Saba Bank

Background:

Located in the Dutch Windward Islands, Saba Bank is a flat-topped seamount (20–45 m deep in the shallower regions). The primary goals of the survey were to improve knowledge of biodiversity for one of the world’s most significant, but little-known, seamounts and to increase basic data and analyses to promote the development of an improved management plan.

Methodology/Principal Findings:

Our team of three divers used scuba to collect algal samples to depths of 50 m at 17 dive sites. Over 360 macrophyte specimens (12 putative new species) were collected, more than 1,000 photographs were taken in truly exceptional habitats, and three astonishing new seaweed community types were discovered. These included: (1) ‘‘Field of Greens’’ (N 17u30.6209, W 63u27.7079) dominated by green seaweeds as well as some filamentous reds, (2) ‘‘Brown Town’’ (N 17u28.0279, W 63u14.9449) dominated by large brown algae, and (3) ‘‘Seaweed City’’ (N 17u26.4859, W 63u16.8509) with a diversity of spectacular fleshy red algae.

Conclusions/Significance:

Dives to 30 m in the more two-dimensional interior habitats revealed particularly robust specimens of algae typical of shallower seagrass beds, but here in the total absence of any seagrasses (seagrasses generally do not grow below 20 m). Our preliminary estimate of the number of total seaweed species on Saba Bank ranges from a minimum of 150 to 200. Few filamentous and thin sheet forms indicative of stressed or physically disturbed environments were observed. A more precise number still awaits further microscopic and molecular examinations in the laboratory. The expedition, while intensive, has only scratched the surface of this unique submerged seamount/atoll. 

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.

Abstract:

Biodiversity surveys were conducted on Saba Bank, Netherlands Antilles, to assess ichthyofaunal richness and to compare with published surveys of other Caribbean localities. The primary objective was to estimate the total species richness of the Saba Bank ichthyofauna. A variety of sampling techniques was utilized to survey the fish species of both the visually accessible megafauna and the camouflaged and small-sized species comprising the cryptic ichthyofauna. Based on results presented herein, the number of species known on Saba Bank is increased from 42 previously known species to 270 species. Expected species-accumulation curves demonstrate that the current estimate of species richness of fishes for Saba Bank under represents the actual richness, and our knowledge of the ichthyofauna has not plateaued. The total expected fish species richness may be somewhere between 320 and 411 species. The Saba Bank ichthyofaunal assemblage is compared to fish assemblages found elsewhere in the Caribbean. Despite the absence of shallow or emergent shore habitats like mangroves, Saba Bank ranks as having the eighth highest ichthyofaunal richness of surveyed localities in the Greater Caribbean. Some degree of habitat heterogeneity was evident. Fore-reef, patch-reef, and lagoonal habitats were sampled. Fish assemblages were significantly different between habitats. Species richness was highest on the fore reef, but 11 species were found only at lagoonal sites. A comprehensive, annotated list of the fishes currently known to occur on Saba Bank, Netherland Antilles, is provided and color photographs of freshly collected specimens are presented for 165 of the listed species of Saba Bank fishes to facilitate identification and taxonomic comparison with similar taxa at other localities. Coloration of some species is shown for the first time. Preliminary analysis indicates that at least six undescribed new species were collected during the survey and these are indicated in the annotated list. 

Findings:

The main conclusion from this study is that the health of the reefs of the Saba Bank has deteriorated since the first observations in 1972, 1996, and 2002. The general impression is that the Bank is still recovering from the 2005 bleaching disaster, but there is not enough data to exclude other reasons (e.g. overfishing, anchor damage, hurricanes).

• In 1996, Meesters et al. estimated coral cover at 7 locations to lie between 60 and 90%. These percentages were nowhere observed this time. The best site visited had an estimated coral cover of around 50%.
• There is now a high cover of algae (mainly Dictyota spp. and Lobophora spp.) on the reefs of the Bank.
• The present absence of important grazers such as the black sea urchin are likely to slow down recovery.
• Fish numbers appeared to be lower than previously observed, though sharks were observed on almost every dive, indicating a still intact food chain. The low numbers of fish may be a seasonal effect, a result of the presence of predators, or a result of changes that followed from the 2005 bleaching event.

However, corals appear healthy and the reefs of the Saba Bank are probably slowly recovering to their previous grandeur.

• Very few coral colonies with diseases were observed.
• Some colonies were bleached as result of the seasonal high water temperatures, but there appeared to be almost no mortality among these bleached colonies. 

