Haemocyte characterization in invasive Carcinus maenas (Linnaeus, 1758) (Decapoda, Portunidae) from unpolluted vs polluted sites in Argentina

Pollution, biological invasions and climate change pose the greatest threats to biodiversity worldwide. Few studies explore the interlink between invasive species and local pollution sites. This study describes the type and cytochemical properties of haemocytes from invasive Carcinus maenas on the southwestern Atlantic coast (Argentina). Moreover, the morphology of haemocytes and the total haemocyte count (THC) as well as the differential haemocyte count (DHC) of crabs sampled at clean or unpolluted and polluted sites were compared, to determine whether environmental stresses were evident in their haemocytes. Our results revealed two groups or subpopulations of haemocytes: hyalinocytes, as well as granulocytes and semi-granulocytes. The type of haemocyte from crabs from both sites showed no differences in their morphology. For cytochemical assays, only neutral red dye showed a more intense staining of crab haemocytes at the polluted site. All haemocytes were positive to Periodic Acid-Schiff and Sudan Black. THC of crabs from the clean site were significantly higher, as well as having a significantly higher proportion of hyalinocytes and a lower proportion of granular cells. This study provides a baseline immunological assessment for C. maenas haemocytes, suggesting a differential haemocytic response to environmental stress.