Factors affecting growth disparity in spiny lobster aquaculture : the effect of physiology, behaviour and feeding

Spiny lobsters are known as a valuable commercial species with limited availability, which makes them a promising candidate for aquaculture. However, to date, the production of spiny lobsters in captivity has been characterised by considerable variation in individual lobster growth rates leading to growth disparity and impacting on biomass production. One explanation for the growth disparity in spiny lobsters is the agonistic behaviour of dominant individuals, whereby they control and consume a disproportionate share of food resources, benefiting their own growth performance. However, the mechanisms of how behavioural and feeding traits of individual lobsters influence growth disparity in culture are poorly understood. Furthermore, research of a range of marine organisms has shown that variability in individual metabolic physiology (metabolic phenotype) can be an important factor influencing behaviour and growth. However, the relationship between metabolic phenotype and individual growth performance has not been previously investigated in any spiny lobster species. Understanding the influence of intraspecific diversity in physiological traits on growth performance of individuals is an important consideration for the development of optimal rearing conditions and management strategies for spiny lobsters aquaculture. This is the first study to focus on the influence of individual variations in physiology, behaviour and feeding on the growth performance of two commercial temperate spiny lobsters species, Sagmariasus verreauxi and Jasus edwardsii juveniles in captivity. In Chapter 2, the influence of metabolic phenotype and social behaviour on growth performance of early juvenile S. verreauxi (5.99±2.77g) that were reared either individually or communally was examined. Findings show that communally reared lobsters have greater growth performance, survival and feed intake indicating that social interaction is vital for promoting the growth of lobsters. Growth performance of individually reared lobsters was positively linked with metabolic rate providing the first evidence of a link between metabolic phenotype and growth performance of a lobster species. Metabolic phenotype was not linked to lobster growth performance in communal culture indicating that social interaction outweighed the direct link between metabolic rate and lobster growth. These results suggest social behaviour plays a dominant role in determining the growth of individuals in populations, however, the factors influencing behavioural interactions between individuals within a population remained to be determined. In Chapter 3, the effect of metabolic phenotype, body size, sex, feeding contest experience and rearing history on the early juvenile S. verreauxi social status was examined using pair-feeding contest behavioural studies. Findings from these experiments showed that larger size lobsters were likely to be more dominant over smaller lobsters. Low metabolic rate lobsters also displayed greater ability to win over high metabolic rate lobsters which may explain why growth was not positively linked with metabolic phenotype in communal culture, as demonstrated in Chapter 2. Female lobsters were more dominant than male lobsters irrespective of size and metabolic phenotype status. These findings showed that the dominance behaviour of S. verreauxi is complex and that a range of factors including body size, metabolic status and sex can influence dominance status and potentially growth of individual lobsters in captivity. Chapter 4 examined the influence of emergent juvenile intraspecific size variation and metabolic phenotype on growth performance of J. edwardsii post-pueruli in individual or communal rearing. Similar to findings with S.verreauxi, communally reared J. edwardsii displayed a greater carapace length increment and a shorter intermoult period indicating that social interaction promotes lobster growth performance. Emergent juvenile body size did not influence lobster growth performance. Also similar to findings with S. verreauxi, metabolic phenotype showed a positive correlation with growth in individually reared lobsters, however, the communally reared lobsters displayed no such relationship suggesting that metabolic phenotype is also an important factor for J. edwardsii growth in the absence of social interaction. However, the underlying mechanism contributing to the relationship between metabolic phenotype and growth of spiny lobsters were not well understood. Chapter 5 examined the effect of metabolic phenotype on individual variation in feed intake and food preference between current best diets of the emergent juveniles J. edwardsii and linked with individual growth performance. Metabolic phenotype was not related to individual lobster feed intake. Moreover, lobster growth performance was also not linked with their feed intake. Mussel, notably mussel gonad, was the most preferred food for J. edwardsii emergent juveniles. Lobster food preference showed no correlation with the individual growth performance. These findings indicated that lobster feed intake and preference are not fundamental factors linking metabolic phenotype and growth. Collectively, findings from my study show that growth of spiny lobsters in culture is highly complex and influenced by a range of intrinsic and extrinsic factors. The present study provided the first evidence that spiny lobsters growth can be directly linked to metabolic phenotype, however, social behaviour appears to play a greater role in promoting the growth of individuals and populations. The dominance status of spiny lobster during feeding competition can be influenced by body size, metabolic phenotype and sex. Thus, growth performance of spiny lobsters in captivity can be explained by a complex interaction between individual lobster physiological traits and social interaction. Emergent juvenile body size and feed intake and preference is not a major driver for growth disparity in culture. The development of aquaculture systems for spiny lobsters may involve a trade-off between systems which promote overall growth at the expense of increases in growth disparity between individuals. Further research is required to determine the mechanism (visual, chemical and or physical) involved in the relationship between social interaction and growth of spiny lobsters in captivity.