benthic cover

Summary

Habitat mapping is crucial for understanding habitat connectivity and for spatial planning, environmental management, conservation, and targeted research, including long-term change monitoring. However, such information has been lacking for many Dutch Caribbean islands, especially regarding marine habitats. This study used 2144 georeferenced images from different surveys to develop habitat models predicting the distribution of habitat types within the Saba Bank National Park. The habitat models link environmental factors to species or habitat occurrence, enabling predictions in unsurveyed areas with known covariates. Machine learning techniques (Random Forests, Gradient Boosting, and weighted K Nearest Neighbor) were applied to interpret and predict ten habitat types over the Bank. Three models were created for each technique: 1) utilizing only geographic coordinates; 2) incorporating covariables such as depth, distance to the edge of the Bank, Topographic Position Index (TPI), and Terrain Ruggedness index (TRI); 3) a combination of the previous two models. All models performed well, accurately predicting habitat types between 67 and 74% of the georeferenced images. However, the most natural representation occurred with models combining geographic and covariate variables. Predicted habitats include coral reef, patch reef, gorgonian reef, sargassum fields, cyanobacteria-dominated fields, Lobophora fields, Neogoniolithon- Lyngbya habitat, other macroalgae fields, sand with a mix of species, and bare sand. Habitat distribution appears to be related to the main currents in the area and depth, with coral reefs occurring mainly along the southern and eastern edge of the Bank, with gorgonians and other soft corals dominating there the shallow areas. Macroalgae, including fields of Sargassum, dominate the back-reef area. Extensive sand plains dominate the center of the Bank, and along the north-western and northern edge of the Bank, between 40 and 60m depth Lobophora fields can occur. In the south-eastern back reef area a number of mounds built up by the coralline alga Neogoniolithon occur. The Luymes Bank, the northeastern part of the Saba Bank, was the only area that was not correctly predicted, indicating that additional field-based observations are needed to refine results in this area.
 

Abstract

A paramount challenge in coral reef ecology is to estimate the abundance and composition of the communities residing in such complex ecosystems. Traditional 2D projected surface cover estimates neglect the 3D structure of reefs and reef organisms, overlook communities residing in cryptic reef habitats (e.g., overhangs, cavities), and thus may fail to represent biomass estimates needed to assess trophic ecology and reef function. Here, we surveyed the 3D surface cover, biovolume, and biomass (i.e., ash-free dry weight) of all major benthic taxa on 12 coral reef stations on the island of Curaçao (Southern Caribbean) using structure-from-motion photogrammetry, coral point counts, in situ measurements, and elemental analysis. We then compared our 3D benthic community estimates to corresponding estimates of traditional 2D projected surface cover to explore the differences in benthic community composition using different metrics. Overall, 2D cover was dominated (52 ± 2%, mean ± SE) by non-calcifying phototrophs (macroalgae, turf algae, benthic cyanobacterial mats), but their contribution to total reef biomass was minor (3.2 ± 0.6%). In contrast, coral cover (32 ± 2%) more closely resembled coral biomass (27 ± 6%). The relative contribution of erect organisms, such as gorgonians and massive sponges, to 2D cover was twofold and 11-fold lower, respectively, than their contribution to reef biomass. Cryptic surface area (3.3 ± 0.2 m2 m−2planar reef) comprised half of the total reef substrate, rendering two thirds of coralline algae and almost all encrusting sponges (99.8%) undetected in traditional assessments. Yet, encrusting sponges dominated reef biomass (35 ± 18%). Based on our quantification of exposed and cryptic reef communities using different metrics, we suggest adjustments to current monitoring approaches and highlight ramifications for evaluating the ecological contributions of different taxa to overall reef function. To this end, our metric conversions can complement other benthic assessments to generate non-invasive estimates of the biovolume, biomass, and elemental composition (i.e., standing stocks of organic carbon and nitrogen) of Caribbean coral reef communities.

