Oil spills can have serious effects on marine life, as highlighted by the photos of dead birds which regularly appear in the news after such an event. Such images fuel the perception of widespread and permanent environmental damage after every spill, and an inevitable loss of marine resources with serious economic repercussions. A science-based appraisal of the effects reveals that whilst damage occurs and may be profound at the level of individual organisms, populations are more resilient and natural recovery processes are capable of repairing the damage and returning the system to normal functions. The first stage on the road to recovery is usually a well conducted clean-up operation but in some specific habitats aggressive clean-up methods can cause more harm than good and then it is better to let natural cleaning processes take their course.
Many spill impacts have been documented in the scientific and technical literature, and although not all the effects of oil pollution are completely understood, an indication of the likely scale and duration of damage can usually be deduced from the information available. However, it can be difficult to present a balanced view of the realities of spill effects, given the often highly charged and emotional nature of a spill and its aftermath. The scientific community can become polarised into opposing camps with one side intent on quantifying every aspect of damage, and the other emphasising the capacity of the environment to recover naturally. The simple reality is that sometimes significant damage occurs, sometimes not and the aim of these pages is to draw together what general information is known about spill effects and their longevity.
The marine ecosystem is highly complex and natural fluctuations in species composition, abundance and distribution are a basic feature of its normal function. The extent of damage can therefore be difficult to detect against this background variability. Nevertheless, the key to understanding damage and its importance is whether spill effects result in a downturn in breeding success, productivity, diversity and the overall functioning of the system.
Spills are not the only pressure on marine habitats; chronic urban and industrial contamination or the exploitation of the resources they provide are also serious threats. The following sections consider some of the types of damage caused by oil spills as well as some of the benefits of conducting post-spill studies.