habitat

Survey of Reef Fish Communities of the Fringing reefs of Bonaire, Netherlands Antilles

The coral reefs of Bonaire have been reported to be one of the most pristine reefs, with the reefs on the leeward coast of Bonaire regarded as one of the healthiest reefs of the Caribbean (NOAA 2008; Sommer et al. 2011; Jackson et al. 2014). Nonetheless, Bonaire is a growing popular tourist destination and the reefs have been increasingly exposed to anthropogenic stress in addition to natural disturbances. The overarching question of this project addressed the large and small-scale variation in benthic and fish communities of the reefs on the leeward side of Bonaire. However, this report focuses on describing the fish communities of these reefs, and looks into the effect of benthic community composition on fish community assemblages. Our fieldwork set-up allowed us to look into large scale differences (between zones), and small-scale differences (between sites, within zones). Additionally, since fish observations were done on the same transect as benthic measurements, with this set-up, we were also able to look into the effects of benthic composition on fish community composition. To visualize trends in species biomass composition we did a cluster analysis and plotted the clusters in a non-metric multidimensional scaling (nMDS). To see which benthic categories had an effect on fish composition, we plotted an environmental fit (Envfit at P < 0.05) with benthic categories. Also, to check the effect of site location, the clusters are plotted on a Bonaire map. We report clear differences in fish species richness, diversity and biomass between the two zones, with the deeper zone showing greater numbers. There was greater variation in both fish and benthic communities in the lower-terrace (the shallower zone), and this variation reflected the degradation gradient along the leeward coast of Bonaire. Sites located around the busy tourist center showed a trend towards lower fish biomass and richness, lower coral cover and diversity, and lower topographic complexity. Whereas sites in the same zone (same depth) located within the marine park, a protected area, scored highest in the same categories. The drop-off, a deeper zone, showed far less variation in all categories. From these results it can be concluded that effects of habitat degradation on benthic communities reflect on fish communities, especially in shallower zones. Our results also demonstrate that protected areas have a positive effect on benthic and fish communities, reiterating the importance of these areas. The inclusion of Bonaire fishery data would provide an interesting insight and would clarify even more the variation found across sites.

Date
2016
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire
Author

Habitat Surveys of Saba Bank, Netherlands Antilles: An Assessment of Benthic Communities and Fish Assemblages

Saba Bank is a large and completely submerged carbonate platform in the northeastern Caribbean Sea located approximately 4 km southwest of Saba Island, Netherlands Antilles. Zonation patterns of reef-like bathymetric features, together with observations of significant shelf edge coral reef development, suggest that Saba Bank is an actively growing coral reef atoll. Little quantitative data exists to evaluate the composition and distribution of marine benthic communities or fish assemblages of Saba Bank. In the present study, habitat surveys were conducted to investigate the abiotic characteristics, benthic community composition, and fish assemblage structure of habitats from an eastern portion of Saba Bank known as Overall Bank. A random stratified sampling design was developed that utilized remote sensing data for bathymetry and ocean color superimposed on reef zones. Five sampling strata, which putatively delineated five distinct marine habitat types, were identified along a shelf edge-to-lagoon gradient. Survey results indicate that the proposed strata correspond to distinct marine habitat types in terms of substrate composition, benthic cover, and dominant macro algae. Significant coral cover was restricted to the outer reef edge in the fore reef habitat (11.5 %) and outer reef flat (2.4 %), declining to near absence in the lagoon habitats towards the bank center. Macro algae dominated benthic cover in all habitats (32.5 – 48.1 % cover) with the composition of dominant algal genera differing among habitats. Gorgonians reached their highest density and greatest average colony height in the fore reef zone. Gorgonian colony height was also pronounced in softbottom habitats of the lagoon. Fish assemblage structure showed patterns that were concurrent with observed habitat zonation. Highest fish densities were observed in the outer reef flat, fore reef, and inner reef flat zones. Fish abundance and diversity was low in the lagoon zone and lowest over softbottom habitats within the lagoon. The greatest diversity of fishes (average number of species per survey, cumulative number of species) occurred in the fore reef zone and outer reef flat zone. Fish biomass followed the same pattern of distribution, with the greatest weight occurring in the outermost zones and least in the lagoon. Queen conch were most frequently encountered in the softbottom lagoon zone and estimates of average conch density were between 42 and 60 individuals per hectare. Abundance of spiny lobster was not adequately surveyed by the methods employed in this study and recommendations are made for improved field assessment of lobster stocks. Collectively, the results of this study indicate that the benthic communities of Saba Bank follow predictable patterns of distribution, diversity, and abundance across a gradient from shelf edge to lagoon. Recommendations for future research are given. 

