Impacts of extreme flooding conditions on cuttlefish early development and behaviour

Extreme events are becoming increasingly frequent and intense, leading to cascading negative effects on marine ecosystems. Here, we aimed to investigate the impact of acute extreme flooding conditions experienced in the Sado estuary, Portugal, on the early ontogeny of cuttlefish ( Sepia officinalis ). More specifically, in June 2024, eggs were collected in Sado estuary (38.48526° N, 8.88560° O) and exposed to ecologically relevant: i) acute extreme salinity levels of 7 and 17, ii) acute non-extreme brackish conditions of 24 and 28, and iii) control conditions of 35, for four days during late embryogenesis. Both short-term extreme flooding conditions (7 and 17) resulted in 100% mortality. Hatching success was not affected at salinities 24 (64.4 ± 8.1%) and 28 (60.0 ± 12.5%) compared to control conditions (72.3 ± 12.5%). Compared to control conditions, newborns’ mantle length was significantly reduced at salinities of 24 and 28 (12.93% and 9.63%, respectively). Moreover, camouflage latency at salinities of 24 and 28 was delayed, and hatchlings had greater difficulty camouflaging and matching the background. Overall, our findings suggest that both acute extreme and mild (non-extreme) flooding conditions can elicit pervasive sub-lethal effects on cuttlefish early ontogeny.