Abstract

Reef-building corals are ecosystem engineers that compete with other benthic organisms for space and resources. Corals harvest energy through their surface by photosynthesis and heterotrophic feeding, and they divert part of this energy to defend their outer colony perimeter against competitors. Here, we hypothesized that corals with a larger space-filling surface and smaller perimeters increase energy gain while reducing the exposure to competitors. This predicted an association between these two geometric properties of corals and the competitive outcome against other benthic organisms. To test the prediction, fifty coral colonies from the Caribbean island of Curaçao were rendered using digital 3D and 2D reconstructions. The surface areas, perimeters, box-counting dimensions (as a proxy of surface and perimeter space-filling), and other geometric properties were extracted and analyzed with respect to the percentage of the perimeter losing or winning against competitors based on the coral tissue apparent growth or damage. The increase in surface space-filling dimension was the only significant single indicator of coral winning outcomes, but the combination of surface space-filling dimension with perimeter length increased the statistical prediction of coral competition outcomes. Corals with larger surface space-filling dimensions (Ds > 2) and smaller perimeters displayed more winning outcomes, confirming the initial hypothesis. We propose that the space-filling property of coral surfaces complemented with other proxies of coral competitiveness, such as life history traits, will provide a more accurate quantitative characterization of coral competition outcomes on coral reefs. This framework also applies to other organisms or ecological systems that rely on complex surfaces to obtain energy for competition.

This study explores the competitive and allelopathic interactions of native sponges and the non-native ascidian, Trididemnum solidum, in the space-limited coral reef environments of Bonaire, NA. The study had two main goals: (1) to identify native sponge species and provide estimates of sponge and T. solidum percent cover, and (2) investigate the allelopathic and overgrowth responses of native sponges and T. solidum when they are engaged in spatial competition with each other. Belt transects and modified nearest-neighbor methods were used to quantify abundance, species diversity, and interactions between native sponges and T. solidum at the Karpata dive site on Bonaire. Overall, it was found that percent cover of sponges significantly increased with depth while percent cover of T. solidum varied among depths, reaching a maximum at 11 – 15 m. Twenty-two species of sponges were recorded with species composition and abundance varying among depths while diversity among depths was not significantly different (p = 0.880). It was found that percent cover of T. solidum had a significant effect on the number of contact interactions. A closer look at contact interactions revealed that T. solidum frequently (87.5 % - 100.0%) overgrew sponges and caused tissue necrosis but was itself never observed to be overgrown. Staged interactions between two abundant encrusting sponges (Ulosa ruetzleri and Halisarca sp.) and T. solidum showed that native sponge growth is impaired by the ascidian and that T. solidum uses allelopathy when expanding its colonies. As described by this study, the success of T. solidum in its expanded range may provide support for two additional hypotheses: the evolution of increased competitive ability hypothesis, which attributes the success of non-native species to their increased ability to overgrow native organisms, and the novel weapons hypothesis which explains that non-native species are successful because they harbor allelopathic chemicals that native organisms have not evolved defenses for.

This student research was retrieved from Physis: Journal of Marine Science V (Spring 2009)19: 2-9 from CIEE Bonaire.

Caribbean coral reef ecosystems are threatened by anthropogenic impacts such as pollution, overfishing, and habitat destruction. In an effort to alleviate these pressures and restore habitat, artificial reefs such as marina breakers, Reef Balls, and mooring blocks have been deployed and consequently colonized by marine species. Many studies have investigated the benthic and fish communities developing on these artificial structures as compared to adjacent natural structures. Results have shown that artificial reefs can successfully be colonized by benthic and pelagic communities but are not always comparable to the associated communities. The purpose of this study was to compare the composition of benthic habitat and the use of this habitat by fish between manmade mooring blocks functioning as artificial reefs and natural coral reefs of Bonaire. Quadrats were used to estimate and compare percent cover of benthic organisms on the top and west faces of mooring blocks versus the top and west faces of physically paired natural reef sites (n = 8). An 8 min visual census was conducted on each face of each site pairing to estimate fish abundance and diversity for those species interacting with the habitat. Results showed greater percent live benthic cover on the natural versus artificial reef. Benthic diversity was highest on the west face of the artificial reef when comparing the interaction of face and reef type, but did not differ significantly between reef types. Fish community diversity also did not differ between reef types. However, the composition of both benthic and reef fish community diversity differed greatly between the natural and artificial reefs. It was found that Montastrea annularis and sponges dominate the natural while the brain corals (Diploria labrinthiformis and Diploria strigosa) dominated the artificial reef. Bicolored damselfish (Stegastes partitus) and brown chromis (Chromis multilineata) were found in the highest densities on the natural reef, while sergeant major (Abudefduf saxatilis) and bluehead wrasse (Thalassoma bifasciatum) were found in the highest densities on the artificial reef. This study provides evidence that placement of artificial reefs does not cause a shift in overall benthic and reef fish community diversity on the natural reef, but may change the composition of this diversity.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 44-52 from CIEE Bonaire.

