Coral reefs

Multi-scale habitat occupancy of invasive lionfish (Pterois volitans) in coral reef environments of Roatan, Honduras

The Indo-Pacific lionfish species [Pterois volitans (Linnaeus, 1758) and P. miles (Bennett, 1828): Family Scorpaenidae] are the first nonnative marine fishes to establish in the Western North Atlantic and Caribbean Sea. Despite the continued documentation of its range expansion and highly publicized invasion (including public-driven removal efforts) there remains a paucity of basic information on lionfish ecology. This knowledge gap limits effective long-term management. In this study we conducted a multi-scale investigation of habitat occupancy of a newly established population of lionfish in Roatan, Honduras. Based on field surveys and citizen sightings in Roatan Marine Park we found that lionfish occurred more frequently on aggregate coral reef habitats (54% of sightings) compared to patch reef habitats (30%) and sea grass lagoons (16%). In general, these aggregate and patch reef habitats contained adults (mean total length =118.9 mm and 114.7mm, respectively) whereas sea grass habitats contained juveniles (mean total length=89.5 mm). At the micro-habitat scale lionfish occupied areas dominated by hard coral and overhanging structure; the same microhabitats containing native fishes of concern – grouper (Nassau grouper, Epinephelus striatus; yellow fin grouper, Mycteroperca venenosa) and snapper (dog snapper, Lutjanus jocu; mutton snapper, Lutjanus analis). Results from this study contribute information on basic habitat requirements of lionfish and inform current management removal efforts focused on containing spread and mitigating their impacts on native species

Date
2011
Data type
Scientific article
Theme
Research and monitoring

The Saba Bank- A large atoll in the northeastern Caribbean

Findings

Abundant coral growth within the Saba Bank is restricted mainly to the two large windward reefs. These two reefs carry a very rich reef fauna.

The rest of the Bank only has a very small growth of corals due to several factors:

  • Most of the food supply is probably filtered away by the large windward reefs.
  • These reefs are located at a least favorable leeward position.
  • These reefs are located at a considerably greater depth.

As in most other atoll lagoons, coral growth in the lagoon area is restricted to small patch reefs; the number of species is not significantly lower than on the reef, but the colonies are smaller in size and number.

The Saba Bank undoubtedly has a volcanic base but no information on this has been collected. This study did uncover some black sand, presumably of volcanic origin, on the southwestern part of the Bank. Geologists believe that a composite volcanic island is buried under the more recent formations.

Only the eastern and largest part of the Saba Bank can be called a living atoll with an open lagoon, while the western part is a bank with drowned fringing reefs.  Whether the western part is included or not, the Saba Bank ranks among the largest atolls in the world.

Date
1977
Data type
Research report
Theme
Research and monitoring
Report number
FAO Fisheries Report no. 200, p.469-481
Geographic location
Saba bank

Eutrophication status of Lac, Bonaire, Dutch Caribbean Including proposals for measures

Abstract:

Lac is a semi-enclosed lagoon located on the south-eastern side of Bonaire, and contains a diversity of shallow water coral reef associated habitats in close proximity such as mangroves, seagrass beds, Halimeda algal beds, the back reef and sand flats. These habitats support a diversity of fish and invertebrates. The bay has numerous international and national legal protections. The Bonaire National Marine Park regulations and various Island Decrees facilitate from the local perspective. However, despite all regulations, the bay faces several changes, and management and protection of the bay is hampered by a lack of scientific information regarding current environmental status.  

Nutrient poor waters are a requirement for healthy coral reefs. When these become enriched with nutrients, it results e.g. in increased algae and affected reef condition. One area of interest for management is the eutrophication status of Lac. Eutrophication is a pressure that might explain some of observed changes in the bay. However, no baseline on the eutrophication status of Lac exists. IMARES and Environics NV conducted a snapshot assessment of the eutrophication status for current understanding and as a basis for future management. Environics conducted the field measurements at Lac, and most of the data analysis. IMARES analysed geographical data and together with Environics cowrited the report.

The purpose of this baseline study was to assess the trophic status of Lac by analyzing 4 potential indicators of eutrophication simultaneously:

  • Nutrient levels
  • Levels of fecal indicator bacteria (enterococci)
  • Epiphyte loads of seagrasses,
  • Benthic community composition of the back reef

The monitoring was performed at 32 sites within the bay and 1 control site outside the bay in December 2010.

