Corals

Abstract: 

Numerous marine invertebrates form endosymbiotic relationships with dinoflagellates in the genus Symbiodinium. However, few studies have examined the fine-scale population structure of these symbionts. Here, we describe the genetic structure of Symbiodinium type ‘‘B1/B184’’ inhabiting the gorgonian Gorgonia ventalina along the Florida Keys. Six polymorphic microsatellite loci were utilized to examine 16 populations along the Upper, Middle, and Lower Keys spanning a range of *200 km. Multiple statistical tests detected significant differentiation in 54–92% of the 120 possible pairwise comparisons between localities, suggesting low levels of gene flow in these dinoflagellates. In general, populations clustered by geographic region and/or reefs in close proximity. Some of the sharpest population differentiation was detected between Symbiodinium from deep and shallow sites on the same reef. In spite of the high degree of population structure, alleles and genotypes were shared among localities, indicating some connectivity between Symbiodinium populations associated with G. ventalina. 

Abstract:

Coral reefs have been more severely impacted by recent climate instability than any other ecosystem on Earth. Corals tolerate a narrow range of physical environmental stress, and increases in sea temperature of just 1 1C over several weeks can result in mass coral mortality, often exceeding 95% of individuals over hundreds of square kilometres. Even conservative climate models predict that mass coral bleaching events could occur annually by 2050. Unfortunately, managers of coral-reef resources have few options available to meet this challenge. Here, we investigate the role that fisheries conservation tools, including the designation of marine reserves, can play in altering future trajectories of Caribbean coral reefs. We use an individual-based model of the ecological dynamics to test the influence of spatially realistic regimes of disturbance on coral populations. Two major sources of disturbance, hurricanes and coral bleaching, are simulated in contrasting regions of the Caribbean: Belize, Bonaire, and the Bahamas. Simulations are extended to 2099 using the HadGEM1 climate model. We find that coral populations can maintain themselves under all levels of hurricane disturbance providing that grazing levels are high. Regional differences in hurricane frequency are found to cause strikingly different spatial patterns of reef health with greater patchiness occurring in Belize, which has less frequent disturbance, than the Bahamas. The addition of coral bleaching led to a much more homogenous reef state over the seascape. Moreover, in the presence of bleaching, all reefs exhibited a decline in health over time, though with substantial variation among regions. Although the protection of herbivores does not prevent reef degradation it does delay rates of coral loss even under the most severe thermal and hurricane regimes. Thus, we can estimate the degree to which local conservation can help buy time for reefs with values ranging between 18 years in the Bahamas and over 50 years in Bonaire, compared with heavily fished systems. Ultimately, we demonstrate that local conservation measures can benefit reef ecosystem services but that their impact will vary spatially and temporally. Recognizing where such management interventions will either help or fail is an important step towards both achieving sustainable use of coral-reef resources and maximizing resource management investments. 

Abstract:

The Saba Bank is a large submerged carbonate platform of approximately 2,200 km2 in the Caribbean Sea which lies partially within the Exclusive Economic Zone of the Netherlands and partially within the territorial waters of Saba and St. Eustatius. It was declared a protected area by the Dutch Government on 15 December 2010 and has been registered as such in the Specially Protected Areas and Wildlife (SPAW) protocol of the Cartagena Convention for the Protection and Development of the Marine Environment of the Wider Caribbean. Applications for a Particularly Sensitive Sea Area (PSSA) at IMO and Ecological or Biological Significant Area (EBSA) at CBD are pending.

As part of the Saba Bank research program 2011-2016, commissioned by the Dutch Ministry of Economic Affairs (EZ), an expedition to the Saba Bank was conducted from 22 to 29 October 2011. The Saba Bank research program aims to obtain information on the biodiversity, key ecological processes and carrying capacity for commercial fisheries to facilitate sustainable management of the area. The primary objectives of the 2011 research expedition were to collect data on benthic and reef fish communities; sponges and nutritional sources of the sponge community; seabirds and marine mammals; water quality, water velocity and other physical parameters. A multidisciplinary team conducted video and visual surveys on benthos, fish and sponges during 10 SCUBA dives at 20-30m depth, while sea birds and marine mammals were surveyed by means of on-board visual surveys and acoustic data loggers. Water velocity and water quality were also measured on-board using an Acoustic Doppler Current Profiler (ADCP) and Conductivity, Temperature and Depth (CTD) device.

During the expedition 8 sponge species were collected and 37 scleractinian coral species and 85 fish species were identified.Fish biomass varied per site between 1.3 kg to 4.4 kg.
Part of the measurements on water velocity, water quality and benthic cover are still in the process of being analysed. Data collected will also be used as baseline for future monitoring and analyses of biodiversity and key ecological processes within the framework of the 2011-2016 research program. 

The Lesser Antilles include high volcanic islands with a limited marine shelf, and low coralline islands with a more extensive shelf. Withinthe group, reefs are affected to a greater or lesser degree by widely differing conditions of rainfall and runoff, hurricane damage, recreational use and fishing pressure. While degradation is reported in many areas, there are few long-term studies that quantify trends in reef status. In recent years there has been an increase in the number of management initiatives, and in the number of reef areas under active and effective management. 

