macro-algae

Macroalgae on Bonaire
Macroalgae are large algae, also called seaweeds, that are typically divided in three major groups: red macroalgae (Rhodophyta), brown macroalgae (Phaeophyceae), and green macroalgae (Chlorophyta). Over 250 seaweed species are known from Bonaire. They vary tremendously in shape and color and are found in a range of habitats. They flourish in shallow and deep areas on coral reefs all around the island, in seagrass beds, mangrove forests and in the intertidal.

Macroalgae – important organisms
Macroalgae are mostly notorious as aggressive competitors for space that can overgrow reef corals. However, macroalgae play an important part in all marine ecosystems: they provide food for herbivores, and they stabilize the structure of reefs. Algae are also remarkable in that they are responsible for the high productivity that characterizes coral reefs and seagrass beds.

Identifying macroalgae
These identification cards provide an overview of almost 60 red, brown and green seaweed species that are frequently encountered on Bonaire, to help you explore the macroalgal biodiversity in the marine parks.

Coral reefs worldwide are currently jeopardized by anthropogenic factors such as land-based pollution, coastal development, and sediment erosion. In the Caribbean alone, nearly two-thirds of coral reefs have been deemed as threatened. This study investigated the potential negative effects of water quality and eutrophication, Enterococci bacteria (found in human gut), and sedimentation on coral disease, bleaching, and macroalgal growth on the near shore reefs of Bonaire, N.A. Monitoring sites were defined according to their proximity to anthropogenic activity: “more impacted” or “less impacted” (< 200 m and > 200 m from coastal development, respectively). Water samples at 5 m were collected weekly and at 12 m biweekly from each site and tested for nutrient concentrations (NO3, NO2 - , NH4-N, PO4), Most Probable Number of Enterococci bacteria, sedimentation rates, and particle size distributions. Video transects (100 m) were also taken at defined depths and analyzed for live coral cover and diversity, percent disease and bleaching, and macroalgal cover. Data showed elevated NH4-N levels at all sites, Enterococci bacteria present at 3 of the 4 sites (mainly at 5 m), and sediment particle counts showed significant differences among sizes at both depths and between the interaction of size and impact at 12 m. There was also a strong trend of finer grained sediments at high impact sites and coarser grained sediments at low impact sites. Very little overall coral disease (1.105 ± 1.563 % at more impacted sites and 0.400 ± 0.566 % at less impacted sites in 12 m) and bleaching (3.245 ± 0.615 % at more impacted sites and 1.390 ± 1.966 % at less impacted sites in 12 m) was found on the reefs however, neither were present at 5 m. There was significantly more macroalgae at 12 m and a strong trend of more macroalgae at the deeper, more impacted sites. This study suggests that increased anthropogenic activity on Bonaire is contributing to the increased NH4- N levels, Enterococci bacteria presence, and finer particle sediments, which future studies may correlate significant interactions between these parameters and coral disease, bleaching, and macroalgal growth.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 35-43 from CIEE Bonaire.

The island of Bonaire has significant contamination from anthropogenic sources such as sewage and landfills, which can cause excess nutrients in groundwater that will eventually enter the ocean. Nutrients have been suggested to increase macroalgal growth. The amount of nutrients and abundance of herbivores play a key role in maintaining a healthy coral dominated reef system. The major objective of this study was to determine the health of Bonaire's reefs by assessing various bioindicators, evaluating bioacummulation of macroalgae, assessing the biocontrol mechanisms, and determining the presence of phase shifts. This study looked at the relationship of herbivorous fish, nitrogen content and abundance of macroalgae to make inferences regarding the overall health of the reef. Two study sites, Kas di Arte and Something Special, were chosen for research over the course of four weeks. Data collection included abundance of herbivorous fish, substrate composition and nutrient level in water and algae samples. No inferences could be determined from the nutrient tests due to the varying concentrations found in both water and macroalgae. The herbivorous fish abundance and macroalgae were found to be inversely proportional. This study is important to determine whether herbivorous fish or nutrient input control phase shifts on Bonaire's reefs and can aid in identifying similar issues in reefs all over the Caribbean.