Management Recommendations:

Begin to regularly monitor the health of the Bank’s coral reefs and the impact of human activities such as fishing as soon as possible (permanent video transects are planned to be installed in 2011 at a number of sites on the Bank).

Botanical and zoological collections may serve as archives for historical ecologi- cal research on the effects of global change and human impact on coral reef biota. Museum collections may harbour old specimens of reef-dwelling species that have become locally extinct. Such collections also help to determine whether early records of invasive species can be obtained from times when they were not yet recognized as such. A case study (2006) involving Saba Bank, Caribbean Netherlands (former Netherlands Antilles), suggests that the coral reef fauna here may have become impoverished when compared with data obtained during an earlier expedition in 1972. However, the 1972 sampling may have been incomplete, as it was performed by professional divers who were not trained taxonomists, whereas the collecting in 2006 was done by expe- rienced marine biologists who knew the taxa they were sampling. As Saba Bank has been under stress due to the anchoring of large vessels, and invasive species have been a potential threat as well, future studies are needed to obtain more insights into the changing reef biota of Saba Bank. Using this Saba Bank exam- ple, we want to address the importance of natural history collections as reser- voirs of valuable data relevant to coral reef biodiversity studies in a time of global change. As such, these collections are still underexplored and underexploited. 

Saba Bank is a 2,200 km2 submerged carbonate platform in the northeastern Caribbean Sea off Saba Island, Netherlands Antilles. The presence of reef-like geomorphic features and significant shelf edge coral development on Saba Bank have led to the conclusion that it is an actively growing, though wholly submerged, coral reef atoll. However, little information exists on the composition of benthic communities or associated reef fish assemblages of Saba Bank. We selected a 40 km2 area of the bank for an exploratory study. Habitat and reef fish assemblages were investigated in five shallow-water benthic habitat types that form a gradient from Saba Bank shelf edge to lagoon. Significant coral cover was restricted to fore reef habitat (average cover 11.5%) and outer reef flat habitat (2.4%) and declined to near zero in habitats of the central lagoon zone. Macroalgae dominated benthic cover in all habitats (average cover: 32.5 – 48.1%) but dominant algal genera differed among habitats. A total of 97 fish species were recorded. The composition of Saba Bank fish assemblages differed among habitat types. Highest fish density and diversity occurred in the outer reef flat, fore reef and inner reef flat habitats. Biomass estimates for commercially valued species in the reef zone (fore reef and reef flat habitats) ranged between 52 and 83 g/m2 . The composition of Saba Bank fish assemblages reflects the absence of important nursery habitats, as well as the effects of past fishing. The relatively high abundance of large predatory fish (i.e. groupers and sharks), which is generally considered an indicator of good ecosystem health for tropical reef systems, shows that an intact trophic network is still present on Saba Bank

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.

Findings

The main conclusion from this study is that the Saba Bank has little modern material/ sediment deposited in relation to present sea level. This contradicts with previous beliefs such as Spencer’s claim that the bank surface “has been leveled by coral growth and sands derived from them”.

The study found the following:

• Minimal reef development.
  • Limited data from the survey revealed a sparse coral cover but   abundant crustose coralline algae and sponges.
  • The Saba community showed no sign of forming an interlocking reef framework.
• Sediments rich in residual material derived from late Cenozoic limestone bedrock.
• Most samples from this area had relatively large quantities of calcite, which suggests erosion of bedrock on Saba Bank.
• The internal structure of Saba Bank remains unknown; the surveys lacked sufficient sub-bottom penetration to disclose information about internal structure.

Abstract:

According to previous studies and anecdotal evidence there are a lot of lost lobster traps at the Saba Bank. One study estimated the loss to be between 210 and 795 lobster traps per year. The Saba Bank is an approximately 2,200 km2 submerged area and spiny lobster (Panulirus argus) is one of the main fisheries with an annual economic value over USD 1 million.

The traps get lost due to a combination of bad weather moving or damaging traps and marker buoy lines, ship traffic running into and cutting marker buoy lines and removal of marker buoy or theft of traps by vandals. Lost traps are a concern for the Saba Bank fisheries management, because of the potential impact of ghost fishing by lost traps and the damage to the benthic environment.

IMARES was commissioned by the Ministry of Economic Affairs, Agriculture and Innovation to advise on a method to detect lost lobster traps. The objective of this desk study was to provide information for the sustainable management of the lobster fisheries and the conservation of the Saba Bank.

