Management for sustainability

Sustainability

Farms should be managed in such a way that both they and their sites are sustainable. A sustainable farm is one that will continue to return an income to its owner, proportionate to capital and labour. A sustainable site is one that will continue to provide the ecosystem goods and services on which the farm depends, and those which other people use. The goods or services might be tangible and obvious, as exemplified by a supply of phytoplankton and pure, well-oxygenated water, for filter-feeding bivalves. They might be tangible but less obvious, as exemplified by the assimilation of some wastes that a farmer might otherwise have to pay to have removed. They might be intangible, exemplified by the satisfaction that some people derive from the existence of a rare animal or plant. Ecologists do not have a complete theory of ecosystem sustainability. We think that it is at least in part dependent on the existence of a variety of species and functions in a community of organisms, and so argue that it is important to maintain biodiversity and the 'balance of organisms' in the plankton and the benthos.

According to Doris Soto (FAO), the Ecosystem Approach for Aquaculture is guided by 3 main principles:

Aquaculture should be developed in the context of ecosystem functions and services (including biodiversity) with no degradation of these beyond their resilience;
Aquaculture should improve human-well being and equity for all stakeholders;
Aquaculture should be developed in the context of other sectors, policies and goals.

Ecosystem 'resilience', or 'resistance', to the effects of human-induced or other change, is an important concept. In general, ecosystems recover easily from small disturbances, which are, indeed, part of the natural state of things. The resistance of an ecosystem indicates the amount of disturbance that it can accept without damage to its prospects for rapid and full recovery. Human disturbance of ecosystems fall into two classes:

those that involve: addition of natural materials (such as organic waste, nutrients, etc) for which the ecosystem has a natural, but finite, assimilative capacity; or removal of renewable resources (such as oxygen, phytoplankton), where the rate of renewal defines the carrying capacity of the ecosystem for that use;
those that involve: addition of synthetic materials (such as PCBs) for which the ecosystem has no natural breakdown pathways and hence no assimilative capacity, and which constitute a growing risk to wild and farmed organisms, and humans, if they are toxic; removal or destruction of new-renewable resources (such as gravel beds used for fish spawning) which are important for ecosystem function.

As is made clear in the Water Framework Directive, type 1 disturbances are to some extent acceptable. Type 2 disturbances must be minimized or abolished. ECASA has studied, mainly, disturbances of type 1, and we now set out a theoretical framework for management of these disturbances.

Environmental Management Principles

In summary, the framework requires the use of indicators of environmental pressure, ecosystem state or impact on the provision of ecosystem goods and services. These terms are defined below, in the context of DPSIR. A graph showing the relationship between a pressure indicator and a state or impact indicator can be used to manage pressures so that disturbances do not exceed tolerable levels. Such graphs can be obtained from observations, or from the models that ECASA has tested.

DPSIR

DPSIR is an acronym that summarizes the cause-&-effect chain from human activities to their effects ecosystems and hence to impacts on human society. The table expands and exemplifies each step in the chain, which can also be seen as a feedback loop.

Driver	the changes in human society or the wider world that result in changes in a human activity that creates ...	e.g. expansion of fish-farming in a water-body
Pressure	an environmental disturbance that might result in a change in ...	e.g. increased inputs of nutrients (compounds of nitrogen and phosphorus)
State	the condition of an ecosystem, as measured in relation to a reference or ideal condition; human-induced change in this might cause ...	e.g. increased concentrations of nutrients, increased growth of phytoplankton or macro-algae, changes in floristic composition
Impact	a dysfunction in, or a perturbation of, an ecosystem that degrades the stability & function of the ecosystem and the ecosystem's provision of goods & services to humans, who may make	e.g. 'undesirable disturbance to the balance of organisms and the quality of water' (i.e., eutrophication)
Response	a reaction to the Impact, ideally resulting in reduction of Pressure and in some cases in changes in public policy	e.g. limitation on fish stock or fish feed input, or constraints on mazimum number and size of farms in the water body

Indicators

As discussed on the Indicator pages of the toolbox, an indicator is "An operational representation of an attribute (quality, characteristics, property) of a system". To be operationally useful, an indicator must be easy to measure and relate specifically to the system attribute. Consider the example of human temperature, easily measured by a thermometer in the mouth. What is the system attribute? It is more than body core temperature, because humans, like other mammals, are homeotherms: the regulation of body temperature is an important part of the physical functioning of human beings, and a departure of more than 1 or 2 degrees from the normal body temperature is a good indicator of a dangerous state of health. Thus temperature is an indicator of system state.

