Climate Change or Overexploitation: Which is the greatest threat to marine conservation?

Conservation is a substantial environmental and socio-economic challenge encompassing a wide variety of stakeholders with an eclectic range of interests. Undeniably, both climate change and human exploitation pose a great threat to biodiversity globally. It is arguably harder to conserve marine systems than terrestrial systems due to the scales of fundamental ecosystem processes, for example population replenishment, which are frequently much larger than marine reserves can encompass (Allison et al., 1998). Traditionally, the impacts of these threats are more widely researched within terrestrial ecosystems; but today we will focus on marine ecosystems.

In recent years, intensified usage of the marine biome by humans has encouraged powerful marine conservation efforts (Allison et al., 1998). Marine species richness patterns, particularly for fish and invertebrates, are strongly correlated with environmental factors (Cheung et al., 2009), therefore climate change and human activity pose great challenges for marine conservation management. Approximately 60% of the global human population is concentrated along coastlines worldwide, with these productive coastal margins being strongly affected by anthropogenic impacts and a conflict of interests (Vitousek et al., 1997; Gray, 1997). Higher incidences of functional extinctions have led to government introduced legislation aimed at reducing waste disposal at sea, banning harmful pollutants and nuclear testing, as well as limiting fishing and protecting specific species (Costello and Ballantine, 2015). Furthermore, an integrated area management framework is highly suggested due to its focus on sustainable use of marine resources (Gray, 1997).

Climate Change

Affecting physical oceanic conditions and influencing ecological and biological processes (Wernberg et al., 2016), climate change has a multitude of devastating impacts on marine ecosystems; such as coral bleaching, stormy weather, decreased mixing and ocean acidification. Furthermore, climate change can also influence fauna directly through physiological alterations (e.g. metabolic and reproductive processes) or indirectly through predator/prey dynamics changes or competitor presence (Wernberg et al., 2016). Species’ distributions will be significantly reformed via climate change, therefore disrupting marine biodiversity patterns (Cheung et al., 2009) and impacting on conservation management strategies as biodiversity patterns no longer reflect protected area and reserve boundaries. Heightened temperatures are also changing critical physiological, demographic and community-scale processes, therefore driving species redistribution worldwide and rapidly breaking down long-standing biogeographic boundaries (Wernberg et al., 2016).

Another critical challenge for marine conservation when implementing protected areas and reserves are phase shifts. For example, when conserving fish stocks, it is important to note that sea surface temperature (SST) modifications and alterations of ocean currents, attributed to climate change, have led to differences in distribution and abundance of commercial and recreational fisheries within many oceans worldwide (Jennings and Brander, 2010), most famously cod stocks migrating north from the North Sea. In the case of ocean warming, alterations in temperature are not uniform globally, therefore creating difficulties when designating protected zones, as some locations are warming faster than others (Wernberg et al., 2016). Strategies are necessary to deal with these phenomena, and to reduce other pressures on marine habitats already stressed by rising water temperatures and levels, to protect precious marine resources and biodiversity.

Climate-driven regime shifts also provide a great challenge to conservation. A marine heat wave led to the reduction of kelp forests across ~2300 km2 of Australia’s Great Southern Reef, directing a regime shift to seaweed turfs (Wernburg et al., 2016), therefore impacting upon coral reef conservation efforts. Undoubtedly, anthropogenic impacts on marine ecosystems are harder to quantify than changes to terrestrial ecosystems; however, various sources of information suggest these alterations are substantial (Vitousek et al., 1997). Climate change is also predicted to increase the frequency of events such as the El-Niño Southern Oscillation (ENSO), having profound influences upon species’ population dynamics, including those of top marine predators (Sprogis et al., 2017), further complicating management efforts.

Coral reefs are one of the most widely-discussed marine ecosystems that face impending threats intensified by climate change. They are a key ecosystem identified for conservation, being the most structurally complex and taxonomically diverse of all marine ecosystems, therefore providing habitat for tens of thousands of associated fishes and invertebrates (Jackson et al., 2001). Furthermore, they provide an array of ecosystem services, with multiple socio-economic benefits – most notably seen within the Coral Triangle and the Great Barrier Reef. By 2050, it has been predicted that there will be a loss of 70% of the coral reefs worldwide (Wilkinson, 2000), predominantly due to coral bleaching. A phase shift from a coral to an algal-dominant environment has been predicted due to increasing sea temperatures causing significant bleaching events (Roy and Pandolfi., 2005), providing significant challenges for conservation management, both economically and strategically.

