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Warmer water temperatures can alter the type, And finally, these impacts can create mismatches
abundance, quality and timing of food sources in the timing of specific food web interactions —
that are available . There are multiple mechanisms for example, shifting the timing of herring spawn
by which higher sea surface temperatures can or zooplankton blooms as related to when salmon
shift how the marine food web will function . outmigrate, which can be make or break for
First, warmer water tends to stratify, or become salmon that miss important food resources .
a layer, on the surface which reduces its ability
to mix with the deeper waters during a process Ocean Acidification
known as upwelling . Upwelling is important Another consequence of the increasing carbon
because it brings up cooler, more nutrient-rich dioxide (CO ) emissions driving climate change
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waters to the surface . Without this mixing there is ocean acidification . Atmospheric carbon has
are fewer nutrients available to support the increased tremendously since the Industrial
marine food web . This will decrease or change Revolution, with fossil fuel burning being the
the type of phytoplankton blooms, which in turn primary source . As part of the normal carbon
will impact the resultant zooplankton biomass and cycle, ocean waters absorb about 25% of all CO
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assemblages . Warm water species of zooplankton emissions, which maintains the pH of seawater at
tend to be less nutritious and their blooms also a slightly basic level (pH > 7) . With higher levels
peak earlier in the season (Johannessen and of CO in the atmosphere, seawater is approaching
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Macdonald 2009) . Another way food web dynamics neutral pH, meaning ocean waters are becoming
can be affected is that warmer temperatures can more acidic . More acidic conditions make it
be more favourable to particular species over more difficult for organisms that rely on calcium
others . For example, there have been alarming carbonate for their shells to form properly . This
jellyfish blooms in the Strait of Georgia in recent will challenge shellfish growers and many of our
warmer than normal years . The jellyfish form huge native shellfish species, including clams and
clusters — that may weigh as much as 120 tonnes crabs . Larval crab and other small crustaceans
— and compete with other organisms for food . It’s are vital to the food web and are an important
been shown that these jellyfish blooms negatively food source for juvenile salmon!
impact salmon and are generally considered a
“trophic dead-end” (Ruzicka et al . 2016) . Photo by: Keith Burgin on FreeImages .com

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