Skeletal Growth Rates in Porites lutea Corals from Pulau Tinggi, Malaysia

Skeletal records of massive Porites lutea corals sampled from reefs around Malaysia have previously shown average decadal declines in growth rates associated with sea warming. However, there was a variability in growth declines between sites that warrant the need for investigations into more site-specific variations. This study analyzed decade-long (December 2004–November 2014) annual growth records (annual linear extension rate, skeletal bulk density, calcification rate) reconstructed from five massive P. lutea colonies from Pulau Tinggi, Malaysia. Significant non-linear changes in inter-annual trends of linear extension and calcification rates were found, with notable decreases that corresponded to the 2010 El Niño thermal stress episode and a pan-tropical mass coral bleaching event. Coral linear extension and calcification were observed to return to pre-2010 rates by 2012, suggesting the post-stress recovery of P. lutea corals at the study site within 2 years. Although no long-term declines in linear extension and calcification rates were detected, a linear decrease in annual skeletal bulk density by ≈9.5% over the 10-year study period was found. This suggests that although coral calcification rates are retained, the skeletal integrity of P. lutea corals may be compromised with potential implications for the strength of the overall reef carbonate framework. The correlation of coral calcification rates with sea surface temperature also demonstrated site-specific thermal threshold at 29 °C, which is comparable to the regional thermal threshold previously found for the Thai-Malay Peninsula.

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.

A new record for a massive Porites colony at Ta’u Island, American Samoa

An exceptionally large, hermatypic colony of Porites sp. has been identified and measured at Ta’u, American Samoa. This coral was measured in November 2019 as part of an effort to catalogue all large (≥ 2 m diameter) Porites colonies around Ta’u. Colonies exceeding 10 m in diameter were recorded on three different sides of the island with seasonally different wave exposures. The largest colony measured 8 m tall, 69 m in circumference and had a diameter of 22.4 m. To date, this is the biggest colony recorded in American Samoa, and one of the largest documented worldwide. It is currently unknown why such large corals exist around this particular island. Possible explanations include mild wave or atmospheric climates and minimal anthropogenic impacts. Physiologically, these colonies may be resistant and/or resilient to disturbances. Large, intact corals can help build past (century-scale) climatic profiles, and better understand coral persistence, particularly as coral communities worldwide are declining at rapid rates.

RAPID SURVEYS REVEAL HEALTHY CORAL-SPONGE COMMUNITIES ON KRAKATAU REEFS

The Krakatau Islands in the Sunda Strait have been significantly impacted by catastrophic volcanic eruptions in 1883 and 2018. The marine habitats are not well studied, neither in the past nor in the present. This research is a report on the distribution and ecology of corals and sponges in the Krakatau Volcanic Complex at the three islands of Anak Krakatau, Rakata, and Panjang. This study used 100 m transects long in 5–7 m depth. Hard coral and soft coral communities are found to live with a coverage varied between 25-53% and 0-24%. Dead coral skeletons covered 14–40% of the surveyed area and did not seem to affect the abundance of sponges recorded. The Sponges occupied 0–6% of the area, and they often acted as coral competitors, shaping the benthic ecosystems. The recorded sponges only belong to the Demospongiae class, which are the Suberitid species that are commonly found in Indonesian waters, e.g., Amorphinopsis excavans, Protosuberites collaris, and Terpios sp. The excavating sponge Cliona cf. orientalis was frequently found to be a successful competitor of massive Porites sp., aggressively overgrowing live parts of the coral. Two Haliclona species and Mycale relicta colonized dead coral skeleton. Overall, the benthic communities appear healthy and are comparable to other similar locations that are not affected by volcanic activity.

Year-long effects of high pCO2 on the community structure of a tropical fore reef assembled in outdoor flumes

In this study, fore reef coral communities were exposed to high pCO2 for a year to explore the relationship between net accretion (Gnet) and community structure (planar area growth). Coral reef communities simulating the fore reef at 17-m depth on Mo’orea, French Polynesia, were assembled in three outdoor flumes (each 500 l) that were maintained at ambient (396 µatm), 782 µatm, and 1434 µatm pCO2, supplied with seawater at 300 l h−1, and exposed to light simulating 17-m depth. The communities were constructed using corals from the fore reef, and the responses of massive Porites spp., Acropora spp., and Pocillopora verrucosa were assessed through monthly measurements of Gnet and planar area. High pCO2 depressed Gnet but did not affect colony area by taxon, although the areas of Acropora spp. and P. verrucosa summed to cause multivariate community structure to differ among treatments. These results suggest that skeletal plasticity modulates the effects of reduced Gnet at high pCO2 on planar growth, at least over a year. The low sensitivity of the planar growth of fore reef corals to the effects of ocean acidification (OA) on net calcification supports the counterintuitive conclusion that coral community structure may not be strongly affected by OA.