Aquatic Habitat Toronto

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The principal biological components of aquatic communities on the Toronto waterfront are:

Phytoplankton and Zooplankton

Phytoplankton and zooplankton provide the principal forage base for many life stages of aquatic organisms. With less eutrophication due to reduced nutrient inputs, plankton productivity has returned to more normal levels in recent years. The degradation of phytoplankton and zooplankton is listed as a potentially impaired use in the Toronto and Region Area of Concern that requires further assessment (studies are planned by TRCA).
image from SOLEC 2000

Algae

Suitable conditions for the growth of attached algae include the availability of hard substrates (such as Etobicoke shale), high levels of phosphorus, and the nearshore thermal bar that forms in spring and early summer. Increased water clarity also boosts algae growth in deeper water.

Attached algae form important habitat for benthic invertebrates, which in turn provide a food source for larger invertebrates, fish, migratory shorebirds and aquatic mammals. However, when algae become detached from their substrate, wash up on the shoreline and decay, they create foul odours that become a nuisance to waterfront residents, particularly in the Etobicoke portion of the Toronto waterfront.

The taste and odour problems in Toronto's water supply are due to free-floating algae that increase rapidly during warm weather, particularly in waters with a high organic content. The cause of the taste and odour impairments is geosmin, a naturally occurring chemical that is created during the metabolisation of the algae as it decays. This problem should be reduced as water quality is improved. In the meantime, Toronto's water treatment plants have now installed powder activated carbon feed systems to control this problem.

Invertebrates

Invertebrates associated with aquatic habitats include a wide range, from tiny plankton to larger insects, mollusks, crayfish and snails. Many of them have two distinct life stages: a larval aquatic one, and an adult one that may be aquatic, aerial or terrestrial. Many larvae and some adults are benthic, or bottom-dwellers, feeding on decaying plant material and bacteria.

The benthic invertebrate communities in depositional areas such as Toronto Bay and the Lower Don River are dominated by pollution-tolerant species such as worms. In other areas, for example away from the influence of the Don River, the densities of pollution-tolerant species are considerably lower. It is expected that implementation of the City of Toronto's Wet Weather Flow Management Master Plan, which will reduce the loadings of organic-rich sediments from combined sewer overflows and storm sewers, will result in increases in the diversity of benthic invertebrates in the Toronto Bay area.

In contrast, areas with hard, rocky substrates and/or plentiful aquatic macrophytes support more diverse and self-sustaining communities of benthic invertebrates which in turn support communities of fish, amphibians, reptiles, birds and mammals.

Recent bioassay tests show that in many places, sediment quality is now good enough to support sensitive species like Hexagenia (mayflies). The limiting factors include quantity, quality and location of substrates, particularly in depositional areas. Hexagenia larvae create burrows in silty sand, but these are easily collapsed in areas with high silt loadings.

One of the best-known invertebrates associated with aquatic communities is the mosquito. There are several different species of mosquito that occur in the Toronto area. West Nile Virus is primarily transmitted by species of mosquito that breed in sheltered, stagnant water in urban areas. The mosquito species found in natural ecosystems such as wetlands and estuaries tend not to be the ones that carry the virus. In addition, complex wetland ecosystems include predatory fish, birds, frogs and insects that help control mosquito populations. For more information on transmission of West Nile Virus, visit www.trca.on.ca.

Reptiles and Amphibians

Reptiles and amphibians (herptiles) are some of the most environmentally sensitive species associated with aquatic and terrestrial near-shore habitats. They depend on healthy, functional wetland and shoreline habitats that are typically found in estuaries, coastal marshes, and vegetated sheltered embayments. Unfortunately, there is very little historical data on reptiles and amphibians on Toronto's waterfront, and their long term population trends are poorly understood.

Over the last several years, scientists, naturalists, and other wildlife watchers have become more concerned about these habitat-dependent herptile species. This has generated numerous amphibian and reptile monitoring programs in attempts to empirically document changes in these populations, and correlate them to environmental conditions.

For example, the TRCA has been participating in the Marsh Monitoring Program (MMP), which was established by Bird Studies Canada and Environment Canada in 1994, and includes a variety of sites across the Toronto waterfront. Herptile abundance and diversity is very low across the Toronto waterfront, which is likely attributed to the physical and biological degradation of waterfront habitats. Populations are primarily restricted to the significant estuary habitats and the remnant coastal marshes.

Monitoring has also shown that these populations have great resilience and quickly respond to improvements in their habitat. The restoration of aquatic habitats, particularly productive emergent marsh habitats, can result in great improvements in coastal herptile communities. The TRCA and other organizations have had great success in improving herptile communities when restoration projects incorporate critical habitat features such as basking/sunning logs, rock piles, hibernacula, isolated ponds, protected nesting sites, deep water over-wintering sites, and vegetated corridors.

