The observed seasonal patterns of the bacterial community of
M. leidyi sampled from the German Bight may indicate that
the microbial associations of ctenophores change over time,
most likely due to changing environmental conditions. On the
one hand, it is obvious that the surface of these species might
occasionally inhabited by seasonally occurring pelagic bacterial
hitchhikers, which thereafter were most likely detected by
chance. On the other hand, the distribution of M. leidyi populations
is closely linked to temperature and food availability,
and their life span is on the order of months (Ghabooli et al.,
2011). Cydippid larvae of M. leidyi primarily feed on protists prey;
however, the morphological transition of M. leidyi from cydippid
to lobate involves a shift from a microplankton diet to a
metazoan-based diet including copepods, cladocera, and the larvae
of fish and mollusks (Rapoza, Novak and Costello 2005).
Therefore, Daniels and Breitbart (2012) speculated that the composition
of the surrounding bacterial community in the water
column, the total food availability as well as the dietary composition
may influence the ctenophores bacterial community.
However, it might be possible that different populations were
sampled. As in our study, Daniels and Breitbart (2012) did not
distinguish the ctenophore population between adult and larval
specimens but showed a variation of the associated bacterial
community in ctenophore over the sampling period. Bickel and
Tang (2014) stated that the environment factors, such as temperature,
salinity, ammonium, chla and all term interactions, influenced
the concentration of the free-living and Acartia-associated
bacterial. As we observed that 19% of PCO variation was explained
by ARISA profiles, except for the month, other factors
(e.g. environmental) may explain the seasonal varition in the
bacterial community of M. leidyi. Thus, the multivariate statistical
analyses between the BCC and environmental factors need
to be analysed in more detail to evaluate the biotic and abiotic
factors that drive the temporal variation in the bacterial community
of ctenophores.