Many animals avoid detection or recognition using camouflage tailored to the visual features of their environment.1,2,3 The appearance of those features, however, can be affected by fluctuations in local lighting conditions, making them appear different over time.4,5 Despite dynamic lighting being common in many terrestrial and aquatic environments, it is unknown whether dynamic lighting influences the camouflage patterns that animals adopt. Here, we test whether a common form of underwater dynamic lighting, consisting of moving light bands that can create local fluctuations in the intensity of light ("water caustics"), affects the camouflage of cuttlefish (Sepia officinalis). Owing to specialized pigment cells (chromatophores) in the skin,6 these cephalopod mollusks can dynamically adjust their body patterns in response to features of their visual scene.7,8,9 Although cuttlefish resting on plain or patterned backgrounds usually expressed uniform or disruptive body patterns, respectively,10,11,12 exposure to these backgrounds in dynamic lighting induced stronger disruptive patterns regardless of the background type. Dynamic lighting increased the maximum contrast levels within scenes, and these maximum contrast levels were associated with the degree of cuttlefish disruptive camouflage. This adoption of disruptive camouflage in dynamically lit scenes may be adaptive, reducing the likelihood of detection, or alternatively, it could represent a constraint on visual processing.

Environments contain various forms of noise that can interfere with the ability of animal sensory systems to perceive information. One ubiquitous type of visual noise in shallow aquatic habitats is caustic flicker (or caustics), consisting of dynamically moving light patterns caused by the refraction of light when passing through the water's rippling surface. While some teleost fish avoid environments with caustic noise (where their prey can be more difficult to detect), it remains untested whether caustics affect the habitat selection of invertebrates. In the present study, we ask whether three invertebrate species, the shore crab Carcinus maenas, the brown shrimp Crangon crangon, and the common cuttlefish Sepia officinalis, prefer or avoid associating with environments with caustic noise, and whether caustics affect their behavioural activity and habitat exploration. To do this, we exposed the three species in binary choice experiments to different simulated caustic noise levels varying in their temporal (speed) and spatial (definition) components. Neither of the three tested invertebrate species spent more or less time in environments with higher caustic noise levels. While we also found no evidence that caustics affected the behavioural activity and exploration of Ca. maenas and S. officinalis, the brown shrimp Cr. crangon reduced its activity with increasing spatial caustic noise. However, all obtained effect sizes in this study were small, suggesting that caustic noise only minimally affects invertebrate behaviour. Overall, our results show that, unlike in teleost fish, caustics have limited influence on the habitat selection, exploration, and activity of crustaceans and cephalopods.

Many animals rely on their visual systems to detect, locate or discriminate information in their environment. Environmental ‘visual noise’, however, may interfere with an animal's ability to detect visual information, affecting decision-making processes. A ubiquitous form of visual noise in aquatic environments is caustic flicker: moving light patterns caused by the refraction of light through surface waves. While caustics impair the ability of fishes to detect prey, the impacts of caustics on the ability of nonvertebrates to target prey remains untested. In the present study, we asked whether the hunting success of the common cuttlefish, Sepia officinalis, is affected by the presence of caustic flicker. To do this, we tested whether both the spatial (definition) and temporal (speed) components of caustic flicker affected the ability of cuttlefish to detect and catch a common prey, the brown shrimp, Crangon crangon. Neither the spatial nor temporal components of caustic flicker affected the detection latency or the capture time of prey. Moreover, cuttlefish did not adapt their hunting behaviour, including their approach speed, movement bouts, attack distance or angle, as a function of caustic flicker. Our results show that visual noise from caustic flicker does not affect the ability of cuttlefish to hunt their prey or their hunting behaviour. We provide multiple explanations, including the role of polarization vision, for why dynamic illumination does not appear to impact the visual sensory processing of cuttlefish.

Many animals use camouflage to avoid detection by others, yet even the most inconspicuous objects become detectable against the background when moving1,2. One way to reduce detection while moving would be to 'hide' behind the movements of objects or other animals3. Here, we demonstrate experimentally that a common marine predator, the trumpetfish (Aulostomus maculatus), can conceal its approach from its prey by performing a behaviour known as 'shadowing' - swimming closely next to another, larger and non-predatory fish3,4,5. Our findings reveal how predators can actively use another animal as a form of concealment to reduce detection by prey.

