Mueller, B.

Spatio–temporal variation in stable isotope signatures (δ13C and δ15N) of sponges on the Saba Bank

Sponges are ubiquitous on coral reefs, mostly long lived and therefore adaptive to changing environmental conditions. They feed on organic matter withdrawn from the passing water and they may harbor microorganisms (endosymbionts), which contribute to their nutrition. Their diets and stable isotope (SI) fractionation determine the SI signature of the sponge holobiont. Little is known of spatio–temporal variations in SI signatures of d13C and d15N in tropical sponges and whether they reflect variations in the environment. We investigated the SI signatures of seven common sponge species with different functional traits and their potential food sources between 15 and 32 m depth along the S-SE and E-NE side of the Saba Bank, Eastern Caribbean, in October 2011 and October 2013. SI signatures differed significantly between most sponge species, both in mean values and in variation, indicating different food preferences and/or fractionation, inferring sponge species-specific isotopic niche spaces. In 2011, all sponge species at the S-SE side were enriched in d13C compared to the E-NE side. In 2013, SI signatures of sponges did not differ between the two sides and were overall lighter in d13C andd15N than in 2011. Observed spatio–temporal changes in SI in sponges could not be attributed to changes in the SI signatures of their potential food sources, which remained stable with different SI signatures of pelagic (particulate organic matter (POM): d13C -24.9‰, d15N +4.3‰) and benthic-derived food (macroalgae: d13C-15.4‰, d15N +0.8‰). Enriched d13C signatures in sponges at the S-SE side in 2011 are proposed to be attributed to predominantly feeding on benthic-derived C.

This interpretation was supported by significant differences in water mass constituents between sides in October 2011. Elevated NO3 and dissolved organic matter concentrations point toward a stronger reef signal in reef overlying water at the S-SE than N-NE side of the Bank in 2011. The depletions of d13C and d15N in sponges in October 2013 compared to October 2011 concurred with significantly elevated POM concentrations. The contemporaneous decrease in d15N suggests that sponges obtain their N mostly from benthic-derived food with a lower d15N than pelagic food. Average proportional feeding on available sources varied between sponge species and ranged from 20% to 50% for benthic and 50% to 80% for pelagic-derived food, assuming trophic enrichment factors of 0.5‰ ± sd 0.5 for d13C and 3‰ ± sd 0.5 for d15N for sponges. We suggest that observed variation of SI in sponges between sides and years were the result of shifts in the proportion of ingested benthic- and pelagic-derived organic matter driven by environmental changes. We show that sponge SI signatures reflect environmental variability in space and time on the Saba Bank and that SI of sponges irrespective of their species-specific traits move in a similar direction in response to these environmental changes.

Date
2018
Data type
Scientific article
Theme
Research and monitoring
Document
Journal
Geographic location
Saba bank

Biofouling of inlet pipes affects water quality in running seawater aquaria and compromises sponge cell proliferation

Marine organism are often kept, cultured, and experimented on in running seawater aquaria. However, surprisingly little attention is given to the nutrient composition of the water owing through these systems, which is generally assumed to equal
in situ conditions, but may change due to the presence of biofouling organisms. Signi cantly lower bacterial abundances and higher inorganic nitrogen species (nitrate, nitrite, and ammonium) were measured in aquarium water when biofouling organisms were present within a 7-year old inlet pipe feeding a tropical reef running seawater aquaria system, compared with aquarium water fed by a new, biofouling-free inlet pipe. These water quality changes are indicative of the feeding activity and waste production of the suspension- and lter-feeding communities found in the old pipe, which included sponges, bivalves, barnacles, and ascidians. To illustrate the physiological consequences of these water quality changes on a model organism kept in the aquaria system, we investigated the in uence of the presence and absence of the biofouling community on the functioning of the lter-feeding sponge Halisarca caerulea, by determining its choanocyte ( lter cell) proliferation rates. We found a 34% increase in choanocyte proliferation rates following the replacement of the inlet pipe (i.e., removal of the biofouling community). This indicates that the physiological functioning of the sponge was compromised due to suboptimal food conditions within the aquarium resulting from the presence of the biofouling organisms in the inlet pipe. This study has implications for the husbandry and performance of experiments with marine organisms in running seawater aquaria systems. Inlet pipes should be checked regularly, and replaced if necessary, in order to avoid excessive biofouling and to approach in situ water quality. 

