Coral Reefs: A Very Short Introduction

Reefs and the coral life that builds them were for centuries a source of mystery to naturalists and hazard to seafarers. Many ideas were developed of what built them and why they all existed so close to sea level but never above it. Darwin developed the theory of how they were built, which was proven a century later. The coral polyp is central to each coral colony and to the reef. Each houses countless symbiotic algal cells that provide the energy that supports the coral reef ecosystem, and the energy needed to extract minerals from seawater to deposit as solid limestone. These are the ocean’s most biodiverse ecosystem. The islands perched on them include many entire nations, and reefs provide land, food, and protection to these as well as parts of many others. The diversity and abundance of other species, from microbial systems that are key to nutrient and energy transfer, to the large predatory fish, are similarly vast, and various components of the reef system have been researched intensively since the advent of scuba techniques. Today, however, local impacts and pressures from pollution to overfishing have degraded and damaged many, and more recently, warming of ocean water resulting from climate change is causing an existential threat to the survival of this rich ecosystem. Arresting the decline is no longer a scientific problem but one for society and governments, and failure to do so will result, indeed already is, in untold damage to human societies that depend on coral reefs.

Mapping coral calcification strategies from in situ boron isotope and trace element measurements of the tropical coral Siderastrea siderea

Boron isotopic and elemental analysis of coral aragonite can give important insights into the calcification strategies employed in coral skeletal construction. Traditional methods of analysis have limited spatial (and thus temporal) resolution, hindering attempts to unravel skeletal heterogeneity. Laser ablation mass spectrometry allows a much more refined view, and here we employ these techniques to explore boron isotope and co-varying elemental ratios in the tropical coral Siderastrea siderea. We generate two-dimensional maps of the carbonate parameters within the calcification medium that deposited the skeleton, which reveal large heterogeneities in carbonate chemistry across the macro-structure of a coral polyp. These differences have the potential to bias proxy interpretations, and indicate that different processes facilitated precipitation of different parts of the coral skeleton: the low-density columella being precipitated from a fluid with a carbonate composition closer to seawater, compared to the high-density inter-polyp walls where aragonite saturation was ~ 5 times that of external seawater. Therefore, the skeleton does not precipitate from a spatially homogeneous fluid and its different parts may thus have varying sensitivity to environmental stress. This offers new insights into the mechanisms behind the response of the S. siderea skeletal phenotype to ocean acidification.

Spatial distribution and feeding substrate of butterflyfishes (family Chaetodontidae) on an Okinawan coral reef

Coral reefs support diverse communities, and relationships among organisms within these communities are quite complex. Among the relationships, clarifying the habitat association and foraging substrate selection relative to habitat characteristics is of central importance to ecology since these two aspects are the fundamentals for survival and growth of organisms. The aims of the present study were to investigate the spatial distribution and feeding substrate selection of 14 species of butterflyfishes on an Okinawan coral reef in Japan. Species-specific spatial distributions varied with habitat characteristics (e.g., encrusting corals, massive corals, branching Acropora and rock). For feeding substrates, seven species of obligate coral polyp feeders exhibited significant positive selectivity for tabular Acropora, corymbose Acropora, encrusting corals and massive corals but significant negative selectivity for dead corals, coral rubble and rock. Among six species of facultative coral polyp feeders, two species exhibited significant positive selectivity for encrusting corals and massive corals, and one species showed significant positive selectivity for dead corals as feeding substrates. In contrast, three species exhibited no significant positive selectivity for any feeding substrates. A similar result was observed for one non-coralline invertebrate feeder. Among the 14 species, 12 species showed a relatively close relationship between spatial distribution and feeding substrates but the remaining two species did not. The present study is the first study to elucidate species-specific spatial distributions and feeding substrate selection of butterflyfishes on an Okinawan coral reef. The results of the present study suggest that diverse substrates, including various types of living corals (especially encrusting corals, massive corals, tabular Acropora, corymbose Acropora and branching Acropora) and non-coralline substrates (rock) are the primary determinants of spatial distributions and feeding sites. Thus, diverse substrates are important for maintaining high species diversity of butterflyfishes and changes of the substrates would likely change the spatial patterns and foraging behavior, although species-specific responses may be found, depending on their species-specific dependence on vulnerable substrates.

