Adult life strategy affects distribution patterns in abyssal isopods – implications for conservation in Pacific nodule areas
Authors: Brix Saskia , Osborn Karen J. , Kaiser Stefanie , Truskey Sarit B. , Schnurr Sarah M. , Brenke Nils , Malyutina Marina , Martinez Arbizu Pedro 
Published: December 2020

Abstract. With increasing pressure to extract minerals from the deep-sea bed,
understanding the ecological and evolutionary processes that limit the
spatial distribution of species is critical to assessing ecosystem
resilience to mining impacts. The aim of our study is to gain a better
knowledge about the abyssal isopod crustacean fauna of the central Pacific
manganese nodule province (Clarion–Clipperton Fracture Zone, CCZ). In total,
we examined 22 epibenthic sledge (EBS) samples taken at five abyssal areas
located in the central northern Pacific including four contracting areas and
one Area of Particular Environmental Interest (APEI3). Additional samples
come from the DISturbance and reCOLonization
experiment (DISCOL) area situated in the Peru Basin, southeastern Pacific.
Using an integrative approach that combined morphological and genetic
methods with species delimitation analyses (SDs) we assessed patterns of
species range size, diversity, and community composition for four different
isopod families (Munnopsidae Lilljeborg, 1864; Desmosomatidae Sars, 1897;
Haploniscidae Hansen, 1916; and Macrostylidae Hansen, 1916) displaying
different dispersal capacities as adults. Isopods are brooders, so their
distribution and connectivity cannot be explained by larval dispersal but
rather by adult locomotion. In particular, our objectives were to (1) identify potential differences in the distributional ranges of isopod
families relative to their locomotory potential and to (2) evaluate the
representativeness of the APEI for the preservation of regional biodiversity
in the CCZ following mining disturbances. From 619 specimens, our SD
analysis could distinguish 170 species, most of which were new to science
(94.1 %). We found that increased locomotory ability correlated with
higher species diversity with 9 species of Macrostylidae, 23 of
Haploniscidae, 52 of Desmosomatidae, and 86 of Munnopsidae. This is supported
by family-level rarefaction analyses. As expected, we found the largest
species ranges in the families with swimming abilities, with a maximum
recorded species range of 5245 and 4480 km in Munnopsidae and
Desmosomatidae, respectively. The less motile Haploniscidae and Macrostylidae
had maximal species ranges of 1391 and 1440 km, respectively. Overall,
rarefaction analyses indicated that species richness did not vary much
between areas, but the real number of species was still not sufficiently
sampled. This is also indicated by the large proportion of singletons
(40.5 %) found in this study. The investigated contractor areas in the CCZ
were more similar in species composition and had a higher proportion of
shared species between each other than the closely located APEI3 and the
distantly located DISCOL area. In fact, the DISCOL area, located in the Peru
Basin, had more species in common with the core CCZ areas than APEI3. In this
regard, APEI3 does not appear to be representative as serving as a reservoir
for the fauna of the investigated contractor areas, at least for isopods, as
it has a different species composition. Certainly, more data from other
APEIs, as well as preservation reference zones within contractor areas, are
urgently needed in order to assess their potential as resources of
recolonization of impacted seabed.