Facetotecta, Grygier, 1985

Olesen, Jørgen & Grygier, Mark J., 2024, Taxonomic diversity of marine planktonic ‘ y-larvae’ (Crustacea: Facetotecta) from a coral reef hotspot locality (Japan, Okinawa), with a key to y-nauplii, European Journal of Taxonomy 929 (1), pp. 1-90 : 55

Relative abundance and constancy of LSN morphospecies of Facetotecta at Sesoko Island in 2018 and 2019

Because the youngest and most common naupliar stages caught in plankton frequently cannot be directly tied to the corresponding LSN and cyprid stages, direct assessments of the relative abundance of different y-larval morphospecies in plankton samples, based on all naupliar stages present, cannot be done. In consequence, the following results concerning relative abundance are based solely on the 420 lecithotrophic individuals that were reared to their LSN and videographed at Sesoko Island in 2018/2019.

The relative abundance of lecithotrophic morphospecies (LSN ‘Types’ and cyprids) is presented visually in a bar chart ( Fig. 20 ). A weak negative correlation (-0.35075) was found between the number of last-stage nauplii and their size ( Table 1 ; cf. the same-scale photos of all morphospecies in Fig. 20 ). Since only about 8% of reared individuals survived to the LSN stage and the identity of the failed individuals was largely unknown and not recorded, the proportions of morphospecies among these LSNs may be different from their proportions in the plankton. Nonetheless, overall, the relative abundance of different y-naupliar forms followed the same pattern in 2018 and 2019 ( Table 1 ), with 22 of 30 morphospecies (73%) occurring in both years. The nine most abundant morphospecies overall (Types O*, E*, C, D*, AH*, AG*, K, G, N*) were, with a few exceptions, the most common ones in both years. Notable exceptions were Type K (only one specimen in 2019) and Types G and N* (few specimens in 2018 and 2019, respectively). Conversely, the same set of low-abundance morphospecies was found in both years. There was a smaller overlap in occurrence between 2018/2019 and the earlier more sporadic collections from 1991 to 2005, involving only 18 of the total of 34 morphospecies (53%).

Figures

Fig. 20. Relative abundance of lecithotrophic y-nauplii at Sesoko Island (Okinawa, Japan) during field work in 2018 and 2019. Grey bars denote the number of lecithotrophic nauplii of each morphospecies that survived until the last naupliar stage during laboratory rearing. Blue bars show the numbers of cyprids that successfully molted from these last-stage nauplii. Images of all lecithotrophic y-naupliar morphospecies obtained during those two years are shown to the same scale.