Damselfish have a considerable effect on benthic composition and have been described as a keystone species because of their role in the maintenance of coral and algal assemblages within their communities. By looking at the different densities of damselfish at varying depths and locations, this study aims to see the effects of damselfish densities on coral reef benthic composition and if the presence of damselfish is beneficial to coral reef benthos. The abundance of all damselfish was recorded within 30 x 2 m belt transects. Random photographs within the belts were taken and still images were analyzed using Coral Point Count software to determine total percent coral cover, total percent algal cover, and coral species richness. A total of 702 damselfishes over 4 species were observed. Thirteen species of coral were identified. Contrary to the predictions, a higher density of damselfish was not correlated to increased coral cover and coral species richness. There was significantly more algae than coral cover throughout the study, but such a trend fits with the theory of phase shifts of coral reefs from coral dominated to algae dominated reefs.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 29-34 from CIEE Bonaire.

The relationship that benthic organisms have on fish that live on the reef is well known. Some benthic organisms can be regarded as bio-indicators, acting as indicators of nutrient levels in an ecosystem. Benthic organisms are also an important food source for fish and other invertebrates. In this study, organisms from sediment cores at five different depths were analyzed. Meiofauna and macrofauna cores were collected at each depth and the organisms were identified to family level. This study provides information on where these organisms prefer to live, and if there are any depths that are more favorable or diverse. The abundance of species increased in macrofauna samples from depth 10 m to 20 m. This was after a decrease in density from 5 m, which had the highest density, to 10 m depths, which had the lowest density. This trend was also present in macrofauna species richness. The meiofauna samples also had the highest species richness and density of individuals at 5 m depth for species, but both variables decreased with increasing depths. The data shows an increase at the 5 m depth. With further testing we can better understand the relationship depth has on the diversity of the benthic zone in the southern Caribbean

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 9-14 from CIEE Bonaire.

Marine sponges provide an important link between the benthic and pelagic environments of coral reef ecosystems, yet there is relatively little known about them. Past studies have indicated that depth and size could be contributing factors in tube sponge filter feeding strategies. This study investigated the effects of depth and size on pumping rate and filtering efficiency of Aplysina lacunosa, a common Caribbean reef sponge. At two different depths, several parameters of the sponges were measured: tube length, wall thickness, tissue volume, pumping rate (using fluorescein dye), and filtering efficiency (percent reduction in turbidity between the ostia and osculum). Water samples collected from the water column had similar food availabilities between the two depths. There was a positive relationship between sponge size and pumping rate but not filtering efficiency. Additionally, no relationship was found between depth and sponge pumping rate and filtering efficiency, which is consistent with my finding that food availability did not differ across depths. The filter feeding strategy of A. lacunosa may be unique in the context of other benthic filter feeders in that its pumping rate but not filtering efficiency is affected by size and that neither pumping rate nor filtering efficiency are affected by depth. Further investigations are needed to learn more about the biology of A. lacunosa and its significance to Caribbean coral reefs.

This student research was retrieved from Physis: Journal of Marine Science XVIII (Fall 2015)19: 40-46 from CIEE Bonaire.

