Sediment

From the abyssal plain to the intertidal zone, benthic fauna are adapted to a variety of extreme physical environments. Shallow water soft-sediment infauna must face rapid environmental changes that could result in fluctuations of oxygen levels, salinity, temperature, or water availability. In the case of closed systems where rainfall is the only significant source of water input, some infauna must adapt to desiccation and high levels of salinity. The result of this dynamic environment is an infaunal community demonstrating an evolutionary path of morphological and behavioral adaptations to periods of environmental stressors. The infaunal community structure of a hypersaline inland lake along a sediment moisture gradient was examined in Saliña Matijs, Bonaire, Netherlands Antilles. Saliña Matijs is a very shallow hypersaline lake comprised of soft, anoxic muddy sediment with a heavy algal layer consistently exposed to high heat intensity. The weather pattern on Bonaire results in high rainfall for short periods of time, followed by prolonged sun exposure. This results in a very dynamic environment where the lake becomes quickly expanded and irregularly saturates the drier sediments. Twelve infaunal core samples and four sediment samples (7.5 cm diameter, 5 cm depth) were collected at four locations with decreasing sediment moisture (20 m to -15 m from the water line). There were gastropod juveniles and adults at all locations, with higher numbers of juveniles in cores with lowest moisture content. The presence of fish scales in every core suggested the presence of a population of small fish. Cluster analysis results show the highest community similarity between the second driest core and the core taken 15 m into the lake.

This student research was retrieved from Physis: Journal of Marine Science I (Fall 2006)19: 13-20 from CIEE Bonaire.

Most hard corals require seawater with low nutrients and sediment loads to thrive. Unfortunately, on a global scale, increases in both are currently occurring due to poor coastal zone management practices. This causes damage that is often fatal to reef building corals. Plants living in near shore areas provide natural filters for sediments and nutrients, and recently managers have been harnessing the filtering capabilities of plants to protect aquatic ecosystems. In the marine environment, mangroves provide protection by filtering sediments and absorbing nutrients from runoff before it reaches coral reefs. Ritterocereus griseus, a common cactus species on Bonaire, N.A., has similar capabilities in the terrestrial realm. The following hypotheses were tested regarding cactus fences in Bonaire: smaller amounts of phosphate and sediments would be transported, and lower amounts of runoff would be collected down-slope of plots with cactus fences than plots without cactus fences. Experimental plots with cactus fences were compared to control plots without cacti. To construct plots, steel guides were used to direct simulated rainfall across plots with and without cactus fences into a collection cup at the base of the set-up. This study determined that R. griseus reduces the volumes of runoff and the amount of sediment and nutrients transported down-slope. The use of cactus fences could increase the resilience on Bonaire’s reefs by decreasing sediment and nutrient inputs to near shore waters and are a sustainable resource on the small island.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 20-26 from CIEE Bonaire.

The small island of Bonaire has seen a dramatic increase in visitation due to diving tourism. The economy of Bonaire depends on this influx of visitors and therefore has had an increasing demand for the development of new housing, resorts, and commercial areas. This study examines how the increased human development affects sediment deposition and nutrient load in an area surrounding a combined marina and salina outlet in Bonaire. Sediment load, sediment compositions, and interstitial water quality (water found in the sediment) were analyzed to determine if sediment or nutrient load had an effect on the reef community in the area. The results of this study show no significant trend suggesting reef degradation north of the marina due to point source pollution from the salina outlet. The results, however, only apply to the limited 26 day sampling period. There is a possible seasonal link that could not be explored here without further year-round data collection. These results show that while sediment, nitrogen and phosphate are present in the marine environment north of the marina outlet, it cannot be specifically linked to the marina using data collected in this study. Interstitial water analysis showed no detectable refined oil. The methodology implemented here could be modified to collect additional data in future research.

This student research was retrieved from Physis: Journal of Marine Science XIII (Spring 2013)19: 17-22 from CIEE Bonaire.

The anthropogenic effect of terrestrial run-off on coral reef ecosystems is a topic of high concern to marine ecologists. In the Caribbean, coral cover is decreasing at an alarming rate, and phase shifts to an algae-dominated reef have been documented. Studies have shown a correlation between densely populated coastal communities and high levels of substances known to be detrimental to marine ecosystems. This study focuses on two contaminants common in waters affected by terrestrial run-off: fine sediment and UV reactive hydrocarbons. Fine sediment cannot be removed easily from the tissues of corals and can prevent corals from receiving enough light. UV reactive hydrocarbons can embed themselves in tissue membranes and cause oxidative damage upon exposure to UV light. The presence and effects of these contaminants were determined near a drain in Bonaire, Dutch Caribbean. The percent distribution of sediment grain sizes was determined at increasing distances from the drain. The results revealed that the percentage of fine sediment is highest close to the drain and decreases with increasing distance from it. The presence of UV reactive hydrocarbons was determined using bioassays of Artemia sp. The results of the bioassays suggest that run-off from the drain contains UV reactive hydrocarbons. The effect of these contaminants on the abundance of organisms in benthic communities was analyzed using endobenthos technique but results were inconclusive. This study determined the presence of fine sediment and UV reactive hydrocarbons due to a point source of terrestrial run-off.

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 79-88 from CIEE Bonaire.

