Seasonal Variations in the Growth and Reproduction of Helcion Concolor (Krauss, 1848) Limpet along The Wild Coast Of South Africa

Growth and reproduction are crucial in understanding the biology and ecology of rocky intertidal limpet species. It is inevitable that seasonal fluctuations affect the different reproductive stages of each limpet species in the wild. This led to this research project investigating the seasonal effects on the reproduction and growth rate of the colour variable limpet Helcion concolor (Krauss, 1848). Growth was quantified by comparing the shell dimensions (i.e. shell length, shell width and shell height) and weight (i.e. total body mass, shell weight, somatic weight and gonad weight) of both male and female individuals across the seasons. Histological studies were conducted to quantify the reproductive variation of both male and female individuals during different seasons. Shell conicity (SC), shell ellipticity (SE) and gonad somatic index (GSI) were then calculated to determine seasonal variability. The results revealed that H. concolor females were longer, broader, taller and heavier than the males. Daily incremental shell length analysis detected that the limpets gained more shell length and width in autumn while they gained more shell height in spring and autumn. The ratio of males to females fluctuated on a monthly basis resulting in more females (51.67 ± 4.41 %) than males (48.33 ± 4.41 %) in this study. Males had a larger GSI than females. GSI for females was lowest in summer and highest in spring. For males, the GSI was highest during the winter season. Regression results revealed that shell length and width were useful in determining GSI in both male and females. Histological analysis detected five stages of germ cells for females (Oogonia, Previtellogenic oocyte, Vitellogenic oocyte, Mature oocyte and Atresic oocyte) and four stages for males (Spermatogonia, Spermatocytes, Spermatids and ii Spermatozoa). Mature oocytes were the most abundant stage for females, mostly abundant in autumn and winter. For males, spermatozoa increased from summer to winter and decreased during spring. Histological studies further revealed that H. concolor was a partial spawner as the gonads always contained sperm and eggs within them. Overall, this study highlighted that seasons had more effect on the reproduction than the growth rate of this limpet. Keywords: histology, gonad somatic index, oocytes, patellid, shell dimensions, spawning

Seasonal Variations in the Growth and Reproduction of Helcion Concolor (Krauss, 1848) Limpet along The Wild Coast Of South Africa

Growth and reproduction are crucial in understanding the biology and ecology of rocky intertidal limpet species. It is inevitable that seasonal fluctuations affect the different reproductive stages of each limpet species in the wild. This led to this research project investigating the seasonal effects on the reproduction and growth rate of the colour variable limpet Helcion concolor (Krauss, 1848). Growth was quantified by comparing the shell dimensions (i.e. shell length, shell width and shell height) and weight (i.e. total body mass, shell weight, somatic weight and gonad weight) of both male and female individuals across the seasons. Histological studies were conducted to quantify the reproductive variation of both male and female individuals during different seasons. Shell conicity (SC), shell ellipticity (SE) and gonad somatic index (GSI) were then calculated to determine seasonal variability. The results revealed that H. concolor females were longer, broader, taller and heavier than the males. Daily incremental shell length analysis detected that the limpets gained more shell length and width in autumn while they gained more shell height in spring and autumn. The ratio of males to females fluctuated on a monthly basis resulting in more females (51.67 ± 4.41 %) than males (48.33 ± 4.41 %) in this study. Males had a larger GSI than females. GSI for females was lowest in summer and highest in spring. For males, the GSI was highest during the winter season. Regression results revealed that shell length and width were useful in determining GSI in both male and females. Histological analysis detected five stages of germ cells for females (Oogonia, Previtellogenic oocyte, Vitellogenic oocyte, Mature oocyte and Atresic oocyte) and four stages for males (Spermatogonia, Spermatocytes, Spermatids and ii Spermatozoa). Mature oocytes were the most abundant stage for females, mostly abundant in autumn and winter. For males, spermatozoa increased from summer to winter and decreased during spring. Histological studies further revealed that H. concolor was a partial spawner as the gonads always contained sperm and eggs within them. Overall, this study highlighted that seasons had more effect on the reproduction than the growth rate of this limpet. Keywords: histology, gonad somatic index, oocytes, patellid, shell dimensions, spawning