Distribution of Macroalgae in the Intertidal Zone of Ghana

Abstract

Marine macroalgae or seaweeds, as they are generally referred to, are primary producers which play a central role in the productivity of coastal habitats and also serve as a source of ecosystem goods and services. They are used directly or indirectly in the production of food products, fertilizer, animal feed additives, bioenergy, nutraceutical, confectionary, textiles, paper, paint, and varnish among others. How far this can be exploited depends on the knowledge of available species. In Ghana, there have been sporadic studies of seaweeds or macroalgae since the 1950s, when inventory of the species began, until recent investigation which considered community structure analysis. Following from what is known about this biological community, this study was designed to comprehensively evaluate macroalgal distribution across the coast of Ghana. The key objectives of the research were to: (1) assess of species diversity within the intertidal zone of Ghana; (2) characterize the distribution and community structure of the macroalgae in the intertidal zone of Ghana; and (3) determine the effect of nutrients on observed distributional patterns. Ten sampling locations were selected in a manner that allowed the entire Ghana coast to be covered – i.e. Dixcove, Takoradi, Aminano, Mumford, Kokrobite, Christianborg Castle, Teshie (Next Door), Tema, Prampram and Old Ningo. The macroalgae were purposively sampled using a 1m x 1m quadrat constructed from polyvinyl chloride pipes. Species abundance were estimated as percentage cover within each quadrat, from the high to the low water mark on selected days where the tidal height was lowest. Water quality at each location was analysed for five nutrients (i.e. phosphate, nitrate, ammonia, silicate and sulphate). The sampling period was from 11th October, 2018 to 5th January, 2019. The data was subjected to various statistical analyses using Plymouth Routines in Multivariate Ecological Research (PRIMER version 6). Altogether, forty-one species belonging to 25 families were identified. Of these, ten species played an important role in influencing the spatial community structure, i.e. Ulva fasciata, Ulva flexuosa, Ulva lactuca, Hydropuntia dentata, Hypnea musciformis, Ralfsia expansa, Lithothamnion bisporum, Centroceras clavulatum, Chaetomorpha linum and Caulerpa taxifolia. This study identified these species as keystone species in terms of their dominance and contribution to observed spatio-temporal patterns in community structure, and zonation within the intertidal region; from the supra-littoral across the mid-littoral to sublittoral zones. This study did not find any evidence of the role of nutrients on the observed macroalgal distributional pattern, and attributed it possibly to the short-term temporal nature of the study. Therefore, it is recommended that long-term investigation, in relation to the effect of nutrients on macroalgae community characterization, be undertaken in future studies. Furthermore, adoption of molecular techniques to assist taxonomic characterization of macroalgae and use of unmanned aerial vehicle in field assessment should be explored towards a more comprehensive assessment.