Microplastics ingestion and heterotrophy in thermally stressed corals.

Rising sea temperatures and increasing pollution threaten the fate of coral reefs and millions of people who depend on them. Some reef-building corals respond to thermal stress and subsequent bleaching with increases in heterotrophy, which may increase the risk of ingesting microplastics. Whether this heterotrophic plasticity affects microplastics ingestion or whether ingesting microplastics affects heterotrophic feeding in corals is unknown. To determine this, two coral species, Montipora capitata and Pocillopora damicornis, were exposed to ambient (~27 °C) and increased (~30 °C) temperature and then fed microplastics, Artemia nauplii, or both. Following thermal stress, both species significantly reduced feeding on Artemia but no significant decrease in microplastics ingestion was observed. Interestingly, P. damicornis only ingested microplastics when Artemia were also present, providing evidence that microplastics are not selectively ingested by this species and are only incidentally ingested when food is available. As the first study to examine microplastics ingestion following thermal stress in corals, our results highlight the variability in the risk of microplastics ingestion among species and the importance of considering multiple drivers to project how corals will be affected by global change.

Sex biased individual variation in movement patterns of a highly mobile, near-shore marine planktivore, the reef manta ray Mobula alfredi.

We examined individual variation and the role of sex on the movements of the reef manta ray Mobula alfredi. Specifically, we analysed several movement metrics using 6 years of nightly observations (1 January 2009-31 December 2014) of 118 individually identifiable manta rays at two discrete but spatially proximate sites, locally known as Manta Heaven and Manta Village, 15 km apart on the west side of the island of Hawaii, USA. Males were slightly more often (33.5%, model fitted mean, P < 0.05) observed than females at Manta Heaven, but females were much more often (156.4%, model fitted mean, P < 0.05) observed at Manta Village. Movement patterns among individuals varied greatly, but the level of variation was similar between sexes. Some animals, mainly females, displayed more resident patterns, whereas other, more mobile, animals moved between sites more frequently and had longer gaps between sightings. We did not detect discrete behavioural groups; rather, individuals varied along a continuous spectrum from many observations and high affinity to few observations and low fidelity to survey locations. These complex and variable movement patterns observed at the individual level, between sexes and between two nearby sites, in Hawaii's manta rays highlight the need for finer scale considerations in conservation and management of highly mobile marine populations.