Sometimes marine scientific studies are deep explorations into the fundamental processes that underpin ecosystem function, yielding critical insights into management and mitigation in the face of anthropogenic impacts. And sometimes marine scientific studies answer basic questions that many stakeholders and practitioners wouldn’t even think to ask. Questions like: Can you distract a clam?
In “Are giant clams (Tridacna maxima) distractible? A multi-modal study”, researchers from University of California endeavored to understand that very question, devising a simple set of experiments to determine if marine noise could distract Tridacna maxima, the giant clam, and what that might mean for the survival of the species in an increasingly noisy ocean.
In this study, giant clams in the wild were exposed to a variety of treatments involving changes to water flow and recorded motor boat sounds. During exposure, the researchers measured the frequency of mantle twitches. The clams were then perturbed by an object and the speed with which clams responded to that stimulus by closing their shell was documented. Giant clams exposed to either elevated noise, increased flow, or both were twitchier than the control clams. Clams that were exposed to both elevated noise and changes to the local flow regime took longer to react to stimulus.
This is not the only recent study into the impact of marine noise on ocean species. With boat traffic at historic lows, the coronavirus lockdowns provided a rare opportunity to study animal behavior in nearshore ecosystems under a much quieter regime. Ocean Network Canada’s hydrophone array has been operating since 2018 and has recorded an average decline in ocean noise of 1.5 decibels in the open ocean and 4 to 5 decibels near major shipping lanes during the pandemic. This has given scientists the chance to study how human-produced noise impacts southern resident killer whales in the region. Humpback whales in Glacier Bay are similarly experiencing dramatically decreased noise levels, in part due to the shutdown of the regular tourist season.
The coronavirus pandemic is not the first time that a major disaster has created an opportunity to study the impact of noise on marine species. The landmark paper which first attempted to use a similar shutdown of ship traffic to assess changes in marine animal behavior was conducted in the fall and winter of 2001, when port closures following the September 11 attacks resulted in a significant decline in vessel traffic. That study presented the first evidence that low-frequency ship noise caused chronic stress in marine mammals.
So what do distracted clams have to do with deep-sea mining? Marine noise is increasingly recognized as a threat to the marine environment, though to date, a majority of studies have focused on large, social marine mammals. Deep-sea mining will present a new and novel challenge to the deep ocean soundscape, as well as other distraction phenomena, including potential changes to the benthic flow regime. This presents an opportunity for thorough and comprehensive studies on the impact of sound not just to marine mammals, but to benthic and mid-water communities.
The importance of understanding the impact of sound is not news to the contractors conducting exploratory studies on the deep sea bed. DeepGreen, notably, was among the first major mining companies to deploy a hydrophone array as part of their environmental baseline monitoring arrays. As science learns more about the long term impact of sound on marine ecosystems, the deep-sea mining industry is in a position to play a lead role in the ongoing efforts to understand and mitigate human impacts for the next generation of extractive industries.
Featured Image: Giant Clam, Kerry Grimshaw, NOAA/NMFS/PIFSC/CRED