Status and Trends of Bonaire’s Reefs in 2017: Clear signs of resilience
The “resilience” of coral reef ecosystems has been an important goal of managers and policy makers for decades. At its most basic level, resilience means that if coral reefs suffer damage from say a hurricane or bleaching mortality event, they will recover to their previous state. Remarkably, this has never been documented for any coral reef ecosystem in the Caribbean.
In a highly cited scientific study entitled: “Disturbance and recovery of coral assemblages” (Connell 1997) all existing data on trends of coral reefs world-wide were reviewed but no examples of coral reefs recovering from disturbance in the Caribbean were found (Fig. 1).
Several important studies have documented the decline of coral reef ecosystems in the Caribbean (Gardiner et al. 2003, Jackson et al. 2014) and in the tropical Pacific (Bruno and Selig 2007). The global decline of coral reefs was the impetus for very high impact scientific papers with titles such as “Confronting the coral reef crisis” (Bellwood et al. 2004) and “Rising to the challenge of sustaining coral reef resilience” (Hughes et al. 2010) or specifically asking the shocking question: “Are U.S. coral reefs on the slippery slope to slime?” (Pandolfi et al. 2005). These alarming titles and the associated press coverage caught the attention of managers and policy makers but to date there has been little progress operationalizing coral reef management for resilience. Nevertheless, some studies gave clear advice to managers such as, “Capturing the cornerstones of coral reef resilience, linking theory to practice” (Nyström et al 2008). In that paper, the authors proposed that research identify:
“...empirical indicators of the cornerstones of coral reef resilience. These indicators include functional group approaches” ... “identifying ‘good’ and ‘bad’ colonizers of space, measurements of spatial heterogeneity, and estimates of potential space availability against grazing capacity. The essence of these operational indicators of resilience is to use them as predictive tools to recognize vulnerability before disturbance occurs that may lead to abrupt phase shifts [of coral loss and seaweed increase]. Moving toward operationalizing resilience theory is imperative to the successful management of coral reefs in an increasingly disturbed and human-dominated environment.”
The Nyström et al. 2008 quote describes precisely the approach we have taken since our reef monitoring began in Bonaire in 2003. In 2005, the Bonaire National Marine Park asked for advice on developing a monitoring program, to which we advocated three points: 1) keep monitoring data simple, 2) focus on known drivers and indicators of reef health and 3) monitor trends among those drivers.
Although coral reefs are complex ecosystems, relatively few “drivers” control much of their structure and how they function. “Drivers” are key processes that control critically important aspects of coral reefs. Several processes can interact with one another (Fig. 2). For example seaweed (also called “macroalgae”) are known to poison corals (Rasher and Hay 2010) and reduce or halt the settlement and survival of juvenile corals (Arnold et al. 2010, Steneck et al. 2014). It has also been shown that herbivorous fishes are capable of reducing or eliminating macroalgae from coral reefs (Lewis 1986, Williams and Polunin 2001). Thus herbivores such as parrotfish enable the recruitment of reef corals, reduce toxic seaweed and facilitate the growth of complex coral habitats into which juvenile reef fish recruit (Caselle and Warner 1996). These drivers and their interactions have been viewed as integral to a complex system of feedbacks that maintain healthy coral reefs (Fig. 2: Mumby and Steneck 2008); they are the “cornerstones” advocated by Nystrom et al. (2008).
Evaluating key drivers of coral reef health and resilience identified in Fig. 2 is complicated because all components interact. Therefore, it is difficult or impossible to define a specific level as being particularly healthy or unhealthy for any given coral reef. Instead, our monitoring protocol measures components to determine changes through time. This is because there is a consensus on trends that constitute healthy trajectories in reef condition. For example, trends of increasing live coral cover or decreasing macroalgal abundance are both moving towards improved conditions (Fig. 3). This allows us to create a very simple means of reporting condition and monitoring trends in key drivers. Importantly, this approach was developed explicitly in the 2005 Bonaire report and has been applied semiannually ever since. All semiannual Bonaire Reports beginning in 2003 are available via STINAPA’s website (http://stinapabonaire.org/nature/coral-reefs-adjacent-waters/).
Managing for coral reef resilience in Bonaire National Marine Park
First, it is important to acknowledge there are several unique biophysical and social factors that play a role in the health of Bonaire reefs. The island is sufficiently far south that hurricane frequency is very low compared to elsewhere in the Caribbean. It is a relatively dry island with very little agriculture, generally low runoff and no rivers that can carry harmful sediment, nutrients and chemicals to coral reefs. In 1971, the island banned the use of spearfishing and there was traditionally very little use of fish traps that are so common throughout the Caribbean. We know of no other coral reef system in the Caribbean with those restrictions but those two factors alone protect herbivorous parrotfish that are easy to shoot with spears and readily enter fish traps. The consequences of these factors are that Bonaire’s coral reefs have relatively intact habitat architecture and an abundance of herbivorous parrotfish that keep seaweed cropped short (Steneck, personal observation, 1990, Kramer 2003).
With the quality of Bonaire’s reefs attracting divers from around the globe, a diver fee was instated to fund a non-governmental organization (STINAPA Bonaire) that manages the Bonaire National Marine Park (BNMP) (Solofa, Chapter 10). Without this NGO, the management of Bonaire’s reefs may have been impossible.
We began monitoring reef sites in Bonaire in 2003. The six initial sites (Fig. 4) were designated by Ms. Kalli DeMeyer who was the first Manager of the Bonaire National Marine Park (BNMP). In 2008 enforcement of the Fish Protected Areas (FPAs) began so in 2009, Mr. Ramón de León the then Manager of BNMP suggested the addition of three sites to balance sampling around the FPAs. In 2010 one additional site (free of divers) was added making the total of 11 monitored sites (Fig. 4).
Stratification of sampling design and repeated sampling at fixed locations is necessary for precision and statistical power. Accordingly, we have repeatedly visited the same sites (adding sites when FPA’s were established), at 10 m depths, employing identical methods for the past 14 years (Fig. 4). These sites are physically similar in terms of wave action and sediment effects so they can be combined to assess long-term trends.
Coral reef ecosystems are created by, and require, live coral for their structure and function. Bonaire’s reefs remain among the healthiest in the Caribbean in that corals occupy more space than any other group (specifically seaweed: Fig. 5; Steneck, Chapter 1). In contrast, most formerly coral-dominated reefs are now seaweed-dominated reefs throughout the Caribbean. Nevertheless, static measures of coral or algal cover are not as telling as are the trends.