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Spineless: status and trends of the world’s invertebrates

Report: Collen, B., Böhm, M., Kemp, R. & Baillie, J.E.M. (2012) Spineless: status and trends of the world’s invertebrates. Zoological Society of London, United Kingdom.

This report contains the most comprehensive assessment of the status and trends of the world’s invertebrates conducted to date. It introduces the staggering diversity of invertebrates, ranging from microscopic zooplankton to giant squid. Together these organisms represent around 80% of the known species on our planet. They not only provide a bewilderingly rich and varied component of the natural world, they are our natural capital; the engineers of the many benefi ts which humans accrue from an intact and fully functioning environment. This report documents several reasons for concern about the health of invertebrates. The conservation attention paid to invertebrates to-date lags far behind that of vertebrates (mammals, birds, reptiles, amphibians and fish). If their path follows that of many of the high profi le vertebrate species, our world would not only be depauperate in the organisms that give it life, but we would compromise the many benefi ts that humans gain from our environment. This collaborative report brings together the work of many thousands of scientists through the IUCN Red List, to document how pressures on the environment are impacting invertebrates. Conservation assessments of the status of the 12,621 species of invertebrates assessed so far demonstrate the highest levels of threat to freshwater species, followed by their terrestrial and marine counterparts. This pattern is consistent with their backboned relatives, the vertebrates. In much the same way as vertebrates, invertebrate extinction risk varies greatly across groups. To generalise, the highest risk of extinction tends to be associated with species that are less mobile and have small ranges. To make a vertebrate-invertebrate comparison, both amphibian and freshwater mollusc species share these traits, and face high threat levels (around one third of species threatened). In contrast, the global extinction risk experienced by flying insects such as dragonfl ies, damselfl ies, and butterfl ies tends to be much closer to that of birds (around one in ten species threatened). It must be emphasized that while this is the most comprehensive assessment of invertebrate extinction risk to-date, the conservation status of less than 1% of all described invertebrates is known. Invertebrate assessment has lagged behind the vertebrates. One of the often cited reasons is a lack of information. Data are indeed often hard to come by, and are particularly poor for deep water marine invertebrates, and freshwater micro-invertebrates. However, this report demonstrates that a full understanding is possible, if a diverse range of approaches are employed.
A number of iconic groups have been comprehensively assessed, including freshwater crabs, crayfish, lobsters, cuttlefish, reef-building corals, and additional comprehensive assessments of squid, octopuses, cone snails, reef-building oysters and sea cucumbers are nearing completion. Even groups that contain vast numbers, many tens of thousands of species, can be included in our measures of the changing state of nature, and are being understood using innovative methods for sampling. Insight into the conservation status of freshwater molluscs, butterfl ies, and dung beetles has been possible using such techniques.

Regional invertebrate assessments have also been carried out, often via national Red Listing. Groups have been assessed in great detail over larger areas, such as the invertebrate groups assessed as part of the pan-African freshwater assessment. The findings from this initial group of global, regional and national assessments provide important insight into the overall status of invertebrates. Together they indicate that the threat status of invertebrates is likely very similar to that of vertebrates and plants. If these findings prove to be representative across biodiversity as a whole, then one in fi ve of all species on the planet may currently be threatened with extinction.
Identifying dominant threats to invertebrates should yield a focus for conservation activities. Findings vary by both major system (Chapter 2 – freshwater, Chapter 3 – marine and Chapter 4 - terrestrial) and by taxonomic group.

Freshwater invertebrates are predominantly threatened by pollution such as nitrate and phosphate run-off from agricultural sources, followed by dam construction and off-take of water for irrigation of crops and domestic use.

Terrestrial invertebrates appear to be equally threatened by agricultural expansion and intensifi cation, and the negative consequences of invasive alien species.

Marine invertebrates on the other hand are most susceptible to exploitation, human disturbance, and climate change. In addition to global warming, which is likely to become the dominant threat across all systems, the CO2 absorbed by the oceans causes the water to become more acidic. The impacts that this will have on invertebrates in this century remain under investigation, but are potentially catastrophic. 

Recognising the growing pressures on invertebrates is important, as local declines lead to global extinctions. This loss is signifi cant as each species is distinct, fascinating and beautiful, and part of the network of life that makes up our global ecosystem. There are additional more utilitarian reasons why we must stem the tide of invertebrate decline. Though their importance to human wellbeing is rarely recognised, invertebrates form the basis of many of the critical services that nature provides. For example, they help store carbon at the bottom of the ocean, fi lter water, decompose waste and recycle its nutrients, pollinate important crops, and are an essential part of the food web - ultimately feeding hundreds of millions of people. Simply put, if they disappeared tomorrow, we would soon follow. Not surprisingly, the value of the services provided by invertebrates is often estimated to be worth billions of dollars annually. Ever-growing human demand for resources is putting tremendous pressures on invertebrates. To tackle these problems, there are two interlinked steps to take – we need to see the diversity of life in order to appreciate and value it, and we need to understand how it is changing in order to plan for the future. Focusing on invertebrates helps to truly illustrate the great diversity of the beautiful, fascinating and weird creatures with which we share the planet. It helps to put our place in the world into perspective, making it clear that we are only one tiny part of a global and interconnected complex web of life. It helps us to understand that we are more dependent on our spineless relatives than we ever imagined, and that it is truly the small things that make life possible. From a moral and ethical perspective we must help ensure the future of the invertebrate creatures with which we share the world. From a selfi sh perspective, we must attempt to better understand the fundamental roles invertebrates play in critical ecosystems to ensure our own future security and wellbeing. It is not surprising our lives are so closely tied to invertebrates; we evolved from them and we have been dependant on them for millions of years. It would be both sad and imprudent to think we can live without them in the future.