Influence of different feeding regimes on the survival, growth, and biochemical composition of Acropora coral recruits

Performance of Orbicella faveolata larval cohorts does not align with previously observed thermal tolerance of adult source populations

Orbicella faveolata, commonly known as the mountainous star coral, is a dominant reef-building species in the Caribbean, but populations have suffered sharp declines since the 1980s due to repeated bleaching and disease-driven mortality. Prior research has shown that inshore adult O. faveolata populations in the Florida Keys are able to maintain high coral cover and recover from bleaching faster than their offshore counterparts. However, whether this origin-specific variation in thermal resistance is heritable remains unclear. To address this knowledge gap, we produced purebred and hybrid larval crosses from O. faveolata gametes collected at two distinct reefs in the Upper Florida Keys, a nearshore site (Cheeca Rocks, CR) and an offshore site (Horseshoe Reef, HR), in two different years (2019, 2021). We then subjected these aposymbiotic larvae to severe (36°C) and moderate (32°C) heat challenges to quantify their thermal tolerance. Contrary to our expectation based on patterns of adult thermal tolerance, HR purebred larvae survived better and exhibited gene expression profiles that were less driven by stress response under elevated temperature compared to purebred CR and hybrid larvae. One potential explanation could be the compromised reproductive output of CR adult colonies due to repeated summer bleaching events in 2018 and 2019, as gametes originating from CR in 2019 contained less storage lipids than those from HR. These findings provide an important counter-example to the current selective breeding paradigm, that more tolerant parents will yield more tolerant offspring, and highlight the importance of adopting a holistic approach when evaluating larval quality for conservation and restoration purposes.

Heat challenge elicits stronger physiological and gene expression responses than starvation in symbiotic Oculina arbuscula

Heterotrophy has been shown to mitigate coral-algal dysbiosis (coral bleaching) under heat challenge, but the molecular mechanisms underlying this phenomenon remain largely unexplored. Here, we quantified coral physiology and gene expression of fragments from 13 genotypes of symbiotic Oculina arbuscula after a 28-d feeding experiment under (1) fed, ambient (24 °C); (2) unfed, ambient; (3) fed, heated (ramp to 33 °C); and (4) unfed, heated treatments. We monitored algal photosynthetic efficiency throughout the experiment, and after 28 d, profiled coral and algal carbohydrate and protein reserves, coral gene expression, algal cell densities, and chlorophyll-a and chlorophyll-c2 pigments. Contrary to previous findings, heterotrophy did little to mitigate the impacts of temperature, and we observed few significant differences in physiology between fed and unfed corals under heat challenge. Our results suggest the duration and intensity of starvation and thermal challenge play meaningful roles in coral energetics and stress response; future work exploring these thresholds and how they may impact coral responses under changing climate is urgently needed. Gene expression patterns under heat challenge in fed and unfed corals showed gene ontology enrichment patterns consistent with classic signatures of the environmental stress response. While gene expression differences between fed and unfed corals under heat challenge were subtle: Unfed, heated corals uniquely upregulated genes associated with cell cycle functions, an indication that starvation may induce the previously described, milder "type B" coral stress response. Future studies interested in disentangling the influence of heterotrophy on coral bleaching would benefit from leveraging the facultative species studied here, but using the coral in its symbiotic and aposymbiotic states.

Similarities in biomass and energy reserves among coral colonies from contrasting reef environments

Coral reefs are declining worldwide, yet some coral populations are better adapted to withstand reductions in pH and the rising frequency of marine heatwaves. The nearshore reef habitats of Palau, Micronesia are a proxy for a future of warmer, more acidic oceans. Coral populations in these habitats can resist, and recover from, episodes of thermal stress better than offshore conspecifics. To explore the physiological basis of this tolerance, we compared tissue biomass (ash-free dry weight cm^-2), energy reserves (i.e., protein, total lipid, carbohydrate content), and several important lipid classes in six coral species living in both offshore and nearshore environments. In contrast to expectations, a trend emerged of many nearshore colonies exhibiting lower biomass and energy reserves than colonies from offshore sites, which may be explained by the increased metabolic demand of living in a warmer, acidic, environment. Despite hosting different dinoflagellate symbiont species and having access to contrasting prey abundances, total lipid and lipid class compositions were similar in colonies from each habitat. Ultimately, while the regulation of colony biomass and energy reserves may be influenced by factors, including the identity of the resident symbiont, kind of food consumed, and host genetic attributes, these independent processes converged to a similar homeostatic set point under different environmental conditions.

