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The freshwater bivalves (Mollusca: Order Unionoida) are classified in six families and about 165 genera worldwide. Worldwide rate of extinction of freshwater bivalves is poorly understood at this time. The North American freshwater fauna north of Mexico is represented by 297 taxa in two families. There are 19 taxa presumed extinct, 44 species listed or proposed as federally endangered, and there are another 69 species that may be endangered. A number of these endangered species are functionally extinct (individuals of a species surviving but not reproducing). Extinction of North American unionoid bivalves can be traced to impoundment and inundation of riffle habitat in major rivers such as the Ohio, Tennessee and Cumberland and Mobile Bay Basin. Damming resulted in the local loss of the bivalves' host fish. This loss of the obligate host fish, coupled with increased siltation, and various types of industrial and domestic pollution have resulted in the rapid decline in the unionoid bivalve fauna in North America. Freshwater communities in Europe have experienced numerous problems, some local unionoid populations have been extirpated, but no unionoid species are extinct. Three taxa from Israel are now reported as extinct. Other nations such as China that have problems with soil erosion and industrial pollution or have numerous dams on some of the rivers (e.g., South America: Rio Parana) are probably experiencing problems of local extirpation if not the extinction of their endemic freshwater bivalve fauna.

Coral reefs, with their vast diversity of invertebrate, vertebrate and algal species, have undoubtedly been subjected to natural disturbance since their appearance millions of years ago. Anthropogenic disturbance has been a factor affecting reefs for a fraction of that time, yet in terms of overall impact, may be of greater concern. Data on habitat destruction, pesticide and heavy metal accumulation, nutrient loading, sedimentation, runoff and related impacts of man's activities indicate that many coastal reefs are endangered by these processes through alterations in animal-algal symbioses, shifts in competitive interactions, direct mortality, reproductive failure, and insufficient recruitment. The death of corals critically affects reef communities, as corals provide an important trophic link as well as the main habitat structure. While natural disturbance is an important factor affecting reef interactions, species diversity and evolution, chronic anthropogenic disturbances combined with unsuitable environments for recovery, are of great concern. Physiological stress can be measured in corals in addition to outright mortality, allowing the impacts of specific disturbances to be assessed. Sufficient data for distinguishing real problems from temporal variability are becoming available, allowing scientists to focus on practical solutions to problems in coral reef management and preservation.

Benthic marine invertebrates with planktonic larvae may exhibit Allee effects in reproduction or recruitment. Hydrodynamic considerations and experimental evidence suggest that species broadcasting gametes suffer greatly reduced fertilization efficiencies as densities decline. There is also evidence for some species, including the red sea urchin, that post-dispersal recruitment success declines at low densities of adults, if adults provide shelter from predators or other sources of mortality. Species displaying strong Allee effects may be susceptible to catastrophic population collapses with slight increases in mortality due to harvesting or natural causes. A simple two patch logistic model suggests that the establishment of a harvest refuge is necessary to prevent collapses and maintain sustainable catches at high levels of harvesting effort. A more detailed, age structured model based on the biology of the red sea urchin, Strongylocentrotus franciscanus produces similar results. Effects of harvesting strategies are sensitive to Allee effects caused by both fertilization efficiency and the disruption of adult spine canopies. Theoretical requirements for the size and spacing of marine reserves depends upon the dispersal abilities of the target species. Multiple reserves, spaced more closely than the average larval dispersal distance, appear to be an effective and conservative strategy for maintaining healthy populations and sustainable levels of harvest.

Endemic terrestrial tree snails of the Hawai'ian Islands, like those of other oceanic islands and even some continental areas, are extremely sensitive to disturbance because of their low population numbers and small geographic ranges. Like many other plants and animals of oceanic islands, they have evolved no defenses against introduced predators and competitors. The range of Achatinella mustelina, a tree-snail species found only in a short mountain range on the island of O'ahu, typifies this problem. Mark-recapture studies at two field locations reveal that the snails exhibit slow growth and late maturity (3-5 years). Fecundity is estimated at about 7 offspring per adult per year. The young are born live at about 4.6 mm. Population growth typically depends on considerable longevity (>10 years). Demographic effects of the depredations by alien predators, rats and a North American predatory snail, Euglandina rosea, were documented in two long-term study sites. The predatory snail eats all sizes of A. mustelina and can rapidly drive populations to extinction (less than one year). Rats tend to select larger snails as prey and may leave an area before destroying all of the prey snails present; while reproductive output is temporarily destroyed, populations may survive. Actions necessary to conserve Hawai'ian tree snails, or indeed any group of relatively sedentary invertebrates with small species ranges, must include predator abatement, but also preservation and restoration of sufficiently large and complex forest habitats that the invertebrates may find refuge from alien predators.

