Developing marine management strategies against regional eutrophication in Caribbean small island nations with limited financial and logistical resources

Abstract

Coral reefs are threatened globally, with habitat degradation and associated resource losses of primary concern. In the Caribbean region these losses have been increasingly well documented over the last forty years, but no clear consensus reached as to their cause. Over recent years however it has become generally accepted that it is multiple interacting factors behind the decline in coral reef health, including (but not limited to): over-fishing, climate change, and reductions in water quality. With climate change a regional stressor that can’t be directly managed on a local level, management usually focuses on over-fishing and water quality. In the past, this latter factor was usually considered to be of a local nature and thus easily managed; that it was primarily caused by local sources of water pollution (such as sewage outflows, agricultural runoff, and industrial waste), and only affected the relatively limited surrounding geographic area.

Using the small, relatively undeveloped island of Anguilla as an example, this thesis set out to illustrate how habitat degradation is taking place in the Caribbean, even when local water quality stressor appear absent, and the implications of degradation for management. It is hypothesised that broad scale degradation may be due to fresh water river plumes that emanate from the Amazon and Orinoco, laden with nutrients from intensive farming in northeastern South America, entering the Caribbean basin via north Brazilian current rings. The nutrient levels within these plumes may have increased with deforestation of the Amazon Basin that accelerated during the 1970’s. Since then, nutrients have been entering the Caribbean region, and via retention and recycling mechanisms, have been gradually building up ever since. These regionally sourced nutrients may be one of the main reasons behind the coral-algae phase-shift in the Caribbean; widely attributed to be causing the overall decline in habitat health throughout the region. It is proposed that the build-up of nutrients has now reached a level that is becoming more readily observable through signs such as the large regional plankton blooms (or Green Water Events) of 2009 and 2010 and the Sargassum spp. inundations of 2011 and 2014. Previously, without these unprecedented events, signs of eutrophication had been limited to the high abundance of macroalgae on Caribbean reefs, and discussions focused upon how much of this was due to the Diadema antillarum (Long-spined Sea Urchin) die off and/or over-fishing versus local nutrient sources.

If water quality is indeed a regional stressor in a similar way to climate change, management options within the Caribbean region become more limited. Focus now has to be placed on local fisheries management and minimizing any potential local sources of water pollution. Ecological assessments are essential when developing these management strategies, but they can be time consuming and expensive. Such resource constraints are often the limiting factor for many small island nations and one of the primary reasons for insufficiently managed protected areas around the globe. In an attempt to overcome this issue, an ecosystem health ranking tool was developed that uses only five ecological variables to ascertain habitat health, and allows managers to identify conservation priority areas. The most effective five variables to use were: percentage coral cover; percentage macroalgae cover; number of fish species; total fish count; and mean size of commercially/ecologically important fish species.

Ecological monitoring, while being the essential foundation work for any managerial regime, must be complimented with all necessary fishery information. Often much of this can come from literature reviews and employing the precautionary principle, but if knowledge gaps exist for any fisheries following this process, a full assessment is necessary to ensure correct management. Again, as with ecological assessments, fishery assessments can be time consuming and expensive. However, by employing the help of local fishers and retail outlets, methodologies are available that minimize these resource constraints. This was undertaken for the Panulirus guttatus (Spotted Spiny Lobster) fishery in Anguilla, and used a novel approach to assess both minimum maturity sizes and breeding seasons for the species. Based on the results of the assessment, it is recommended to introduce a minimum landing size of 52 mm carapace length in order to mitigate the potential of the hand-capture fishery capturing immature individuals, and a closed season of three months duration, January through March, to protect breeding females. By characterizing flaws in conservation managerial processes that often lead to stalling or insufficient management, a further critical stage that lies between these conservation assessments and management plan design was identified: deciding which stressors were influential; which can be managed against; and how best to conduct this management. In order to bridge this gap a model was developed that employed a threat assessment phase, where ecological monitoring data was used to identify stressors with management potential. This process used rapid assessment methodologies to examine stressors and the effectiveness and implication of stressor management. The culmination of the structured approach to integrating survey information and threat assessments is a more robust and realistic set of management objectives. This is illustrated in this thesis by a plan for marine conservation in Anguilla, which was subsequently accepted by the Island’s government.