Ontogenetic, social, spatial and seasonal variations in condition of the reef herbivore Sparisoma viride

Abstract

We studied the condition of stoplight parrot- fish, Sparisoma viride, collected from the fringing reef of Bonaire (Netherlands Antilles) between March 1987 and October 1991. To this end, we compared length- weight relationships using analysis of covariance. The condition of different life phases (juveniles, initial phase (IP) and terminal phase (TP) adults) and social categories (territorial and group adults) is compared in different seasons, taking into account spatial variability along a depth gradient. Variations in condition are related to differences in behaviour, the use of space and the distribution of food. The average length weight relationship of fish with empty guts is described by the equation: WEmpty = 9.115 x 10 -6 X FL 3"1r176 (n = 386, R 2 = 99.82%, W in g, FL in ram). Territorial TP males were found to be in poorest condition, whereas (sexual- ly inactive) group TP showed the best and IP fish an intermediate condition. These differences are ascribed to varying investments in territory defence and repro- duction, which affect condition more than the vertical distribution of food. All categories were in minimum condition between May and July, the season with longest day lengths and increasing water temperatures. This seasonal effect cannot be ascribed to increased reproductive effort and suggests that the higher ener- getic demands due to the longer active period of fish are not completely met by increased food uptake. It is inferred that food may be a limiting factor at times.