Effects of acidification on meroplanktonic oyster larval settlement in a tropical estuary

Abstract

<span style="font-size:9.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:calibri;mso-bidi-font-family:="" "times="" roman";mso-ansi-language:en-us;mso-fareast-language:en-us;="" mso-bidi-language:ar-sa"="" lang="EN-US">Monthly variations in salinity, temperature and pH were studied in relation to settlement of meroplanktonic oyster larvae on cultches in Vembanad Lake, a tropical estuary along the southwest coast of India. A strong correlation between monthly pH values and oyster spat density (P=0.002) was evident. W<span style="font-size:9.0pt;line-height:115%;font-family:" times="" new="" roman";="" mso-fareast-font-family:"times="" roman";mso-bidi-font-family:"times="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">hen the pH values in the estuary were low, <span style="font-size:9.0pt;line-height:115%;font-family:" times="" new="" roman";="" mso-fareast-font-family:calibri;mso-bidi-font-family:"times="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">the spat settlement density was poor (4.5/cultch), which was nearly half of the value (7.8/cultch) when the <span style="font-size:9.0pt; line-height:115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" mso-bidi-font-family:"times="" roman";mso-ansi-language:en-us;mso-fareast-language:="" en-us;mso-bidi-language:ar-sa"="" lang="EN-US">pH<span style="font-size:9.0pt; line-height:115%;font-family:" times="" new="" roman";mso-fareast-font-family:calibri;="" mso-bidi-font-family:"times="" roman";mso-ansi-language:en-us;mso-fareast-language:="" en-us;mso-bidi-language:ar-sa"="" lang="EN-US"> was alkaline. Experiments were conducted to evaluate the effects of extremes of temperature (20 to 35^oC) and pH (6.5 to 8.5) on metamorphosis and survival of oyster larvae. In pH 6.5 there was 100% mortality and complete dissolution of dead shells in 24 h. <span style="font-size:9.0pt;line-height:115%;font-family:" times="" new="" roman";="" mso-fareast-font-family:"times="" roman";mso-bidi-font-family:"times="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">Survival was highest (81%) in the control temperature of <span style="font-size:9.0pt;line-height:115%;font-family:" times="" new="" roman";="" mso-fareast-font-family:calibri;mso-bidi-font-family:"times="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">27^oC <span style="font-size:9.0pt;line-height:115%;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-bidi-font-family:="" "times="" roman";mso-ansi-language:en-us;mso-fareast-language:en-us;="" mso-bidi-language:ar-sa"="" lang="EN-US">and less than 50% in 25 and 20^oC. Treatment-wise differences in survival were significant (P<0.01). <span style="font-size:9.0pt;line-height:115%;font-family:" times="" new="" roman";="" mso-fareast-font-family:calibri;mso-bidi-font-family:"times="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">Study indicated that, if the pH drops below 7.0 during the meroplanktonic phase of oyster, recruitment will be affected and therefore oyster spat densities can be used as an indicator for acidification in tropical estuaries.</span></span></span></span></span></span></span></span></span>