What Makes Up Marine Ecosystems Environmental Sciences Essay
An ecosystem can be defined as an area where there is an interaction between all the non-living and living components. The complete group of organisms inhabiting the ecosystem can be called a community. The abiotic non-living components include such items as air, water, soil sunlight all of which may be critical to the survival of the organisms (Soper et al 1997). Odum (1969) described the ecosystem as a single entity composed of many different parts dynamically interacting with transfers of energy and considers the ecosystem to be ”a unit of biological organization made up of all the organisms in a given area (that is ”community”) interacting with the physical environment so that a flow of energy leads to characteristic trophic structure and material cycles within the system”. This more elaborate explanation is still applied today and is more relevant as it takes into account the important issue of energy flow between the components. Marine ecosystems include oceans, coral reefs, estuaries and coastal areas such as lagoons and kelp beds.
An appreciation of the fundamental definition described above allows us to understand how the ecosystem concept can be extrapolated from smaller marine ecosystems such as coral reefs or sea grass beds to bigger ones such as the Caribbean Large Marin Ecosystem (CLME) which is an interconnected complex of these and many other smaller ecosystems. Duda (2002) describes the large marine ecosystem (LME) as a vast marine area which begins with and includes coastal regions and estuaries and eventually stretches out to continental shelf limits and areas dominated by coastal current systems.
Sherman et al (2004) use the following more detailed factors to develop criteria for demarcating LMEs ; bathymetry, hydrography, productivity, and trophically dependent populations. Several of the 64 LMEs spread out across the globe also occupy spaces which are semi-enclosed seas for example the Caribbean and Baltic seas are two semi enclosed seas which form the respective CLME and Baltic Sea LME (BSLME). Another factor used in determining the seaward extent of LMEs is the area affected by the major ocean currents of the world, hence, for example the North Brazil Shelf LME (NBSLME) is delimited by the North Brazil Current system and its extent. This factor therefore sometimes supercedes the 200 nautical mile of EEZ fisheries zone limits criteria.
The understanding of the concept of the LME is fundamental to this study as the area of interest transcends the boundary between two adjacent LMEs namely the CLME and the NBSLME (see figure 1.) (Polygon delimiting actual study area needs to be inserted on this diagram)
Figure 1. The Caribbean and adjacent Large Marine Ecosystems. (Fanning et al. 2009)
Resources and Ecosystems
Seagrass, coral reefs and mangroves are very common marine coastal ecosystems within the CLME. The outflows of two of the largest river systems in the world, the Orinoco and the Amazon have a great impact the LME of the Caribbean (CLME, 2007)., the former having the greater effect due to its closer proximity, approximately 100 km from the south coast of the island of Trinidad. The North Equatorial Current moves in a generally westward direction from the mid Atlantic region into the Caribbean basin through the Lesser Antilles and thus many of the islands within this area are impacted by its nutrient poor nature (see fig 2). The islands of the South Eastern Caribbean however, especially the twin island nation of Trinidad and Tobago are heavily impacted by the Guiana Current which enters the Caribbean along the northern coast of South America (fig 3). It has been stated that the freshwater outflows from the Amazon and Orinoco has a significant impact on the Guiana current (Morrison and Smith 1990). Muller-Karger et al. (1988) illsutrate that the Amazon River discharges the most amount of freshwater into the ocean from any single point source.
The North Equatorial Current (NEC) as represented by the Mariano Global Surface Velocity Analysis (MGSVA). The NEC is the broad westward flow that is the southern component of the N. Atlantic subtropical gyre. It is fed by the Canary Current and its waters eventually end up in the Gulf Stream system, either via the Antilles current or through the Caribbean via the Guiana current. (Bischof et al. 2004)
South equatorial current, North Brazil Current and North Brazilian Current are all terms which have been applied to the Guyana current. Flagg et al. (1986) suggest that the misappropriation of the names is due mainly to the seasonal nature of the adjacent currents. The Guyana Current starts off as the North Brazil Current which carries along the south American coastline up to the region of French Guiana where part of it diverges and rejoins the North Equatorial Counter Current. The Guiana Current is formed from the remainder which continues along the coast in a northwestward direction (Condie 1991)
The Caribbean current as represented by the Mariano Global Surface Velocity Analysis (MGSVA). The Caribbean Current transports significant amounts of water northwestward through the Caribbean Sea and into the Gulf of Mexico, via the Yucatan Current. The source water for the Caribbean Current is from the equatorial Atlantic Ocean via the North Equatorial, North Brazil, and Guiana Currents. The counter-clockwise circulation of the Columbia-Panama Gyre is evident off-shore of southern Central America (Nicaragua, Costa Rica, and Panama) and northern Colombia. (Gyory et al. 2004)
(Gyory et al. 2004)
The Caribbean exhibits a great degree of spatial and temporal differences when it comes to its marine environment. Coral reefs are a prime example of the diversity of its ecosystems and its species as most of the corals and associated species found in the region are endemic making this biodiversity of international importance (Burke and Maidens 2004)
The interdependence and flow of energy from the nearshore more productive habitats such as the reefs, mangroves and seagrass beds to the less productive open ocean areas such as the planktonic and pelagic systems and the environmental conditions that influence them are not well understood at this point.
