Aquarium Corals Research Articles

Using size-weight relationships to estimate biomass of heavily targeted aquarium corals by Australia’s coral harvest fisheries

Coral reefs are highly threatened environs subject to ongoing unprecedented degradation as a result of anthropogenic activities. Given the existential threat to coral reef ecosystems, extractive industries that make use of coral reef resources, are facing significant public and political pressure to quantify and justify their environmental impact. In Australia, hundreds of thousands of live scleractinian (hard) corals are harvested annually directly from the wild to supply the growing international marine aquarium trade. Many of the most popular and high value aquarium corals are believed to be slow growing, which would make them particularly vulnerable to over-fishing. Corals present a number of unique challenges for fisheries management, not least of which, is the marked variation in the size of corals, which may be harvested in whole or in part. This issue is further compounded because harvest limits are typically weight-based, but there is very limited information on the standing biomass of corals in targeted stocks. Herein, we describe size-weight relationships for some of Australia’s most heavily targeted coral species (Catalaphyllia jardinei, Duncanopsammia axifuga, Euphyllia glabrescens, Homophyllia cf. australis, Micromussa lordhowensis, Trachyphyllia geoffroyi), which allows estimation of standing biomass from transect surveys. This work represents an important first step in the development of ecologically sound management strategies by bridging the gap between catch reporting and stock assessments.

Size-weight relationships for estimating harvestable biomass of Acropora corals on Australia's Great Barrier Reef

Although hard corals (order Scleractinia) are listed in Appendix II of the Convention for the International Trade in Endangered Species (CITES), there is significant ongoing wild harvest and international trade, mostly for the aquarium industry. Acropora corals account for the majority of aquarium corals harvested and traded, but are also extremely vulnerable to fisheries-independent threats, especially climate-induced coral bleaching. Reconciling effects of coral harvesting is complicated as harvest limits are based on weight, while there is limited data on standing biomass of Acropora from different reef environments. Here, a management-friendly methodology that allows for quantification of Acropora spp. biomass is described and demonstrated, thus providing means for the development and implementation of a rigorous sustainable harvest strategy. We establish size-weight relationships for four growth forms of Acropora spp. harvested from Australia's Great Barrier Reef, to facilitate estimates of harvestable biomass and better understand the ecological context of current weight-based harvest levels and limits. Using these relationships, and field-based sampling at 12 sites across seven distinct reefs, the estimated biomass of Acropora spp. ranges from 0.12 kg ⋅ m−2 to 4.7 kg ⋅ m−2. These estimates necessitate further consideration of catch composition and the specific abundance of individual species that are heavily harvested, and how impacts of current harvest practices interact with species-specific vulnerability to climate change and other escalating human pressures contributing to the degradation of coral reef ecosystems. This study is a crucial first step towards quantifying the ecological impacts of the fishery to develop management strategies that are underpinned by research.

Bleaching susceptibility of aquarium corals collected across northern Australia

There are a wide range of Scleractinian corals that are collected for the global reef aquarium market, often from non-reefal environments. The sustainability of coral harvesting is potentially threatened by increasing anthropogenic disturbances and climate change, though it is unknown to what extent many commonly harvested corals are susceptible to environmental change, or actually bleach during marine heatwaves. In this study, we experimentally tested the temperature sensitivity and bleaching susceptibility of six coral species (Homophyllia australis, Micromussa lordhowensis, Catalaphyllia jardinei, Trachyphyllia geoffroyi, Duncanopsammia axifuga, and Euphyllia glabrescens), which are important components of the aquarium coral fisheries across northern Australia, in Western Australia, the Northern Territory, and/or Queensland. Interspecific differences were evident in the temperature sensitivity and bleaching susceptibility among the study species. Homophyllia australis, and M. lordhowensis were found to be particularly susceptible to elevated temperatures, whereby all corals subjected to elevated temperatures died within the course of the experimental treatment (75 d). Catalaphyllia jardinei and E. glabrescens also exhibited significant increases in mortality when exposed to elevated temperatures, though some of the corals did survive, and C. jardinei mostly died only after exposure to elevated temperatures. The other species (T. geoffroyi and D. axifuga) exhibited marked bleaching when exposed to elevated temperatures, but mortality of these corals was similar to that of conspecifics held at ambient temperatures. This study highlights the potential for environmental change to impact the sustainability and viability of Australian coral harvest fisheries. More importantly, this study highlights the need for specific and targeted in situ monitoring for important stocks of coral fishery target species, to assess their vulnerability to fishery and fishery-independent effects.

