Changes in Coral Skeleton Growth Recorded by Density Band Stratigraphy, Crystalline Structure, and Hiatuses

Next-generation high resolution brightfield microscopy, x-radiography, and microcomputed tomography (microCT) analyses indicate that coral skeleton high density band (HDB) and low density band (LDB) stratigraphic sequences record dynamic changes in coral growth history. HDB-LDB sequences were studied within three small heads of Orbicella annularis, an ecological keystone species in the Caribbean Sea, collected from the leeward fringing reefs on Curaçao. Results indicate that HDB layers are formed by the thickening of exothecal and endothecal dissepiments, costae, and theca located at the margin and external to individual skeletal cups (corallites). Conversely, septa and columellas located inside individual corallites do not change in thickness. HDB-LDB stratigraphic sequences were laterally traced from the center to the margins of individual coral heads, demonstrating that shifts took place in the trajectory of coral skeleton growth. Normal HDB layers in the center of individual coral heads are formed at the same time (age-equivalent) as surfaces of erosion and no skeleton growth (hiatuses) on the margins of the heads. These hiatus surfaces within HDB-LDB stratal geometries indicate that multiple marine ecological and environmental processes affect the orientation, size, shape, and geometry of coral skeletons during coral growth history. The presence of these hiatus surfaces in other large coral heads would strongly impact sclerochronology and the interpretation of multiple environmental factors including sea surface temperature (SST).

Field measurements of a massive Porites coral at Goolboodi (Orpheus Island), Great Barrier Reef

An exceptionally large coral Porites sp. has been identified and measured at Goolboodi (Orpheus Island), Great Barrier Reef (GBR). This coral was measured in March 2021 during citizen science research of coral reefs in the Palm Islands group. We conducted a literature review and consulted scientists to compare the size, age and health of the Porites with others in the GBR and internationally. This is the largest diameter Porites coral measured by scientists and the sixth highest coral measured in the GBR. The health of the Porites was assessed as very good with over 70% live coral cover and minor percentages of sponge, live coral rock and macroalgae. An estimated age of 421–438 years was calculated based on linear growth models. Manbarra Traditional Owners were consulted and suggested that the Porites be named Muga dhambi (big coral) to communicate traditional knowledge, language and culture to indigenous, tourists, scientists and students.

The Importance of Home Cleaning: Sediment Transport by Alpheid Shrimps Provides a Competitive Advantage to Their Host Anemones

Bartholomea annulata is a facultative host of the A. armatus species complex. In the Mexican Caribbean it is commonly found in cracks and crevices located where the vertical walls meet the sandy bottom or on large coral patches away from the sand. To protect themselves from predators, anemones often contract their hydraulic body into a cavernous den and extend the stinging tentacles toward the entrance. The high sediment dynamics of the region, however, result in a permanent risk of animal shelters to be obstructed by sand. By both analysing field data and conducting laboratory experiments with artificial shelters, the present study explored the den cleaning behaviour widely extended amongst alpheid shrimp, and its role in the alpheid-anemone symbiotic interaction. Videorecordings showed that den cleaning was composed of three main behaviours: digging, tossing and tamping. It commenced as soon as 7.2 ± 10.5 min after anemones were recognised by alpheids, and behaviours were displayed systematically amongst all 12 replicates. Despite being completely burrowed in sand, Alpheus spp. were capable of finding the anemone and liberating the entrance of the artificial shelters in less than 2.5 h. In addition, manipulative experiments showed that anemones confronted with shelters that were obstructed with sediment had a 25% probability of fully retracting when Alpheus spp. were absent, compared to a 75% probability when shrimps had cleaned the shelter’s entry and internal passage. The analysis of field data indicated that the presence of alpheid shrimps as symbionts of B. annulata was 30% higher amongst anemones in close contact with sandy bottoms than when inhabiting crevices on the top or lateral walls of hard substrates, away from the sediment. Overall, our study concludes that den cleaning constitutes a quick and effective mechanism to assure the anemone’s full retraction into their den, and by keeping the sediment away, alpheids provide the necessary conditions that serve both the anemone’s and the shrimp’s higher chances of acquiring maximum protection from predators. This advantageous exchange in protection partially explains why alpheids are more frequently present in B. annulata in interface microhabitats where the benefit of the interaction is maximised.

Late Pennsylvanian carbonate platform facies and coral reef: new insights from southern China (Guizhou Province)

The Pennsylvanian is characterized by intense paleoenvironmental changes related to glacio-eustatic sea-level fluctuations and major tectonic events, which affected the evolution of biocommunities. Most known Pennsylvanian tropical reefs and mounds are predominantly composed of calcareous algae (e.g. phylloid algae, Archaeolithophyllum), calcareous sponges, fenestrate bryozoans, Tubiphytes, and microbialites. However, in Houchang (southern China), the Late Pennsylvanian carbonate platform records a large coral reef lacking any analogs in age (Gzhelian), size (80–100 m thick) and composition (high biodiversity). The large coral reef developed at the border of the Luodian intraplatform basin. The intraplatform basin is characterized by the deposition of green algal grainstone, coated grain grainstone and bioclastic packstone, grainstone, floatstone and rudstone in shallow-waters. In the deep-water shelf, lithofacies are composed of burrowed bioclastic wackestone, microbioclastic peloidal packstone, grainstone, and fine-grained burrowed wackestone and packstone. In this context, the coral reef developed on a deep-shelf margin, in a moderate to low energy depositional environment, below the FWWB. The scarcity of Pennsylvanian coral reefs suggests global unfavorable conditions, which can be attributed to a complex pattern of several environmental factors, including seawater chemistry (aragonite seas), paleoclimatic cooling related to continental glaciation, and the biological competition with the more opportunistic and adaptive phylloid algal community that occupied similar platform margin paleoenvironments. The existence of the large Bianping coral reef in southern China, as well as a few additional examples of Pennsylvanian coralliferous bioconstructions, provides evidence that coral communities were able to endure the Late Paleozoic fluctuating paleoenvironmental conditions in specific settings. One of such settings appears to have been the deep shelf margin, where low light levels decreased competition with the phylloid algal community.