In this report we investigate the most efficient method for the detection of lost lobster traps from a small vessel in water between 15 and 50 meter depth. We not only address methods for the location of traps, but also recommend methods for the retrieval of traps and measurement of ghost fishing.

Findings:

The main conclusion from this study is that side scan sonar in combination with a magnetometer is the best and most efficient method to locate and retrieve lost lobster traps.

Side scan sonar is recommended for two reasons:

• The resolution of the images can be small enough to detect 1m2 traps, while the swath width and vessel speed are high enough to cover a reasonable area in an 8-hour survey day.
• In general, the survey environment at the Saba Bank is suitable for side scan sonar, as most lobster traps are located on flat surfaces with substrate composed of hard bottom pavement, rubble or sediment.

A magnetometer is recommended in combination with a side scan sonar because acoustic shadowing can occur for lobster traps located at the edge of the lobster fishing grounds. A magnetometer will detect (partial) buried, damaged or overgrown traps that have lost their distinct rectangular shape necessary to accurately identify traps from the side scan images.

The three suggested methods for retrieval are:

• Autonomous Underwater Vehicle (AUV)
• Remotely Operated Vehicle (ROV)
• Drop Camera

Management Recommendations:

Since it is not reasonable to survey the entire potential lobster fishing grounds of 1.850 km2, a pilot is recommended. The pilot can be accompanied by a cost benefit analysis to advise decision makers if the costs per trap retrieved do not exceed the benefits.

It is recommended to introduce a reporting and registration system on gear loss to collect more comprehensive data on gear lost, date, coordinates, depth (unless this can be easily retrieved from coordinates data) and reason for loss. This can be incorporated in an existing fisheries landings registration system. Data on gear loss not only provide useful information for curative measures such as trap detection. It also provides information for preventive measures, as a detailed understanding of why gear is lost is needed to take effective preventive measures. They can be split in measures to prevent loss and measures to prevent ghost fishing. One measure to prevent ghost fishing is already in place, which is the use of biodegradable escape panels in the lobster traps. However, this regulation of 1992 has not been implemented properly due to lack of enforcement and compliance

Abstract:

This report contains a study regarding the biodiversity of the Saba Bank, one of the three largest atolls in the world. All scientific and anecdotic evidence suggests that the area is a hot spot of biodiversity and one of the few areas in the Caribbean that is still in a relatively pristine condition. The atoll is likely also important as a source of larvae for other areas in the region because of its enormous dimensions and diverse habitats. Major damage however may already be inflicted by the anchoring of large oil tankers. More scientific research is necessary with regards to the damage inflicted by anchoring and to the sustainability of current fishing practices, but to date there is already sufficient data to call for strong protection of the Saba Bank as soon as possible.
Therefore, an application to the International Maritime Organization (IMO) to designate the Saba Bank as a Particularly Sensitive Sea Area (PSSA) in order to prevent possibly irreversible damage to the ecosystem and to enable sustainable protection of it’s vulnerable resources seems crucial and urgent.

This research is performed within ‘Beleidsondersteunend Onderzoek’ (BO-11), cluster NLP of LNV-programs.

Findings:

The main conclusion from this study is that the Saba Bank is a hot spot of biodiversity and one of the few
areas in the Caribbean that is still in a relatively pristine condition. The Bank is likely also important as a source of
larvae for other areas in the region because of its enormous dimensions and diverse habitats.

• Scientific evidence that the Saba Bank constitutes a major hot spot in marine biodiversity in the Caribbean region has strongly increased over the last couple of years and is now overwhelming.
• All studies to date express surprise and wonder at the number of different habitats and species within the Saba Bank.
• With limited sampling effort new species have already been found within the Bank and more are to be expected.
• The Bank is likely be one of the very few places in the Caribbean that as yet has largely escaped human related pressures and may still be considered as being in a relatively pristine condition.

There is to date already sufficient data to call for strong protection of the Saba Bank as soon as possible. Designating the Saba Bank as a
Particularly Sensitive Sea Area (PSSA) in order to prevent possibly irreversible damage to the ecosystem and to
enable sustainable protection of its vulnerable resources seems crucial and urgent.

Management Recommendations:

• Study the effects of fishing to ensure that it remains at a sustainable level.
• Draft and implement a management plan as soon as possible. At present anchoring outside the 12 miles zone is not regulated and anchor damage could be devastating to the whole ecosystem.
• Carry out more research about the ecological processes of the Saba Bank so as to protect it in the most effective way.