Usage of UV-curable oligomer-based adhesive agent in hermatypic coral experimental research

The global decline of the tropical and subtropical coral reefs requires urgent completion of various experiments that will reveal the factors influencing coral health. We describe the procedure of a new inexpensive, easy, and fast method for attaching fragments of the hermatypic coral Acropora spp. to small polycarbonate hexagon head bolts using Bondic®, an ultraviolet (UV)-curable oligomer-based adhesive agent made by Laser Bonding Tech, Inc. (Aurora, ON, Canada). The attachment was hardened within 10 s after applying the adhesive to the cut surface of the coral fragment. The corals attached to polycarbonate bolt were tolerant to long-distance aerial transport 3 days after the attachment. In addition to its implementation in various experiments using hermatypic corals, this method will contribute to aquaculture of hermatypic corals, exhibition of corals in aquariums, and coral reef restoration.The advantages of this new method are summarized below:•A new UV-curable oligomer-based adhesive agent is used as an artificial substrate for coral.•This method is inexpensive, easy to use, and coral attaches quickly to the artificial substrate.•Corals attached to the artificial substrate can withstand long periods of transportation.

Assessing the conservation potential of fish and corals in aquariums globally

Aquatic ecosystems are indispensable for life on earth and yet despite their essential function and service roles, marine and freshwater biomes are facing unprecedented threats from both traditional and emerging anthropogenic stressors. The resultant species and ecosystem-level threat severity requires an urgent response from the conservation community. With their care facilities, veterinary and conservation breeding expertise, reintroduction and restoration, and public communication reach, stand-alone aquariums and zoos holding aquatic taxa have great collective potential to help address the current biodiversity crisis, which is now greater in freshwater than land habitats. However, uncertainty regarding the number of species kept in such facilities hinders assessment of their conservation value. Here we analyzed, standardized and shared data of zoological institution members of Species360, for fish and Anthozoa species (i.e. Actinopterygii, Elasmobranchii, Holocephali, Myxini, Sarcopterygii and Anthozoa). To assess the conservation potential of populations held in these institutions, we cross-referenced the Species360 records with the following conservation schemes: the Convention on the International Trade of Endangered Species of Fauna and Flora (CITES), the IUCN Red List of Threatened species, climate change vulnerability, Evolutionary Distinct and Globally Endangered (EDGE) and The Alliance for Zero Extinction (AZE). We found that aquariums hold four of the six fish species listed by the IUCN Red List as ‘Extinct in the Wild’, 31% of Anthozoa species listed by Foden et al. (2013) as vulnerable to climate change, 19 out of the 111 Anthozoa EDGE species, and none of the species prioritized by the AZE. However, it is very likely that significant additional species of high conservation value are held in aquariums that do not manage their records in standardized, sharable platforms such as Species360. Our study highlights both the great value of aquarium and zoo collections for addressing the aquatic biodiversity crisis, as well as the importance that they maintain comprehensive, standardised, globally-shared taxonomic data.

Assessment of the microbial communities associated with white syndrome and brown jelly syndrome in aquarium corals

Bacterial and ciliate assemblages associated with aquarium corals displaying white syndrome (WS) and brown jelly syndrome (BJS) were investigated. Healthy (n = 10) and diseased corals (WS n = 18; BJS n = 3) were analysed for 16S rRNA gene bacterial diversity, total bacterial abundance and vibrio-specific 16S rRNA gene abundance. This was conducted alongside analysis of 18S rRNA gene sequencing targeting ciliates, a group of organisms largely overlooked for their potential as causal agents of coral disease. Despite significant differences between healthy and diseased corals in their 16S rRNA gene bacterial diversity, total bacterial abundance and vibrio-specific rRNA gene abundance, no dominant bacterial ribotypes were found consistently within the diseased samples. In contrast, one ciliate morphotype, named Morph 3 in this study (GenBank Accession Numbers JF831358 for the ciliate isolated from WS and JF831359 for the ciliate isolated from BJS) was observed to burrow into and underneath the coral tissues at the disease lesion in both disease types and contained algal endosymbionts indicative of coral tissue ingestion. This ciliate was observed in larger numbers in BJS compared to WS, giving rise to the characteristic jelly like substance in BJS. Morph 3 varied by only 1 bp over 549 bp from the recently described Morph 1 ciliate (GenBank Accession No. JN626268), which has been shown to be present in field samples of WS and Brown Band Disease (BrB) in the Indo-Pacific. This result indicates a close relationship between these aquarium diseases and those observed in the wild.

