For animal embryos that develop externally, the physio-chemical environment can substantially affect offspring viability. In the case of the American horseshoe crab (Limulus polyphemus), sediment conditions along estuarine shorelines influence development rates and embryonic viability. Sandy beach habitats are considered to have optimal conditions for horseshoe crab embryonic development; however, spawning is often observed outside of these optimal habitats, in areas such as salt marshes, where reduced oxygen availability is thought to decrease the viability of eggs laid in these sediments. We excavated horseshoe crab eggs, embryos, and trilobites laid naturally in marsh and beach sediments in South Carolina to compare their development and viability between habitats. We found all developmental stages in both marsh and beach habitats. For two of three sampling areas, trilobites were more likely to be found at beaches than at marshes. Multivariate analyses demonstrate that the prevalence of early and middle developmental stages was similar between habitats but that beaches had a greater proportion of late-stage trilobites than marshes. The lower likelihood of finding trilobites at some marshes may reflect differences in spawning phenology between habitats or reduced rates of embryonic development in marshes compared to beaches, leading to potentially different developmental timelines rather than a true reduction in viability. Nevertheless, the substantial proportions of eggs laid in salt marshes that survive to the trilobite stage indicate that spawning in this habitat could represent a previously underappreciated source of recruitment for horseshoe crab populations that may need to be incorporated into population assessments.

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评估盐沼和沙滩栖息地中美国Horse（Li）胚胎的生存力

对于外部发育的动物胚胎，理化环境会大大影响后代的生存能力。以美国horse为例（Li）），沿河口海岸线的沉积物条件会影响发育速度和胚胎的生存能力。沙滩栖息地被认为是horse蟹胚胎发育的最佳条件。但是，通常在这些最佳栖息地之外的地方观察到产卵，例如盐沼等地区，那里的氧气供应减少会降低这些沉积物中产卵的生存能力。我们挖掘了南卡罗来纳州沼泽和海滩沉积物中自然产的horse蟹卵，胚胎和三叶虫，以比较它们在各个生境之间的发育和生存能力。我们发现了沼泽和海滩栖息地的所有发育阶段。对于三个采样区域中的两个，在海滩而不是在沼泽中更容易发现三叶虫。多变量分析表明，生境之间早期和中期发育阶段的患病率相似，但海滩晚期三叶虫的比例高于沼泽。与海滩相比，在某些沼泽中发现三叶虫的可能性较低，可能反映了生境之间产卵物候的差异或沼泽中胚胎发育速率的降低，导致潜在的发育时间轴而不是生存力的真正降低。然而，在盐沼中存活到三叶虫阶段的卵中有很大一部分表明，在该生境中产卵可能代表了以前不为人所知的horse蟹种群招募来源，可能需要将其纳入种群评估中。