Using camouflage for conservation: colour change in juvenile European lobster

Abstract

25Changes in coloration enable animals to refine their camouflage to match different 26 visual environments. Such plasticity provides ecological benefits and could 27 potentially be exploited to support conservation or stock enhancement efforts. One 28 application could be ensuring that hatchery-reared animals, reared to stock wild 29 populations, are appropriately matched to their environment on release. European 30 lobster (Homarus gammarus) hatcheries aim to restock or enhance local lobster 31 populations by rearing juveniles through their most vulnerable stages, then releasing 32 them into the wild. However, little consideration has been given to their camouflage 33 and the implications of matching individuals to their release site. This study assesses 34 to what extent juvenile lobsters can change coloration to match their background and 35 whether hatchery practices could be altered to enhance lobster camouflage . We test 36 this by switching individuals between black or white backgrounds in the laboratory 37 and monitoring their coloration over time. Our work demonstrates the capacity of 38 juvenile lobsters to change lightness in response to their surroundings. We show that 39 juvenile lobsters are capable of small changes in luminance (perceived lightness) to 40 better match their background over 2-3 weeks. These changes potentially 41 correspond to improved camouflage, based on a model of predator (European 42 pollack, Pollachius pollachius) vision. However, over a longer period (5 weeks), 43 lobsters maintained on either background converged on the same darker coloration, 44suggesting that lobsters also experience changes in appearance associated with 45 ontogeny. By refining the approaches used here, there is potential for hatcheries to 46 rear lobsters on backgrounds that better match their release site. However, such release timing (which varies between stocking programmes). This study highlights 49 the potential to use colour change in stocking and aquaculture, as well as gaps that 50 could be addressed through further research in this area. 51 52 53 54 Background matching is one of the most widely used anti-predator defence 55 strategies in nature (1), with many species using colours and patterns to match their 56 surroundings and avoid detection and predation. In a wide range of taxa, both 57 terrestrial and aquatic, camouflage can be achieved through plastic changes in 58 appearance (2,3). This enables animals to respond to either fast and unpredictable 59 changes in the visual environment through rapid (seconds and minutes) colour 60 change, or slower and more predictable environmental change with gradual (hours, 61 days, and weeks) appearance changes (4). One of the most widely studied groups, 62 particularly in terms of the mechanisms and functions of colour change, are the 63 crustaceans (3,5). Many crustacean species employ camouflage to conceal 64 themselves from predators and several have been shown to change colour to better 65match their background, including crabs (6-8), prawns (9,1...

European lobster Homarus gammarus aquaculture: Technical developments, opportunities and requirements

“…Feeds deficient in carotenoids also produce unpigmented lobsters, requiring supplementation to promote wild‐type colouration and assist camouflage following release 86 or to improve market appeal for RAS production 33 . Carotenoids also improve survival, growth, reproductive capacity, disease and stress resistance in crustaceans 87,88 .…”

“…Further development is required towards drying method, digestibility and absorption, which impact feed assimilation and growth, alongside the ration and physical requirements of the pellets for use in large-scale RAS. 40,41,85 Feeds deficient in carotenoids also produce unpigmented lobsters, requiring supplementation to promote wild-type colouration and assist camouflage following release 86 or to improve market appeal for RAS production. 33 Carotenoids also improve survival, growth, reproductive capacity, disease and stress resistance in crustaceans.…”

Colour preference in juvenile European lobster (Homarus gammarus)

“…Extremely intense light for prolonged durations can induce stress signals and may lead to the death of cultivated species (Fitch and Lankford, 2013). Another study alternated between white and black backgrounds for H. gammarus juveniles, utilising Pollack ( Pollachius pollachius ) fish as a model for vision whilst monitoring carapace colourimetry (Mynott et al, 2018). In addition, darker colours (black) are preferred for aquaculture cultivation due to their positive photophobic response and orientation to reflective surfaces (Martin-Robichaud and Peterson, 1998).…”