ECASA has sought indicators of human Drivers, environmental Pressures, ecosystem States, Impacts on ecosystem goods and service, and human socio-economic Responses, as defined above. In addition we have also examined more general categories of indicators, including those that show whether a site, water body or region may be Sensitive to the potential effects of aquaculture and those that indicate whether an aquaculture site or industry is Sustainable in socio-economic as well as environmental terms. add links to relevant pages

On this page, however, we focus on indicators of pressure and indicators of state or impact. Here are a few examples of such indicators that ECASA has studied:

realm	scale	environmental Pressure	ecosystem State	Impact on goods & services
benthos	A: farm	redox Eh	AMBI	AMBI in context of WFD
pelagos	A: farm	ammonia	-	cultivated animal growth rate compared with expectation
pelagos/all	B: water-body	winter nutrients	Transparency	Decrease in extent and health of seaweeds or seagrasses (and hence of places for fish larval growth
pelagos/all	B: water-body	bivalve filter feeder production (hence demand for phytoplankton)	chlorophyll	cultivated bivalve growth rate lower than expectation; deprivation of wild filter feeders of food, with impact on harvest of fish or wild shellfish

Some of these ecosystem goods and services - such as the provision of good conditions at the farm, or adequate food for bivaves - are those important to a fishfarmer, and so might be, largely, self-managed. Others - such as decrease in the extent of seagrasss - appear to be intangible, but might be expected to impact further on tangible goods such as those obtained from fisheries or, more generally, on ecological quality, which the Water Framework Directive (WFD) aims to protect in the interests of long-term, wie-area, sustainability. In these latter cases it will be better for the management to be carried out by public officers. Finally, it will be seen that the AMBI indicator of the state of macrobenthic communities appears also in the 'impact column'. This is because it has been proposed for use in evaluating ecological quality according to the WFD, and any degradation of ecological quality below 'good' must be considered to be an impact as it requires a response under the Directive.

Pressure-state/impact relationships, thresholds, and Assimilative Capacity

Management of a site, water body, or region, requires at least one indicator of pressure and one of state (or impact). The§ diagram shows how scientific knowledge of a relationship between a pressure indicator and a state or impact indicator can be used to manage the pressure in the interests of sustainability. This relationship can be obtained from observations of pressure and state/impact over many sites, or by the used a mathematical model. In either case, it is likely that there will be uncertainity in our knowledge of the relationship, and this uncertainity must be respected in management.

The diagram shows a line, intersecting the vertical axis, labelled 'maximum tolerable change'. In some circumstances this threshold might correspond to an 'Ecological Quality Objective', or EcoQO, such as 'the value of AMBI should not exceed ??'. The corresponding vertical line, labelled 'maximum safe pressure' might in some cases correspond to an 'Environmental Quality Standard', or EQS, such as '1.5 times reference nutrient concentrations'. However, the primary objective of management for sustainability is to preserve ecological quality. Because sites and water bodies differ in sensitivity to pressures, EcoQOs often offer a better guide than EQSs.

A variety of reasons determine the values at which EcoQOs are set. In most cases, the most valid ecological reason is to avoid exceeding an ecosystem's resistance to disturbance. However, more stringent objectives might be set, for example, to protect species or habitats tht have been publically designated for conservation. The intersection between the functional relationship and the 'maximum tolerable change' is what determines the assimilative capacity of a site or water body for the pressure due to fish waste.

Carrying capacity

This diagram modifies the previous pressure-state/impact diagram to refer to carrying capacity. In this case, the pressure is due to removal of a renewable resource, such as the planktonic micro-algae that provide food for filter-feeding shellfish.

Indicators of sustainability and sensitivity

According to the theory set out above, scale-related indicators of sustainability might be constructed from the frequency of sites, water-bodies, and regions, that are within their assimilative or carying capacities, as appropriate. However, ECASA did not aim to investigate indicators of sustainability as such. Instead, see the CONSENSUS project web-site.

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