Why conserve and manage marine ecosystems?
The importance of marine ecosystems and hence the need for their sustainable management can be best illustrated by two main factors; the direct and indirect services they provide and the ensuing natural and human based stressors that they face.
Marine ecosystem services
Humans often view the oceans as a huge waste bin while simultaneously as a perpetual source of food. With five percent of the world’s protein supply coming from the sea and up to 15 percent is selected areas such as China and Japan our dependence on the ocean for food is immense. There is a wide range of services apart from being a food source that humans garner from the oceans, to fully appreciate these one must first come to terms with the varying scales of spatial distribution and time which these services may be provided. Obviously different regions will provide various services due to their different physical makeup and constituents for example near shore coastal ecosystems provide most of the services of a particular type due to their highly productive nature whereas open ocean areas provide most of the regulating services and chemical balancing mainly due to its immense size.
The medical, spiritual, aesthetic values of the ocean are also great but often receive lesser attention. Recently much interest has been placed in carbon sequestration and the role of the oceans and marine ecosystems in acting as carbon sinks slowing the global climate change process Garcia and Cochrane (2005) mentions this and categorizes ecosystem services into four main areas; provisioning, supporting, regulating or cultural. The function of coral reefs, mangroves and even salt marshes in buffering coastal areas from wave and storm damage was apparent during the 2004 Asian tsunami and the 2005 Gulf of Mexico Hurricanes. It is well known that coastal habitats such as mangroves, salt marshes, coral reefs, and sea grass beds act as nurseries for young fish and other species while also providing a source of income and employment generation. The fisheries sectors of many a nation is fuelled by the highly productive upwelling zones mainly in and around New Zealand, Chile/Peru, South Africa and the western United States. Also in terms of biodiversity 16 of the 36 animal Phyla that exist occur only in the oceans, this fact has implications for the biochemical and medical fields for human use (Baskett et al 2005).
Marine ecosystem stressors
Most of the world’s population lives in or near to coastal areas for many different reasons. Primarily most of the jobs exist in and around the coastal zone as this is where many of the major cities and ports occur. Also food and recreation and leisure activities are gained quite easily from the seas. As a result of the high population densities experienced by the coastal regions a lot of the significant ecosystems and coastal marine communities are being negatively impacted due to human activities (Halpern et al., 2007, 2008). Pollution of various forms have caused increase nutrient enrichment, eutrophication, sedimentation due to land degradation and mismanagement and changes in the hydrological patterns. Climate ahnge is another signifjicant contributor the the deterioration of the marine ecosystems and have taken a heavy toll on coral reef systems in particular (Baker et al. 2008). GESAMP (2001) lists the modification and demolition of habitats, sewage run off and impacts on human health, rising eutrophication and nutrient enrichment and the decrease in fish stocks as well as alteration of sedimentation pattern due to hydrological changes and land degradation as some of the most significant issues facing coastal and marine areas and ecosystems.
How are they Managed?
Ecosystem Based Management (EBM)
Conventional types of natural resource management have been replaced over the years by a more rounded approach ecosystem based management (EBM) which focuses not only on specific sectors but is more all inclusive. Traditionally, activities that influence the management process have been engaged independently and have not considered the collective impacts on the ecosystem (Curtin and Prezello 2010). EBM is a new approach that considers a broader range of contributing factors (ecological, environmental and anthropogenic) in designing a management technique. Management techniques including coastal management, fisheries management and the designation of marine protected areas (MPAs) help to drive EBM related models. Christie et al. (2007) also stress that ecological function and pertinent scales must be considered in the EBM process. Arkema et al (2006) summarize it most effectively: “Ecosystem based management represents a much broader view than how marine ecosystems have been managed tradition- ally, taking into account the interconnectedness and inter- dependent nature of the components of ecosystems, and the fundamental importance of ecosystem structure and functioning in providing humans with the broad range of services that are taken for granted”.
