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.