Changes in the physical environment of marine ecosystems

Sea temperature, salinity, wind patterns, and ocean circulation have significant impacts on marine biodiversity. For example, zooplankton community composition and several fish trends are correlated with largescale climate signals in the Pacific Ocean, including the El Niño Southern Oscillation and the Pacific Decadal Oscillation.5

Sea temperature, Newfoundland and Labrador Shelves
Mean annual temperature
Graph: sea temperature in the Newfoundland and Labrador Shelves. Click for graphic description (new window).
Source: adapted Oceans Canada (DFO), 20077
Sea temperature, Pacific Coast
Mean annual temperature ºC, up to 2006
Three graphs: sea temperature on the Pacific Coast. Click for graphic description (new window).
Note: the horizontal line represents the average temperature for the reference period, 1961 to 1991.
Source: adapted from Fisheries and Oceans Canada (DFO), 20105

Mean sea surface temperature has increased:5

  • from 1978 to 2006 in the North Coast and Hecate Strait and West Coast Vancouver Island, following a period of colder surface water in the previous 25 years, although 2007 and 2008 were cooler than average;6
  • since the 1970s in the Beaufort Sea;
  • since the late 1970s in the Canadian Arctic Archipelago and in the Hudson Bay, James Bay, and Foxe Basin;
  • since the early 1990s in the Newfoundland and Labrador Shelves;
  • since the 1980s in the Estuary and Gulf of St. Lawrence.

The ocean has become fresher (less saline)5 in several ecozones+:

  • since 1978 in the North Coast and Hecate Strait, following a 30-year period of high salinity;
  • since the 1970s in the Beaufort Sea, as a result of melting sea ice, input from the Pacific Ocean, and surface water from the Arctic Ocean.

Ocean acidification

Photo: mussels ©

When carbon dioxide dissolves in the ocean, it lowers the pH, making the ocean more acidic.8 Since pre-industrial times, the oceans have become more acidic by a pH of approximately 0.1. This seems like a small amount – but the biological effects of small changes in ocean acidity can be severe. For example, a pH change of 0.45 from pre-industrial times, which is predicted by the end of this century, could have dire consequences for marine organisms that build a calcium carbonate skeleton or shell, such as corals, molluscs (oysters, mussels, scallops), crustaceans (crabs, shrimp), echinoderms (starfish, and many species of plankton.9 Impacts are expected to occur first in the polar regions.10

Ocean acidification is already occurring in four marine ecozones+: West Coast Vancouver Island, Beaufort Sea, Estuary and Gulf of St. Lawrence, and Gulf of Maine and Scotian Shelf. It is predicted to occur in all oceans and to have severe consequences for biodiversity as early as the end of this century.5

Oxygen depletion in marine waters

Dissolved oxygen in the St. Lawrence Estuary
Percentage, 1930 to 2008
Graph: dissolved oxygen in the St. Lawerence Estuary. Click for graphic description (new window).
Source: adapted from Dufour et al., 201014

Critically low oxygen concentrations have been observed at some sampling points in the Estuary and Gulf of St. Lawrence and the three ecozones+ in the Pacific. In the St. Lawrence Estuary, low oxygen conditions have been observed since 1984.5 Declines in oxygen concentration are caused by a number of factors, including changes in ocean circulation patterns, freshwater inputs, rising temperatures, and increases in organic matter on the sea floor. The latter may be caused by increases in primary production on the surface and by human activities.11

Observed effects of low oxygen content on biodiversity in Canadian waters include declines and mortality of bottomdwelling animals and altered food webs.5 Some impacts observed globally include fish and crab kills,12 more prevalent jellyfish blooms,13 changes in marine biochemical pathways that favour some species over others,11 creation of dispersal barriers for larval fish and crustaceans that are less tolerant of low oxygen than adults,11 and altered food webs.11


Global Trends

Low-oxygen zones where ocean species cannot live have increased globally by close to 5.2 million km2 since the 1960s.11