Signaling pathways in the coral polyp bail-out response

Polyp bail-out is a stress response exhibited by some pocilloporid corals, with mechanisms and consequences distinct from those of bleaching. Although induction of polyp bail-out has been demonstrated in the laboratory, molecular mechanisms underlying this response have rarely been discussed. We conducted genetic analyses of Pocillopora acuta during initiation of hyperosmosis-induced polyp bail-out, using both transcriptomic and qPCR techniques. Beyond upregulation of apoptosis and proteolysis, corals showed significant activation of tumor necrosis factor and fibroblast growth factor (FGF) signaling pathways during induction of polyp bail-out. In our qPCR analysis, a common upregulation profile, peaking at 43.0‰ salinity, was found in the FAS and CASP8 genes, whereas a different profile, showing significant upregulation up to 45.0‰, was displayed by matrix metalloproteinases and genes in the FGF signaling pathway. These results suggest parallel involvement of an extrinsic apoptotic signaling pathway and FGF-mediated extracellular matrix degradation in polyp bail-out. Furthermore, in the XIAP, JNK, and NFKB1 genes, we detected a third expression profile showing linear upregulation that becomes maximal at the endpoint salinity level of the experiment (46.0‰), indicating activation of anti-apoptotic and cell survival signals during polyp bail-out. Our results provide new insights into signaling pathways responsible for polyp bail-out and suggest the feasibility of inducing bail-out by specifically triggering these pathways without exerting lethal stresses on the corals, which in turn will facilitate acquisition of viable polyps for possible use in coral reef restoration.

An artificial aquatic polyp that wirelessly attracts, grasps, and releases objects

The development of light-responsive materials has captured scientific attention and advanced the development of wirelessly driven terrestrial soft robots. Marine organisms trigger inspiration to expand the paradigm of untethered soft robotics into aqueous environments. However, this expansion toward aquatic soft robots is hampered by the slow response of most light-driven polymers to low light intensities and by the lack of controlled multishape deformations. Herein, we present a surface-anchored artificial aquatic coral polyp composed of a magnetically driven stem and a light-driven gripper. Through magnetically driven motion, the polyp induces stirring and attracts suspended targets. The light-responsive gripper is sensitive to low light intensities and has programmable states and rapid and highly controlled actuation, allowing the polyp to capture or release targets on demand. The artificial polyp demonstrates that assemblies of stimuli-responsive materials in water utilizing coordinated motion can perform tasks not possible for single-component devices.

KELIMPAHAN DAN KERAGAMAN JENIS IKAN FAMILI CHAETODONTIDAE BERDASARKAN KONDISI TUTUPAN KARANG HIDUP DI KEPULAUAN SPERMONDE SULAWESI SELATAN

The family Chaetodontidae known as butterfly fishes (kepe-kepe) is a species that associated with coral by consumes coral polyp as its feed. This study aimed to determine the abundance and fish diversity of Chaetodontidae and to look the relationship of fish Chaetodontidae abundance with live coral coverage at Spermonde Island. To determines the abundance and fish diversity of Chaetodontidae by using direct census, while to determine the condition of coral reel used line intercept transect (LIT) method. This study was conducted for 6 (six) station at Spermonde Island by collecting data on depth 4 – 6 m with 3 replicate in each station. Result of study found 5 genera and consist of 16 species fishes from family Chaetodontidae. The overall of Chaetodontidae found is 70 Ind/250 m2 with the largest abundance in Kapoposang island (46 Ind/250 m2) and the smallest is Karanrang island (1 Ind/250 m2). Percentage of live coral coverage on research station at Spermonde Island at “good” to “bad” categories highest coral coverage at Badi island (72.6%) and the lowest is Balanglompo island (5%). Fish diversity of Chaetodontidae is high at station that dominated by Acropora coral. Abundance and fish diversity of Chaetodontidae are no relationship significantly on the percentage of live coral coverage of research station at Spermonde Island.Keyword : Chaetodontidae, coral reef, Spermonde.