Copepod abundance and impact of selected human induced stressors on calanoid copepod in the coastal sea of Ghana

Abstract

According to the UN, sea surface temperatures (SST) are increasing at alarming rates and the oceans are increasingly polluted by anthropogenic activities. This thesis sought to determine how two pollutants – cadmium (Cd) and pyrene (PY) interacting with sea surface warming affect copepod egg production (EP), mortality and recycling of ingested food through faecal pellet (FP) production. A field study was conducted on transects established on the Western, Central and Eastern Coast Transects of Ghana during the dry season to evaluate copepod taxonomic composition as well as the supportive environment of the animals. The copepods were dominated by the Order Calanoida (51-53 %), followed by Cyclopoida (18-30 %), Poecilostomatoida (10-22 %) and Harpacticoida (8-10 %). The abundance of these copepods was highest (16-1276 ind. l-1) on the Western Coast Transect. The combined effects of the pollutants and warming were assessed on Temora Stylifera, a dominant copepod found in Ghana, using a microcosm experiment involving different concentration levels of Cd (0.1- 100 µg/l), PY (1-100 nM) and warming (1-3 °C) above Ghana’s average dry season SST of 28 °C. Recorded EP (average: 1.73 ± 0.05 female-1.day-1) increased by ≈ 62 % with Cd concentration but had insignificant change with PY. FP (average: 54.14 ± 8.02 copepod-1.day-1) declined only under PY at concentration > 5.41 ± 0.61 nM. These effects worsened under warming. At the end, the Cd level at which 50 % mortality of the copepods were recorded (LC50) decreased by ≈ 117 µg. l-1 per every degree of warming. In contrast, LC50 for PY increased by ≈ 6 nM per every degree of warming. These observations agree with previous studies, suggesting that warming may alter the toxicity of Cd and PY with harmful effects on marine copepods