Macrobenthic infaunal assemblage structure in nearshore and offshore seabeds of Ghana

Abstract

Abstract. Commey NA, Armah AK, Lamptey E. 2021. Macrobenthic infaunal assemblage structure in nearshore and offshore seabeds of Ghana. Indo Pac J Ocean Life 5: 50-60. This research aimed to compare and contrast the sediment properties and benthic macrofaunal assemblage composition of nearshore and offshore habitats. Also, the existing state of benthic macrofaunal assemblages in the Jubilee Fields, Ghana in 2015 is determined. A baseline is established for these communities before constructing a coal-powered plant in the nearshore area of Ekumfi Aboano, Ghana (deep-sea). The research was conducted in the shallower nearshore Ekumfi Aboano (average depth: 15 m) and deeper offshore portions of the Jubilee Fields (average depth: 1,250 m). A Van Veen grab was used to collect sediment samples from the nearshore area, while a box corer was used to collect samples from the deep water. PRIMER was used to look into the distribution of benthic macrofauna. Using GRADISTAT, it was determined that the nearshore sediment (mean grain size of 99.80 m) is fairly sorted with very fine sand. In contrast, offshore sediment (mean grain size of 109.79 m) was poorly sorted and comprised of extremely coarse silty fine sand. It was determined from studies of macrobenthic infauna that there were 11,131 individuals in the nearshore environment, with a density of 38 individuals/m2, and 22,105 individuals in the deep-sea environment, with a density of 47 individuals/m2. Data for the nearshore and offshore environments showed a total of 194 and 983 polychaetes, 827 and 696 crustaceans, 35 and 229 mollusks, 14 and 37 echinoderms, and 43 and 260 "others" (foraminiferans, nematodes, nemerteans, and sipunculids). Crustaceans > polychaetes > molluscs > others > echinoderms dominated the shallow Ekumfi seabed, whereas polychaetes > crustaceans > molluscs > others > echinoderms dominated the offshore Jubilee seabed. There were 116 species discovered close to shore, while 188 were discovered in the deep water. Both locations displayed a high level of diversity (H' > 4; 1-D > 0.9) and were evenly distributed (J' > 0.8). The nearshore was dominated by arthropods (74.30%), while the offshore was dominated by polychaetes (44.58%). A greater variety of macrobenthic infauna was found in the deep sea compared to the nearshore, with a difference of 75% between the two environments.