Crab larvae already showing effects of coastal acidification

As part of the study, which involved scientists from across the USA, Canada and Slovenia, the crabs were examined under a high-magnification scanning electron microscope.

It revealed that the corrosive conditions of coastal waters had affected portions of the fragile, still-developing external shell and legs of the post-larval crabs, leaving tell-tale features such as abnormal ridging structures and scarred surfaces. This could, the researchers say, impair larval survival by altering swimming behaviours and competence, including the ability to regulate buoyancy, maintain vertical position and avoid predators.

The study showed that crabs with signs of carapace dissolution were smaller than other larvae. This was disconcerting, scientists said, because the damage during the crab’s larval stages could cause potential developmental delays that could increase energy demands and interfere with maturation.

The team also found that the low pH water in some coastal areas damaged the canals where hair-like bristles called mechanoreceptors stick out from the shell. These receptors transmit important chemical and mechanical sensations to the crab, and may help crabs navigate their environment.

Examination showed that carapace dissolution destabilises the attachment of the mechanoreceptor anchor, resulting in them falling out in some individuals. This is a new aspect of crustacean sensitivity to ocean acidification that has not been previously reported.

The team hypothesise that the absence or damage of mechanoreceptors within their neuritic canals may in part explain potential aberrant behavioural patterns, such as slower movement, less tactile recognition, and prolonged searching time, as well as impaired swimming, that have been observed in various crustacean species exposed to low pH conditions in laboratory settings.

The full study - Exoskeleton dissolution with mechanoreceptor damage in larval Dungeness crab related to severity of present-day ocean acidification vertical gradients by Bednaršek et al - is published in Science of The Total Environment, doi: 10.1016/j.scitotenv.2020.136610.