In this study, three of the four observed indicators point towards an ecosystem that is under stress from eutrophication. The levels of nutrients in the bay exceeded thresholds for open coral reef systems due to lack of better. Overall, concentrations show that enrichment with nitrogen was widespread and levels commonly exceeded threshold values. No clear source or “hotspot” could therefore be identified in this study. Phosphate only exceeded threshold values at a few locations, but no clear source was identified. The diffuse enrichment of nutrients across the bay probably results from multiple factors such as water circulation, residence time, freshwater input, rainfall, groundwater contamination, tidal range, and geology. Besides the (semi-) natural conditions the nutrient status is likely to be affected by human impacts as greywater inputs and lacking of proper sewerage. All these factors should be considered regarding the future state and measures to tackle the eutrophication of the bay.  

Enterecocci bacteria were detected at levels above acceptable levels as determined by ISO for bathing waters. The mean levels of enterococci decreased as the distance from shore increases with the highest levels found at groundwater sites and zero enterococci found on the back reef sites. Based on this dispersion we assume that sources of enterococci in this study are most likely birds and cattle (donkey and goat manure). The identification of the true sources of enterococci in Bonaire is however compelling and further study on this aspect is necessary to protect public health.  

The levels of epiphytes on seagrass blades, showed differences in biomass among studied stations. This could mean that seagrass beds in different regions of the bay are experiencing different levels of water column nutrients but no clear relation between nutrient levels and epiphyte cover was observed in this study.

The benthic composition monitoring revealed high abundance of calcareous algae (Ramicrusta sp.). This abundance is likely to be a bloom (pers. observations over time). The bloom of Ramicrusta sp. might be indicative of nutrient enrichment and uptake occurring in Lac. The alga is currently taking over habitat where hard corals lived and changes the benthic composition of the back reef and potentially affecting the integrity of the reef crest. The degradation of the reef crest will diminish the protective role provided by the structure and increase exposure to wave and storm action from the adjacent sea.  

Management Recommendations:

Despite the current eutrophic state of Lac, studies elsewhere indicate that eutrophic bays may begin to recover within months after implementation of proper measures. To do so, natural sources of nutrients should be distinguished from anthropogenic sources. Based on the results of this study and historical accounts of other bays in the Caribbean that have been degraded by eutrophication; the following recommendations for Lac are suggested:

  • a. Reduction of nutrient and fecal bacteria inputs by removing donkeys and goats from the watershed, and ensuring adequate toilet facilities and sewerage at Cai and Sorobon, including greywater disposal.
  • b. Continuation of nutrient monitoring nutrient in order to locate clear sources and fate of the eutrophic state of Lac. We recommend adding urea to the suite of nutrients monitored in this study.
  • c. Implementation of a regular monitoring program to identify sources and fates of fecal bacteria in order to support public health. Effectiveness of above measures can then be assessed as well.
  • d. In general, to understand the outcomes of the water quality management plan it would be of great value to have an understanding of groundwater flows, circulation patterns and residence time of water in Lac.
Date
2011
Data type
Research report
Theme
Research and monitoring
Report number
C093/11
Geographic location
Bonaire

Coral reefs and their zonation in the Netherlands Antilles

Although coral reefs are well developed in the Leeward islands of the Netherlands Antilles, they are poorly developed in the Windward group. Coral communities are common in the Dutch Windward islands, but no structural reefs have been observed. Flat, sandy bottoms there seem to prevent reef development, as is also the case on large parts of the southwest coast of Aruba.

The zonation of corals on the reefs, with respect to depth, distance from shore, and conformation to the bottom, resembles that of other Caribbean reefs. Density of living-coral cover ranges in the several zones from nearly zero to almost 100%. Below 20 to 25 m on the forereef slope the corals are areally less abundant than crustose coralline algae. Generic diversity of hermatypic corals is comparable in the Leeward and Windward groups of the Dutch islands, with 24 and 23 genera present, respectively. These numbers are comparable to those of other highly diverse reefs in the Caribbean. The number of species in the Windward group, however, is relatively low. The differences in abundance of coral genera (and species) throughout the Caribbean needs more thorough investigation.

Date
1977
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Aruba
Bonaire
Curacao
Saba
St. Eustatius
St. Maarten
Author

Working paper on the economic valuation of country St. Maarten's coral reef resources

The St. Maarten Nature Foundation conducted an Economic Valuation of St. Maarten’s coral reef ecosystems in the fall of 2010. This attempted to put a monetary estimate on the coral reefs surrounding the island. Coral Reefs are one of the island’s most valuable resources; they provide a livelihood through dive tourism and fishery and provide protection from large, damaging waves caused by hurricanes. In order to properly manage the coral reef ecosystem, an economic valuation is a useful tool to determine what exactly the monetary value of a coral reef is. With an attached value, better management decisions can be made to adequately protect this most precious of resources.