Date
2015
Data type
Scientific article
Theme
Research and monitoring
Document
Journal

Four-year-old Caribbean Acropora colonies reared from field-collected gametes are sexually mature

Rehabilitating populations of Caribbean coral species that have declined in recent decades has become a management priority throughout the region, stimulating the development of new methodologies to arti cially reseed degraded reefs. Rearing lar- vae of ecologically important coral species appears a particularly attractive method to aid the recovery of degraded populations because genetic recombination could yield new genotypes better capable of coping with the altered conditions on modern Caribbean reefs. Well-developed elkhorn coral (Acropora palmata Lamarck, 1816) populations form dense thickets that contribute to the maintenance of healthy and productive reefs by providing shelter to a variety of other reef organisms (Gladfelter and Gladfelter 1978). After >95% of A. palmata populations were decimated by a disease beginning in the mid-1970s, this species was listed as critically endangered under the Red List of threatened Species (IUCN 2013) and restoration e orts were initiated throughout the region to assist its recovery (Young et al. 2012). In 2011, we collected gametes from eight A. palmata colonies in situ o Curaçao, which were subsequently cross-fertilized to generate larvae. Competent larvae were settled on clay tiles (Panel A) and reared in a ow-through land-based nursery for one year (Panels B–C), after which they were outplanted to a breakwater at 2–5 m depth (Panel D) [refer to Chamberland et al. (2015) for details on methodology]. Seven out of nine outplanted colonies survived and continued to grow in situ (Panels D–E), reaching a size of 30–40 cm diameter and 20–30 cm height after 4 yrs (Panel F). On 8 and 10 September, 2015, nine and 11 d after the full moon, two colonies were ob- served releasing gametes between 155 and 175 min after sunset (Panels G–H). is is the rst time that an endangered Caribbean Acropora coral species was raised from larvae and grown to sexual maturity in the eld. Indeed, only one other study has documented age and colony size at reproductive onset in a broadcast spawning scler- actinian coral reared from larvae (Baria et al. 2012). e relatively short time until onset of spawning (≤4 yrs) observed for A. palmata shows that recovery of degraded coral populations by enhancing natural recruitment rates may be practicable if out- planted colonies are able to rapidly contribute to the natural pool of larvae. 

Date
2018
Data type
Scientific article
Theme
Research and monitoring

First documentation of encrusting specimen of Cliona delitrix on Curaçao: a cause for concern?

The coral excavating sponge Cliona delitrix is one of the most aggressive and conspicuous excavating sponges on Caribbean reefs. While C. delitrix is very prominent displaying its typical encrusting growth form (β-stage) on the Caribbean island of Bonaire, it is rather elusive and only exhibits a papillated habitus (α-stage) on the neighboring island of Curaçao. Here I document the first two encrusting specimen of C. delitrix on Curaçao and discuss potential explanations for island-specific differences in its habitus and occurrence. An increase of encrusting specimen could have profound consequences for Curaçaoan reefs and should thus be monitored closely.

Date
2017
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Curacao
Author

Exploring the occurrence of and explanations for nighttime spikes in dissolved oxygen across coral reef environments

Primary producers release oxygen as the by-product of photosynthetic light reactions during the day. However, a prevalent, globally-occurring nighttime spike in dissolved oxygen in the absence of light challenges the traditional assumption that biological oxygen production is limited to daylight hours, particularly in tropical coral reefs. Here we show: 1) the widespread nature of this phenomenon, 2) its reproducibility across tropical marine ecosystems, 3) the influence of biotic and abiotic factors on this phenomenon across numerous datasets, and 4) the observation of nighttime oxygen spikes in vitro from incubations of coral reef benthic organisms. The data from this study demonstrate that in addition to physical forcing, biological processes are likely responsible for increasing dissolved oxygen at night. Additionally, we demonstrate an association between these nighttime oxygen spikes and measures of both net community calcification and net community production. These results suggest that nighttime oxygen spikes are likely a biological response associated with increased respiration and are most prominent in communities dominated by calcifying organisms.

