Distribution of calanoid copepod eggs in seabed sediments of Masan Bay, Korea

Abstract

The distribution of calanoid copepod eggs was studied in the bottom sediment of Masan Bay (South Sea, Korea), where hypoxic conditions develop every summer, during a hopoxic period (August 2011) and a normoxic period (April 2012). In addition, an analysis was carried out concerning the relationship between seabed environments and the distribution pattern of morphologically normal and abnormal eggs. In August all stations showed hypoxic condition with sea bottom dissolved oxygen below 1.2 mg L-1, whereas in April they showed normoxic condition with sea bottom dissolved oxygen above 5.0 mg L-1. A measurement taken in the inner part of the bay during the hypoxic period gave a low pH (< 7.7) and a high concentration of H2S (> 20 &#61549;mol L-1) at sediment&#8211;water interface, whereas during the normoxic period there was no significant difference between stations. As for the abundance of eggs found in sediment, a higher range of density (between 0.61 and 2.01 × 106 eggs m-2) was observed during the hypoxic period compared to the normoxic period, and this level of abundance was higher than the levels reported to be observed at various global locations. The hypoxic period showed high proportion (maximum 77.1%) of abnormal eggs, including empty egg shells, in the inner part of the bay; whereas the normoxic period showed homogeneous distribution of normal eggs (> 80%) among all stations. The generation of abnormal eggs that either failed to develop to hatching or hatched into deformed nauplii is presumed to be related to the high concentration of H2S and low pH caused by hypoxia. This study will discuss the influences of hypoxia and seabed environments on hatching success of calanoid copepod eggs.