In order to complete the study four questionnaires were distributed. Two dealt specifically with fisheries, one with hotel accommodations, and one with dive tourism. Data was also provided through independent research and stakeholder analysis. Coral reefs have direct and indirect influences on a wide range of economic factors, and the generation of data was crucial to the successful completion of this study. Data was inputted into a computer program created by the United Nations Environment Program and the World Resource Institute (WRI) and which was adjusted by the St. Maarten Nature Foundation to reflect St. Maarten’s unique ecological and economic situation.

The findings of this study have outlined that St. Maarten’s coral reef resources provide important goods and services to the economy of the island. The revenue that the resource is able to generate through coral reef associated tourism and fishery is approximately USD $57,586,976. Although this number is high, and highlights the importance of coral reefs to the island, it also suggests that there is an increased need for conservation in order for this value not to diminish. It is therefore in the best interest of St. Maarten to incorporate environmental economic data to: (1) Establish Marine Protected Area, (2) Incorporate economic valuation into EIAs, (3) Include economic impacts in assessing fines for damages to coral reefs from activities such as anchoring in the reserves, oil spills etc, (4) Weigh revenues from a growing tourism industry against long-term economic losses from environmental impacts, (5) Evaluate distributional effects (“winners” and “losers”) of proposed coastal development projects, (6) Invest in Scientific Research, (7) Increase support from the private and public sector in the proposed Marine Park Management Authority, St. Maarten Nature Foundation. 

Date
2010
Data type
Research report
Theme
Research and monitoring
Geographic location
St. Maarten
Author

Coral reef crisis in deep and shallow reefs: 30 years of constancy and change in reefs of Curacao and Bonaire

Coral reefs are thought to be in worldwide decline but available data are practically limited to reefs shallower than 25 m. Zooxanthellate coral communities in deep reefs (30–40 m) are relatively unstudied. Our question is: what is happening in deep reefs in terms of coral cover and coral mortality? We compare changes in species composition, coral mortality, and coral cover at Caribbean (Curacao and Bonaire) deep (30–40 m) and shallow reefs (10–20 m) using long-term (1973–2002) data from permanent photo quadrats. About 20 zoo- xanthellate coral species are common in the deep-reef communities, dominated by Agaricia sp., with coral cover up to 60%. In contrast with shallow reefs, there is no decrease in coral cover or number of coral colonies in deep reefs over the last 30 years. In deep reefs, non- agaricid species are decreasing but agaricid domination will be interrupted by natural catastrophic mortality such as deep coral bleaching and storms. Temperature is a vastly fluctuating variable in the deep-reef environ- ment with extremely low temperatures possibly related to deep-reef bleaching. 

Date
2005
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Bonaire
Curacao

An Assessment of the Health and Resilience of Bonaire’s Coral Reefs

Abstract:

From July 19-26, 2010, a dedicated team of researchers completed transect surveys on 25 reefs located on the leeward side of Bonaire and the adjacent Klein Bonaire to characterize the current status, threats, and resilience of Bonaire’s reefs. The assessments focused on corals, fish, algae and motile invertebrates using belt transects, point intercept methods and photographic documentation, incorporating attributes of the Atlantic and Gulf Rapid Reef Assessment (AGRRA) protocol and the IUCN bleaching resilience protocol. The main purpose of this work was to 1) assess changes in reef structure and health since the last region-wide AGRRA assessments (1998-2000) and other surveys (2001, 2005) by Bruckner; 2) identify sites in excellent health, exhibiting a high biodiversity and cover of reef building corals and an intact fish communities; and 3) characterize the health and resilience of these reefs. The intent of this project was to provide critical information that can assist the Bonaire government and Bonaire Marine Park in the conservation and management of their precious resources.

Between 5-15 m depth, cover of living coral was high on all reefs (approximately 50%), with exception of a few sites impacted by white plague outbreaks and shallow areas scoured by strong waves during previous storms. Cover by fleshy macroalgae was generally low, as compared to reefs in other Caribbean localities, although some deeper sites did have high cover of Lobophora and Dictyota spp. (brown macroalgae), and cyanobacterial mats were prominent in several locations (especially on Klein Bonaire); these algae occasionally carpeted the margins of coral colonies and were competing with living corals. Montastraea annularis (complex) were the dominant corals, in terms of living cover, occupying approximately 20-25% of the benthos, and making up over 50% of the total live coral cover. Agaricia, Madracis and Porites spp. were the other dominant corals, in terms of living cover. M. annularis complex was also most abundant taxa (numbers of colonies) at all sites overall, and also the dominant taxa between 5-10 m depth, while Agaricia was slightly more abundant at 15 m depth. While the proportion (number of colonies) of brooding species (especially Agaricia, Porites) was very high, their contribution to living coral cover was less than M. annularis (complex) because most colonies were small in size.