Corals in the genus Acropora generate much of the structural complexity upon which coral reefs depend, but they are susceptible to damage from toxic seaweeds. Acropora nasuta minimizes this damage by chemically cuing symbiotic goby fishes (Gobiodon histrio or Paragobiodon echinocephalus) to remove the toxic seaweed Chlorodesmis fastigiata. Within minutes of seaweed contact, or contact from only seaweed chemical extract, the coral releases an odor that recruits gobies to trim the seaweed and dramatically reduce coral damage that would otherwise occur. In turn, chemically defended gobies become more toxic after consumption of this noxious alga. Mutualistic gobies and corals appear to represent a marine parallel to terrestrial ant-plants, in that the host provides shelter and food in return for protection from natural enemies

Findings:

Combining the findings of this study with that of other studies, the authors conclude that the coral assemblage on the Saba Bank is diverse and healthy; it is representative and typical of those found elsewhere in the Caribbean.

Coral Richness

• A total of 43 species were documented.
• There were no significant differences in coral composition amongst bottom types or depth classes.
• There was a significant difference between sites near and far from the platform edge. The number of coral species observed ranged from 0 and 1 in algal dominated habitats to 23 at a reef habitat on the Bank’s southern edge.
• Coral species richness was higher on reef dominated areas as opposed to algal dominated ones.

Coral Condition

• Bleaching was evident at 82% of the sites assessed with 43 colonies bleached.
• Only three coral colonies were observed to have disease.
• Five reef sites had stands of Staghorn Coral (Acropora cervicornis), a critically endangered species on the IUCN Red List.
• No physical damage consistent with anchor usage or sand scour from shipping activity was noted at any of the sites assessed.

Management Recommendations

1. Immediate action is necessary to protect the diverse coral reef habitats documented.
2. The five healthy stands of staghorn coral (A. cervicornis) and their surrounding should be given highest priority for full protection in the zoning use plan under development (in consultation with all stakeholders).
3. More information is needed on the Saba Bank to create a comprehensive zone use plan. For example, more sites need to be studied so as to get a more comprehensive coverage of the bank’s coral composition.

Linear extension of branches in the same Acropora palmata (Lamarck, 1816) population in Curaçao was measured, employing exactly the same methods, in 1971–1973 and in 2002–2004, and the resulting coral growth rates are compared. Linear growth shows the same pattern over seasons in both periods with growth being significantly higher in summer than in winter. Growth in the 2002–2004 time interval was significantly slower than in 1971–1973. Mean monthly growth ranged from 0.69 cm (winter) to 0.81 cm (summer) in 1971–1973 and from 0.62 cm (winter) to 0.75 cm (summer) in 2002–2004. This means that linear growth rates in 2002–2004 were 7.2% lower in summer and 10.7% lower in winter compared with 1971–1973. Considering possible causative environmental factors relating to these decreases in growth rate, we cannot preclude the possibility that a change in ocean pH could be responsible for the drop in extension rate.

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. 

Reefs of the windward Netherlands Antilles (Saba, Saba Bank, St. Eustatius, St. Maarten) were assessed at 24 sites in the late 1999. The Atlantic and Gulf Rapid Reef Assessment (AGGRA) protocol was used with modifications to detect recent hurricane impacts. Live coral cover averaged 18%. The assemblage of >10 cm stony corals was primarily composed of small-sized colonies (mean diameter = 37 cm) of which the Montastraea annularis complex was the most abundant (30% of colonies). Overall, =1% of the individually surveyed colonies had been physically damaged by Hurricane Lenny but injury levels were higher in Saba (2.6%). Bleaching was noted in 23% of colonies at the time of the assessment with the greatest percentage occurring on St. Maarten (44%) and the lowest on Saba Bank (9%). Total (recent + old) partial mortality of reef-building corals averaged less than 18% although levels were higher (26%) in Colpophyllia natans. Coral recruitment densities were relatively consistent (mean = 5 recruits/m2) across sites. Commercially significant fish species (i.e. serranids, lutjanids, haemulids >5 cm) were present with mean densities of 4.5 individuals/100 m2. High biomass (mean = 5.8 kg/100 m2) of grazing, herbivorous fishes (acanthurids, scarids >5 cm, Microspathodon chrysurus) partially explains the relatively low macroalgal cover (mean = 7%) throughout this area. Saba’s fish community had a greater total biomass than those in the other three geographic areas (mean = 11 kg/100 m2 versus 7 kg/100 m2). While the coral reefs of St. Maarten show signs of disturbance (i.e., increased bleaching and sedimentation), those of Saba, Saba Bank, and southern St. Eustatius have been relatively little disturbed by coastal development and remain potential sources of marine life. Nevertheless, reef development in the windward Netherlands Antilles is limited by frequent hurricanes.