Feeding of a Scleractinian Coral, Goniopora columna, on Microalgae, Yeast, and Artificial Feed in Captivity

Simple Summary

Coral aquaculture is an innovative and sustainable aquaculture industry. Coral husbandry can address ecological environment conservation needs and industrial demand for corals. Many previous studies have confirmed that corals also belong to heterotrophic organisms. Heterotrophic feeding is essential for overcoming nutrient deficiency. The preliminary results of this study indicate that Goniopora columna have high levels of proteases, and artificial feeds containing high protein can be used for feeding during aquaculture, which can increase the growth rate. In conclusion, we have initially explored that Goniopora columna will have better growth by feeding artificial PUFA rich in animal protein. In addition, the best feeding time is 6:00–12:00 in the morning, when there is better digestion and absorption. It is hoped that this research will be helpful to the development of coral aquaculture in the future.

Abstract

Nutritional requirements are critical in the process of coral aquaculture. In addition to energy from symbiotic algae, corals obtain sufficient nutrition through heterotrophic feeding. Microalgae and yeast are commonly used as nutritional supplements for many aquaculture organisms. In addition, if artificial feed can match or improve upon the nutritional supplementation provided by microalgae and yeast in the case of G. columna, then feeding this coral would be markedly easier. Hence, this article preliminarily discusses feeds suitable for G. columna. In this study, artificial PUFA rich in animal protein (R), Saccharomyces cerevisiae, Isochrysis galbana tml, and Nannochloropsis oculate were fed to G. columna at quantities of 5% and 10% of body weight. Growth, survival, body composition, and digestive enzymes were assessed. Regarding body composition, the coral’s protein content is higher than that of carbohydrate or fat; thus, evaluating the heterotrophic nutrition of G. columna by using protein absorption is appropriate. The protease content is also high in digestive enzymes. Protein content, protease activity, and specific growth rate were significantly higher in the R group than in other groups. The number of polyps in the groups fed R at 5% and 10% of body weight increased by 40.00 ± 2.43 and 47.33 ± 0.89 number, respectively, significantly greater increases than those achieved in the other groups (p < 0.05). Changes in body composition and digestive enzymes over a 24-h period were compared to determine the optimal feeding time. Protein content and protease activity increased markedly between 6:00 and 12:00. The experimental results suggest that R can improve the activity of G. columna digestive enzymes and their protein and lipid content in body tissue, shorten the cultivation time, and enhance the profitability of coral aquaculture.

Feeding and thermal conditioning enhance coral temperature tolerance in juvenile Pocillopora acuta

Scleractinian corals form the foundation of coral reefs by acquiring autotrophic nutrition from photosynthetic endosymbionts (Symbiodiniaceae) and use feeding to obtain additional nutrition, especially when the symbiosis is compromised (i.e. bleaching). Juvenile corals are vulnerable to stress due to low energetic reserves and high demand for growth, which is compounded when additional stressors occur. Therefore, conditions that favour energy acquisition and storage may enhance survival under stressful conditions. To investigate the influence of feeding on thermal tolerance, we exposed Pocillopora acuta juveniles to temperature (ambient, 27.4°C versus cool, 25.9°C) and feeding treatments (fed versus unfed) for 30 days post-settlement and monitored growth and physiology, followed by tracking survival under thermal stress. Feeding increased growth and resulted in thicker tissues and elevated symbiont fluorescence. Under high-temperature stress (31-60 days post-settlement; ca 30.1°C), corals that were fed and previously exposed to cool temperature had 33% higher survival than other treatment groups. These corals demonstrated reduced symbiont fluorescence, which may have provided protective effects under thermal stress. These results highlight that the impacts of feeding on coral physiology and stress tolerance are dependent on temperature and as oceans continue to warm, early life stages may experience shifts in feeding strategies to survive.