Date
2008
Data type
Research report
Theme
Research and monitoring
Report number
Saba Bank Project 2007, Report 1
Geographic location
Saba bank
Author
Image
Bathymetric map of Saba Bank with study area

A landscape ecological vegetation map of Saba (Lesser Antilles)

A semi-detailed landscape-based vegetation map (scale: 1: 37,500) is presented for the 13 km2 Lesser Antillean steep volcanic island of Saba, Netherlands Caribbean. The map is based on a total of 49 vegetation plots that were sampled in 1999 using a stratified random sampling design and analysed using TWINSPAN cluster analysis. Three hundred and fourteen (314) plant species, representing 56% of the total known flora (565 species), were recorded in the sample plots. The principal lower sections of the island possess a tropical savannah climate whereas the upper slopes reaching a maximum altitude of 870 m can best be characterized as a tropical rainforest climate.
A total of two main and nine different sub-landscape types were distinguished based on geology, geomorphology and nine distinguished vegetation types. In Saba, sharp contrasts in soil, geomorphology and climatic factors are found on a small spatial scale and this meant that compared to the other islands of the Dutch Caribbean there is little mixing and merging of vegetation types at the landscape vegetation level. Consequently, vegetation type translates relatively directly into landscape vegetation units. Aside from important contrasts in vegetation that correspond to what is known about differences in soil and climate, our study also shows that large vegetation changes have taken place on the island since the survey by STOFFERS, five decades earlier. These largely appear to be due to three major forces: a) hurricane impacts; b) natural succession made possible due to diminished agricultural activity and; c) invasive plants and plant pest species.
The most recent hurricane, hurricane Georges, which struck the island one year before this study, clearly caused much damage to the vegetation, especially high on Mount Scenery. As a consequence, the elfin woodland vegetation has virtually disappeared, while remnant sections have been radically altered. Based on studies elsewhere in the region, the elfin woodland can be expected to take very long (if at all) to gradually recover. The impact of various hurricanes in the last 60 years has clearly caused major disturbance of the vegetation throwing it back into earlier stages of succession. The development of the “Tree fern brake” into “Pioneer forest” vegetation must be seen as a positive change where a secondary community had entered a higher stage in the sequence of succession. The virtual disappearance of the formerly prominent secondary shrub communities like Miconia thickets, Piper dilatatum thickets and Leucaena thickets can also be seen as likely evidence of natural successional forces thanks to diminished agriculture and woodcutting. Invasive species was the third major force of change that clearly appears to have been active on Saba in recent decades. The lasting impacts of insect invaders which have decimated formerly prominent Opuntia (cactus) and Tabebuia (tree) populations testify to the impact of invasive species as a major driver of recent vegetation changes on Saba.
Our field data show that most wilderness areas of Saba remain strongly affected by roaming grazing goats even though the contribution of goats to the local island economy is negligible. Goat dung or traces of grazing were recorded in or adjacent to 46% of the sample plots. Grazing by exotic mammals reduces the resilience of natural vegetation types and interferes with natural succession. Highest livestock densities and impacts seem to be in the more vulnerable coastal arid zones along the western and southern sections of the island with poor soil conditions and more open and shrubby vegetation. The development of ‘Dry evergreen woodland’ under similar conditions on the more remote, windy and salt spray-affected, but less-grazed, northern sectors of the island, suggest that those disturbed areas of the southern and western coastal zones should have potential for woodland recovery if and when goat grazing is reduced. Therefore, a key priority for terrestrial conservation in Saba should be to reduce feral grazer densities to allow vegetation recovery and reduce vulnerability to erosion. We suggest the use of pilot demonstration projects for grazer exclusion as a useful way to help build stronger arguments and public support for tackling the roaming goat problem in Saba.

