4.1. CAB diversity between the copepod genera
Calanus spp. are filter feeders and mostly herbivores, but they
do feed on ciliates and other heterotrophic protists during reproduction
and energy shortfall [39, 40]. This might be a
reason behind their high H index. Most of the gene sequences used for
this meta-analysis were from Calanus finamarchicus . However,Centropages sp. feeds on different sources from microalgae to
fish larvae [41]. Acartia spp. are
primarily omnivorous (with a high degree of carnivore behaviour),
feeding on phytoplankton, occasionally ciliates, and rotifers[42], whereas Temora spp. frequently
switches its feeding behaviour, i.e. an omnivore or herbivore based on
the season and food availability [43]. The
bacterial alpha diversity analysis in the Temora sp. revealed a
significantly lower Shannon diversity. However, in an early study, no
difference was reported in the alpha diversity between the Temoraspp. and Acartia spp. [38]. This can be
explained based on the source of copepods involved for the study, Wega
et al. [38], which was based only on a single
source, i.e. the central Baltic sea; however, in our case the CAB
sequences for Acartia spp. were from the central Baltic sea[38] as well as the Gulf of Maine[10]. The occurrence of high Faith’s_PD inPleuromamma spp. maybe due to their range distribution in the
water column and few species within Pleuromamma spp. are known to
migrate vertically [11, 44] or might also be due
to their food uptake, which includes phytoplankton,
microzooplankton(ciliates and flagellates) and detritus
[11, 45].
The consensus phylogram revealed that, at genera level, Calanusspp. was phylogenetically closer to Pleuromamma spp. and form two
distinct clusters in the PCoA plot. Further, the difference in
dissimilarity percentage of CAB between Pleuromamma spp. andCalanus sp. may be attributed to the difference in vertical
migration, life stages and the feeding behaviour between the two copepod
genera. Pleuromamma spp., an omnivorous feeder[11, 45]. can migrate vertically up to 1000m[11, 44] whereas Calanus sp., mostly
herbivores, but occasional omnivores [37, 38], can
migrate up to 600m [46, 47]. Also, it may be due
to the difference in the life stage of Calanus (the microbial
communities varied between the diapausing and active feeding)[2].