Moreover, climate change is projected to cause multiple local extinction events within the sub-polar regions, the tropics and semi-enclosed seas (Cheung et al., 2009). Concurrently, intense species invasions are predicted in the Arctic and Southern Ocean (Cheung et al., 2009); consequently, alterations in over 60% of present biodiversity will lead to ecological disturbances that could disrupt ecosystem services having profound impacts on human livelihoods (Cheung et al., 2009). A more global perspective of the impacts climate change will have on an eclectic variety of marine species is urgently required to have a more comprehensive viewpoint of the threat of climate change (Cheung et al., 2009). Nevertheless, these impacts are predicted to strengthen, with their intensity varying geographically according to alterations in oceanic conditions and species sensitivity (Munday et al., 2008). Large logistical difficulties and financial costs have limited the ability of long-term datasets to be generated, therefore our understanding of extreme climatic events and marine biodiversity is also limited (Bost et al., 2015).

Anthropogenic Activity

Anthropogenic impacts to marine ecosystems include overfishing, habitat loss and pollution locally and globally, alongside widespread local, ecological, and commercial extinctions generating trophic cascades and changed ecosystems (Costello and Ballantine, 2015); as well as inadequate protection, tourism and development, oil and gas extraction, shipping and aquaculture.

Overfishing is arguably the biggest threat to marine ecosystems globally caused by human activity. Regardless of method, fishing of dominant species leads to changes in age structure, population size, relative abundance of predators and prey, food webs, and ecosystems (Costello and Ballantine, 2015). Ecological extinction triggered by overfishing precedes all other prevalent human disturbance to coastal ecosystems, including pollution, degradation of water quality and anthropogenic climate change (Jackson et al., 2001). Many of these fisheries orientate on top predators, altering trophic food webs (Vitousek et al., 1997). Furthermore, technologies utilised to intensify capture rates, such as dredges and trawls, are dragged across the sea floor causing substantial damage to critical marine habitats (Vitousek et al., 1997) – for example, scallop dredging.
Commercial fisheries are only one side of the coin, however, as small-scale fisheries provide food for more than one billion people on the planet (Rice and Garcia, 2011). Globally, fish provides a significant source of protein for two-thirds of the world’s inhabitants, particularly for coastal and less-economically developed countries, due to it being rich in essential amino-acids and minerals (FAO, 2010; Rice and Garcia, 2011).

Traditional capture fisheries are also overexploited, thus have depleting fish stocks, therefore resulting in economic and social uncertainty for future food security. Additionally, the impacts of overfishing will be exacerbated by human population growth as it nears 9 billion in 2050 and food sovereignty and heightened food security is reached (Merino et al., 2012). Although human exploitation occurs in many forms, pollution, eutrophication, habitat destruction, disease outbreaks, invasive species, and anthropogenic climate change all take place later than overfishing (Jackson et al., 2001), suggesting it is a leading problem facing conservation success.

Land-use change and intensified agricultural production can also have vast implications for marine ecosystems. For example, higher incidences of harmful algal blooms within coastal areas indicates that human activity has impacted the base and the top of marine food chains (Vitousek et al., 1997). Modification of nutrient concentrations within coastal waters are correlated with increased incidences of human farming activity as chemicals, such as nitrogen-rich fertilisers, are leached into water bodies then flow into the wider ocean (Vitousek et al., 1997). Furthermore, land-use change has also caused the loss of substantial coastal habitat. Mangrove ecosystems, for example, have been reduced by roughly 50% due to human activity (Vitousek et al., 1997); however, climate change is projected to have a larger impact on coastal and estuarine systems.

Conserving Our Marine Environments

Marine Protected Areas (MPAs) are currently the most championed conservation management strategy within marine environments. Defined as being “any area of the intertidal or subtidal terrain, together with its overlying water and associated flora, fauna, historical, and cultural features, which has been reserved by law or other effective means to protect part or all of the enclosed environment” (Sala et al., 2013), networks of MPAs are “collection of individual MPAs operating cooperatively and synergistically, at various spatial scales, and with a range of protection levels, in order to fulfil ecological aims more effectively and comprehensively than individual sites could alone” (IUCN, 2007). They improve oceanic conditions by protecting and restoring marine habitats, increasing resilience to environmental changes and protecting species and rebuilding fish stocks, with a global review showing that well-managed MPAs can substantially increase fish size, density, biomass and species density (IUCN, 2007).

Networks of marine protected areas are being established globally to protect and conserve marine biodiversity and ecosystem services (Halpern et al., 2010). Holistically, climate change presents a novel and alarming threat to these ecosystems; however, very few studies have investigated how MPAs must be designed to provide the maximum resilience to this developing risk (Halpern et al., 2010). The management of MPAs in the 21st century is increasingly difficult due to a range of anthropogenic threats such as overfishing, pollution and coastal development, along with the adverse climate-change impacts, including rising temperature and sea-level rise as well as ocean acidification (Halpern et al., 2010). It is critical that MPA networks encompassing mitigation strategies toward these climate impacts are designed, otherwise major investment may potentially be made in areas that will not survive the next several decades (Halpern et al., 2010). Protection of biodiversity at any level is certainly better than none; however, MPAs which allow fishing cannot maximise biodiversity conservation (Costello and Ballantine, 2015).