Cury et al. (2005) notes three key issues that must be adhered to in EBM; establishing lasting goals that are pertinent to the particular ecosystem, defining meaningful indicators, and determining suitable models, data gathering tools and means for analysis.
INDENT (2006) provides an assessment of a wide range of indicators, while mechanisms for marine ecosystem management and monitoring are outlined by Hoffman and Gaines (2008). Biological monitoring makes use of indicator species and also considers numbers of particular species, this is especially useful in fisheries monitoring to detect when a disturbance in a specific area in this regard fisheries monitoring is considered a tool on its own. Tracking variations in the water quality or physical habitat is termed environmental monitoring and is separate from biological and fisheries monitoring.
The multitude of stressors which influence the marine environment can have many sources, including estuaries, coastal areas and even far away areas such as watersheds. At the highest level therefore EBM should take into account watershed impacts (Guery et al. 2005). Also from a management perspective it has been suggested that an approach which begins at the lowest scale and then makes its way up to the level of large marine ecosystems thereby allowing a greater number of stressors and the services that they impact to be considered Agardy (2007) and Rosenberg (2006). Sustainable management and application of marine ecosystem services always need to consider the relationship between the socioeconomic and ecological parts of the entire system across the various scales involved.
The fisheries resources within an ecosystem are directly related to the primary productivity of that ecosystem (Pauly and Christensen 1995). The ever increasing problem of coastal eutrophication can be monitored by utilizing ecosystem productivity as an indicator. Ecosystem characteristics can be observed through the use of satellite data. Satellite data that has been tuned to a specific region can provide data on nutrients, productivity, phytoplankton, and sea surface temperature (Aiken et al. 1999; Berman and Sherman 2001; Melrose et al. 2006).
The 2004 National Coastal Condition Report II illustrates the use of five indices for coastal assessment put forward by the United States Environmental Protection Agency (USEPA). These include water quality, sediment quality, benthic communities, coastal habitat, and fish tissue contaminants. These indicators and the entire methodology are gradually being applied to the international global environment facility (GEF) funded LME projects.
The Gulf of Mexico LME and many European LME’s have suffered due to nitrogen overenrichment over recent decades. The 1970’s Green Revolution which saw much of the wetlands of the world being transformed to agricultural lands and the subsequent fertilizer and livestock increase are said to be the major contributors to this process (Howarth et al. 2000 and Duda and El-Ashry 2000) with other contributors coming from urban sewage sources and automobile exhaust.
Indicators used for Marine Management
The increasing range and intensity of human uses has led to a need for efficient management of marine ecosystems in the region. Marine ecosystem indicators can play a key role in improving the planning and management practices within the marine environment for sustainable use (Borja et al. 2008b; 2009). Indicators enable managers and stakeholders to monitor the condition of an ecosystem and the impacts of its associated human activities. Indicators can also be used to support planning and decision-making for ecosystem-based management, including problem identification and policy implementation.
More than a decade ago the chief method employed in assessing marine quality was the use of indicator species collected from the benthic communities. A wider approach is now being undertaken with the inclusion of the physical components as well as a greater range of biological components (Pinto et al., 2009). Fishes, phytoplankton and zooplankton are biological components that are now part of the ecosystem assessment process and are being used as indicators for marine quality evaluation (Borja et al 2009). True marine quality assessment is usually done by incorporating the various physico-chemical and biological elements of the system (Borja, 2005, 2006). Moloney and Shillington (2007) show that it is necessary to have indicators for ecosystem health however, individual indices can be applied for various aspects of the physical and chemical environment. Further work is required for the establishment of an effective method of defining the single indicator for assessment of marine quality (Borja et al., 2008a).
The past approach had several deficiencies chief of which was it usually was based on just a few indicator organisms which may not have been a true representation of the ecosystem condition. On the other hand developing several indices based on several different organisms has seen a proliferation of indices (Diaz et al., 2004). Another key point to consider is the validation and testing of an index once it has been developed to ensure its accuracy. Obviously the usefulness or applicability of an index lies in its ability to accurately transmit the information about the quality of the study area for which it was designed (see Borja and Dauer, 2008).
It is important to note that local scale indices have been generated in abundance in recent times not taking into account the interconnected nature of the larger marine ecosystems. A key step in index development is the multivariate analysis over areas where the ecosystem compositions are close by comparison. Borja et al (2009) have illustrated clearly that stakeholders and decision makers often need information on larger regions that cross habitat boundaries and thus scale is an important factor in index development.