Histopathological changes in the greenshell mussel, Perna canaliculus, in response to chronic thermal stress

Joanna S Copedo; Stephen C Webb; Norman L C Ragg; Jessica A Ericson; Leonie Venter; Alfonso J Schmidt; Natalí J Delorme; Andrea C Alfaro

doi:10.1016/j.jtherbio.2023.103699

Histopathological changes in the greenshell mussel, Perna canaliculus, in response to chronic thermal stress

J Therm Biol. 2023 Oct:117:103699. doi: 10.1016/j.jtherbio.2023.103699. Epub 2023 Sep 1.

Authors

Joanna S Copedo¹, Stephen C Webb², Norman L C Ragg², Jessica A Ericson², Leonie Venter³, Alfonso J Schmidt⁴, Natalí J Delorme², Andrea C Alfaro³

Affiliations

¹ Cawthron Institute, Private Bag 2, Nelson, 7042, New Zealand; Aquaculture Biotechnology Research Group, Department of Environmental Science, School of Science, Auckland University of Technology, Private Bag 92006, Auckland, 1142, New Zealand. Electronic address: Joanna.copedo@cawthron.org.nz.
² Cawthron Institute, Private Bag 2, Nelson, 7042, New Zealand.
³ Aquaculture Biotechnology Research Group, Department of Environmental Science, School of Science, Auckland University of Technology, Private Bag 92006, Auckland, 1142, New Zealand.
⁴ Hugh Green Cytometry Centre, Malaghan Institute of Medical Research, PO Box 7060, Wellington, 6242, New Zealand.

PMID: 37708787
DOI: 10.1016/j.jtherbio.2023.103699

Abstract

Climate change associated temperature challenges pose a serious threat to the marine environment. Elevations in average sea surface temperatures are occurring and increasing frequency of marine heatwaves resulting in mortalities of organisms are being reported. In recent years, marine farmers have reported summer mass mortality events of the New Zealand Greenshell mussel, Perna canaliculus, during the summer months; however, the etiological agents have yet to be determined. To elucidate the role of thermal stress, adult P. canaliculus were exposed to three chronic temperature treatments: a benign control of 17 °C and stressful elevations of 21 °C and 24 °C. Eight mussels per treatment were collected each month throughout a 14-month challenge period to identify and investigate histopathological differences among P. canaliculus populations exposed to the three temperatures. Histopathology revealed several significant deleterious alterations to tissues associated with temperature and exposure time. Increasing temperature and progression of time resulted in 1) an increase in the number of focal lipofuscin-ceroid aggregations, 2) an increase in focal hemocytosis, 3) an increase in the thickness of the sub-epithelial layer of the intestinal tract and 4) a decreased energy reserve cell (glycogen) coverage in the mantle. Prolonged exposure, irrespective of temperature, impacted gametogenesis, which was effectively arrested. Furthermore, increased levels of the heat shock protein 70 kDa (HSP 70) were seen in gill and gonad from thermally challenged mussels. The occurrence of the parasite Perkinsus olseni at month 5 in the 24 °C treatment, and month 7 at 21 °C was unexpected and may have exacerbated the fore-mentioned tissue conditions. Prolonged exposure to stable thermal conditions therefore appears to impact P. canaliculus, tissues with implications for broodstock captivity. Mussels experiencing elevated, temperatures of 21 and 24 °C demonstrated more rapid pathological signs. This research provides further insight into the complex host-pathogen-environment interactions for P. canaliculus in response to prolonged elevated temperature.

Keywords: Atresia; Environmental stress; Gametogenesis; Greenshell mussel; Histopathology; Perkinsus olseni.