Aggregation and the energetics of the barnacle Balanus glandula Darwin

Barnacles (Balanus glandula) were allowed to settle in 5 pre-determined patterns with an increasing degree of aggregation (i. e. isolated individuals, paired individuals, 9 individuals in a group, 81 individuals in a group and 'crowded' individuals with number > 12295 m⁻²). The energy budget:-C = P.BT. + P.E. + H.AQ. + R.AER. + M + F (Where :- C=Consumption, P.BT.=Production of body tissue, P.E.=Production of egg, R.AQ.=Aquatic respiration, R.AER.=Aerial respiration, H=Molting, F=Faecal production) was constructed for barnacle individuals for the first year settlement of each of the above 5 patterns. All the budget items on the right hand side of the equation were measured and consumption was found by their summation. Laboratory feeding experiments showed that consumption values derived from the summation method balanced closely with those obtained from feeding experiments. B. glandula had a very high assimilation efficiency (91.8 to 99.4 %) but a low gross production efficiency (22.8 to 26.4 %) and net production efficiency (24.7 to 28.6 %). A large proportion of energy intake (64.8 to 67.7 J) was lost in respiration. The second most important budget item was egg production (12.3 to 15.3 %); followed in decreasing order by shell production (6.1 to 7.2 %) > body tissue production (3.9 to 4.6 %) > molting (1.1 to 2.3 %). Aggregation significantly reduces the consumption, assimilation, production, as well as the energy standing crop of body tissue, egg and shell of an individual barnacle. Among these, egg production appears to be most sensitive to crowding. When comparing the egg: body tissue ratio and shell: tissue ratio between crowded and uncrowded individual barnacles, a decrease in degree of crowding was associated with: (1) an increase in the egg: body tissue ratio and (2) a decrease in shell: tissue ratio of the individuals. This appears to suggest a difference in energy partition in the barnacles with different degrees of crowding. Uncrowded individuals acquiring an adequate amount of energy, could afford to channel more energy into egg output and hence produce more progeny. On the other hand, crowded individuals acquire a limited amount of energy and apparently conserve a larger proportion of their energy in (1) building body tissue rather than egg and (2) building a taller shell so as to increase the general feeding area of the population. Finally, the energetics of a natural barnacle (B. glandula) population was studied. The consumption, energy flow (assimilation) , production and mortality were found to be : 6844.9, 6666.6 , 2897.1 and 2518.1 Kcal m⁻² yr⁻¹, respectively. The energy flow and production values are among the highest when compared with that of other animal populations and therefore strongly suggest the functional importance of B. glandula in the littoral system. The young age groups (< 1 year settlements) were most important in contributing to the population energy flow and production .Science, Faculty ofZoology, Department ofGraduat