Date
2017
Data type
Other resources
Theme
Research and monitoring
Geographic location
Curacao

DOC concentrations across a depth gradient on a Caribbean coral reef

The dissolved organic carbon (DOC) pool on tropical coral reefs is mainly fueled by photosynthates released from benthic primary producers (BPP), such as reef algae and scleractinian corals. DOC concentrations near BPP have repeatedly been observed to be elevated compared to those in the surrounding water column. As the DOC release of BPP increases with increasing light availability, elevated DOC concentrations near them will, in part, also depend on light availability. Consequently, DOC concentrations are likely to be higher on the shallow, well-lit reef terrace than in deeper sections on the fore reef slope. We measured in situ DOC concentrations and light intensity in close proximity to the reef alga Dictyota sp. and the scleractinian coral Orbicella faveolata along a depth gradient from 5 to 20 m depth and compared these to background concentrations in the water column. DOC concentrations near Dictyota sp. were significantly higher at 10 m than at 5 and 20 m depth. Furthermore, at 10 m DOC concentrations near Dictyota sp. were elevated by 15 μmol C L-1 compared to background concentrations in the water column, but not at 5 and 20 m. DOC concentrations near O. faveolata and in the water column did not differ between depths and concentrations near O. faveolata were not elevated compared to background concentrations at any of the tested depths. Our results indicate that DOC concentrations near Dictyota sp. can differ along a depth gradient from 5 to 20 m. However, the occurrence of elevated DOC concentrations did not follow a natural light gradient across depth. Instead, a combination of light availability (including a restriction by photoinhibition) and water movement are proposed to interactively determine the DOC concentrations in the close vicinity of BPP across the reef slope. 

Date
2017
Data type
Other resources
Theme
Research and monitoring
Geographic location
Curacao

Effect of light and nutrient availability on the release of dissolved organic carbon (DOC) by Caribbean turf algae

Turf algae increasingly dominate benthic communities on coral reefs. Given their abundance and high dissolved organic carbon (DOC) release rates, turf algae are considered important contributors to the DOC pool on modern reefs. The release of photosynthetically fixed carbon as DOC generally, but not always, increases with increased light availability. Nutrient availability was proposed as an additional factor to explain these conflicting observations. To address this proposed but untested hypothesis, we documented the interactive contributions of light and nutrient availability on the release of DOC by turf algae. DOC release rates and oxygen production were quantified in incubation experiments at two light levels (full and reduced light) and two nutrient treatments (natural seawater and enriched seawater). In natural seawater, DOC release at full light was four times higher than at reduced light. When nutrients were added, DOC release rates at both light levels were similar to the natural seawater treatment at full light. Our results therefore show that low light in combination with low nutrient availability reduces the release of DOC by turf algae and that light and nutrient availability interactively determine DOC release rates by this important component of Caribbean reef communities.

Date
2016
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Curacao

High dissolved organic carbon release by benthic cyanobacterial mats in a Caribbean reef ecosystem.