Enhancing coral recruitment through assisted mass settlement of cultured coral larvae

The escalating rate at which coral communities are declining globally requires urgent intervention and new approaches to reef management to reduce and halt further coral loss. For reef systems with limited natural larval supply, the introduction of large numbers of competent coral larvae directly to natural reef substrata provides a potentially useful approach to replenish adult coral populations. While few experiments have tested this approach, only one experiment has demonstrated its long-term success to date. Given the differences in life-history traits among corals, and different sensitivities of larvae to abiotic and biotic factors, coupled with the dynamic nature of post-settlement survivorship and recruitment processes, trials of the larval enhancement technique with larvae of different coral species are needed to test the broader applicability and viability of this approach. Accordingly, in this paper we examine the applicability of the larval enhancement technique to restore a population of Acropora loripes in the Bolinao-Anda Reef Complex, Pangasinan, northwestern Philippines. Larvae were cultured ex situ following spawning of collected A. loripes colonies in June 2014. Competent larvae were transported to degraded reef areas and approximately 300,000 larvae were introduced in each of three 6 × 4 m plots directly on the reef. Fine mesh enclosures retained the larvae inside each treatment plot for five days. Three adjacent 6 × 4 m plots that served as controls were also covered with mesh enclosures, but no larvae were introduced. Each plot contained ten 10 × 10 cm conditioned settlement tiles cut from dead tabulate Acropora that were used to quantify initial larval settlement. After allowing larval settlement for five days, mean settlement on tiles from the larval enhancement plots that were monitored under stereomicroscopes was significantly higher (27.8 ± 6.7 spat per tile) than in control plots, in which not a single recruit was recorded. Post-settlement survivorship and growth of spat and coral recruits on tiles and reef substrata inside the experimental plots were monitored periodically for 35 months. After 35 months, the mean size of each of the remaining 47 A. loripes coral colonies surviving on the reef substrata was 438.1 ± 5.4 cm³, with a mean diameter of 7.9 ± 0.6 cm. The average production cost for each of the surviving A. loripes colonies at 35 months was USD 35.20. These colonies are expected to spawn and contribute to the natural larval pool when they become reproductively mature, thereby enhancing natural coral recovery in the area. This study demonstrates that mass coral larval enhancement can be successfully used for restoring populations of coral species with different life-history traits, and the techniques can rapidly increase larval recruitment rates on degraded reef areas, hence catalysing the regeneration of declining coral populations.

Effects of low pH and feeding on calcification rates of the cold-water coral Desmophyllum dianthus

Cold-Water Corals (CWCs), and most marine calcifiers, are especially threatened by ocean acidification (OA) and the decrease in the carbonate saturation state of seawater. The vulnerability of these organisms, however, also involves other global stressors like warming, deoxygenation or changes in sea surface productivity and, hence, food supply via the downward transport of organic matter to the deep ocean. This study examined the response of the CWC Desmophyllum dianthus to low pH under different feeding regimes through a long-term incubation experiment. For this experiment, 152 polyps were incubated at pH 8.1, 7.8, 7.5 and 7.2 and two feeding regimes for 14 months. Mean calcification rates over the entire duration of the experiment ranged between −0.3 and 0.3 mg CaCO₃ g⁻¹d⁻¹. Polyps incubated at pH 7.2 were the most affected and 30% mortality was observed in this treatment. In addition, many of the surviving polyps at pH 7.2 showed negative calcification rates indicating that, in the long term, CWCs may have difficulty thriving in such aragonite undersaturated waters. The feeding regime had a significant effect on skeletal growth of corals, with high feeding frequency resulting in more positive and variable calcification rates. This was especially evident in corals reared at pH 7.5 (Ω_A = 0.8) compared to the low frequency feeding treatment. Early life-stages, which are essential for the recruitment and maintenance of coral communities and their associated biodiversity, were revealed to be at highest risk. Overall, this study demonstrates the vulnerability of D. dianthus corals to low pH and low food availability. Future projected pH decreases and related changes in zooplankton communities may potentially compromise the viability of CWC populations.