Date
2016
Data type
Research report
Theme
Research and monitoring
Report number
C195/15
Geographic location
Saba

Categories of habitat and depth are structuring reef fish assemblages over no-fishing and fishing zones in the Saba Marine Park (Caribbean Netherlands)

Reef fish assemblages are structured by many factors like depth, habitat and zonation’s in marine protected areas (MPAs). These fish assemblages can be determined by different sampling methods and design. For instance, stereo Baited Remote Underwater Video (stereo-BRUV) allows for monitoring fishes at various depths (>40m) beyond the reach of conventianol diver-based methodologies. This is relevant in a way that fish diversity, biomass and species richness changes with depth. Furthermore, the spatial distribution and composition in fish assemblages can have a strong correlation with fine-scale habitat differences. However, fine-scale measurerements of habitats are rarely available for marine research, particularly for deeper (>40m) marine environments. Stereo-BRUV studies lacking this information prior of sampling reef fish assemblages had to rely upon hierarchical classifications of habitat. One of the aims of this study was to examine which habitat classification was most sensitive to the detection of small-scale changes in fish assemblages by sampling different habitats and depths (e.g, 15, 50 and 100 meters) in the Saba Marine Park (SMP) area. We compared three categorization methods of habitat commonly used in literature 1) two scale on “habitat”; low (sand) and high (reef) relief (Colton et al. 2010); 2) three scale on “relief”; low, medium and high relief (Watson et al. 2005) and 3) fine-scale consisting of 6 types of “habitat complexity” (Polunin et al. 1993). The “habitat complexity” category method produced less variance among fish populations’ mean within each habitat. This increased the probability of finding a significant difference between two fish populations’ mean, as smaller variations lowered the possibility of overlapping standard deviations. For this reason we found a significant interaction effect of zonations (fishing vs. no-fishing zone) within the habitat complexity category on fish biomass, density and species richness, in all depths within the SMP boundary (15 and 50m). This effect was not found when using the habitat or relief category. However, the differences among the habitat category methods were less significant on the statistical power of detecting those changes in fish biomass, density and species richness. Overall, habitat characteristics, such as sand bottom or low complexity in substrate structure, were associated with lower values of fish biomass, density and species richness. These values increased gradually with habitats containing more complex, reef-based structures. From the shallow (15m) to deeper (50 and 100m) areas the habitat complexity in terms of reef structures significantly declined. Along this depth gradient, the structure of reef fish assemblages changed from higher densities of herbivorous species at 15 meter depth and higher carnivorous species richness and densities found at 50 and 100 meters depth. Some species (within families of Lutjanidae and Serranidae), also important to fisheries, were distributed over the full depth range. Moreover, stereo-BRUV detected high densities of larger predatory species (Carcharhinus perezii, Ginglymostoma cirratum), especially at depths of 50 meters. The changes found in fish assemblages were less determined by the effect of the no-fishing zone. On the contrary, the mean fish biomass and density were higher in the zone without protection from fisheries, indicating that fishing pressure was low in the SMP. In conclusion, depth and finer-scale habitat complexity were the main drivers that structure reef fish assemblages. These results indicate that the chosen categories of habitat and depth have a significant effect on studying reef fish assemblages across different zones in the SMP.