Coral diseases in aquaria and in nature

Many reef coral diseases have been described affecting corals in the wild, several of which have been associated with causal agents based on experimental inoculation and testing of Koch's postulates. In the aquarium industry, many coral diseases and pathologies are known from the grey literature but as yet these have not been systematically described and the relationship to known diseases in the wild is difficult to determine. There is therefore scope to aid the maintenance and husbandry of corals in aquaria by informing the field of the scientifically described wild diseases, if these can be reliably related. Conversely, since the main driver to identifying coral diseases in aquaria is to select an effective treatment, the lessons learnt by aquarists on which treatments work with particular syndromes provides invaluable evidence for determining the causal agents. Such treatments are not commonly sought by scientists working in the natural environment due the cost and potential environmental impacts of the treatments. Here we review both wild and aquarium diseases and attempt to relate the two. Many important aquarium diseases could not be reconciled to those in the wild. In one case, however, namely that of the ciliateHelicostomasp. as a causal agent of brown jelly syndrome in aquarium corals, there may be similarities with pathogenic agents of the wild coral diseases, such as white syndrome and brown band syndrome. We propose thatHelicostomais actually a misnomer, but improved understanding of this pathogen and others could benefit both fields. Improved practices in aquarium maintenance and husbandry would also benefit natural environments by reducing the scale of wild harvest and improving the potential for coral culture, both for the aquarium industry and for rehabilitation programmes.

Diversity of zooxanthellae from corals and sea anemones after long-term aquarium culture

Aquarium systems allow technically sophisticated experiments that promise new opportunities to answer urgent questions about reef coral biology, for instance assessing the responses to decreasing environmental pH and/or increased temperatures. Over recent years, long-term culture and (predominantly asexual) propagation of corals has become possible in such systems. At present however, only limited data are available that clarify whether or not responses of the coral holobiont are dominated by the acclimatization to life in captivity or continue to reflect, for example, taxonomic differences seen in nature. We studied the diversity of the symbiotic algae in corals and sea anemones after long-term aquaculture by analysis of their small subunit (SSU) ribosomal DNA gene. A field sample ofAcropora clathratafrom the Arabian Gulf which was used as a control contained clade C zooxanthellae. The aquarium corals also harboured clade C symbionts, but sequencing of the SSU DNA suggested that the analysed animals host different subclades. A prevalence of clade C is also found among corals from the Indo-Pacific region, the origin of most of the aquarium samples. An individual of the temperate sea anemoneAnemonia sulcata (viridis)contained clade A symbionts, similar to those found in nature, even after nearly 10 years of co-culture with sea anemones(Entacmaea quadricolor)and corals hosting clade C symbionts. The results indicate that the specific host–symbiont association occurring in nature appears to persist over >2 years timescales in captivity, with no mixing of symbionts between hosts maintained in the same aquarium or apparent selection of stress-tolerant symbiont strains such as clade D.

Epizoic acoelomorph flatworms compete with their coral host for zooplankton

Satisfying nutrient requirement of corals is still a major constraint for maintaining corals in marine aquariums. Corals are polytrophic in nature. Heterotrophic feeding on zooplankton is one of the corals’ strategies to overcome nutrient deficiency. Artemia salina nauplii are commonly used as biocarriers for many fish larvae in aquaculture and can also serve as a biocarrier for coral in aquariums, provided coral acceptability, optimal feeding rate, and digestibility of the nauplii are well understood. Feeding rate and digestibility of coral fed on A. salina nauplii at 100, 2,000, 4,000, 6,000, and 10,000 ind. l-1 under light and dark conditions was assessed in this study. The maximum feeding rates of Galaxea fascicularis under light and dark conditions was 113.6 ind. polyp-1 h-1 and 76.9 ind. polyp-1 h-1, respectively. The daily feeding rates of G. fascicularis varies and depends on nauplii density. Light plays an important role in coral feeding. Nevertheless, the quantity of A. salina nauplii consumed by the coral under light and dark conditions was not significantly different (P > 0.05). A. salina nauplii are well accepted by G. fascicularis. Complete nauplii digestion was observed after 180 min. Digestibility of A. salina nauplii by G. fascicularis was positively correlated with digestion time.

SYMBIODINIUM (DINOPHYTA) DIVERSITY AND STABILITY IN AQUARIUM CORALS(1).

