Development of Swimming Abilities in Squid Paralarvae: Behavioral and Ecological Implications for Dispersal

Abstract

This study investigates the development of swimming abilities and its relationship with morphology, growth, and nourishment of reared Doryteuthis opalescens paralarvae from hatching to 60 days of age. Paralarvae (2.5–11 mm mantle length – ML) were videotaped, and their behavior quantified throughout development using computerized motion analysis. Hatchlings swim dispersed maintaining large nearest neighbor distances (NND, 8.7 ML), with swimming speeds (SS) of 3–8 mm s-1 and paths with long horizontal displacements, resulting in high net to gross displacement ratios (NGDR). For 15-day-old paralarvae, swimming paths are more consistent between jets, growth of fins, length, and mass increases. The swimming pattern of 18-day-old paralarvae starved for 72 h exhibited a significant reduction in mean SS and inability to perform escape jets. A key morphological, behavioral, and ecological transition occurs at about 6 mm ML (>35-day old), when there is a clear change in body shape, swimming performance, and behavior, paths are more regularly repeated and directional swimming is evident, suggesting that morphological changes incur in swimming performance. These squid are able to perform sustained swimming and hover against a current at significantly closer NND (2.0 ML), as path displacement is reduced and maneuverability increases. As paralarvae reach 6–7 mm ML, they are able to attain speeds up to 562 mm s-1 and to form schools. Social feeding interactions (kleptoparasitism) are often observed prior to the formation of schools. Schools are always formed within areas of high flow gradient in the tanks and are dependent on squid size and current speed. Fin development is a requisite for synchronized and maneuverable swimming of schooling early juveniles. Although average speeds of paralarvae are within intermediate Reynolds numbers (Re < 100), they make the transition to the inertia-dominated realm during escape jets of high propulsion (Re > 3200), transitioning from plankton to nekton after their first month of life. The progressive development of swimming capabilities and social interactions enable juvenile squid to school, while also accelerates learning, orientation and cognition. These observations indicate that modeling of the lifecycle should include competency to exert influence over small currents and dispersal patterns after the first month of life.

The Tentacular Strike Behavior in Squid: Functional Interdependency of Morphology and Predatory Behaviors During Ontogeny

“…Paralarvae ranging in size from 2 to 13 mm mantle length (ML) were filmed at 0, 1,2,6,10,11,13,14,17,20,30,40,50,55, and 60 days of age. Mean ML for paralarvae of these ages (0 = 2.65 mm ML, 6 = 2.7 mm ML, 14 = 3.8 mm ML, 20 = 4.1 mm ML, 30 = 4.7 mm ML, 40 = 6.7 mm ML, 55 = 7.8 mm ML, 60 = 9.8 mm ML) were obtained from Vidal et al (2018) as filming used in the present study were conducted simultaneously with the experiments reported in that particular study. A round aquarium (7 cm H, 12 cm diameter and holding a center core of 9 cm) was constructed as a miniature of the large rearing tanks, in which filming was performed from above (dorsal perspective).…”

“…Arm-crown morphology and predatory behaviors revealed close adjustments with progressive complexity and efficiency as paralarvae go through major developmental milestones. Hatchlings have a rudimentary arm-crown and fins, bell-shaped body, limited swimming abilities (Vidal et al, 2018) and display only a basic predatory behavior (BA). In this behavior, the arms and tentacles frame prey from underneath (Figure 6).…”

“…Upon hatching, squid paralarvae have bell shape, limited swimming and behavioral abilities (Chen et al, 1996;Vidal et al, 2018) and an underdeveloped arm-crown and beak . In contrast, during their first month of life, squid undergo foremost morphological, behavioral, and ecological changes, leading to enhanced swimming performance and cognitive abilities, which make them competent to swim in schools and control their distribution (Vidal et al, 2018). This coincides with the end of the paralarval dispersive phase and the transition from plankton to nekton, representing a shift in paralarvae physiological ecology (Vidal et al, 2018).…”

“…In contrast, during their first month of life, squid undergo foremost morphological, behavioral, and ecological changes, leading to enhanced swimming performance and cognitive abilities, which make them competent to swim in schools and control their distribution (Vidal et al, 2018). This coincides with the end of the paralarval dispersive phase and the transition from plankton to nekton, representing a shift in paralarvae physiological ecology (Vidal et al, 2018). In concert with these major developmental landmarks that squid goes through during early ontogeny, their predatory behavior and functional morphology changes.…”

“…The present study integrates behavioral observations with morphological and morphometric data to obtain a detailed understanding of tentacular kinematics and morphology, while also evaluating the role played by the arms and tentacles during predatory behavior in D. opalescens reared under laboratory conditions from hatching to 80 days of age. Importantly, comprehensive available information on feeding behavior and prey types, growth, body and beak morphology, and swimming abilities for D. opalescens (Chen et al, 1996;Vidal et al, 2002Vidal et al, , 2018Vidal and Boletzky, 2014) provides the unique opportunity to encompass several levels of knowledge in examining how predatory behavior relates to key events during ontogeny. Thus, the aims of this study are to evaluate the ontogeny of predatory behavior, particularly the TS behavior, and its relationship with morphological development.…”