Foraging by the stoplight parrotfish Sparisoma viride II. Intake and assimilation of food, protein and energy

Jh Bruggemann,P Verburg,J Begeman,Em Bosma,Am Breeman

doi:10.3354/meps106057

Abstract

Daily food intake by the herbivorous parrotfish Sparisoma viride, as well as assimilation efficiencies of algal food, protein and energy, were quantified through a combination of laboratory feeding trials and field observations. The intake of algal ash-free dry wt (AFDW) per bite increases linearly with fish wet wt (FWW, g) and algal biomass (mg AFDW CM-2), and is further determined by the skeletal density of the limestone substrate. Low-density substrates yield higher amounts of AFDW per bite than do high-density substrates. The percentage of the total food intake that is derived from endolithic and crustose coralline algae increases with the size of the fish, and can be > 70 % depending on the biomass of epilithic algae. The daily pattern of foraging activity is positively correlated with diurnal changes in food quality, while seasonal daylength variations result in 13 % variation in total daily bites taken. Daily number of bites of S. viride in the field decreases with fish size, and is further dependent on life phase and foraging depth. In experiments, fish attained an assimilation efficiency of ca 20 % from a natural diet of low algal biomass and high-density dead coral substrates that predominates in the shallow reef. Assimilation efficiency was ca 70 % from a diet of high algal biomass and low-density substrates that predominates on the deeper reef parts. In spite of lower daily foraging effort, territorial fish, living in deeper parts of the reef, ingest and assimilate higher amounts of AFDW, protein and energy per day than non-territorial fish foraging on the shallow reef. The difference is caused by increased availability of high-yield food and substrate types inside territories compared to the situation on the shallow reef. Daily assimilated energy (kJ d-1) is 0.85 x FWW 0.773 for fish foraging in the shallow reef zone, and 1.22 x FWW0.854 for S. viride foraging inside territories on the deeper reef.

Highlights

Herbivory on some coral reefs is probably more intense than in any other habitat, either terrestrial or marine (Hatcher & Larkum 1983, Carpenter 1986, Lewis 1986, Choat 1991).On reefs subject to minimal human disturbance, fish, as the main consumers of the primary production, are often estimated to consume between 50 and 100% of total algal production (Carpenter 1986)
The percentage of the total food intake that is derived from endolithic and crustose coralline algae increases with the size of the flsh, and can be 9 0 % depending on the biomass of epilithic algae
Fish attained an assimilation efficiency of ca 20% from a natural diet of low algal biomass and high-density dead coral substrates that predominates in the shallow reef

Summary

Introduction

Herbivory on some coral reefs is probably more intense than in any other habitat, either terrestrial or marine (Hatcher & Larkum 1983, Carpenter 1986, Lewis 1986, Choat 1991).On reefs subject to minimal human disturbance, fish, as the main consumers of the primary production, are often estimated to consume between 50 and 100% of total algal production (Carpenter 1986). Parrotfish (family Scaridae) have been widely recognized as a major component of the herbivorous fish community (Williams 1982, Russ 1984a, b, Choat & Bellwood 1985), and can be expected to play an important role in the transfer of food materials and energy from primary producers to the remaining members of the food chain. Parrotfish are intense feeders whlch can profoundly affect the diversity and bion~assof reef-inhabiting algae (Brock 1979).In terms of feeding biology, and in analysis of the fish community structure, it has been convenient to view scarids as a relatively uniform group of grazing herbivores that scrape filarnentous algae from the reef matrix (Choat 1991). The impact of these herbivores on the algal communities will vary with species composition and reef habitat.

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Conclusion