4: Avoid fragmentation

Breaking up the working parts of our ecosystem is like separating the working parts of an engine, it prevents it from working properly. Designing healthy ecosystems requires that we keep habitats connected.

Fragmenting ecosystems by changing habitats or by changing populations reduces an ecosystems capacity to renew itself. Over-harvest of Northern abalone has left animals that are too spread out to mate successfully. Photo: N. Brown

Human activities that break otherwise contiguous habitat (land and seascapes) into smaller pieces fragment ecosystems, reduce their ecological integrity, and threaten their capacity to renew themselves.

Habitat is the place where species interact and form complex communities. Habitat size is directly linked to population size and the nature of species interactions. All species require a minimum number and density of individuals to persist, thus they also require a minimum amount of suitable habitat.

For most species, habitat configuration is also important. When habitats are fragmented, and shrink below the size required to support a minimum viable population or are significantly modified or disturbed, a sequence of events begins that can end with species extinction.

At low densities (associated with small habitats) individuals may be unable to find mates. For example, this is particularly critical for benthic animals with little mobility such as abalone and some rockfish species. Small populations are more susceptible to extinction by extreme natural events and are more likely to lack the genetic diversity needed to adapt to changing physical and biological conditions such as climate change or competition from invasive species.

Unlike the terrestrial environment, where habitat size is visible and easily monitored, fragmentation in the marine environment is notoriously hard to study. Thus it has received far less attention.

There are many ways in which people inadvertently fragment marine habitats. For instance, seafloor trawling can have devastating effects on the seafloor and result in isolated “islands” of unaltered submarine habitats too small to maintain viable populations. 

Pelagic species and large mammals can experience habitat fragmentation through fisheries and reserve policies. For instance, reserve areas may be too small to contain the necessary food resources to sustain populations of marine mammals.

Where the land meets the ocean, anthropogenic shoreline alterations can fragment the nearshore marine habitat and reduce productivity. For example, terrestrial insects falling into nearshore marine water are an important food source for migrating juvenile salmonids and the removal of overhanging shoreline vegetation reduces this important food source. Additionally removal of overhanging shoreline vegetation can alter the microclimate of beaches and reduce their suitability for incubating eggs of intertidal spawning fish.

Some tools used to address ecosystem fragmentation in terrestrial ecosystems also could be used to address ecosystem fragmentation in coastal ecosystems. Fragmentation through land subdivision and the loss of large-scale dynamic processes such as wildlife migrations and fire was identified as the major threat to the world’s grassland ecosystems. Cultural exchange between Maasai pastoralists from Kenya and ranchers from the United States helped address these fragmentation threats by speeding up understanding and adaptation.