There are eight species of amphibians which are commonly found in Lake Ontario, and these include; Northern Leopard Frog, Wood Frog, Green Frog, Bullfrog, Chorus Frog, Spring Peeper, Grey Tree Frog, and American Toad.

The Toronto Waterfront currently supports only three of the eight common species including Northern leopard frog, green frog, and American toad. Two other species, Chorus Frog, and Grey Tree Frog have been listed as probable, but have not been confirmed.

Birds

The importance of shorelines and associated aquatic habitats to birds and avian communities is well documented, and has been the subject of considerable study in along the Toronto waterfront. The presence of self-sustaining, diverse, aquatic communities is not only necessary to the bird species that live and reproduce on the waterfront year-round, but are also critical for other birds that forage and migrate through waterfront areas.

The shorelines of large waterbodies like Lake Ontario are documented biological centres of organization which support high diversities of bird species, act as fall-out and staging areas during migration, and provide corridors which facilitate regional movement of species.

The dependence of avian communities on aquatic habitats can be generally categorized into the following groups:

Dependent on wetland habitat for all stages of lifecycle eg. Virginia rail
Migrational stopover and staging species eg. Canada warbler
Seasonally-dependent (eg over-wintering) species eg. Common loon
Colonial waterbirds eg. Caspian tern

The value of diverse aquatic habitats to bird life on the Toronto waterfront is probably best described through the example of Tommy Thompson Park. Tommy Thompson Park (TTP), also known as the Leslie Street Spit, has been formally designated as an Important Bird Area (IBA) of global significance by Birdlife International. The designation is based on a variety of criteria including:

Occurrence of breeding populations of colonial waterbirds
Value of the area for migratory waterfowl
Value of the area for both migratory and resident songbirds
Value of the area for migratory owl and raptor species

The existence and persistence of the avian communities associated with TTP can be attributed to the complex of natural and created habitats that exist within the park. In addition, the biological value of these habitats is greatly increased by their location or proximity on the north shoreline of Lake Ontario.

There is no definitive count of the number of avian species which use the Toronto Waterfront, although local naturalist groups, agencies and bird professionals suggest a number of just over 300 species. That is higher than other well known natural areas on the north shore of Lake Ontario, such as Second Marsh (288), and just below other IBAs such as Presquille Point (320).

Mammals

As an indication of good general health one of the factors to consider is the presence of a well balanced and functioning mammal population. The distribution of mammal species can vary greatly and are usually regulated by several environmental factors. The factors can be grouped into four major categories: weather/ climate, food, other animals and disease, habitat. (Dobbyn,1994). The complex of aquatic, wetland and terrestrial habitats currently found along the waterfront should attract a wide range of mammal species. However, currently waterfront sites support relatively low numbers of mammal species in comparison with less urban sites. Smaller, less mobile species such as the rodents are more likely to remain isolated in small pockets of habitats and are physically unable to disperse do to development barriers, roads, houses etc. The lack of connecting corridors between habitat blocks is one major factor. Larger more mobile species such as coyote and raccoons tend to move more freely through the developed areas and use all types of natural blocks, parks, brown fields and habitat nodes for foraging and habitation. Habitat quality is impacted by invasive species, chemical contamination and urban population influences. Waterfront aquatic and near-shore terrestrial habitats could, through enhancement, provide areas for resident wildlife while connecting corridors between isolated habitats located along the waterfront and those running north south along watershed green space.

Mammals commonly found on the Toronto waterfront include several species of bat, red fox, eastern cottontail, groundhog, eastern grey squirrel, meadow vole, raccoon, opossum, mink, weasel species, striped skunk, red squirrel, eastern chipmunk, shrews, mole, white footed mouse and muskrat. Less common are beaver, coyote and white-tailed deer. (Dobbyn, 1994)

Small mammals perform a notable role in wetland, nearshore and terrestrial ecosystems and are considered keystones to these systems while serving as a food source to larger mammals (eg coyote) and predatory birds (eg owls and hawks). Some of the many small mammals that take advantage of waterfront habitats include mice, muskrats, fox and rabbits.

The relatively small size of most waterfront habitat areas limits their value to large mammals such as deer. The small blocks are most likely used to provide migration routes, temporary cover, and occasional forage.

Beavers living in urbanized areas can disrupt parks and naturalized areas by girdling, cutting or felling trees onto pathways and roads. Dams built by beavers may cause flooding, alter watercourses and have a potential negative effect on fish habitat. They can also damage or kill newly planted trees. Both the beaver and coyote take advantage of large isolated blocks of natural areas such as Tommy Thompson Park and these areas need to be properly managed to strike a balance between natural predator and prey to keep the population of these species at a desirable level.

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