This student research was retrieved from Physis: Journal of Marine Science XV (Spring 2014)19: 58-65 from CIEE Bonaire.

In the microbial loop, heterotrophic bacteria utilize dissolved organic matter (DOM) as an energy source. DOM becomes remineralized into inorganic material and nutrients available for primary production. As the amount of nutrients increase, the abundance of each trophic level increases, which is known as the bottom-up effect. This study investigates the effect of the increasing human population density on an intertidal community along the waterfront of Kralendijk, Bonaire. DOM, fecal indicator bacteria (enterococci, Escherichia coli, and coliform bacteria), nutrients (nitrate, phosphate, and ammonia), primary producers (percent cover of macroalgae), and herbivorous consumers (density of sea urchins) were sampled. There was no pattern between the variables and the increase of the adjacent population density. Factors such as rainfall, changes over time, tides, and herbivore grazing may have influenced the results. When graphed over time, rainfall impacted the concentrations of nutrients and fecal indicators. Nitrate, ammonia, and coliform bacteria increased, while phosphate, enterococci, and E. coli decreased. Concentrations of ammonia were found to exceed the threshold for a healthy coral reef ecosystem (6x). No correlation was found between DOM and heterotrophic bacteria, although concentrations of E. coli and nutrients were high at one site. This intertidal ecosystem does not appear to be influenced by bottom-up controls, as there was neither a correlation found between the percent cover macroalgae and nutrients or the density of sea urchins. The site with the highest percent cover of macroalage had the lowest density of urchins and vice versa.

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 91-99 from CIEE Bonaire.

When overly abundant, macroalgae can be a major threat to the health of a coral reef ecosystem due to its capability to smother live coral and reduce the rates of recruitment. Several factors can contribute to macroalgal growth, one of the controlling elements being a lack of herbivorous grazing. When grazing pressure is high the ecosystem remains balanced, but when grazing pressure is low reefs can experience macroalgal blooms that have a lasting negative effect. This study examined the indirect causes of macroalgal cover change through assessing damselfish aggression. Stegastes planifrons, also known as the Three Spot Damselfish, are highly aggressive and territorial fish that will defend their territories against a number of intruding species. This study looked at the relationship between damselfish abundance and aggression and the grazing behavior of parrotfish, as well as the relationship between damselfish abundance and macroalgal cover on Bonaire, Dutch Caribbean. Video transects were implemented over the chosen study stations and then analyzed with Coral Point Count (CPCe) software to attain the percentages of macroalgae cover at each station. Aggressive behavior of the three spot damselfish as well as the grazing behavior of parrotfish were observed and recorded using SCUBA diving. It was found that damselfish aggression and parrotfish grazing were negatively correlated, and that parrotfish grazing followed the same trend line as the macroalgae cover. Based on the findings of this study it was concluded that S. planifrons aggression has no considerable effect on the grazing behavior of parrotfish,and it can be assumed that it does not contribute to increased macroalgal cover.

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 16-21 from CIEE Bonaire.

This report characterizes the state of Bonaire’s reefs as of March 2005. We pay particular attention to structural and functional attributes of reefs that have changed in so many other Caribbean reefs. We characterize coral reefs by their resident organisms and the forces regulating their distribution and abundance. Thus, corals, algae and fish define the “structure” of coral reefs but climate changes, diseases, hurricanes, overfishing, sedimentation and excess nutrients may affect how they “function”. Recent unfavorable changes in the structural and functional attributes of reefs have caused “the coral reef crisis” (Bellwood et al. 2004). In Caribbean coral reefs the most alarming changes have been the declines in the abundance of corals, sea urchins and reef fishes and the accompanying increases in large harmful seaweeds (called “macroalgae”). The decline in coral and increase in macroalgae, called a “phase shift”, represents a significant change in the structure of coral reef ecosystems that could lower its resilience.