A Modeling Approach for Assessing Groundwater Resources of a Large Coral Island under Future Climate and Population Conditions: Gan Island, Maldives

This study assesses the future groundwater supply of a large coral island, Gan Island, Republic of Maldives, under influences of rainfall patterns, sea level rise, and population growth. The method described in this paper can be used to estimate the future groundwater supply of other coral islands. Gan is the largest inhabited island (598 ha) of the Republic of Maldives with a population of approximately 4500. An accurate estimate of groundwater supply in the coming decades is important for island water security measures. To quantify future groundwater volumes in Gan, a three-dimensional, density-dependent groundwater and solute transport model was created using the SUTRA (Saturated Unsaturated Transport) modeling code. The Gan model was tested against observed groundwater salinity concentrations and then run for the 2012–2050 period to compare scenarios of future rainfall (from General Circulation Models), varying rates of population growth (i.e., groundwater pumping), and sea level rise. Results indicate that the total fresh groundwater volume increases approximately 20% if only future rainfall patterns are considered. If moderate pumping is included (2% annual population growth rate), the volume increases only by 13%; with aggressive pumping (9% annual population growth rate), the volume decreases by 24%. Sea level rise and associated shoreline recession leads to an additional 15–20% decrease in lens thickness and lens volume. Results can be used to make decisions about water resource management on Gan and other large coral islands in the Indian and Pacific Oceans. Methods used herein can be applied to any coral island to explore future groundwater security.

SEBARAN DAN KEPADATAN MEGABENTOS DI PERAIRAN PULAU BUTON, SULAWESI TENGGARA

Perairan Pulau Buton dan sekitarnya dengan wilayah terumbu karang yang cukup luas, kaya keanekaragaman hayati laut dan nilai estetika yang tinggi. Terumbu karang bermanfaat banyak bagi manusia dalam berbagai aspek ekonomi, sosial, dan budaya. Penelitian megabentos pada ekosistem terumbu karang ini telah dilakukan pada 2016 (April), 2017 (Juni) dan 2018 (Mei). Pengamatan dilakukan pada 15 stasiun yang tersebar pada pulau-pulau besar dan kecil dari timur hingga barat. Tujuan penelitian ini untuk mengetahui sebaran dan kepadatan megabentos serta kemiripan spesies antar stasiun pada perairan tersebut. Pengambilan data dilakukan dengan menggunakan metode Reef Check Benthos (RCB). Hasil pengamatan menunjukkan ada delapan spesies megabentos, diantaranya Drupella cornus menyebar secara luas (100%), dan memiliki nilai total kelimpahan individu tertinggi, berkisar antara 35,7 – 57,9%, (472 – 704 individu). Sedangkan Acanthaster planci memiliki sebaran yang terbatas dengan kelimpahan individu yang rendah (0,3 – 1,0%). Kepadatan individu megabentos pada pengamatan April berkisar antara 0,16 – 2,31 individu/140m2, pada Juni berkisar antara 0,11 – 1,47 individu/140m2 dan 0,11 – 1,24 individu/140m2 pada Mei. Dari tiga tahun pengamatan (2016 – 2018) kelimpahan rata-rata individu megabentos tidak ditemukan adanya perbedaan yang signifikan. Hasil analisa klaster menunjukkan bahwa kehadiran setiap spesies megabentos antar stasiun pengamatan dipengaruhi oleh kemiripan tipe substrat dan habitat.The waters of Buton Island and its surrounding, has a large coral reef area with high species biodiversity and has an aesthetics value and beneficial for human being in many aspects such as economics, social and culture. Researches on megabenthos in coral reef ecosystems have been conducted in 2016 (April), 2017 (June) and 2018 (May) at 15 stations around large and small islands scattered from east to west. The aims of this study were to know the distribution and abundance of megabenthos and similarity of species between stations in these waters. Data collection is conducted using the Reef Check Benthos (RCB) method. The results shows that eight megabenthos was found, where Drupella cornus has a wide distribution (100%), and has the highest total value of individual abundance, ranging from 35.7 - 57.9%, (472 - 704 individuals). Whereas Acanthaster planci has a limited distribution with a low abundance of individuals (0.3 - 1.0%). The abundance of megabenthos in April’s observations ranged from 0.16 - 2.31 individuals/140m2, in June it ranged from 0.11 - 1.47 individuals/140m2 and 0.11 - 1.24 individuals/140m2 in May. In three years of observation (2016 - 2018) the average abundance of megabenthos individuals is not significantly different. The results of cluster analysis showed that the similarity of megabenthos species between observation stations was influenced by similarities in substrate type and habitat.