Habitat destruction and fragmentation

Fig. 1. Marine habitats in Europe, such as kelp forests, support a high diversity of marine life and are threatened by human activity. Photo © BIOMAR

The information for this article was obtained mostly from Airoldi, L., Balata, D., Beck, M.W. 2008. The Gray Zone: Relationships between habitat loss and marine diversity and their applications in conservation. Journal of Experimental Marine Biology and Ecology 366, 8-15

Habitat destruction and fragmentation is a process that describes the emergences of discontinuities (fragmentation) or the loss (destruction) of the environment inhabited by an organism. Marine ecosystems are experiencing high rates of habitat loss and degradation, and these processes are considered as the most critical threat to marine biodiversity . It is estimated that every day between 1960 and 1995, a kilometer of coastline was developed, causing permanent losses of valuable habitats, such as coastal wetlands, seagrass meadows and rocky shores . Approximately 20% of the world’s coral reefs were lost and an additional 20% degraded in the last several decades of the twentieth century, and approximately 35% of mangrove area was lost during this time.

Habitat can be defined as predominant features that create structural complexity in the environment, such as plants (e.g., seagrass meadows, kelp forests), or animals (e.g. Sabellaria reefs, burrowing fauna in sandflats).

Habitat loss and biodiversity

Researchers have identified three major components of habitat loss that relates to species diversity has been identified :

1) The loss of resident species.

There is a unique plant and animal diversity living in close association with specifics habitats or habitat forming species. For example, invertebrate assemblages associated with mussel beds, epiphytic and epibenthic assemblages communities living in kelp forests or fish communities associated with coral reefs. It has been predicted that the consequences of habitat loss would probably be much more profund than than the loss of individual species, because of the ecological interactions between species leading to a chain of impacts .

Fig. 2. The loss of habitats can lead to the formation of barren areas where only few species are able to survive. Photo © NOAA

2) The loss of food resources.

Most biogenic habitats are highly productive compared to simpler habitats. They produce large amounts of nutrients and organic matter that can be directly used by other organisms as food resources. The habitat loss also implies the loss of these food resources having a negative effect in the survival of other species and the productivity of individual species or communities, with more profound effects that are likely to propagate along food chains .

3) The loss of ecosystem functions provided by the habitat.

Structurally complex habitats provide a wide range of ecosystem functions to the environment including food and refuge provision for other species, trapping sediment, modifying light and hydrodynamic conditions, providing resilience to the system. When the habitats are lost this functions are lost with them . For example, the replacement of macroalgal canopies by turfs affects sediment dynamics on rocky coasts, where fronds prevents accumulation of sediments while turfs tend to trap sediments even on exposed coasts

Effects of habitat loss on biodiversity

Fig. 3. Coral reefs are an important structurally complex habitat that provide food resources and refuge to many fish species. Photo © David Balata

Habitat loss has been generally associated to drastic declines in overall abundance and diversity of marine organisms. For example, in the Wadden Sea, the destruction of biogenic habitats has caused the regional extinction of at least 26 species during the past 2000 years . Similarly, the loss of seagrass meadows results in a reduction in the number of species and abundance of fishes. Generally, the environmental changes associated with the destruction of natural habitats promote the arrival and colonization of opportunistic species that can benefit from conditions in disturbed condition. One example is the expansion of opportunistic green ephemeral algae or turf forming algae following the destruction of removal of canopy forming species, such as kelp. Other species that can favor from disturbed habitats condition are alien species. Once alien species are established they can contribute further to reduce local diversity by interacting with native species.

Human activities as driver of habitat loss

Some anthropogenic activities responsible for habitat destruction include the construction of coastal protection, land reclamation, aggregate (sand and gravel) extraction, recreation and developments including ports, harbours and industries. Additionally, the growing number of tourists presents a significant threat to many coastal habitats in Europe, which can disturb by trampling or direct harvesting. In offshore waters, exploration and development of oil and gas activities threaten marine habitats, mainly with discharges of oil and other pollutants. Physical damage to marine habitats can result from fishing activities such as bottom trawling. Deep-water trawlers use heavy rock-hopping equipment, which has been reported to cause long-term to seabed habitats such as cold-water coral reefs in Norwegian, Scottish and Irish waters.

Implications for conservation and management

Habitat loss often leads species to get endangered or threatened, and eventually extincted leading to significant loss of overall diversity and changes in ecosystem functioning. Conservation efforts of coastal and marine habitats have been driven in part by the effects of habitat loss on declines in species richness. However, looking at the effect of habitats loss on species richness is not sufficient. Conservation efforts must consider the effects habitat loss and fragmentation on all components of species diversity and the ecosystem functioning and services provided by habitas:

Fig. 3. No take marine reserves are one of the most effective managment tools to protect endangered habitats. Photo © David Balata

• regulating services such as shoreline buffering from storms
• provisioning services such as fish production
• cultural services such as tourism
• supporting services such as primary production.

There is an urgent need for the implementation of long-term and large scale monitoring programs of changes to marine habitats and species distributions. This monitoring should be coupled with studies designed to treat management actions that result in habitat loss as large-scale experiments. For example, the use of marine protected areas (MPAs) and marine reserves as tools to underpinned the relationships between the functionality of habitats and the distribution and abundance of target taxa. According to the Global Biodiversity Asessment the most effective way to conserve biodiversity, by almost any reckoning is to prevent the conversion or degradation of habitat.

There is an ongoing debate among conservationist biologist about whether is preferable to protect several already fragmented patches of habitats or a single large area, often referred as the SLOSS (Single Large or Several Small) debate.

One important aspect that also needs to be considered is habitat restoration. On land there is a long tradition of restoring habitats, such as mining waste tips. There are some examples of habitat restoration in the marine environment, such as the well-publicized clean-up of the River Thames in the UK where salmon can now be found in London. The developing science of restoration ecology should be a part of a strategy for conservation of coastal biodiversity.