Ph.D. Hinojosa-Toledo, Ivan

Anthropogenic marine debris (AMD) is a global problem and the identification of its sources is essential for adequate mitigation strategies. Herein we examined whether AMD density and composition differed between two countries with contrasting socio-economic backgrounds and marine litter sources (i.e. Chile and Germany). In nationwide beach litter surveys, we used a citizen science approach with schoolchildren and their teachers. Litter densities were substantially higher in Chile than in Germany. The different geographic zones surveyed in both countries showed strong grouping tendencies according to their main economic activities (tourism, shipping, fisheries/aquaculture), major litter sources, and AMD composition, in terms of dominance and diversity of AMD types. The results suggest that beach litter composition can be used as a simple proxy to identify AMD sources, and also that law enforcement and education can help mitigate the problem; however, for efficient solutions, production and consumption of plastics must be reduced.

Anthropogenic Marine Debris (AMD) in the SE Pacific has primarily local origins from land-based sources, including cities (coastal and inland), beach-goers, aquaculture, and fisheries. The low frequency of AMD colonized by oceanic biota (bryozoans, lepadid barnacles) suggests that most litter items from coastal waters of the Humboldt Current System (HCS) are pulled offshore into the South Pacific Subtropical Gyre (SPSG). The highest densities of floating micro- and macroplastics are reported from the SPSG. An extensive survey of photographic records, unpublished data, conference proceedings, and published studies revealed interactions with plastics for 97 species in the SE Pacific, including 20 species of fish, 5 sea turtles, 53 seabirds, and 19 marine mammals. Sea turtles are most affected by interactions with plastics, underlined by the fact that 4 of the 5 species suffer both from entanglement and ingestion. Reports gathered in this review suggest that interactions along the continental coast are mostly via entanglement. High frequencies of microplastic ingestion have been reported from planktivorous fish and seabirds inhabiting the oceanic waters and islands exposed to high densities of microplastics concentrated by oceanic currents in the SPSG. Our review also suggests that some species from the highly productive HCS face the risk of negative interactions with AMD, because food and plastic litter are concentrated in coastal front systems. In order to improve the conservation of marine vertebrates, especially of sea turtles, urgent measures of plastic reduction are needed.

Consumer pressure in benthic communities is predicted to be higher at low than at high latitudes, but support for this pattern has been ambiguous, especially for herbivory. To understand large-scale variation in biotic interactions, we quantify consumption (predation and herbivory) along 2500 km of the Chilean coast (19°S–42°S). We deployed tethering assays at ten sites with three diferent baits: the crab Petrolisthes laevigatus as living prey for predators, dried squid as dead prey for predators/scavengers, and the kelp Lessonia spp. for herbivores. Underwater videos were used to characterize the consumer community and identify those species consuming baits. The species composition of consumers, frequency of occurrence, and maximum abundance (MaxN) of crustaceans and the blenniid fsh Scartichthys spp. varied across sites. Consumption of P. laevigatus and kelp did not vary with latitude, while squid baits were consumed more quickly at mid and high latitudes. This is likely explained by the increased occurrence of predatory crabs, which was positively correlated with consumption of squidpops after 2 h. Crabs, rather than fsh, were the principal consumers of squid baits (91% of all recorded predation events) at sites south of 30°S. Fish and crustaceans preyed in similar proportion on P. laevigatus, with most fsh predation events at northern sites. The absence of any strong latitudinal patterns in consumption rate of tethered prey is likely due to redundancy among consumers across the latitudinal range, with crustaceans gaining in importance with increasing latitude, possibly replacing fsh as key predators.

We examined the hypothesis that in an emerging economy such as Chile the abundances of Anthropogenic Marine Debris (AMD) on beaches are increasing over time. The citizen science program Científicos de la Basura (“Litter Scientists”) conducted three national surveys (2008, 2012 and 2016) to determine AMD composition, abundance, spatial patterns and temporal trends. AMD was found on all beaches along the entire Chilean coast. Highest percentages of AMD in all surveys were plastics and cigarette butts, which can be attributed to local sources (i.e. beach users). The Antofagasta region in northern Chile had the highest abundance of AMD compared with all other zones. Higher abundances of AMD were found at the upper stations from almost all zones. No significant tendency of increasing or decreasing AMD densities was observed during the 8 years covered by our study, which suggests that economic development alone cannot explain temporal trends in AMD densities.

Larval behavior plays an important role in dispersal and settlement of marine organisms with cues from the environment often providing crucial guidance for facilitating these processes. The postlarvae, or pueruli, of the southern rock lobster, Jasus edwardsii (Hutton, 1875), are known to migrate over long distances from oceanic water and settle on coastal reefs using a combination of onshore transport and active nocturnal swimming. In laboratory experiments, we examined environmental cues used for this migration, specifically whether chemical cues in coastal vs oceanic seawater influenced their swimming orientation and their rate of development to juveniles. In total, 66% of pueruli actively swam toward coastal water rather than oceanic water (n = 41), indicating that they may use chemical cues in their settlement processes. Holding pueruli in coastal water vs artificial seawater did not expedite the development of pueruli to benthic juvenile stage, indicating that other cues could be important to the final settlement process. The present study suggests that chemical cues are being used in settlement processes during the onshore migration to settlement sites in this ecologically and economically important species.

Coastal marine upwelling famously supports elevated levels of pelagic biological production, but can also subsidize production in inshore habitats via pelagic‐benthic coupling. Consumers inhabiting macroalgae‐dominated rocky reef habitats are often considered to be members of a food web fuelled by energy derived from benthic primary production; conversely, they may also be subsidized by materials transported from pelagic habitats. Here, we used stable isotopes (δ13C, δ15N) to examine the relative contribution of pelagic and benthic materials to an ecologically and economically important benthivorous fish assemblage inhabiting subtidal macroalgae‐dominated reefs along ~1,000 km of the northern Chilean coast where coastal upwelling is active. Fish were isotopically most similar to the pelagic pathway and Bayesian mixing models indicated that production of benthivorous fish was dominated (median 98%, range 69–99%) by pelagic‐derived C and N. Although the mechanism by which these materials enter the benthic food web remains unknown, our results clearly highlight the importance of pelagic‐benthic coupling in the region. The scale of this subsidy has substantial implications for our basic understanding of ecosystem functioning and the management of nearshore habitats in northern Chile and other upwelling zones worldwide.