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What's the Deal with Flatfish?

Overview

Blog post by PhD Student Jackson Chu. Originally posted on Wiring the Abyss 2014 Expedition portal. An important part of climate change research is measuring and predicting the magnitude of ecosystem response. The northeast Pacific is a global hotspot for future oxygen loss driven by climate change. Overall oxygen content in the oceans will drop if sea surface temperatures continue to rise because warmer sea water holds less oxygen. If oxygen levels drop too low (hypoxia), animals will have to migrate, adapt or die – but how do you measure these thresholds for animal life? Part of our ongoing ecological research on the impacts of oxygen loss on marine biodiversity is to determine low oxygen thresholds for animals living in hypoxic environments on Canada’s Pacific Coast. From years of surveying the life living around the Ocean Networks Canada instrumentation in Saanich Inlet, we have identified the slender sole (Lyopsetta exilis) as one of the key indicator species that drives assembly patterns for communities living in hypoxia. In order to measure hypoxia thresholds, we need to capture the fish with a trawl, keep them alive, and then measure physiological parameters such as metabolic rates and critical oxygen tensions under lab-controlled conditions.

Young scientist maps how animals are responding to decreasing oxygen in NE Pacific Ocean

Overview

Jackson Chu is a PhD candidate at the University of Victoria who has a passion for seeking answers to the mysteries of the ocean at his doorstep, including how changing oxygen levels affect animals in the ocean. Chu is the lead author on a paper with Dr. Verena Tunnicliffe, professor in Biology and the School of Earth and Ocean Science at the University of Victoria and Canada Research Chair in Deep Ocean Research, which was published in the journal Global Change Biology (April 2015). “Ocean animals, including those of cultural and economic value, require oxygen to live,” explains Chu, “but oxygen is slowly decreasing from the oceans because of climate change. The west coast of North America is especially a hot spot for expanding hypoxia, or waters that have insufficient oxygen to support life.”

Ocean Networks Canada and Victoria’s Capital Regional District monitor ocean conditions

Overview

Victoria is infamous for its practice of discharging screened, but otherwise untreated, municipal sewage into Juan de Fuca Strait. Starting in early 2013, Ocean Networks Canada (ONC) has been partnering with Victoria’s Capital Regional District to help measure the impacts of their outfalls on the local marine environment. With ONC’s help and expertise, two special purpose bottom moorings capable of measuring the salinity, temperature, and amount of dissolved oxygen in the water were deployed near the sewage outfall to look for signs of oxygen depletion or hypoxia. These two moorings—at Macaulay Point and Victoria Sill—complement a set of three other identical moorings that ONC had deployed in the fall of 2012 in western Juan de Fuca Strait and Boundary Pass. Together, the set of five moorings collect the longest continuous electronic time series measuring dissolved oxygen in the region.

The extent of habitat compression and hypoxia in Saanich Inlet from the 2016 hypoxia cycle

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**Guest post by Dr. Jackson Chu, Post-doctoral fellow, Fisheries & Oceans, Canada**

Saanich Inlet and the science of dead zones

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Saanich Inlet is one of the best-studied marine basins in the world. The combination of easy access and unusual features has attracted researchers to this glacially carved fjord since the 1930’s. A unique feature is the combination of geography, dense plankton populations, and deep water that is a natural “dead zone”—an area depleted in oxygen. Once a year, in the late summer or early fall, oxygen is restored. The result is a fascinating study area for biologists, chemists, and sedimentologists.

The cumulative effects of bottom trawling and low oxygen on marine life

Overview

In November 2016, Ocean Networks Canada (ONC) scientists co-authored a [publication in Deep-Sea Research II](http://www.sciencedirect.com/science/article/pii/S0967064516303769) on the effects of deep-sea bottom trawling on seafloor marine life, already stressed by the naturally low oxygen waters of the north Pacific. This is the first study to measure the effects on the fauna living on the soft-sediment seabed of Vancouver Island’s continental shelf and slope. Previous scientific research has focused on by-catch (species accidentally caught in the fishing net), particularly in areas where deep-water coral and sponge reefs occur. This article is based on a University of Victoria Master’s thesis by Maéva Gauthier. The data originates from remotely operated vehicle surveys along the cable route for ONC’s NEPTUNE observatory in 2007, prior to the installation of the observatory. The deep-sea video and sonar data from the surveys reveals a decline in invertebrate and fish populations, and a reduced biodiversity in the oxygen minimum zone—where oxygen saturation is at its lowest—off Vancouver Island (depth 600-1100 m). This coincides with the most heavily trawled areas primarily targeting thornyhead fishes (Sebastolobus alascanus and S. altivelis).

New research explains why Saanich Inlet is good for the climate

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Research that demonstrates low oxygen levels in the depths of Saanich Inlet might seem like concerning news. But on a planet facing climate change, there is a silver lining: specialized organisms can thrive in the depths of Saanich Inlet, and when they die, they will not decompose due to the lack of oxygen. This reduces the amount of carbon that cycles back to the atmosphere as carbon dioxide, a powerful greenhouse gas.

Summer 2021 low oxygen event in the northeast Pacific

Overview

*by Tetjana Ross, Ana C. Franco, John A. Barth, Akash Sastri, Marie Robert, Debby Ianson, Charles Hannah, Francis Chan, Richard Feely, Richard Dewey, and Angelica Peña* Reprinted with permission: [PICES North Pacific Marine Science Organization Newsletter Vol. 30, No.1 / Winter 2022 p.38](https://meetings.pices.int/publications/pices-press/volume30/PPJan2022.pdf#page=38) While hypoxic or low oxygen events are known to occur seasonally in coastal bottom waters along the west coast of North America, 2021 was more severely hypoxic. The onset of low oxygen water was the earliest in 35 years (NOAA, 2021), lasted longer (Lundeberg, 2021), was anomalously low (Figures 1 and 4), and covered a larger extent, reaching north into Canadian waters (Figure 5) where hypoxia is rare (Figure 6; Crawford and Peña, 2013). The seasonal near-bottom hypoxia was observed as early as mid-May (Figure 1) on the Washington shelf. Low-oxygen water was observed near the seafloor over the Washington, USA, continental shelf for much of the summer 2021. Oxygen levels continued to decrease throughout the summer, reaching “severe” hypoxia (O₂< 0.5 ml/l)—that can harm important marine species like Dungeness crab (Keller et al, 2015)—at the end of July and even approached anoxia, zero oxygen, in late August/early September. This seasonal decrease in near-bottom dissolved oxygen is consistent with similar measurements off central Oregon (Adams et al., 2013), but these 2021 levels are lower than typical. The return of near-bottom dissolved oxygen to levels above hypoxia occurred in mid-late September (not shown) as early-season storms swept across the region.