Based on size structure, abundance, levels of recruitment, and coral condition, coral communities could be divided into two primary groups, the M. annularis complex (M. annularis, M. faveolata and M. franksi) and all other species. Corals lumped into “other species” were small to medium- sized (mean=24 cm), and population structure exhibited a monotonic decline in size; most colonies were < 20 cm in diameter and very few colonies were over 60 cm. Although a small proportion of colonies showed active signs of disease and competition from other biotic stressors, these corals had low levels of partial mortality (8%), few completely dead colonies were observed (0.4%), and they were the predominant species colonizing dead skeletal surfaces of other corals as well as reef substrates.

The original size of M. annularis (complex) colonies was significantly larger (58 cm diameter) than all other species, although many had been reduced in size due to partial mortality and skeletal surfaces of colonies often contained numerous smaller tissue remnants. These corals were being affected to the greatest degree by coral diseases (white plague, yellow band disease, black band disease, dark spots disease) and other biotic stressors, including competition and overgrowth by sponges, encrusting gorgonians, hydrozoan corals and a tunicate, predation by snails and parrotfish, and damselfish algal lawns. Colonies of M. annularis (complex) were missing on average 30% of their tissue, although the largest corals (mean size =61 cm; about 50% of all colonies) exhibited significantly higher amounts of partial mortality (mean loss=50%) than smaller (mean=41 cm) corals (mean tissue loss=11%). The extent of partial mortality, large numbers of completely dead colonies (4.5% of 1602 examined corals), ongoing stressors that continue to plague this taxa, and absence of colonies less than 10 cm in diameter (indicative of a lack of recruitment success) is of serious concern for these reefs, as these are the dominant frame-builders and characteristically the longest lived corals in the western Atlantic. The better overall health and high levels of recruitment observed in other taxa, in combination with recent declines in M. annularis complex, may indicate these reefs are undergoing a shift in species assemblages, with communities being replaced by smaller, shorter lived corals.

Fish communities on Bonaire were relatively high in diversity, with a dominance by herbivores (especially parrotfishes and damselfishes). Many species of important predatory fishes were present, including the dominant western Atlantic species of snapper, grouper, jacks and grunts, although these predatory fishes may be declining as the size structure was dominated by small and medium-sized fish. In particular, grouper over 30 cm total length were very rare. Large- sized groupers are the most important members of the family, as these species change sex (large individuals are females) and the larger fish produce an exponentially higher number of offspring.

In general, Bonaire’s reefs show signs of high resilience and a good ability to recover from acute disturbances. Reefs had high coral cover, low levels of disease, high levels of recruitment, and low amounts of fleshy macroalgae. There are minor problems that need to be addressed through management actions and conservation strategies. This could include 1) a program to eradicate lionfish before their numbers get out of control (these species were seen, but they appear to be rare as compared to other Caribbean Islands); 2) community-based efforts to remove an encrusting tunicate, coral-eating snails, and three-spot damselfish; 3) a nursery/restoration program to propagate A. cervicornis and A. palmata and reintroduce these corals into their former habitat; 4) steps to increase the abundance of herbivorous sea urchin (Diadema antillarum) populations; 5) elimination of fishing on herbivores (parrotfish caught along the shoreline using handlines) and top predators (groupers); and 6) better sewage treatment and other strategies to reduce run-off and nutrient input from hotels located along the coastline. 

Date
2010
Data type
Research report
Theme
Research and monitoring
Geographic location
Bonaire

Scuba diver behaviour and the management of diving impacts on coral reefs

Coral reefs worldwide are attracting increasing numbers of scuba divers, leading to growing concern about damage. There is now a need to manage diver behaviour closely, especially as many dive companies offer unlimited, unsupervised day and night diving from shore. We observed 353 divers in St. Lucia and noted all their contacts with the reef during entire dives to quantify rates of damage and seek ways of reducing it. Divers using a camera caused significantly more contacts with the reef than did those without cameras (mean 0.4 versus 0.1 contacts min-1), as did shore versus boat dives (mean 0.5 versus 0.2 contacts min-1) and night versus day dives (mean 1.0 versus 0.4 contacts min-1). We tested the effect of a one-sentence inclusion in a regular dive briefing given by local staff that asked divers to avoid touching the reef. We also examined the effect of dive leader intervention on rates of diver contact with the reef. Briefing alone had no effect on diver contact rates, or on the probability of a diver breaking living substrate. However, dive leader intervention when a diver was seen to touch the reef reduced mean contact rates from 0.3 to 0.1 contacts min-1 for both shore and boat dives, and from 0.2 to 0.1 contacts min-1 for boat dives. Given that briefings alone are insufficient to reduce diver damage, we suggest that divers need close supervision, and that dive leaders must manage diver behaviour in situ.

Date
2004
Data type
Scientific article
Theme
Research and monitoring