nussey et al., 2013; 
Gnanalingam and Butler, 2018). Still, it remains the case 
that L,, and L,, are correlated within different popula- 
tions of the same species and even between species (see 
Pauly, 1984, 2019a). 
Respiration 
Sponges are considered textbook examples of animals 
that use current-induced flow (e.g., Vogel, 1996), but 
Ludeman et al. (2017) have demonstrated that at least 5 
demosponge species respond to increased current veloc- 
ity by reducing their filtration. The results of their study 
also indicate that pumping rates (mean volumetric flow 
rate: liters per hours per grams of dry weight), although 
variable, are positively correlated (y=1.7559+x° "1°. coef- 
ficient of determination [r?]=0.66) with oxygen consumed 
by the sponge (mean oxygen removal: micromoles per 
hours per grams of dry weight). Estimates of the ener- 
getic cost of pumping in demosponges varies widely from 
<1% for temperate sponges (Riisgard et al., 1993) to 25% 
or more for tropical demosponges (Hadas et al., 2008; 
Leys et al., 2011; Ludeman et al., 2017), such as the wool 
sponge. 
Recall that the volume of a sphere is calculated as 
V=(4/3)nr°. Therefore, the volume in a layer of a sphere 
can be obtained by using this equation: 
r= (% x Vin), (10) 
where r = the radius of a spherical sponge. 
Measurements of oxygen levels in the interior of a 
roughly spherical sponge, the Barrett’s horny sponge 
(Geodia barretti), performed by Hoffmann et al. (2005) 
were read off their figure 2, re-expressed as fractions of 
ambient oxygen levels, and fitted with a logistic curve 
with the following form: 
Fraction of ambient oxygen level =1 / (1 + ental) (11) 
where r = the radius, measured as the depth within the 
sponge; 
S = the slope; and 
I= the inflection point at which oxygen is 50% of 
the ambient level. 
The confidence interval (CI) of the slope S at the inflexion 
point J is estimated through bootstrapping (Fieberg et al., 
2020). 
Sponges in fisheries, ecosystems, and ecosystem models 
Pending a more detailed “reconstruction” of the catches of 
wool sponges and other commercial sponges in the world, 
to match the reconstruction of the catches of exploited fish 
and invertebrates (Pauly and Zeller, 2016a, 2016b; see 
also Pauly et al.'), we extracted the main features of the 
sponge harvest data in the global fisheries catch statistics 
submitted by member countries to, and harmonized and 
disseminated by, the FAO. 
In shallow-water tropical ecosystems, sponges compete 
for substrate with corals and algae, and they alter plank- 
ton communities in the water column and water chemistry 
(Peterson et al., 2006; Valentine and Butler, 2019). They 
also provide food and structure for animals (Herrnkind 
et al., 1997; Duffy, 2007; Butler et al., 2016), among other 
services. As such, they are frequently included in food-web 
models for ecosystems. However, they are usually included 
as a group (e.g., as a group called sponges in Opitz, 1996) 
or as part of larger groups (e.g., as epibenthos in Okey 
et al., 2004), not as distinct species, even in cases in which 
one species was clearly dominant. 
The growth parameters presented herein, comple- 
mented by generic estimates of food consumption and 
turnover ratio for sponges (Table 2), may lead to better 
food-web models, at least for the areas of Florida and the 
Caribbean where sponge biomass is substantial in shallow 
coastal waters and on coral reefs. In the Florida Keys, a 
hectare of hard-bottom habitat in shallow waters harbors 
" Pauly, D., D. Zeller, and M. L. D. Palomares (eds.). 2020. Sea 
Around Us concepts, design and data. [Available from website.] 