Abstract

Benthic cyanobacterial mats (BCMs) are increasing in abundance on coral reefs worldwide. However, their impacts on biogeochemical cycling in the surrounding water and sediment are virtually unknown. By measuring chemical fluxes in benthic chambers placed over sediment covered by BCMs and sediment with BCMs removed on coral reefs in Curaçao, Southern Caribbean, we found that sediment covered by BCMs released 1.4 and 3.5 mmol C m(-2) h(-1) of dissolved organic carbon (DOC) during day and night, respectively. Conversely, sediment with BCMs removed took up DOC, with day and night uptake rates of 0.9 and 0.6 mmol C m(-2) h(-1). DOC release by BCMs was higher than reported rates for benthic algae (turf and macroalgae) and was estimated to represent 79% of the total DOC released over a 24 h diel cycle at our study site. The high nocturnal release of DOC by BCMs is most likely the result of anaerobic metabolism and degradation processes, as shown by high respiration rates at the mat surface during nighttime. We conclude that BCMs are significant sources of DOC. Their increased abundance on coral reefs will lead to increased DOC release into the water column, which is likely to have negative implications for reef health.

 

Date
2015
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Curacao

Effect of light availability on dissolved organic carbon release by Caribbean reef algae and corals

Dissolved organic carbon (DOC) release of three algal and two coral species was determined at three light intensities (0, 30–80, and 200–400 μmol photons m−2 s−1) in ex situ incubations to quantify the effect of light availability on DOC release by reef primary producers. DOC release of three additional algal species was quantified at the highest light intensity only to infer inter-specific differences in DOC release. For species tested at different light intensities, highest net release of DOC occurred under full light (200–400 μmol photons m−2 s−1). DOC released by benthic algae under full light differed (up to 16-fold) among species, whereas DOC release by scleractinian corals was minimal (Orbicella annularis Ellis and Solander, 1786) or net uptake occurred (Madracis mirabilis Duchassaing and Michelotti, 1860) independent of light availability. DOC concentrations and light intensities were also measured in situ near seven benthic primary producers, sediment, and in the water column at nine sites evenly distributed along the leeward coast of Curaçao. In situ DOC concentrations increased with light availability, although the magnitude of this positive effect differed among species and bottom types tested. In situ DOC concentrations were on average lower in November–December [87 (SD 45) μmol L−1] compared to May–June [186 (SD 136) μmol L−1], which can, at least partly, be explained by the lower light availability in the latter period. Our results suggest that DOC release by Caribbean benthic primary producers varies considerably among species and depends on light availability in reef algae. 

Date
2014
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Curacao

Natural Diet of Coral-Excavating Sponges Consists Mainly of Dissolved Organic Carbon (DOC)

Abstract:

Coral-excavating sponges are the most important bioeroders on Caribbean reefs and increase in abundance throughout the region. This increase is commonly attributed to a concomitant increase in food availability due to eutrophication and pollution. We therefore investigated the uptake of organic matter by the two coral-excavating sponges Siphonodictyon sp. and Cliona delitrix and tested whether they are capable of consuming dissolved organic carbon (DOC) as part of their diet. A device for simultaneous sampling of water inhaled and exhaled by the sponges was used to directly measure the removal of DOC and bacteria in situ. During a single passage through their filtration system 14% and 13% respectively of the total organic carbon (TOC) in the inhaled water was removed by the sponges. 82% (Siphonodictyon sp.; mean6SD; 13617 mmol L21) and 76% (C. delitrix; 10612 mmol L21) of the carbon removed was taken up in form of DOC, whereas the remainder was taken up in the form of particulate organic carbon (POC; bacteria and phytoplankton) despite high bacteria retention efficiency (72615% and 87610%). Siphonodictyon sp. and C. delitrix removed DOC at a rate of 4616773 and 3546562 mmol C h21 respectively. Bacteria removal was 1.860.961010 and 1.760.661010 cells h21, which equals a carbon uptake of 46.0621.2 and 42.5614.0 mmol C h21 respectively. Therefore, DOC represents 83 and 81% of the TOC taken up by Siphonodictyon sp. and C. delitrix per hour. These findings suggest that similar to various reef sponges coral-excavating sponges also mainly rely on DOC to meet their carbon demand. We hypothesize that excavating sponges may also benefit from an increasing production of more labile algal-derived DOC (as compared to coral-derived DOC) on reefs as a result of the ongoing coral-algal phase shift. 

Date
2014
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Curacao