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In March of 2005, a team of graduate students from the University of Maine revisited six study reefs on Bonaire to determine the status of those reefs and to detect if any change has occurred since March of 2003 when the last such survey was conducted. The study sites established in 2003 from north to south are: Karpata, Barcadera, Reef Scientifico, Forest on Klein Bonaire, Plaza and Windsock. Bonaire’s shallow (10 m) reefs remain in good condition. Coral cover averaged 47% in 2005 compared to 46% in 2003 (no change). Turf algae have increased and coralline algae have declined slightly over the past two years. Harmful seaweed “macroalgae” abundance remains low (2% in 2005 and 5% in 2003; see Steneck in this report) at the 10 m depth we studied. At depths below 20 m, macroalgae are now and have been (for at least the past 30 years) much more abundant (e.g. Van den Hoek et al. 1975) The absence of macroalgae in Bonaire most likely relates to the abundance of seaweedeating species or “herbivores”. Caribbean-wide, harmful macroalgal seaweed abundance corresponds inversely with the abundance of grazing fish such as parrotfish and tangs (Fig. 1). No comparable plot exists for seaweed abundance and any other measured factor on reefs.

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Changes over the past two decades
Comparisons between the status of reefs over a few years tell us little about long-term changes. For example, today there is a distinct demarcation between where Bonaire’s fringing reefs begin at 5 to 10 m depth and the shore. This region today is largely coralfree and dominated by rubble and sediment laden turf algae. However, this may not have always been the case. Prior to whiteband disease that killed nearly 90% of the elkhorn and staghorn corals in the Caribbean (i.e. Acropora palmata and A. cervicornis) (Aronson et al. 1998, Aronson and Precht 2001), most of the near shore zone was coral-dominated.
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Coral cover in the near shore zone surrounding Bonaire has declined dramatically and is now dominated by dead coral rubble where once elkhorn and staghorn corals had formed near monocultures prior to white band disease. Five of our six study sites have changed dramatically over the past 20 years except for Karpata. The decline of the Acropora species may have allowed competitively inferior species such as lettuce, pencil, finger and fire corals (Agaricia spp, Madracis spp, Porites porities and Millepora complanata) to expand since all have increased in abundance since the Van Duyl study (1985). Corals are not the only group to have changed dramatically since the 1980s. Diadema antillarum, the dominant grazing sea urchins was abundant in the near shore zone until it succumbed to the mass mortality of the mid 1980s. Today, more than 20 years later it remains below detectable levels at most of the sites we studied (Smith and Malek this report, Steneck this report). These changes, along with the significant declines in large predator finfish (see Bonaire Report 2003) indicate that several key players for the resilience of coral reefs (e.g. Fig. 3) have declined in abundance.

Bonaire’s reefs remain among the best in the Caribbean. However, our monitoring has revealed some potentially troubling trends that may require management action. In 2005, we reported to the Bonaire Marine National Park on the status of Bonaire’s coral reefs, and we suggested a strategy for monitoring trends among four key reef attributes we believe track the health and resilience of Bonaire’s reefs (Steneck and McClanahan 2005). Here we report the results of monitoring studies conducted 2003, 2005 and now 2007 at each site. Where appropriate, we drew from Bonaire’s first AGRRA assessment conducted in February 1999 (Kramer and Bischof 2003) to extend temporal trends over a period of eight years. 
Troubling trends
We see three troubling trends of increased macroalgae, declining herbivory from parrotfish, and increases in damselfish populations. Of these, the first two are most serious (see Chapters 1, 2 and 3). Secondary trends of concern, increases in damselfish populations (Chapter 4) and declines in coralline algae (Chapter 1), could lead to reduced recruitment of reef corals (Chapter 7), but to date this is not evident (Chapter 7). Importantly, coral cover remains relatively high (Chapter 1). The monitored group of carnivorous fishes, the lutjanid snappers, are holding constant but we remain concerned about the past (Steneck and McClanahan 2003) and continued loss of other larger bodied reef carnivores such as groupers and barracuda. The positive ecological role of parrotfish is well documented (e.g. Mumby et al. 2006) so their decline is troubling. It is unclear exactly why their population densities are declining. While parrotfish are not currently a widely sought group of reef fish (Chapter 8), fishing pressure on them is growing. It is possible they are vulnerable to even modest fishing pressure, particularly from fish traps. Accordingly, we recommend that the capture and killing of parrotfish be stopped because of their key ecological role on Bonaire’s coral reefs. Further, other groups of grazing herbivores such as the longspined sea urchin (Diadema antillarum) are increasing but too slowly to effectively replace the functional role of parrotfish (Chapter 1). We suggest continued monitoring of key drivers of reef health (coral cover, algal abundance, herbivory and coral recruitment). Some standard protocols such as the Atlantic and Gulf Rapid Reef Assessment (AGRRA) are entirely commensurable with the data presented in our reports in 2003, 2005 and 2007 (this report). A streamlined monitoring protocol is likely to be most useful to managers to alert them as a potential problem is growing and, perhaps more importantly, to show improvement when it occurs.
 
