In addition to physiological impacts, internal calcified structures
such as squid statoliths may also be affected by reduced seawater
pH [18,19,42,43]. Located in paired statocysts and analogous in
function and similar in structure to fish otoliths, statoliths are vital
for sensing gravity and movement [44]. Squid statolith formation
is initiated directly after gastrulation during early embryonic
development [45]. Initial results for one squid species, L. vulgaris,
suggest statolith surface area may increase with greater pCO2
levels (850 and 1500 matm) [42]; however, aragonite saturation
states were not calculated, which makes it difficult to assess these
changes. Even small impacts to statolith growth are of concern
because improper formation can severely impact balance and
orientation [46].