Spatial and temporal dynamics of common cuttlefish, Sepia officinalis, spawning at north European shores was studied using data collected by the Cephalopod Citizen Science Project, Seasearch between 1995 and 2021 and a range of other internet sources for the same period. Reproduction begins in the western English Channel in March and gradually progresses eastward following water warming, attaining the Netherlands in May, when peripheral spawning grounds expand north to Norfolk and the Irish Sea. Despite a thermal regime favourable for egg development existing around the UK and Ireland, spawning is normally restricted to the English Channel and southernmost North Sea with egg masses occasionally observed as far north as Isle of Man and Norfolk.

Abstract Cuttlefish are an important global fisheries resource, and their demand is placing increasing pressure on populations in many areas, necessitating conservation measures. We reviewed evidence from case studies spanning Europe, Africa, Asia, and Australia encompassing diverse intervention methods (fisheries closures, protected areas, habitat restoration, fishing-gear modifications, promoting egg survival, and restocking), and we also discuss the effects of pollution on cuttlefish. We conclude: (1) spatio-temporal closures need to encompass substantial portions of a species’ range and protect at least one major part of their life cycle; (2) fishing-gear modifications have the potential to reduce unwanted cuttlefish capture, but more comprehensive trials are needed; (3) egg survival can be improved by diverting and salvaging from traps; (4) existing lab rearing and restocking may not produce financially viable results; and (5) fisheries management policies should be regularly reviewed in light of rapid changes in cuttlefish stock status. Further, citizen science can provide data to reduce uncertainty in empirical assessments. The information synthesized in this review will guide managers and stakeholders to implement regulations and conservation initiatives that increase the productivity and sustainability of fisheries interacting with cuttlefish, and highlights gaps in knowledge that need to be addressed.

Sepiolidae (Cephalopoda: Sepiolida) are growing in popularity as model organisms, not least because of their well-studied symbiotic relationship with light producing bacteria. Their easy maintenance and cultivation requirements in captivity have further facilitated their use in a wide range of developmental, anatomical, neurophysiological, behavioural and genetic studies, exhibiting promising opportunities for these cephalopods in research. Considering the rising interest in sepiolids, a detailed overview of their behavioural ecology is necessary to understand their evolution and conservation, as well as to aid establishment of good welfare practice when held in captivity. To date, not all aspects of the sepiolid ecology have been investigated in detail, and our current knowledge of their behavioural ecology is, for the most part, restricted to descriptions from less than 10 of the approximately 80 species, occasionally resulting in a generalisation of specific observations across species, genera, or even subfamilies. This review summarises current knowledge on sepiolid behavioural ecology and life history, including discussions on their habitat, life span, activity patterns, hunting and feeding behaviour, anti-predator behaviour, burying behaviour, and reproductive behaviour. Moreover, future directions as well as areas of interest for upcoming research studies are highlighted.

The inshore commercial squids, Loligo vulgaris and L. forbesii, co-occur in the ecoregions of Celtic Seas and Greater North Sea but the spatio-temporal structure of their spawning ranges is poorly understood. To help solve the problem, data sets collected during the last 30 years by British, German, French, and Irish scientists, as well as observations from multinational Citizen Science, were combined. Spawning grounds of L. forbesii were found to form an external semi-circle around the spawning grounds of L. vulgaris, with the latter being centred on the English Channel and southernmost North Sea. The nursery grounds of both species appear to coincide with the respective spawning grounds, though L. forbesii makes much wider use of the North Sea. Seasonally, the position of the spawning grounds of both species is driven by the local temperature regime, although this is possibly subject to interannual variability. Spawning of both species begins around November and gradually progresses eastward following favourable currents and increasing water temperatures. Spawning in both species is mostly over by July, though some egg masses persist until August–November. Nursery grounds follow the same seasonal shift from west to east, at least in L. forbesii.

In shallow water, downwelling light is refracted from surface waves onto the substrate creating bands of light that fluctuate in both time and space, known as caustics. This dynamic illumination can be a visual hindrance for animals in shallow underwater environments. Animals in such habitats may have evolved to use polarization vision for discriminating objects while ignoring the variations in illumination caused by caustics. To explore this possibility, crabs (Carcinus maenas) and cuttlefish (Sepia officinalis), both of which have polarization vision, were presented with moving stimuli overlaid with caustics. Dynamic caustics inhibited the detection of an intensity-based stimulus but not when these stimuli were polarized. This study is the first to demonstrate that polarization vision reduces the negative impacts that dynamic illumination can have on visual perception.

