2.4. Degree of preservation of A. salina nauplii.
Small portions of the sediment with carcasses were put in the Petri dish, diluted with ASW, and investigated under optical microscope (Zeiss Stemi SV11) to count the nauplii and assess the degree of their preservation. We categorized the remains in five groups according to the presence of morphologically recognizable limbs and gut and the general body shape. The procedure and the characteristics of the five preservatonal groups are described in detail in Naimark et al., 2018c.
Group 1 comprised carcasses with all limbs, gut and body shape well preserved. Specimens in group 2 had well preserved limbs and body shape but no traces of the gut. Unlike freshly killed specimens or specimens from other preservational groups, the group 2 specimens were rigid and did not tend to fold in wrinkles when placed on a hard surface. Group 2 was rare in sediment-free controls but common in sediments. Groups 3-5 comprised specimens with preservation gradually deteriorating from only moderately damaged cuticle, gut and limbs in group 3 to separate limbs or limbless bodies in group 5 (Naimark et al., 2018c). The overall degree of preservation was estimated as the ratio of the well-preserved groups 1 and 2 to the poorly preserved groups 3, 4, and 5.