Macro- and microhabitat use patterns of holothurians in Buena Vista, Nggela, Solomon Islands: rock climber and bottom crawler species

Abstract

Densities and habitat use patterns of holothurians, including nocturnal species, were assessed in Buena Vista, Nggela, Solomon Islands, for community-based resource management. Nighttime snorkeling surveys were conducted along transects (maximum 1.6 km) with 3 to 5 searchers in nearshore, channel, and outer reef macrohabitats. Only the population in the seagrass macrohabitat was separately assessed in 30 m line transects during the daytime. Microhabitats were clearly separated between species living on 3-dimensional structures (e.g. surfaces of knolls and reef slopes; rock climber group) and those on flat bottoms (bottom crawler group), although they coexisted at macrohabitat scales. Potential shelters adjacent to each individual differed between the 2 groups. Among bottom crawler species, Bohadschia koellikeri, which was recently taxonomically divided from B. vitiensis, occupied macrohabitats intermediately ranging between those of B. argus in the channel and outer reef macrohabitats and those of B. vitiensis and B. marmorata in the nearshore and seagrass macrohabitats. The high-density population was observed in the seagrass macrohabitat, mainly composed of Holothuria scabra, B. marmorata, and H. fuscogilva, although most individuals of these species were smaller than the national legal size limits. Moreover, the body lengths of H. atra and H. fuscogilva increased from the seagrass macrohabitat to the outer reef macrohabitat, implying their migration during growth and the roles of seagrass areas as nurseries. These results revealed diversity of macro- and microhabitat use patterns among species and their growth stages and highlight the importance of considering these factors for conserving diverse species by areal-based protection measures.