Group living is a common behavioural feature in many different animal species. It offers a multitude of fitness benefits, such as increased opportunities to find resources, improved predator vigilance and potentially even social learning. In cephalopods, social grouping behaviour has mainly been reported for squid species, with up to several thousand individuals displaying different forms of shoaling and even schooling behaviour. Despite being held in groups in captivity, cuttlefish (Cephalopoda: Sepiidae) have long been considered rather asocial animals. However, reports of breeding aggregations and one recent schooling observation from the wild started to bring this characterisation into question. Following this, we here present 10 observations of the European cuttlefish Sepia officinalis (Linnaeus 1758) forming groups of up to 30 individuals along the South Coast of the UK. The majority of the observed cuttlefish appeared to be juveniles or subadults and showed different shoaling orientations, such as linear or spherical-shaped formations. This indicated the grouping behaviour did not derive from coincidental accumulations. No mating or courtship behaviour could be identified in these groups, and as all observations were made in August or September, and therefore outside their mating season (March to June), it is unlikely that reproductive behaviour motivates these aggregations. As S. officinalis is known to migrate to deeper overwintering grounds in autumn, we propose that cuttlefish may temporarily form groups in late summer/early autumn as part of their migration pattern, and that their shoaling behaviour likely offers similar fitness benefits as in other migrating shoaling species.

Bottletail squids (Cephalopoda: Sepiadariidae) spend the daytime buried in sediment; however, their burying behaviour has not yet been described in detail. In the present study, the burying pattern of a single tropical bottletail squid Sepiadarium kochii Steenstrup, 1881 is analysed for different behavioural characteristics. Burying in S. kochii consists of a rapid sequence of strong, alternating forward- and backward directed funnel jets which obscure the individual almost fully with sediment, followed by a single flinging movement of the dorsolateral arm pair to cover the remaining exposed body parts with sand. A comparison of the burying pattern of S. kochii with that of closely related bobtail squids (Cephalopoda: Sepiolidae) is drawn. Moreover, differences between these two cephalopod families in terms of the execution and duration of their burying procedure as well as its behavioural use are discussed.

Many animals go to great lengths to stabilize their eyes relative to the visual scene and do so to enhance the localization of moving objects and to functionally partition the visual system relative to the outside world. An important cue that is used to control these stabilization movements is contrast within the visual surround. Previous studies on insects, spiders and fish have shown that gaze stabilization is achromatic ('colour blind'), meaning that chromatic contrast alone (in the absence of apparent intensity contrasts) does not contribute to gaze stabilization. Following the assumption that polarization vision is analogous in many ways to colour vision, the present study shows that five different crustacean species do not use the polarization of light alone for gaze stabilization, despite being able to use this modality for detecting predator-like objects. This work therefore suggests that the gaze stabilization in many crustaceans cannot be elicited by the polarization of light alone.

Bobtail squids (Sepiolidae, Cephalopoda) have recently been growing in popularity in scientific studies due to their symbiotic relationship with light producing bacteria and their corresponding light emitting organs. However, the overall knowledge on the behaviour of sepiolids is based on observations on just a few of the roughly 70 extant species and must still be considered as sparsely. Understanding their behavioural ecology is not only beneficial to further grasp the complex behavioural patterns of cephalopods, it is also vital for establishing a good welfare practice when holding sepiolids in captivity. Hence, the present study characterised several behavioural aspects of the spotty bobtail squid Euprymna parva. Although the burying, hunting and mating behaviour as well as most escape responses of this less investigated sepiolid species greatly resembled those of other observed bobtail squids, differences to sepiolids from other genera or even from the same genus could be identified in the present study. Additionally, the first observation of an up to now undescribed inking behaviour of sepiolids is reported. E. parva was observed to eject a stretch of ink (‘ink rope’), approximately 4–5 times the length of the animal, and hold on to it motionless, potentially as a masquerade to resemble a floating seagrass leave. The present study further provides detailed information on daily time and activity budgets as well as the tentacular strike speed during hunting, two up to now barely investigated behavioural aspects of the sepiolid ecology.