 

Although reef corals are dependent of the di- noflagellate Symbiodinium, the large majority of corals spawn gametes that do not contain their vital symbiont. This suggests the existence of a pool of Symbiodinium in the environment, of which surprisingly little is known. Reefs around Curac ̧ao (Caribbean) were sampled for free- living Symbiodinium at three time periods (summer 2009, summer 2010, and winter 2010) to characterize different habitats (water column, coral rubble, sediment, the macroalgae Halimeda spp., Dictyota spp., and Lobophora variegata, and the seagrass Thalassia testudinum) that could serve as environmental sources of symbionts for corals. We detected the common clades of Symbiodinium that engage in symbiosis with Caribbean coral hosts A, B, and C using Symbiodinium-specific primers of the hyper- variable region of the chloroplast 23S ribosomal DNA gene. We also discovered clade G and, for the first time in the Caribbean, the presence of free-living Symbiodinium clades F and H. Additionally, this study expands the habitat range of free-living Symbiodinium as environmental Symbiodinium was detected in T. testudinum seagrass beds. The patterns of association between free-living Symbio- dinium types and habitats were shown to be complex. An interesting, strong association was seen between some clade A sequence types and sediment, suggesting that sediment could be a niche where clade A radiated from a free-living ancestor. Other interesting relationships were seen between sequence types of Symbiodinium clade C with Halimeda spp. and clades B and F with T. testudinium. These relationships highlight the importance of some macroalgae and seagrasses in hosting free-living Symbio- dinium. Finally, studies spanning beyond a 1-yr cycle are needed to further expand on our results in order to better understand the variation of Symbiodinium in the environ- ment through time. All together, results presented here showed that the great diversity of free-living Symbiodinium has a dynamic distribution across habitats and time. 

Bonaire’s coral reefs remain among the healthiest in the Caribbean. Although the island’s reefs have suffered bleaching disturbances similar to those plaguing reefs throughout the Caribbean, they uniquely show signs of recovery. Here we highlight key findings from our March 2015 biennial coral reef monitoring expedition. We put the findings in the context of both the trends recorded since 2003 when we began our regular monitoring and the most recent research related to the factors controlling the structure and functioning of healthy coral reef ecosystems. 

The Littler’s team [including Barrett Brooks, Don Hurlbert, Barbara Watanabe and Larry Gorenflo (Conservation International)] traveled to the island of Bonaire, Netherlands Antilles (1 Nov 06 to 14 Nov 06). The purpose of this expedition was to assist the Ministry of Nature Affairs for the Netherlands Antilles (MINA) and the Center for Applied Biodiversity Science at Conservation International to assess the current status of Bonaire’s marine flora. The team collected over 300 specimens from the upper reef to a depth of 56 m. This assessment increased the known species reported from Bonaire by 35% (Appendix II, List of Species). The marine flora is typical of many Caribbean reefs with no specific areas of extremely high diversity or unique species composition. Also included in this evaluation are over 100 digital images (Appendix III), properly identified to the species level in most cases. These images may be used by managers in web sites, oral presentation, training manuals, brouchures, etc., to make marine plant identification possible for Bonaire’s many divers, volunteers, conservationists or interested agencies.
The team surveyed the health of the reefs using key indicator species (recognized from our >30 continuous years of coral-reef research) in reference to the growing problems associated with eutrophication and overfishing along tropical and subtropical shorelines worldwide. The ecological responses of corals and macroalgae to nutrient enrichment and release from predation have been repeatedly cited as priority areas in need of further research (National Research Council, 2000; Littler & Littler 2006).