Daily accumulation rates of marine litter on the shores of Rapa Nui (Easter Island) in the South Pacific Ocean.

Large amounts of floating litter accumulate in the subtropical gyres, and the shorelines of oceanic islands in the vicinity of these accumulation zones receive large amounts of litter. The dynamics of marine litter arrival were evaluated on a small pocket beach on Rapa Nui (Easter Island) between November 2016 and June 2017 over a total time period of 190 days. Plastics dominated the stranded litter, with the majority of the items showing indications to come from the high seas fisheries operating in the South Pacific. Litter accumulation rates varied between 0 and 1.90 items m-1 day-1, and were highest following days of strong winds from northern directions. The results indicate that the shores of Rapa Nui are exposed to continuous input of plastic litter from the contaminated waters of the subtropical gyre, which is intensified during strong onshore winds.

Temperature alters the physiological response of spiny lobsters under predation risk.

Predation risk can strongly shape prey ecological traits, with specific anti-predator responses displayed to reduce encounters with predators. Key environmental drivers, such as temperature, can profoundly modulate prey energetic costs in ectotherms, although we currently lack knowledge of how both temperature and predation risk can challenge prey physiology and ecology. Such uncertainties in predator-prey interactions are particularly relevant for marine regions experiencing rapid environmental changes due to climate change. Using the octopus (Octopus maorum)-spiny lobster (Jasus edwardsii) interaction as a predator-prey model, we examined different metabolic traits of sub adult spiny lobsters under predation risk in combination with two thermal scenarios: 'current' (20°C) and 'warming' (23°C), based on projections of sea-surface temperature under climate change. We examined lobster standard metabolic rates to define the energetic requirements at specific temperatures. Routine metabolic rates (RMRs) within a respirometer were used as a proxy of lobster activity during night and day time, and active metabolic rates, aerobic scope and excess post-exercise oxygen consumption were used to assess the energetic costs associated with escape responses (i.e. tail-flipping) in both thermal scenarios. Lobster standard metabolic rate increased at 23°C, suggesting an elevated energetic requirement (39%) compared to 20°C. Unthreatened lobsters displayed a strong circadian pattern in RMR with higher rates during the night compared with the day, which were strongly magnified at 23°C. Once exposed to predation risk, lobsters at 20°C quickly reduced their RMR by ~29%, suggesting an immobility or 'freezing' response to avoid predators. Conversely, lobsters acclimated to 23°C did not display such an anti-predator response. These findings suggest that warmer temperatures may induce a change to the typical immobility predation risk response of lobsters. It is hypothesized that heightened energetic maintenance requirements at higher temperatures may act to override the normal predator-risk responses under climate-change scenarios.

Inter-hemispherical shoreline surveys of anthropogenic marine debris - A binational citizen science project with schoolchildren.

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.

Spatio-temporal variation of anthropogenic marine debris on Chilean beaches.

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 8years covered by our study, which suggests that economic development alone cannot explain temporal trends in AMD densities.

Habitat coupling writ large: pelagic-derived materials fuel benthivorous macroalgal reef fishes in an upwelling zone.

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 (δ13 C, δ15 N) 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.

Reef Sound as an Orientation Cue for Shoreward Migration by Pueruli of the Rock Lobster, Jasus edwardsii.

The post-larval or puerulus stage of spiny, or rock, lobsters (Palinuridae) swim many kilometres from open oceans into coastal waters where they subsequently settle. The orientation cues used by the puerulus for this migration are unclear, but are presumed to be critical to finding a place to settle. Understanding this process may help explain the biological processes of dispersal and settlement, and be useful for developing realistic dispersal models. In this study, we examined the use of reef sound as an orientation cue by the puerulus stage of the southern rock lobster, Jasus edwardsii. Experiments were conducted using in situ binary choice chambers together with replayed recording of underwater reef sound. The experiment was conducted in a sandy lagoon under varying wind conditions. A significant proportion of puerulus (69%) swam towards the reef sound in calm wind conditions. However, in windy conditions (>25 m s-1) the orientation behaviour appeared to be less consistent with the inclusion of these results, reducing the overall proportion of pueruli that swam towards the reef sound (59.3%). These results resolve previous speculation that underwater reef sound is used as an orientation cue in the shoreward migration of the puerulus of spiny lobsters, and suggest that sea surface winds may moderate the ability of migrating pueruli to use this cue to locate coastal reef habitat to settle. Underwater sound may increase the chance of successful settlement and survival of this valuable species.

Inducers of settlement and moulting in post-larval spiny lobster.