Bonaire’s reefs remain among the best in the Caribbean. However, our monitoring has revealed some potentially troubling trends that may require management action. In 2005, we reported to the Bonaire Marine National Park on the status of Bonaire’s coral reefs, and we suggested a strategy for monitoring trends among four key reef attributes we believe track the health and resilience of Bonaire’s reefs (Steneck and McClanahan 2005). Here we report the results of monitoring studies conducted 2003, 2005 and now 2007 at each site. Where appropriate, we drew from Bonaire’s first AGRRA assessment conducted in February 1999 (Kramer and Bischof 2003) to extend temporal trends over a period of eight years. 
Troubling trends
We see three troubling trends of increased macroalgae, declining herbivory from parrotfish, and increases in damselfish populations. Of these, the first two are most serious (see Chapters 1, 2 and 3). Secondary trends of concern, increases in damselfish populations (Chapter 4) and declines in coralline algae (Chapter 1), could lead to reduced recruitment of reef corals (Chapter 7), but to date this is not evident (Chapter 7). Importantly, coral cover remains relatively high (Chapter 1). The monitored group of carnivorous fishes, the lutjanid snappers, are holding constant but we remain concerned about the past (Steneck and McClanahan 2003) and continued loss of other larger bodied reef carnivores such as groupers and barracuda. The positive ecological role of parrotfish is well documented (e.g. Mumby et al. 2006) so their decline is troubling. It is unclear exactly why their population densities are declining. While parrotfish are not currently a widely sought group of reef fish (Chapter 8), fishing pressure on them is growing. It is possible they are vulnerable to even modest fishing pressure, particularly from fish traps. Accordingly, we recommend that the capture and killing of parrotfish be stopped because of their key ecological role on Bonaire’s coral reefs. Further, other groups of grazing herbivores such as the longspined sea urchin (Diadema antillarum) are increasing but too slowly to effectively replace the functional role of parrotfish (Chapter 1). We suggest continued monitoring of key drivers of reef health (coral cover, algal abundance, herbivory and coral recruitment). Some standard protocols such as the Atlantic and Gulf Rapid Reef Assessment (AGRRA) are entirely commensurable with the data presented in our reports in 2003, 2005 and 2007 (this report). A streamlined monitoring protocol is likely to be most useful to managers to alert them as a potential problem is growing and, perhaps more importantly, to show improvement when it occurs.
 
 

Bonaire has long been considered to have amongst the healthiest reefs of the Caribbean. However, at the 2002 Annual Meeting of Pew Fellows for Marine Conservation in Bonaire, several scientists with a long history of research on Bonaire’s coral reefs, expressed concern over the future of the island’s reefs. Specifically, they identified the decline in large predatory fish such as groupers as a noticeable change during the past decade. They suspected that this change resulted from increased fishing pressure on Bonaire’s reefs. They also suggested the Bonaire authorities take action to protect the reef-fish stocks. In response to those concerns, officials of the Bonaire Marine Park consulted with scientists and fishermen on Bonaire to explore the possibility of establishing fish protected areas (FPAs), as a way to protect the reef fish stocks. If FPAs improve both fish stocks and the condition of the coral reef, all stakeholders will profit. If fish stocks increased significantly in FPAs, a “spill over” of these fish to adjacent fished areas would be expected. Also, fish that perform important ecological functions could improve the quality of the coral reef ecosystem. Therefore, areas protected from fishing should have healthier coral reefs, which would also improve the island’s valuable ecotourism businesses. The Pew Fellows program funded a research project designed to identify potential FPAs. The Bonaire Marine Park authority, in consultation with the local fishing community would determine the location and size of the FPAs. To monitor the effects of fish protection areas so fishing impacts can be isolated from other factors (such as natural changes, shore-based impacts or effects of scuba divers), an equal number of similar reef sites were selected for study, with half closed to fishing while half remaining open (as “control” reefs). This report reviews the status and recent trends of coral reefs in the Caribbean and Bonaire. It identifies the key features of healthy reefs and how Bonaire’s reefs compares with those elsewhere in the Caribbean. The seven chapters go into scientific detail on factors contributing to the condition of Bonaire’s reefs as of March and April 2003. Special focus will be on factors that threaten reef health or are critical to reef resilience such as seaweed overgrowth, nutrient inputs from land and the ecology of juvenile corals. The report concludes with chapters on the socioeconomic effects of Bonaire’s coral reefs on the fishing and diving industries that depend on them.
Summary Results 2003: The Biological Status of the Coral Reefs of Bonaire & Socioeconomic Implications
 In March and April of 2003, teams of researchers studied the coral reefs of Bonaire to establish the baseline conditions that currently exist and against which trends can be determined and future changes from fish protection areas be assessed. Six study sites were chosen with advice from the Bonaire Marine Park. They represent a range of comparable reefs minimally affected by the 1999 Hurricane Lenny. The sites selected for this study were: Windsock, Plaza, Forest on Klein Bonaire, Scientifico, Barcadera and Karpata (Fig. 0.4). When feasible, parallel studies were conducted at 5 and 10 m depths, however, only the latter depth had fully developed reefs at all sites. The study was designed to quantify the patterns of abundance of the dominant reef organisms as well as to study the processes that control their abundances or threaten their stability. This was done to establish a baseline and to determine if significant differences exist among any of the study sites that would make them a poor choice as a FPA. We also examined some socioeconomic factors related to fishing and scuba diving activities if FPAs are established in Bonaire.