Description and quantification of developmental abnormalities in a natural Sepioteuthis australis spawning population (Mollusca: Cephalopoda)

Abstract

Eggs of the southern calamary Sepioteuthis australis were sampled from spawning sites off eastern Tasmania, Australia, during an austral spring/summer spawning season. At fortnightly intervals, 3 unfouled and 3 biofouled egg strands were sampled from 6 to 23 distinct egg masses (Neggs = 2649). Highly significant variation was noted between sample dates in the frequency of unfertilised eggs, de- velopmental abnormalities and egg mortalities. Unfertilised eggs were only found during late October and early November and represented a mean 2.12 ± 1.25% SE and 0.58 ± 0.58% SE eggs per strand respectively. Frequency of abnormality varied significantly between sample dates and ranged from 8.35 ± 1.86% SE eggs per strand in late November to 0.92 ± 0.41% SE in late December. Abnormalities were arbitrarily categorised as defects in external yolk sac morphology, reduced embryonic size, mantle deformities, eye deformities and arm deformities. Defects in external yolk sac morphology were found throughout the spawning season and accounted for 46.3% of all abnormalities. Incidence of mortality varied significantly between sample dates and ranged from 1.40 ± 0.68% SE per strand in late October to 11.61 ± 3.23% SE in early January. Highly significant correlation was noted between incidence of developmental abnormality and within-strand egg position. Biofouled egg strands were characterised by comparatively low incidences of unfertilised and dead eggs. The influences of environment, egg position and biofouling upon embryonic development in S. australis are discussed.