A review of giants: Examining the species identities of the world's heaviest extant bony fishes (ocean sunfishes, family Molidae).

The world's heaviest extant bony fish has long been considered the ocean sunfish Mola mola (family Molidae). However, recent taxonomic research suggests the world record specimen (2300 kg) was actually a misidentified giant sunfish M. alexandrini. Moreover, the history of taxonomic confusion in the genus Mola, combined with anecdotal size information perpetuated in both media and literature, has resulted in uncertainty in regard to species identity and actual weights of very large Mola specimens. In this study, we searched for records of molid specimens with reported body mass over 2000 kg, with a focus on the north-west and south-west Pacific. For each specimen, we reviewed the species identification and assessed the reliability of the information, including if the specimen had actually been weighed. Of the 15 specimens uncovered, we identified one M. mola and 14 M. alexandrini, and found that only five had actually been weighed (one with the viscera removed). Furthermore, we collected length-weight data for verified M. alexandrini specimens from the literature and museum specimens, and established the first length-weight relationship for this species [body mass (kg) = 1.1 × 10-5 × total length (cm)3.3248 (29-330 cm total length, n = 20)]. These findings are discussed in the context of other extant bony fish species, which allegedly also exceed 2000 kg in body mass, i.e., other Molidae species and the beluga sturgeon Huso huso. Overall, we conclude that M. alexandrini is the only extant bony fish species we could confirm that exceeds 2000 kg, and that basic biological information is generally not collected when very large molid specimens occasionally are stranded or are caught. Finally, we confirm that the world's heaviest extant bony fish specimen actually weighed was a female M. alexandrini (2300 kg, 272 cm total length) captured from Kamogawa, Chiba Prefecture, Japan, on August 16, 1996.

Response to Britz (2022) regarding the validity of the giant sunfish Mola alexandrini (Ranzani, 1834) (Teleostei: Molidae).

The small family of ocean sunfishes has a long and complicated taxonomic and nomenclatorial history dating back several centuries. Most recently, Britz (2022) questioned the validity of Mola alexandrini (Ranzani, 1839) as the valid name for Mola sp. A sensu Yoshita et al. (2009). Specifically, he questioned the authenticity of the purported Orthragoriscus alexandrini holotype rediscovered by Sawai et al. (2018) due to uncertainties regarding the original units of measurement, along with discrepancies between the original illustration and the purported holotype. He also questioned the reliability of the illustration to reflect the fresh morphology, and the adequacy of the species description (sans illustration and holotype) to link it to any of the currently recognized Mola species. In summary, Britz (2022) opined that M. alexandrini is a species inquirenda. Here we respond to Britzs concerns with the findings from an additional literature review. Firstly, the original species description appears to give measurements in Parisian units, yielding a discrepancy in length with the purported holotype within human error. However, due to various uncertainties, length does not appear to be a robust piece of evidence to neither confirm nor refute the specimens authenticity. Secondly, the morphological differences between the original illustration and the purported holotype were found to be within the expected level of accuracy for Mola illustrations at the time, by both Ranzani and others. Thirdly, a contemporaneous publication describes how Ranzani himself bought the specimen which became the Or. alexandrini holotype, suggesting he would likely have seen it in its fresh state, rendering it unlikely he would have produced a species description and illustration incongruent with this. Fourthly, re-examining the original species description suggests this provides adequate and sufficient information to link Or. alexandrini to Mola sp. A, even in the absence of a holotype. Finally, during this review, we came upon an even older paper describing Or. alexandrini, and we conclude that the currently valid name for Mola sp. A sensu Yoshita et al. (2009) is Mola alexandrini (Ranzani, 1834).

Catastrophic loss of tropical seagrass habitats at the Cocos (Keeling) Islands due to multiple stressors.

Seagrass habitats at the Cocos (Keeling) Islands (CKI), a remote atoll in the Indian Ocean, have suffered a catastrophic decline over the last decade. Seagrass monitoring (1996-2020) in relation to dredging and coastal development works (2009 to 2011) provide a historical baseline, and document the decline of mixed tropical seagrass Thalassia hemprichii and macroalgal (predominantly Caulerpa spp.) beds over a decadal scale time series. Attribution of loss to coastal development is confounded by lagoon-wide die-off events in 2007, 2009 and 2012 and high air and water temperatures from 2009 to 2016, with evidence of broad scale changes, visible in satellite imagery between 2006 and 2018. We conclude that up to 80% of seagrass habitats in the CKI lagoon (~1200 ha) have been lost due to multiple stressors including episodic die-off events related to high temperatures and calm conditions, and loss due to sediment disturbance and increased turbidity. Grazing pressure from the resident green sea turtles (Chelonia mydas) may have also exacerbated the loss of seagrass, which in turn poses a dire threat to their ongoing health and survival. This study highlights the fragility of tropical seagrass habitats and the cascading effect of system imbalance as a result of anthropogenic pressures and climate drivers. Although small in comparison to global estimates, the loss of seagrass habitats at CKI could change the entire ecosystem of a remote atoll. Due to the significance of the Thalassia beds for coastal stability, as food for an isolated population of green sea turtles and as a fish nursery, rehabilitation efforts are warranted.

Species identification of sunfish specimens (Genera Mola and Masturus, Family Molidae) from Australian and New Zealand natural history museum collections and other local sources.

This data-in-brief comprises a summary of sunfish specimens (Genera Mola and Masturus, Family Molidae, >29 cm total length) from natural history museum collections and other sources, such as strandings, in Australia and New Zealand. Each specimen was evaluated morphologically and identified to lowest possible taxon based on recent advances in the understanding of the Mola taxonomy. References to phylogenetic analyses, where applicable, are included. The summary was collated in support of publication Giant jelly eaters on the line: species distribution and bycatch of three dominant sunfishes in the Southwest Pacific[1].