Ocean Acidification

The squid-centric view of life (from Clark, 1996). Nearly everything in the ocean feeds upon, or is food for, squid at some point.

Cephalopods are critical components of many marine ecosystems. Squid in particular are often considered key species because of their central role in trophic webs, as the primary prey of numerous top predators, and the consumer of smaller meso- and epipelagic prey.  While ocean acidification (OA) is poised to substantially impact a diverse array of marine organisms, there is little understanding of if or how decreasing pH and higher levels of CO₂ may impact squid. Effects upon squid embryos and paralarvae may be of most concern because: (i) these developmental stages and their metabolism are highly sensitive to environmental conditions, (ii) they are initiating the construction of aragonite statoliths vital to orientation and sensory biology, and (iii) their successful early life history growth, behavior and survival are critical to founding future cohorts which support ecosystem food webs and global fisheries.

A paralarval squid used in our early OA experiments (photo by M. Kaplan).

In our early OA work, Atlantic longfin squid (Doryteuthis pealeii), an ecologically and economically valuable taxon, were reared from eggs to hatchlings (paralarvae) under ambient and elevated CO₂ concentrations in replicated experimental trials. Animals raised under elevated pCO₂ demonstrated significant developmental changes including increased time to hatching and shorter mantle lengths, although differences were small. Aragonite statoliths, critical for balance and detecting movement, had significantly reduced surface area and were abnormally shaped with increased porosity and altered crystal structure in elevated pCO₂-reared paralarvae. These developmental and physiological effects could alter squid paralarvae behavior and survival in the wild, directly and indirectly impacting marine food webs and commercial fisheries.

SEM images of paralarval statoliths. Six squid statoliths imaged using SEM. Statoliths of squid raised in elevated CO₂ (2200 ppm) concentrations were more porous and more irregular in shape, compared to statoliths from individuals reared under ambient (390 ppm) CO₂ levels. Statoliths A1 and A2 are grade 1 (ambient), statoliths B1 (ambient) and B2 (elevated) are grade 2, and statoliths C1 and C2 (elevated) are grade 3.

 
The goal of our upcoming work is to quantify how ocean acidification conditions impact squid (Loligo pealeii) embryo and paralarval development, behavior, and survival, as well as address the mechanisms that potentially induce these changes.  Our initial data indicate that high CO₂ levels (2200 ppm) and low pH (7.4) induce changes in squid paralarval length, development time, rate of hatching, statolith length, and statolith structure.  Our current tests  encompass current and predicted future CO₂ levels (390-2200 ppm).  We will hopefully produce effectual dose-response curves which are valuable for dynamic organisms which can occur in a range of environmental conditions.  This upcoming work includes investigations of energy expenditures (via yolk sack size and swim velocity) and statolith mass and densities to address the potential mechanisms for changes in development, behavior and sensory physiology.  Maintaining animals beyond hatching will allow estimates of survival potential.  Final measurements will quantify the selectiveness of adults to lay eggs in the CO₂ conditions in which effects were shown.

See our first paper on this work, led by Joint Program student Max Kaplan

Kaplan, M*, Mooney, TA, McCorkle, D, Cohen, A.  Adverse Effects of Ocean Acidification on Early Development of Squid (Doryteuthis pealeii). PLoS ONE 8(5): e63714. doi:10.1371/journal.pone.0063714

Casey Zakroff, is taking over as PhD student lead of this project.
See their info on the people page of the lab website.

This is an NSF Ocean Acidification funded project.