Feeding increases the number of offspring but decreases parental investment of Red Sea coral Stylophora pistillata

Successful reproductive output and recruitment is crucial to coral persistence and recovery following anthropogenic stress. Feeding is known to alter coral physiology and increase resilience to bleaching.The goal of the study was to address the knowledge gap of the influence of feeding on reproductive output and offspring phenotype.Colonies of Stylophora pistillata from the Northern Gulf of Aqaba (Red Sea) were fed an Artemia diet or unfed for 5 months during gametogenesis, fertilization, and brooding. In addition, time to settlement and mortality of planulae were assessed at water temperatures ranging from winter temperature (22°C) to three degrees above average peak summer temperature (31°C). A range of physiological parameters was measured in parents and offspring.In brooding parents, feeding significantly increased protein concentration and more than tripled the number of released planulae. Planulae from unfed colonies had higher chlorophyll per symbiont concentration and concomitantly higher photosynthetic efficiency compared to planulae from fed parents. In settlement assays, planulae showed a similar thermal resistance as known for this Red Sea adult population. Mortality was greater in planulae from unfed parents at ambient and 3°C above ambient temperature despite higher per offspring investment in terms of total fatty acid content. Fatty acid profiles and relative abundances were generally conserved between different fed and unfed colonies but planulae were enriched in monounsaturated fatty acids relative to adults, that is, 16:1, 18:1, 20:1, 22:1, and 24:1 isomers.Ultimately the availability of zooplankton could influence population physiology and recruitment in corals.

Ex situ co culturing of the sea urchin, Mespilia globulus and the coral Acropora millepora enhances early post-settlement survivorship

Reef restoration efforts, utilising sexual coral propagation need up-scaling to have ecologically meaningful impact. Post-settlement survival bottlenecks, in part due to competitive benthic algae interactions should be addressed, to improve productivity for these initiatives. Sea urchins are keystone grazers in reef ecosystems, yet feeding behaviour of adults causes physical damage and mortality to developing coral spat. To investigate if microherbivory can be utilised for co-culture, we quantitatively assessed how varying densities of juvenile sea urchins Mespilia globulus (Linnaeus, 1758), reared alongside the coral Acropora millepora (Ehrenberg, 1834) effected survival and growth of coral recruits. Spawning of both species were induced ex situ. A comparison of A. millepora spat reared in three M. globulus densities (low 16.67 m⁻², medium 37.50 m⁻², high 75.00 m⁻²) and a non-grazed control indicated coral survival is significantly influenced by grazing activity (p < 0.001) and was highest in the highest density treatment (39.65 ± 10.88%, mean ± s.d). Urchin grazing also significantly (p < 0.001) influenced coral size (compared to non-grazing control), with colonies in the medium and high-densities growing the largest (21.13 ± 1.02 mm & 20.80 ± 0.82, mean ± s.e.m). Increased urchin density did however have a negative influence on urchin growth, a result of limited food availability.

Comparing the capacity of five different dietary treatments to optimise growth and nutritional composition in two scleractinian corals

Developing an optimal heterotrophic feeding regime has the potential to improve captive coral growth and health. This study evaluated the efficacy of three exogenous diets: Artemia nauplii (ART), a commercially available coral diet (Reef Roids) (RR), and a novel, micro-bound diet (ATF), against a comparatively natural, unfiltered seawater treatment (RAW), and an unfed, ultra-filtered seawater treatment (CTL), in adult Acropora millepora and Pocillopora acuta nubbins. After 90 days, both species showed significantly positive weight gain in response to one treatment (A. millepora-RAW, P. acuta-ART), and comparatively low growth in response to another (A. millepora-ATF, P. acuta-RR). The results highlighted substantial differences in the nutritional requirements between species. The nutritional composition of A. millepora in the best performing treatment was dominated by high-energy materials such as storage lipids and saturated and monounsaturated fatty acids. In contrast, the P. acuta nutritional profile in the superior treatment showed a predominance of structural materials, including protein, phospholipids, and polyunsaturated fatty acids. This study demonstrates that Artemia nauplii can successfully replace a natural feeding regime for captive P. acuta, yet highlights the considerable work still required to optimise supplementary feeding regimes for A. millepora.