The population dynamics of the estuarine isopod Exosphaeroma hylocoetes (Barnard, 1940) within three temporarily open/closed southern African estuaries

<strong><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;"><p>The population dynamics of the estuarine isopod,</p></span></span></span><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;"><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;">Exosphaeroma hylocoetes, </span></em></span></em><span style="font-size: xx-small; font-family: CharterBT-Bold;"><strong><span style="font-size: xx-small; font-family: CharterBT-Bold;">was investigated monthly from February 2006 to August 2007 in three temporarily open/closed Eastern Cape estuaries, the East and West Kleinemonde and Kasouga Estuaries. Mean isopod abundances </span></strong></span><strong><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">and biomasses ranged between 0 and 4791 ind/m</span></span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">2 </span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">and 0 and 9.65 mg/dwt/m</span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">2 </span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">in the West <span style="font-size: xx-small; font-family: CharterBT-Bold;">Kleinemonde Estuary and between 0 and 108 ind/m</span></span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">2 </span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">and 0 and 0.318 mg/dwt/m</span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">2 </span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">in the nearby East Kleinemonde Estuary. In the Kasouga Estuary, the values ranged between 0 and <span style="font-size: xx-small; font-family: CharterBT-Bold;">3650 ind/m</span></span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">2 </span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">and 0 and 5.105 mg/dwt/m</span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">2</span></span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><strong><span style="font-size: xx-small; font-family: CharterBT-Bold;">. Temporal changes in the abundance and biomass of </span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><strong><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;"><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;"><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;"><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;">E. hylocoetes </span></em></span></em></span></em></span></em><span style="font-size: xx-small; font-family: CharterBT-Bold;"><strong><span style="font-size: xx-small; font-family: CharterBT-Bold;">within the three systems was primarily linked to mouth phase, with populations crashing when the mouth was open and to a lesser extent, seasonality. In all three estuaries <strong><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">maximum abundance and biomass was recorded in the middle reaches, which could be <span style="font-size: xx-small; font-family: CharterBT-Bold;">ascribed to the presence of submerged macrophytes. </span></span></span><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;"><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;">E. hylocoetes </span></em></span></em><span style="font-size: xx-small; font-family: CharterBT-Bold;"><span style="font-size: xx-small; font-family: CharterBT-Bold;">demonstrates strong sexual <span style="font-size: xx-small; font-family: CharterBT-Bold;">dimorphism, with males being significantly larger than females (</span></span></span><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;"><em><span style="font-size: xx-small; font-family: CharterBT-BoldItalic;">P </span></em></span></em><span style="font-size: xx-small; font-family: CharterBT-Bold;"><strong><span style="font-size: xx-small; font-family: CharterBT-Bold;">< 0.05). Sex ratios were </span><span style="font-size: xx-small; font-family: CharterBT-Bold;"><strong><span style="font-size: xx-small; font-family: CharterBT-Bold;"><p><strong><span style="font-size: xx-small; font-family: CharterBT-Bold;">skewed in favour of females in all three estuaries. Females were encountered carrying young from an overall length of 2.5 mm throughout the year</span></strong></p></span></strong></span></strong></span></strong></span></strong></span></strong></span></strong></span></strong></strong>