Environmental Engineering Reference
In-Depth Information
the fact that half of all i sh biomass is found in only 17% of the world's ocean
area (Jennings et al. 2008).
Another recent estimate of marine zoomass reevaluated the amount of Antarctic
krill, more than 80 species of tiny (typically just 1-2 cm) shrimplike crustaceans,
dominated by
Euphausia superba,
that add up to one of the biosphere's largest
sources of easily accessible protein. Krill's maximum distribution covers about 19
Mkm
2
, and with a mean total abundance of 8
10
14
post-larvae its total zoomass
is 379 Mt (Atkinson et al. 2009). The authors also estimated that the annual gross
postlarval production of 342-536 Mt supports a predator consumption of 128-470
Mt/year by i sh, squids, seabirds, and baleen whales.
Quantii cations of the global whale zoomass may get even the order of magnitude
wrong because the extant numbers of most of the massive species are known only
within unhelpfully broad bands. For example, the IUCN (2011) offers best estimates
of “hundreds of thousands” for sperm whales (
Physeter macrocephalus
) and any-
where between 10,000 and 25,000 for blue whales (
Balaenoptera musculus
), and
because we do not have sufi ciently detailed understanding of the age and sex com-
position of these animals, calculating errors will only increase when the total
numbers are multiplied by uncertain body mass averages.
None of this has prevented Christensen (2006) from reconstructing historical
(prewhaling) and modern abundances on the global scale (implausibly, down to the
nearest 10 or 100 individuals of all species), and Pershing et al. (2010) from using
these numbers, in conjunction with age-structured models and average body masses,
to calculate the biomasses of eight species or species groups of baleen whales (blue,
i n, humpback, sei/Bryde's, gray, right, minke, and bowhead; sperm whales were
excluded). The prewhaling zoomass added up to about 103 Mt in 2.56 million
animals, while the totals for 2001 were, respectively, about 16 Mt and 880,000
individuals, implying an overall loss of about 85% of the original baleen whale
zoomass.
Terrestrial invertebrates are more important for the maintenance of ecosystems
than vertebrates, but they are harvested by humans only in relatively small quanti-
ties. Insectivory (including the larvae and pupae of some species, with relatively
common choices including ants, crickets, and grasshoppers) is still practiced in many
traditional societies (while bees and silkworms remain the most important domes-
ticated insects), and many snails are also eaten (Menzel and D'Aluisio 1998). But
in aggregate, terrestrial invertebrates make only a marginal contribution to global
nutrition, whereas marine invertebrates (cephalopods, mollusks, crustaceans) are an
important source of dietary protein.
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