Coral recruits on concrete hemispherical artificial reef (HSAR) with different composition in Pasir Putih, Situbondo, Indonesia

Abstract

Artificial reefs (AR) are artificial habitats laid in seabed by mimicking some of the characteristics of natural reefs, hence can be used as natural substrates for recruitment process for coral larvae. One of well-developed AR is concrete hemispherical artificial reef (HSAR) which serve as a solid platform for settlement and recruitment processes of coral larvae. In this study, we constructed HSAR made of concrete with crushed shell waste (CSW) and fly ash-bottom ash (FABA) as substitutes for coarse and/or fine aggregates. The purpose of the research is to compare the diversity, density and level of coral recruitment on HSAR with different composition; namely C1), conventional concrete composed by a mixture of Portland cement, sand and gravel (1:3:2); C2), concrete with CSW as substitutes for gravel or coarse aggregates (1:3:2); and C3) concrete composed by Portland cement, FABA, sand and CSW (1:2:2:1). Observation of coral recruits conducted in-situ in Pasir Putih beach, Situbondo, East Java, Indonesia. All observed ambient environmental parameters (temperature, salinity, lucidity, level of dissolved oxygen and sedimentation level) are in range for tolerance level of coral growth and development as well as to support larval settlement and recruitment. Results of one-way Anova and LSD test (p = 0.05) showed that there was no difference in term of density of recruits in C1 (9.5±2.07 colonies/m2) and C2 (8.7±2.5 colonies/m2), yet significantly differed with C3 (6.5±1.43 colonies/m2). We identified at least 12 genera of coral recruits grown on the surface of HSAR, dominated by Acropora (60.08%), Porites (26.98%) and Seriatopora (17.06%), respectively; with relatively similar genera composition on each AR. These results suggest that addition of CSW to concrete AR may not have significant positive effect on the coral larval settlement. Furthermore, concrete AR contain FABA was presumably less suitable for coral recruitment process.