Patterns in reproductive dynamics of burrowing ghost shrimp Trypaea australiensis from small to intermediate scales

Abstract

Many studies have examined latitudinal differences in reproduction of marine invertebrates, but few have measured variation at small to intermediate scales (kilometres to hundreds of kilometres), which may confound comparisons across broader geographic regions. Here, we examined variation in the reproductive biology of a little-studied species of burrowing ghost shrimp (Trypaea australiensis) at spatial scales ranging from km (between sites within estuaries) to 100s of km (among estuaries), over a 2-year period in south-eastern Australia. Sex ratios of populations were consistently biased towards females through time and space. Although reproduction started in summer months across all spatial scales, there was a pattern of earlier spawning from southern to northern estuaries. Integration of results from previous studies of T. australiensis supported a similar pattern of earlier breeding from high to low latitudes. Fecundity of shrimp increased linearly with female size, but the relationship varied inconsistently across the different spatial scales. Similarly, sizes at maturity varied from small to intermediate scales and observed patterns were not consistent with general predictions e.g. shrimp were smaller and ovigerous at smaller sizes at sites in the southern-most estuary, compared to estuaries further north. We found no differences in the sizes of embryos across the different spatial scales, but confirm that T. australiensis employs a strategy of high fecundity and small embryo size compared to other thalassinidean shrimp. Our results suggest that factors at smaller scales (e.g. food availability) may be important in affecting reproductive dynamics of T. australiensis, but further research is needed in testing hypotheses about patterns observed here. A lack of similar studies on other marine organisms remains an impediment to understanding life-history strategies and the sustainable management and conservation of populations.