Friday, April 9, 2010

Chapter 20: Impacts of Biodiversity Loss on Ocean Ecosystem Services by: Boris Worm et al.

For the final chapter review for our unit we return to the oceans and animals life. And once more the chapter starts off with and intro paragraph. "Ecologists think the loss of biodiversity is a problem because it threatens the stability of of ecosystems and the potential ability of life to adapt to changes in climate and other conditions." A human connection to this concern is from farmer who have noticed a decline in the number of wild bees and other pollinators. This means that crops are starting to come under threat. Overfishing has become threat to fish populations which in turn could lead to a major economic impact on the live of individual fishers. This was found by Dalhousie Universities Boris Worm et al.
"Human-dominated marine ecosystems are experiencing accelerating loss of populations and species, with largely unknown consequences." Worm ant eh University analyzed local experiments as well as long term regional time series, etc, to test how a loss of biodiversity will marine ecosystems. They determined that loss of biodiversity is "increasingly impairing the the ocean's capacity to provide food, maintain water quality, and recover from perturbations." Recent surveys suggest that local biodiversity may enhance the productivity and stability of an ecosystem. However it is less clear how the importance of biodiversity changes at the landscape level and local experiments and theories don't seem to easily extend to long-term long-scale management decisions. Changes in marine biodiversity are cause by pollution, exploitation, habitat destruction and through indirect means such as climate change and perturbations in ocean biochemistry. Regional ecosystems such as coral reefs and coastal and oceanic fish communities are losing populations, species or entire functional groups rapidly.


Now onto the next section which is titled Experiments and deals with the...experiments... performed by Worm and the University. First off was a look at the effects of variation in marine diversity in areas such as primary and secondary productivity, resource use, nutrient cycling and ecosystem stability in a total of 32 controlled experiments. I will simply quote the results directly from the chapter since it is worded best here: "Increased diversity of both primary and secondary producers and consumers enhanced all ecosystem processes. Observed effect sizes correspond to a 78 to 80% enhancement of primary and secondary production in diverse mixtures relative to monocultures and a 20 to 36% enhancement of resource use efficiency." That's a pretty profound set of conclusions. Experiments that manipulated species or genetic diversity also showed that diversity enhanced ecosystem stability. Experiments with diet came to similar ends. Different diets were needed for various processes such as growth, survival and fecundity.

Now we come to the section describing experiments related to Coastal Ecosystems. Here long term regional trends were documented from a detailed database of 12 coastal estuarine ecosystems and other sources. Trends were examined in 30-80 different economically and ecologically important species per ecosystem. Records show that over the past millennium have shown a rapid decline in native species diversity. "Overall, histroical trends led to the present depletion Ihere defined as >50% decline over baseline abundance), collapse (>90% decline), or extinction (100% decline) of 91, 38, or 7% of species, on average." Only about 14% recovered from collapse and these species were mostly protected birds and mammals. "These regional biodiversity losses impaired at least three critical ecosystem services: number of viable (non-collapsed) fisheries (-33%); provision of nursery habitats such as oyster reefs, sea grass beds, and wetlands (-69%); and filtering and detoxification services provided by suspension feeders, submerged vegetation, and wetlands (-63%). The loss of the filtering services were suspected of contributing to declining water quality and the increase in algal blooms, fish kills, oxygen depletion and shellfish and beach closures. Sea level rise was suspected to be caused by loss of floodplains through the decline of wetlands. Loss of native biodiversity also coincided with the invasion of non-native species and these invasion did not compensate for the loss of diversity. The data suggests that substantial loses in biodiversity are closely associated with the loss of regional ecosystem services and increasing risks for coastal inhabitants.

Now for a look at Worm's et al work on Large Marine Ecosystems. The experiments performed here were the largest in scale, due to the nature of the ecosystem being tested. The global catch database from the United Nations Food and Agriculture Organization (FAO) and other sources were used to gather data. Data on 65 Large marine Ecosystems (LME) was taken from 1950 to 2003. LME's are large (>150,000 square km) reaching from estuaries coastal areas to seaward boundaries of continental shelves and major current systems. These areas collectively produce 83% of global fishing yield since 1950. "Globally, the rate of fisheries collapses, defined here as catches that drop below 10% of the recorded maximum, has been accelerating over time, with 29% of currently fished species considered collapsed in 2003." Cumulative yields across all species has dropped by 13% or 10 million metric tons since passing a maximum in 1994. These collapses occurred at a higher rate in species-poor ecosystems. Fish diversity ranged from 20-4000 species and was influenced fishery related services in several ways. "First, the proportion of collapsed fisheries decayed exponentially with increasing species richness." Diversity also appeared to increase robustness to overexploitation. "Rates of Recovery, here defined as any post-collapse increase above the 10% threshold, were positively correlated with fish diversity. This positive relationship between diversity and recovery became stronger with time after collapse (5 years, r = 0.10; 10 years, r = 0.39; 15 years, r = 0.48)." A reason for enhanced recovery at high diversity may be that fishers can switch more readily amongst the species and thus potentially providing over fished taxa with a chance to recover.

Marine Reserves and Fishery Closures. One question floating around management is if the loss of services can be reversed, once it has occurred. Data was analyzed from 44 fully protected marine reserves as well as four large-scale fisheries closures. An average of 23% increase in species richness of target and non-target species (the species that are a staple of the fishing industry and others that are not fished for yet exist in the ecosystem of the target species). The increase in biodiversity also lead to increases in productivity seen in a four fold increase in in catch per unit effort in fished areas around reserves. ``Community variability, as measured by the coefficient of variation in aggregate fish biomass, was reduced by 21% on average. Finally, tourism revenue measured as the relative increase in dive trips within 138 Caribbean protected areas strongly increased after they were established." These results suggest that at this point it is still possible to recover lost biodiversity at least on local scales. This recovery is accompanied by increase in productivity and tourism.
Now, for the Conclusions. Worm et al state that with the current extrapolation of data the collapse of all fisheries taxa will occur sometime in the mid 21st century (a 100% regression by 2048). Another conclusion is that the elimination of locally adapted populations and and species impairs and the ability of marine ecosystems to feed our growing human population and sabotages their stability and recovery potential. High-diversity systems were found to provide more services with less variability. This has economic and policy implications. ``First, there is no dichotomy between biodiversity conservation and long-term economic development, they must be viewed as interdependent societal goals. Second, there is no evidence for redundancy at high levels of diversity; the improvement of services was continuous on a log-linear scale. Third, the buffering impact of species diversity on the resistance and recovery of ecosystem services generates insurance value that must be incorporated into future economic valuations and management decisions." To wrap it all up, increasing biodiversity act as a safe guard/buffer against environmental collapse (as well as economic) and we must handle our oceanic resources carefully so as to ensure we do not lose this buffer.

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