Date
2014
Data type
Other resources
Theme
Research and monitoring
Geographic location
Saba

The analysis of ecological networks: habitat connectivity and population viability on St.Eustatius

This student thesis research is in support of a Tourism Master Plan for Sint Eustatius; this plan is focused on the development of sustainable tourism on St. Eustatius. St. Eustatius is part of the Lesser Antilles and belongs to the Dutch Caribbean islands. The aim of this project was to analyse the connectivity of St. Eustatius’ habitats and the viability of St. Eustatius’ wildlife populations for the current situation and a hypothesized future situation. Increased tourism and other developments could lead to an increase in urban areas and infrastructure. As these developments can be at the expense of nature areas it is of importance that these threats for nature are minimized. Human activities influence biodiversity, where in the past the ranges of species were reduced and several species went extinct. Human activities could lead to a decrease and a further fragmentation and degradation of the remaining nature areas (Moorcroft, 2009). Loss, fragmentation and degradation of habitat are considered as the main threats to biodiversity (Dennis et al., 2013). Small and isolated populations are extra vulnerable for inbreeding depression and the loss of genetic variation, so it reduces the reproductive fitness and the ability to adapt to environmental changes (Simberloff et al., 1992; Traill et al., 2010). Landscape connectivity is described as the ability of a landscape to enable exchange of organisms, material and energy between different areas and is dependent on the structural connectedness of a landscape and the movement characteristics of the considered species or processes (Wu, 2009). Species may utilize specific corridors for their movements. The main purpose of corridors is to enable individuals from various species to migrate to other areas. Migration diminishes isolation and results in a metapopulation structure (Beier, 1992). Species-specific characteristics and landscape connectivity determine whether or not a metapopulation will sustain in an ecological network consisting of physically separated habitat patches. In this report the model LARCH (Landscape ecological Analysis and Rules for Configuration of Habitat) was used to test landscape connectivity and population viability on Sint Eustatius. St. Eustatius covers approximately 21 km2. The southern part of the island consists of a volcano, the Quill National Park; this park hosts several different ecosystems with some endangered species. The northern part of the island is also a National Park area covering four volcano hills, also with some endangered species. The northern and southern parts of the island are separated from each other by the urban centre part of the island. The centre part of the island is divided into different suburbs, mainly consisting of residential and small-scale industrial areas. These areas are located from the northeastern coastline towards the south-western coastline. Fieldwork on St. Eustatius was done between the end of July and the beginning of September 2015 to prepare a habitat map and a barrier map of the island, and to gather information about the island species and about the island policies and possible future changes. All this information was required for the LARCH model: two models were used: LARCH-Scan for the connectivity of habitats and LARCH-Classic for the viability of populations. Six species were modelled for the current situation: the Green-throated carib (Eulampis holosericeus), the Lesser Antillean green iguana (Iguana delicatissima), 4 the Red bellied racer (Alsophis rufiventris), the Caribbean hermit crab (Coenobita clypeatus), the Cloudless sulphur (Phoebis sennae) and the Caribbean duskywing (Ephyriades arcas) representing St. Eustatius’ biodiversity. The Lesser Antillean green iguana and Red bellied racer were modelled for the proposed future scenario. It can be concluded that the two National Parks contain the most suitable habitats for all studied species. The connecting corridor for the studied species is limited to a narrow vegetated strip near the south of the airport and through the residential areas. Besides these residential areas and the airstrip also the NuStar oil terminal, waste heaps and overgrazed grasslands reduce the habitat connectivity. All studied populations form one viable network, except for the Caribbean hermit crab. Four proposed future plans were incorporated in a scenario along with more intense barriers.  Local populations and population viability will decrease with the new proposed plans. Residential development in the Lodi suburb and industrial development in “the Farm” area would reduce the connectivity between the northern and southern National Parks. Based on these modelling results recommendations have been proposed. There are several areas that need special consideration if future developments are proposed in those areas. These are the two National Parks, the remaining corridor area and areas near the coastline. Modelling results show that urban developments in these areas decrease connectivity, isolate local populations and affect population viability. Also development plans in other areas need to be considered carefully regarding its size and location and its impact on the landscape connectivity and animal population viability. In the event of unavoidable negative impact, measures should be considered to compensate for the losses, such as the establishment of culverts or the restoration of areas. Study results show that ground dwelling animals are most affected by the presence of roads, fences and unsuitable habitats, it is therefore recommended that future developments of potential barriers are minimized, with mitigating measures such as open fences or culverts under roads. It is also highly recommended to preserve the remaining habitats of the two species that were modelled and that are considered endangered by the IUCN Red list; the Lesser Antillean green iguana and the Red bellied racer. And it might be worth it to consider the restoration of suitable habitats, enlarging the ecological carrying capacity, to protect these endangered species. At last there are recommendation for a second corridor near the northern coastline of the island that should increase connectivity. This recommendation involves alterations regarding the waste management and the exile of roaming cattle

