Investigating adult reproduction as a potential barrier to recovery of wild Manila clam (Venerupis philippinarum) populations impacted by the Nathan E. Stewart oil spill, Central Coast, B.C.

Abstract

Understanding the chronic effects of environmental disasters, such as oil spills, is critical to assessing long-term impacts on marine ecosystems and guiding recovery efforts. We assessed the reproductive potential of adult Manila clams (Venerupis philippinarum) from sites impacted by the Nathan E. Stewart oil spill (Central Coast, British Columbia, Haíɫzaqv Territory, October 2016) to determine if reduced reproductive capacity may be driving a delayed population recovery among the impacted clam populations. Clams from both reference and impacted sites were conditioned under controlled laboratory settings, with reproductive metrics (gonadosomatic index, progression of gamete development, fertilization success, spawning success) showing no significant differences between sites, suggesting that reproductive output in adults is not currently limiting recovery. Adult clams from all sites successfully spawned under controlled laboratory conditions. However, despite successful spawning and fertilization, larval survival was uniformly low across sites; this low survival may be attributable to methodological factors, such as temperature or handling stress rather than direct impacts of the oil spill. Findings suggest factors other than adult reproductive capacity are causing continued delay of population recovery, warranting further investigation.