Indo-Pacific reef corals growing for years in closed-system aquaria provide an alternate means to investigate host-symbiont specificity and stability. The diversity of dinoflagellate endosymbionts (Symbiodinium spp.) from coral communities in private and public aquaria was investigated using molecular-genetic analyses. Of the 29 symbiont types (i.e., species) identified, 90% belonged to the most prevalent group of Symbiodinium harbored by Indo-Pacific reef corals, Clade C, while the rest belonged to Clade D. Sixty-five percent of all types were known from field surveys conducted throughout the Pacific and Indian oceans. Because specific coral-dinoflagellate partnerships appear to have defined geographic distributions, correspondence of the same symbionts in aquarium and field-collected specimens identifies regions where particular colonies must have been collected in the wild. Symbiodinium spp. in clade D, believed to be "stress-tolerant" and/or "opportunistic," occurred in a limited number of individual colonies. The absence of a prevalent, or "weedy," symbiont suggests that conditions under which aquarium corals are grown do not favor competitive replacements of their native symbiont populations. The finding of typical and diverse assemblages of Symbiodinium spp. among aquarium corals living many years under variable chemical/physical conditions, artificial and natural light, while undergoing fragmentation periodically, indicates that individual colonies maintain stable, long-term symbiotic associations.

Feeding of scleractinian coral, Galaxea fascicularis, on Artemia salina nauplii in captivity

Satisfying nutrient requirement of corals is still a major constraint for maintaining corals in marine aquariums. Corals are polytrophic in nature. Heterotrophic feeding on zooplankton is one of the corals’ strategies to overcome nutrient deficiency. Artemia salina nauplii are commonly used as biocarriers for many fish larvae in aquaculture and can also serve as a biocarrier for coral in aquariums, provided coral acceptability, optimal feeding rate, and digestibility of the nauplii are well understood. Feeding rate and digestibility of coral fed on A. salina nauplii at 100, 2,000, 4,000, 6,000, and 10,000 ind. l−1 under light and dark conditions was assessed in this study. The maximum feeding rates of Galaxea fascicularis under light and dark conditions was 113.6 ind. polyp−1 h−1 and 76.9 ind. polyp−1 h−1, respectively. The daily feeding rates of G. fascicularis varies and depends on nauplii density. Light plays an important role in coral feeding. Nevertheless, the quantity of A. salina nauplii consumed by the coral under light and dark conditions was not significantly different (P > 0.05). A. salina nauplii are well accepted by G. fascicularis. Complete nauplii digestion was observed after 180 min. Digestibility of A. salina nauplii by G. fascicularis was positively correlated with digestion time.

Coral mucus-associated bacterial communities from natural and aquarium environments

The microbial biota dwelling in the mucus, on the surface, and in the tissues of many coral species may have an important role in holobiont physiology and health. This microbiota differs with coral species, water depth, and geographic location. Here we compare the surface mucus microbiota of the coral Fungia granulosa from the natural environment with that from individuals maintained in aquaria. Molecular analysis revealed that the microbial community of the mucus microlayer of the coral F. granulosa includes a wide range of bacteria and that these change with environment. Coral mucus from the natural environment contained a significantly higher diversity of microorganisms than did mucus from corals maintained in the closed-system aquaria. A microbial community shift, with the loss of several groups, including actinobacterial and cyanobacterial groups, was observed in corals maintained in aquaria. The most abundant bacterial class in F. granulosa mucus was the Alphaproteobacteria, regardless of whether the corals were from aquaria or freshly collected from their natural environment. A significantly higher percentage of bacteria from the Betaproteobacteria class was evident in aquarium corals (24%) when compared with corals from the natural environment (3%). The differences in mucus-inhabiting microbial communities between corals from captive and natural environments suggest an adaptation of the mucus bacterial communities to the different conditions.

Stress-induced rapid release of antibacterials by scleractinian corals

Mechanical stress on the coral Pocillopora damicornis caused the release of material that killed the coral pathogen Vibrio coralliilyticus. The bactericidal material was released into the surrounding seawater rapidly, reaching a maximum killing activity within 1 min of the stress. The coral antibacterial activity, referred to as CAA, was retained following filter sterilization and storage at −20°C. Exposure of V. coralliilyticus to CAA for 30 s, 1 min and 6 min resulted in the death of 82%, 89% and 99% of the bacteria, respectively. Release of CAA following mechanical stress was also observed with four other coral species tested. P. damicornis CAA was bactericidal to a wide variety of Gram-negative and Gram-positive bacteria. This is the first report that hard corals rapidly release fast-acting bactericidal material following mechanical stress. The release of CAA was demonstrated with both aquarium corals and corals taken directly from the sea. It is suggested that CAA is part of hard corals’ host defense system against infection, the natural stimulation for release of CAAs being the bite of a predator. Previous failures to detect antibacterial activity in hard corals can be attributed to a lack of understanding of the sensitive mechanism by which they are released.