Phototoxic polycyclic aromatic hydrocarbons (PAHs) have been welldocumented as major marine pollutants. While PAHs are known to have negative ecological effects, the spread of point-source PAHs into coral reefs is poorly understood. This study focuses on a potential source of marine PAH contamination from a drain into a coral reef in Bonaire, Dutch Caribbean. PAHs were believed to be detected outside of the drain between October and November 2013, providing incentive for continued monitoring of PAH presence. Insight from this investigation is important not only to the general understanding of point-source marine pollution pathways, but holds implications for drain management strategies. Water samples from sites of varying distances from the drain were analyzed for UV-reactive toxicity using two Artemia sp. bioassays. Results from the bioassays indicated that PAH presence was undetectable, and that there was no relationship between distance from the drain and UVreactive toxicity. It was concluded that sediment dispersion and marine organism bioaccumulation likely accounted for the apparent temporal discrepancy in PAH presence. Field observations displayed noticeable coral reef degradation, which was assumed to be largely caused by factors other than PAH pollution. Despite the lack of evidence for current PAH presence, observations of poor reef health outside of the drain suggest that further studies and management strategies be considered for the drain and cement trough.

This student research was retrieved from Physis: Journal of Marine Science XVI (Fall 2014)19: 66-73 from CIEE Bonaire.

Free-living marine nematodes are a functionally and morphologically diverse group of animals. They have important ecological functions, many of which are not currently well understood, and may be bioindicators of climate change and pollution. Nematode abundance is impacted by many factors; the focus of this paper is to study the effects of sediment composition on nematodes. Within a study site on the west side of the island of Bonaire in the Dutch Caribbean, three stations with different sediment compositions and mean grain sizes were selected. Endobenthos samples were taken at each station and abundance of nematodes was recorded and compared between the stations. Mean grain size was not found to have a correlation with the density of nematodes, non-nematode organisms, or total organisms across the study stations. The overall average density of nematodes found at the site (1.71 ± 0.32 nematodes per cm3 , ± SD) is lower than values found in comparable studies, which could be related to pollution or change in temperature affecting the endobenthic community in the study site. This data may have been insufficient to support the hypothesis due to having a small sample size and too narrow a range of mean grain size between the stations. Despite this, this paper provides the first published data on nematode communities in Bonaire, and is an important foundation for future study of the ecological functions of marine nematodes in this area.

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 1-8 from CIEE Bonaire.

Seagrasses comprise 78 species and are rarely invasive. But the seagrass Halophila stipulacea, firstly recorded in the Caribbean in the year 2002, has spread quickly throughout the region. Previous works have described this species as invasive in the Caribbean, forming dense mats that exclude native seagrass species. During a reconnaissance field survey of Caribbean seagrass meadows at the islands of Bonaire and Sint Maarten in 2013, we observed that this species was only extremely dense at 5 out of 10 studied meadows. Compared to areas with sparse growth of H. stipulacea, these dense meadows showed consistently higher nutrient concentrations, as indicated by higher leaf tissue N contents of the seagrass Thalassia testudinum (dense when C:N < 22.5) and sediments (dense when %N > 11.3). Thus, the potential invasiveness of this non-native seagrass most likely depends on the environmental conditions, especially the nutrient concentrations.

During the spring of 2006, hydrographic survey vessel HNLMS “Snellius” ran an extensive multibeam and sidescan survey of the Saba bank, a large submerged atoll located in the north-eastern Caribbean. The survey provided an excellent opportunity for a number of small-scale geoacoustic inversion experiments in a shallow water environment which attracts many divers for its unique tropical ecosystem and rich marine wildlife. The feasibility of a rapid deployment of ocean-acoustic sensors and equipment was demonstrated for the purpose of an environmental assessment of the area southwest of the small volcanic island of Saba. The environmental impact was kept to a minimum by exploiting the hydrographic ship as a sound source of opportunity that was moving along the survey lines and passing by a sparse vertical line array that was deployed from a rubber boat at anchor. Several low-frequency narrowband tones were identified for the inversion process that provided an accurate account of the experimental geometry in terms of moving source and receiving array positions, and detailed geoacoustic properties of the sea floor and sub-seafloor. 

This report gives an overview of the most prominent problems currently encountered at the Lac bay area. To change the currently negative situation at the Awa di Lodo area with dying mangrove and unfavorable conditions for fish, it is recommended to improve water circulation at the Awa di Lodo area. This will lead to a better water quality and especially to a lower salt concentration. Based on this analyses, recommendations are made for five specific management actions which individually or in combination could be part of a management plan for the ecological rehabilitation of Lac Bonaire.

Management actions are conducted both from the land and sea side, they are short or long term and they can be summarized as follows:

• To clear the upstream (north) section at the labado from sediments in order to restore its function as sediment trap.
• To clear the east and west side feeder channels from sediment and mangrove in order to improve water circulation in the Awa di Lodo area.
• To construct a new central feeder channel following an existing creek pattern to improve water circulation in the Awa di Lodo area. Whether or not this new feeder channel is going to be constructed, will depend on monitoring results of changes in salt concentration in the Awa di Lodo after the existing feeder channels have been cleaned.
• To start a discussion with livestock owners in the greater catchment area on how over-grazing by roaming livestock can be stopped while at the same time these owners can make a living from their business.
• To remove Rhizophora established propagules at the sea side in order to slow down mangrove occupation of the bay area.

Each operation can be separately budgeted and they can be phased in time.