MPAs form only part of marine conservation management strategies (Gray, 1997); particularly considering the challenges faced by marine ecosystems via climate change and anthropogenic impacts. The majority of MPAs are centred on fishery management rather than conservation, with 94% of MPAs allowing fishing (Costello and Ballantine, 2015). As a result, MPAs cannot protect all aspects of biodiversity due to their allowance of fishing, despite being utilised as an indicator of conservation progress (Costello and Ballantine, 2015). This has led to the recommendation of no-take marine reserves, despite less than 1% of the ocean currently being designated marine reserves (Costello and Ballantine, 2015). No-take zones, such as Lamlash Bay, United Kingdom, are an additional marine conservation strategy, predominately focussed on the impacts to marine biodiversity caused by overfishing (Lundquist and Granek, 2005). It is critical that stakeholder engagement comprises a substantial element of marine conservation management design, development and implementation (Lundquist and Granek, 2005), to ensure success in the face of economic, cultural and political interests.

A recent upsurge in marine reserves presents them as a vastly encouraged form of marine conservation (Allison et al., 1998). Due to conflicting usages of coastal habitats, losses of marine diversity are highest in coastal areas (Gray, 1997). Arguably, the best way to conserve marine biodiversity is through conservation of habitat and landscape diversity within coastal areas, with MPAs being only part of the necessary conservation strategy (Gray, 1997). However, marine reserves provide inadequate protection in isolation as they are not secluded from all critical impacts (Allison et al., 1998). Despite this, reserves provide a platform for critical conservation efforts via exclusive protection for significant areas, spatial escape for overexploited species, and afford buffers against occasional management miscalculations and unforeseen circumstances (Allison et al., 1998).

There is also an argument as to what ecosystems to conserve considering the radically increasing threats of climate change and intensified anthropogenic activities, particularly due to the limited funding that conservation efforts receive. Biodiversity hotspots are one framework which aim to conserve areas with exceptionally prominent levels of biodiversity. One incidence is the Indonesia archipelago, with the highest level of marine species diversity, decreasing radially from there (Gray, 1997). An additional way of locating areas of marine conservation are ‘Hope Spots’, like the Ross Sea, created by Dr. Sylvia Earle’s Mission Blue initiative. These areas focus on “recognising, empowering and supporting individuals and communities around the world in their efforts to protect the ocean” (Mission Blue, 2017). Hope Spots operate by expanding on the current MPA framework, identifying areas that necessitate new protection as well as mounting existing MPAs where more action is required, but are faced with huge economic challenges as they are established via a non-governmental organisation.

Furthermore, both climate change and human exploitation of marine resources pose great challenges for political decision-making and maritime law, as conflicts of interests among stakeholders come into play. The 1982 United Nations Convention on the Law of the Sea aimed to conserve marine resources through responsible management; however, the impending threat of climate change matched with deep-sea mining, gas and oil exploration, alongside overfishing has led experts to argue this legislation requires updating (Guruswamy 1998). Another legislative example includes the Antarctic Treaty System (Nicoll and Day 2017), created to reduce exploitation of krill – a fundamental organism at the base of Antarctic food webs. Further from its initial creation, the international Antarctic Treaty System has led to the creation of MPAs, such as the Ross Sea (the world’s largest); however, these protective boundaries will only be in place for 35 years from December 2017 due to a conflict of interests among committee members (Nicoll and Day 2017). Undoubtedly, legislation at international, regional and local levels is required to maximise conservation efforts; however, for it to be successful and sustainable, stakeholders must be engaged at all levels and their interests considered.

Concluding Comments

In short, climate change and human exploitation of marine ecosystems are inextricably linked, therefore producing profound challenges for conservation management strategies of these uniquely diverse ecosystems. Conservation should ideally occur in natural environments, untouched my human activity; however, this is particularly difficult within marine environments where so many people depend on the natural resources offered by its ecosystems. It will be incredibly difficult to prevent the impacts of climate change, such as increasing sea-surface temperatures and ocean acidification, within a fluid and interconnected environment; particularly as the conservation methods, like marine protected areas and no-take zones, do not isolate these environments from climatic variability; they only ensure human exploitation is minimised.

Although human activity exacerbates the effects of climate change and the two are inextricably linked, it is arguable that climate change is the largest challenge to marine conservation efforts as with overfishing and pollution, measures can be put in place to reduce or stop these activities all together. Climate change impacts will vary temporally and spatially, providing benefits for some, where costs are delivered to others. It is key to note that this issue is far more complex than simply stating whether climate change or human exploitation are more threatening to conservation management of marine biodiversity, as arguably one drives the other. Multidisciplinary approaches are key to the task of conserving such a vast and diverse biome, which provides significant resources for a large-proportion of the globe.


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