Date
2016
Data type
Other resources
Theme
Research and monitoring
Geographic location
St. Eustatius
Author

Fish assemblages on the Saba bank (Dutch Caribbean): the effect of habitat, depth and fisheries

Many environmental variables may influence fish assemblage structures in terms of abundance, biomass and mean size. The aim of this study is to provide a baseline survey on reef fish assemblages and shark presence covering the whole Saba bank (Dutch Caribbean). Hereby determining the influence of habitat, depth and fishing pressure on the structure of reef fish assemblages and shark presence. Baited Remote Underwater Video (BRUV) survey was used to describe reef fish assemblage structures on the Saba bank. Between 2012-2014, a total of 165 60 min BRUV deployments were conducted on locations varying in habitat complexity (0-4, Polunin and Roberts, 1993), depth (15-40m) and fisheries. The eleven most abundant fish species observed on the Saba bank represented eight families and accounted for nearly 50% of the total number of individual fish observed. Labridae was the most abundant fish family observed with a relative abundance of 22%. Most abundant fish species by number of individuals were Thalassoma bifasciatum (N=849 (9.8%)) Stegastus partitus (N=725 (8.4%)) and Acanthurus bahianus (N=430 (5.0%)).

Habitat complexity was positively correlated with species richness (Nsp), fish abundance (MaxN), and mean biomass, and negatively correlated with mean fish length. Strongly developed vertical relief habitats were found to support high numbers of fish species (N=19.1±0.6SE) of relatively low mean lengths (22.4cm±0.3SE), whereas less complex habitats were characterized by low numbers of species (N=8.3±0.8SE) with relatively high mean lengths (24.6cm ±0.81SE). Depth was negatively correlated with Nsp, MaxN and mean biomass and positively correlated with mean fish length. These relationships were all according to expectations based on earlier studies.

A minor part of the variability in the structure of reef fish assemblages was explained by differences in fisheries activity, indicating that no clear fisheries effect was observed in fish assemblages in this study. Furthermore, no significant differences in average size of target species were observed between areas with different fishing pressure. However, the general absence of piscivores such as large snappers and groupers was an indication of the indelible effects of past fisheries on the Saba bank.

A total of 85 shark observations were made with Ginglymostoma cirratum as most abundant species (N=41), followed by Carcharhinus perezii (N=36), Galeocerdo cuvier (N=5) and Carcharhinus limbatus (N=3). Relatively high shark abundances (0.20 sharks hour-1) were observed on the Saba bank compared with other Caribbean regions (The Bahamas: 0.14 sharks hour-1, Belize, 0.17 sharks hour-1). Shark abundance (CPUE) was positively correlated with habitat complexity, whereas depth exerted a negative influence on shark abundances. High shark numbers are a good sign for the health of the Saba Bank ecosystem, since sharks are apex predators, making them a prime indicator for ecosystem health.

Besides ‘traditional’ measures, ecomorphology was presented as an alternative measure in explaining variation in reef fish assemblages. For ecomorphological analysis insight in trophic morphology was obtained by using a Fish Food Model (FFM). The FFM in this study quantitatively related properties of 14 marine food types to morphological characterics of 15 common fish species on the Saba bank and predicted the capacity of utilizing these food types for each species. Strong differences in morphology and little overlap was observed for all different fish species in the FFM-analysis, which was mainly explained by two sets of variables involving predatory and herbivorous lifestyle. By multiplying each species’ capacity of using food types with its abundance an ecomorphological profile of each fish assemblage was calculated. On a functional level reef fish assemblages showed less variability than on species composition level, this possibly is an indication for high levels of robustness in niche differentiation in reef fish communities on the Saba bank.

Date
2014
Data type
Research report
Theme
Research and monitoring
Report number
T 1940 THESIS
Geographic location
Saba bank
Author