Nudibranch

Improved access to field survey infrastructure throughout SouthEast Asia has allowed for a greater intensity of biodiversity surveys than ever before. The rocky bottoms and coral reef habitats across the region have been shown to support some of the highest sea slug biodiversity on the planet, with ever increasing records. During the past ten years, intensive SCUBA surveys have been carried out at Koh Tao, in the Gulf of Thailand, which have yielded remarkable findings in sea slug biology and ecology. In this work a brief history of sea slug biodiversity research from Thailand is covered and a complete inventory of sea slugs from Koh Tao, Gulf of Thailand is provided. This inventory is based on surveys from 2012 to 2020, with previously unreported findings since 2016. Habitat specificity and species-specific ecology are reported where available with a focused comparison of coral reef habitats and deeper soft-sediment habitats. The findings contribute 90 new species records for Thai waters (92 for the Gulf of Thailand) and report a remarkable consistency in the proportional diversity found to be exclusive to one habitat type or another. Additionally, taxonomic remarks are provided for species documented from Koh Tao that have not been discussed in past literature from Thailand, and a summary of previous records in the Indo-West Pacific is given.

Opisthobranchs are fascinating molluscs with species diversifying not only in colours but also in their specificity of feeding habit and habitat. Historical studies are centred mostly on known species rich localities and are not evenly distributed along all coastal states. Opisthobranchs are among the least studied group of molluscs in India and the work carried out on the opisthobranch fauna is scanty and sparse. Though India has over 8000 km long coastline along nine coastal states and two oceanic archipelagos and have diverse habitats such as coral reefs, sandy shores, rocky patches, mangroves as well as large mud flats; yet records of Indian opisthobranchs are very less. This study revealed that 311 species are known from India distributed over 7 orders, 53 families and 141 genera.

The Ratnagiri coast is among the least studied areas for marine life in India. The coast is known to host a high diversity of marine habitats, and flora and fauna. Opisthobranchs have received attention only recently, Maharashtra coast being the least explored. The paper presents 16 species of opisthobranch of which 15 are new records to Maharashtra and 8 to India.

Rapid ocean warming may alter habitat suitability and population fitness for marine ectotherms. Susceptibility to thermal perturbations will depend in part on plasticity of a species' upper thermal limits of performance (CT max). However, we currently lack data regarding CT max plasticity for several major marine taxa, including nudibranch mollusks, thus limiting predictive responses to habitat warming for these species. In order to determine relative sensitivity to future warming, we investigated heat tolerance limits (CT max), heat tolerance plasticity (acclimation response ratio), thermal safety margins, temperature sensitivity of metabolism, and metabolic cost of heat shock in nine species of nudibranchs collected across a thermal gradient along the northeastern Pacific coast of California and held at ambient and elevated temperature for thermal acclima-tion. Heat tolerance differed significantly among species, ranging from 25:4750:57C to 32:2751:87C (x 5 SD), but did not vary with collection site within species. Thermal plasticity was generally high (0:52 5 0:06, x 5 SE) and was strongly negatively correlated with CT max in accordance with the trade-off hypothesis of thermal adaptation. Metabolic costs of thermal challenge were low, with no significant alteration in respiration rate of any species 1 h after exposure to acute heat shock. Thermal safety margins, calculated against maximum habitat temperatures, were negative for nearly all species examined (28:5755:37C, x 5 CI [confi-dence interval]). From these data, we conclude that warm adaptation in intertidal nudibranchs constrains plastic responses to acute thermal challenge and that southern warm-adapted species are likely most vulnerable to future warming.

We report here a unusual observation of active predation by the coral Goniopora lobata on the benthic corallivorous Trichesiid nudibranch in a laboratory set-up. This observation indicates that not only can some corals capture pelagic plankton for food, they could also actively identify and hunt for benthic preys.