Biodiversity of zooplankton in 0–3000 ​m waters from the eastern Indian Ocean in spring 2019 based on metabarcoding

Global mesozooplankton communities show lower connectivity in deep oceanic layers

“…Our results indicate that mesozooplankton community composition is structured across both vertical and horizontal oceanic gradients. Vertical structuring was particularly strong in both mlCOI and mac18S datasets either analysing the data globally or at each oceanic basin separately, thus adding evidence for a global, solid vertical structuring of mesozooplankton in the ocean, corroborating many previous observations (Cheng et al, 2022;Fernández de Puelles et al, 2019;Hirai et al, 2020;Pearman & Irigoien, 2015;Sommer et al, 2017;Stefanoudis et al, 2019). Horizontal mesozooplankton structuring (i.e., according to oceanic basins) was also overall supported in both datasets, although it was strongly supported in mlCOI than in mac18S, most likely due to a higher capability of the former to detect intraspecific genetic variants (Turon, Antich, Palacín, Praebel, & Wangensteen, 2020), and thus better detect regional diversity and dissimilarities between distant communities and populations (Chust et al, 2016).…”

“…Previous studies on microzooplankton point to a general pattern of decreasing alphadiversity (richness and diversity indices) along the vertical oceanic gradient (Canals, Obiol, Muhovic, Vaqué, & Massana, 2020;Countway et al, 2007;Giner et al, 2020); however, to date there is no clear consensus on whether mesozooplankton alpha diversity increases or decreases with depth. For instance, while a decreasing trend in mesozooplankton richness and/or H index has been observed in Fernández de Puelles et al ( 2019), Vereshchaka et al (2017), and Pearman and Irigoien (2015), among others, peaks in alpha-diversity at mesopelagic or/and bathypelagic depths have also been reported for copepods (Hirai et al, 2020;Kosobokova & Hirche, 2000;Stefanoudis et al, 2019) and for the whole mesozooplankton community (Cheng et al, 2022;Sommer et al, 2017). Here, we did not observe any consistent pattern in mesozooplankton alpha diversity with depth, but our results seem to support the deep sea (down to the bathypelagic layer) as an ecosystem harbouring a level of diversity comparable to the ones at upper depths.…”

“…Additionally, exploring the deep ocean has added challenges related to the sampling at high depths. To date, most studies on mesozooplankton have been carried out at local (Domínguez et al, 2017;Ershova & Kosobokova, 2019;Kim, Lee, Lee, Oh, & Kim, 2020;Pearman & Irigoien, 2015) or regional (Carlotti et al, 2018;Cheng et al, 2022;Feliú, Pagano, Hidalgo, & Carlotti, 2020;Landry, Hood, & Davies, 2020;Siokou et al, 2019) scales, and only some studies covered large oceanic transects (Bode et al, 2018;Hirai et al, 2020;Vereshchaka, Abyzova, Lunina, & Musaeva, 2017) or global oceanic areas (Fernández de Puelles et al, 2019;Soviadan et al, 2022). Another limitation lies on the taxonomic identification of mesozooplankton being a time-consuming task that greatly depends on often lacking taxonomic expertise and information of the targeted organisms (Hirai & Tsuda, 2015).…”

Revealing zooplankton diversity in the midnight zone

“…In contrast, other Eucarida, Euphausiacea, and Halocyprida exhibit higher diversity in the upper layer, possibly due to better adaptation to primary productivity in the photic zone and a close relationship with the shallow oxygen minimum zone (OMZ) typical of this region (Antezana, 2002;Mujica et al, 2022). A few studies have assessed the vertical trend of species richness of the entire zooplankton community, using metabarcoding analysis, and revealed either a peak of diversity in the upper mesopelagic depth (200-300 m) of the North Pacific central gyre (Sommer et al, 2017), or a bimodal vertical pattern with a first peak in the upper 200 m and a second one below 1000 m found in the Indian Ocean (Cheng et al, 2022), and two other regions with a marked oxygen minimum zone in the mesopelagic depths. However, both studies reached maximum depths of 1500 m and 3000 m, respectively.…”

“…However, studies on zooplankton diversity have mainly focused on epipelagic habitats (0-200 m) (Tittensor et al, 2010;Costello and Chaudhary, 2017), and very few studies have dealt with their vertical patterns of diversity (e.g., Sommer et al, 2017;Laroche et al, 2020). In general terms, largescale patterns of zooplankton diversity show increasing species richness in subtropical areas (Tittensor et al, 2010), while vertical trends exhibit a species richness peak in the upper mesopelagic layer (200-300 m) (Sommer et al, 2017), or a bimodal distribution between the surface and 3000 m (Cheng et al, 2022).…”