Historical or recent extinctions (here called neoextinctions) are rarely reported among marine and estuarine invertebrates. Four case histories of neoextinctions, using gastropod mollusks (snails) as examples, are reviewed: the periwinkle Littoraria flammea (last collected < 1840 in China), the rocky shore limpet \"Collisella\" edmitchelli (1861/3 in southern California), the eelgrass limpet Lottia alveus (1929 in Maine), and the marsh horn snail Cerithidea fuscata (1935, southern California) are all probably extinct. The central element in the demise of all four species may have been a vulnerable, extinguishable habitat. Three considerations suggest that neoextinctions among marine invertebrates have been generally overlooked: 1), hundreds of taxa have not been reported since the 18th and 19th centuries (these are treated by systematists as either unrecognizable, rare, or synonyms of known species); 2), species may have become extinct prior to their description; and 3), there has been a precipitous decline in systematics, biogeography, and natural history at the end of the 20th century-leaving too few workers to tell the story of neoextinction in the ocean. Searches in the literature and museums for overlooked neoextinctions would fruitfully focus on species reported from highly impacted, urbanized coastal habitats-saltmarshes, estuaries, lagoons, seagrass communities, and supralittoral (maritime) zones-habitats now largely obliterated on most coastal margins of the world.

It is likely that roughly one billion gallons of oil enters our oceans each year as a result of man's activities. Only 8% of this input is believed to derive from natural sources. At least 22% is intentionally released as a function of normal tanker \"operational discharges,\" 12% enters from accidental tanker spills and another 36% from runoff and municipal and industrial wastes. Invertebrate populations and communities form the foundation for marine ecosystems and are continually subjected to stresses from both chronic and acute oil toxicity. The diversity of invertebrate taxa represented in the marine environment exhibit a wide range of responses to oil. Mortality is an obvious impact resulting from catastrophic spills or even chronic toxicity. Sublethal impacts on individuals are manifested by physiological, carcinogenic and cytogenetic effects. Impacts typically felt at the population level involve changes in abundance, age structure, population genetic structure, reproduction and reduced recruitment potential. Community level impacts are typified by modified interactions between competitors, predator/prey and symbionts. Most importantly, changes in community structure represented by altered trophic interactions tend to produce the most dramatic alterations to natural invertebrate assemblages. Invertebrate communities respond to severe chronic oil pollution and/or acute catastrophic oil pollution in much the same way. Initial massive mortality and lowered community diversity is followed by extreme fluctuations in populations of opportunistic mobile and sessile fauna (and flora). Oscillations in population numbers slowly dampen over time and diversity slowly increases to original levels. The time over which these events occur depends on the type of oil, the extent of the initial contamination, habitat type, weather conditions, latitude, the species assemblages represented and a myriad of other complex factors.

The nature of overfishing of marine invertebrates is complex, ranging from the perception of overfishing because of competition by user groups for a common property resource to extensive overfishing to near extinction because of poaching by either licensed or unlicensed fishers. As a group, marine invertebrates seem particularly resistant to overfishing, primarily because their relative immobility and scattered concentrations means refuge populations often exist. However, this distribution pattern also means a fishery is scattered over an often large geographical area with relatively small, frequent landings at any location. A minimum legal size regulation, enforceable anywhere before consumption, is the primary regulation applied by managers for many species to ensure against overfishing. Overfishing concerns arise primarily for those species where price is sufficiently high to encourage illegal fishing or where harvest by fishers is not easily monitored or controlled because of the nature of the fishing activity or because only part of the animal (e.g., the flesh) is harvested. Instances of overfishing by cause are discussed, and examples are presented to demonstrate how managers are dealing with or have dealt with different situations.

Problems of measuring invertebrate diversity in natural communities are discussed, together with the rationale of setting priorities for effective conservation of invertebrates. The \"Crisis\" in invertebrate conservation has scientific, logistic, and ethical dimensions. There is need to estimate these in conjunction with a range of values and educational imperatives to overcome public prejudice against invertebrates and to increase conservation funding for invertebrates. Values for selecting priority groups are discussed, and a suite of priority taxa defined to maximise the conservation value of the limited resources available.

Old-growth forests of the Pacific Northwest extend along the coastal region from southern Alaska to northern California and are composed largely of conifer rather than hardwood tree species. Many of these trees achieve great age (500-1,000 yr). Natural succession that follows forest stand destruction normally takes over 100 years to reach the young mature forest stage. This succession may continue on into old-growth for centuries. The changing structural complexity of the forest over time, combined with the many different plant species that characterize succession, results in an array of arthropod habitats. It is estimated that 6,000 arthropod species may be found in such forests-over 3,400 different species are known from a single 6,400 ha site in Oregon. Our knowledge of these species is still rudimentary and much additional work is needed throughout this vast region. Many of these species play critical roles in the dynamics of forest ecosystems. They are important in nutrient cycling, as herbivores, as natural predators and parasites of other arthropod species. This faunal diversity reflects the diversity of the environment and the arthropod complex provides a sensitive barometer of the conditions of the forest. Conservation efforts for forest arthropods are limited at present and controlled largely by land-use policies. For example, an effort is being made to include arthropods in conservation efforts for the Northern Spotted Owl and arthropods will be included in the Forest Health Monitoring program now underway by the U.S. Forest Service. Evidence from other parts of the world suggest that arthropods that depend upon large pieces of dead wood may be particularly threatened by forest management practices. Much remains to be done in the conservation of forest arthropods.