Demise of monocultural algal farms by exclusion of territorial damselfish

• Published in: Marine ecology. Progress series (Halstenbek) 2003-11, Vol.263, p.159-167
• Main Authors: Hata, Hiroki, Kato, Makoto
• Format: Article
• Language: English
• Subjects: Agnatha. Pisces; Agricultural management; Agronomy. Soil science and plant productions; Algae; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Biomass; Coral reefs; Demecology; Farms; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Herbivores; Intensive production; Macrophytes; Marine; Monoculture; Plant aquaculture, algal production (macroalgae); Polysiphonia; Species diversity; Stegastes nigricans; Vertebrata; weeding
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps263159

Resident herbivorous damselfishes exclude other herbivores from their territories and maintain dense stands of filamentous algae as algal farms. The damselfishStegastes nigricansoccupies coral reefs in the Okinawa Islands, southern Japan, and is unique in maintaining monocultural algal farms of the filamentous rhodophytePolysiphoniasp. One of the mechanisms by whichS. nigricansmaintains these unique algal farms is by selective weeding of indigestible algae. This study tested the hypothesis that, were it not for management byS. nigricans, monocultures would be taken over by algal succession, even without grazing by other herbivores. We set upS. nigricans-exclusion cages inside and grazer-exclusion cages outside the territories ofS. nigricans, and monitored algal succession. After exclusion ofS. nigricans, thePolysiphoniasp. monoculture deteriorated rapidly and algal biomass decreased simultaneously. Filamentous rhodophytes replacedPolysiphoniasp. within 2 wk, and were in turn displaced by corticated macrophytes and calcareous algae (which are usually selectively weeded byS. nigricans). Monocultures ofPolysiphoniasp. did not appear in the grazer-exclusion cages; pioneerPolysiphoniasp. colonized the areas just after caging, but thereafter was replaced by other filamentous rhodophytes, corticated macrophytes, and calcareous algae. Our experiments demonstrated thatS. nigricansmaintained monocultures and high biomass of palatable pioneerPolysiphoniasp. against algal succession by intensive farm-management, involving selective weeding.