Cuttlefish Buoyancy in Response to Food Availability and Ocean Acidification.

Eve Otjacques,José Ricardo Paula,Tiago Repolho,Rui Rosa,Miguel Baptista,Silvia Simão

doi:10.3390/biology9070147

Abstract

Carbon dioxide concentration in the atmosphere is expected to continue rising by 2100, leading to a decrease in ocean pH in a process known as ocean acidification (OA). OA can have a direct impact on calcifying organisms, including on the cuttlebone of the common cuttlefish Sepia officinalis. Moreover, nutritional status has also been shown to affect the cuttlebone structure and potentially affect buoyancy. Here, we aimed to understand the combined effects of OA (980 μatm CO2) and food availability (fed vs. non-fed) on the buoyancy of cuttlefish newborns and respective cuttlebone weight/area ratio (as a proxy for calcification). Our results indicate that while OA elicited negative effects on hatching success, it did not negatively affect the cuttlebone weight/area ratio of the hatchlings—OA led to an increase in cuttlebone weight/area ratio of fed newborns (but not in unfed individuals). The proportion of “floating” (linked to buoyancy control loss) newborns was greatest under starvation, regardless of the CO2 treatment, and was associated with a drop in cuttlebone weight/area ratio. Besides showing that cuttlefish buoyancy is unequivocally affected by starvation, here, we also highlight the importance of nutritional condition to assess calcifying organisms’ responses to ocean acidification.

Highlights

Human-induced environmental changes pose multiple threats to oceanic ecosystems [1,2]
This CO2, when combined with seawater, forms carbonic acid (H2 CO3 ), which dissociates into bicarbonate (HCO3 − ) and hydrogen ions (H+ ) [2,4], resulting in a consequent decrease in pH—a process known as ocean acidification
Since we show that longer-exposed cuttlefish embryos have lower hatching success under ocean acidification (OA), this suggests that cuttlefish at later embryonic developmental stages are more tolerant to high CO2 than earlier stages

Summary

Introduction

Human-induced environmental changes pose multiple threats to oceanic ecosystems [1,2]. Since the industrial revolution, this equilibrium has been threatened by an increase in atmospheric CO2 from 280 ppm, during the preindustrial period, to levels exceeding 400 ppm nowadays and the concentration of atmospheric CO2 is expected to rise to 730–1020 ppm by the year 2100 [1,3]. This CO2 , when combined with seawater, forms carbonic acid (H2 CO3 ), which dissociates into bicarbonate (HCO3 − ) and hydrogen ions (H+ ) [2,4], resulting in a consequent decrease in pH—a process known as ocean acidification.

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Discussion

Conclusion