The rapid and often remote location of suitable habitats used by migrating organisms is often critical to their subsequent recruitment, fitness and survival, and this includes in the marine environment. However, for the non-feeding post-larval stage of spiny lobsters, effective settlement cues for habitat selection are critical to their success but are poorly described. Therefore, the current study examined whether acoustic and substrate cues have the potential to shorten the time to moulting and affect their subsequent nutritional condition in the pueruli of the southern spiny lobster, Jasus edwardsii. Individuals moulted to first instar juveniles up to 38% faster when exposed to the underwater sound from two types of typical settlement habitat (coastal kelp- and urchin-dominated reefs) compared to those with no underwater sound. The settlement delay in the post-larvae without underwater sound also resulted in juveniles in poorer survival and nutritional condition as measured by their protein and lipid contents. In a separate experiment, post-larvae presented with seaweed and rock substrates were found to complete settlement and moult to juvenile by as much as 20% faster compared to those on the sand and control treatments. Overall, the results are the first to demonstrate that the pueruli of J. edwardsii have the ability to detect and respond to underwater sound, as well as determining that both acoustic and substrate cues play a role in modulating physiological development during settlement.

PHYSIOLOGICAL PERFORMANCE OF FLOATING GIANT KELP MACROCYSTIS PYRIFERA (PHAEOPHYCEAE): LATITUDINAL VARIABILITY IN THE EFFECTS OF TEMPERATURE AND GRAZING(1).

Rafts of Macrocystis pyrifera (L.) C. Agardh can act as an important dispersal vehicle for a multitude of organisms, but this mechanism requires prolonged persistence of floating kelps at the sea surface. When detached, kelps become transferred into higher temperature and irradiance regimes at the sea surface, which may negatively affect kelp physiology and thus their ability to persist for long periods after detachment. To examine the effect of water temperature and herbivory on the photosynthetic performance, pigment composition, carbonic anhydrase (CA) activity, and the nitrogen (N) and carbon (C) content of floating M. pyrifera, experiments were conducted at three sites (20° S, 30° S, 40° S) along the Chilean Pacific coast. Sporophytes of M. pyrifera were maintained at three different temperatures (ambient, ambient - 4°C, ambient + 4°C) and in presence or absence of the amphipod Peramphithoe femorata for 14 d. CA activity decreased at 20° S and 30° S, where water temperatures and irradiances were highest. At both sites, pigment contents were substantially lower in the experimental algae than in the initial algae, an effect that was enhanced by grazers. Floating kelps at 20° S could not withstand water temperatures >24°C and sank at day 5 of experimentation. Maximal quantum yield decreased at 20° S and 30° S but remained high at 40° S. It is concluded that environmental stress is low for kelps floating under moderate temperature and irradiance conditions (i.e., at 40° S), ensuring their physiological integrity at the sea surface and, consequently, a high dispersal potential for associated biota.

Nest-building behavior by the amphipod Peramphithoe femorata (Kroyer) on the kelp Macrocystis pyrifera (Linnaeus) C. Agardh from Northern-Central Chile.

Many small arthropod herbivores from terrestrial and marine environments construct tubicolous nest-like domiciles on their host plants or algae by rolling up selected portions of the leaf or blade. Nests serve as both shelter and food, which results in conflicting needs for the grazers because feeding activity continuously destroys parts of the nests. While the nesting habit of ampithoid amphipods and other peracarid crustaceans is widely known, very little is known about the nest dynamics and how the conflict between shelter and food requirements is resolved. Herein we examined the nest-building behavior and nest occupancy of the kelp-dwelling amphipod Peramphithoe femorata on the giant kelp Macrocystis pyrifera. Domiciles on the distal-most part of the blades were occupied by amphipods and were steadily advanced toward the blade base. Since the blades grow from a basal growth meristem, blades and nests develop in opposite directions. Thus, the amphipods exploit the kelp growth pattern to maintain their nests in the medium-distal part of the blades. During a 2-week-long experiment, we observed that blade elongation equaled nest advancement during the first 8 days after nest construction. Thereafter, blade growth slowed down and was surpassed by nest advancement rates, possibly forcing amphipods to seek out new blades. Nest occupancy was generally short (1-4 days), but some amphipods resided longer (>4 days) in their nests. The sophisticated nest-building behavior of P. femorata and other ampithoids maximizes nest persistence, offers optimal protection against predators, and promotes feeding on nutritive or, alternatively, on less defended tissues.

Floating marine debris in fjords, gulfs and channels of southern Chile.

Floating marine debris (FMD) is reported from all oceans. The bulk of FMD are plastics, which due to their longevity cause multiple negative impacts on wildlife and environment. Identifying the origins of FMD (land- or sea-based) is important to take the necessary steps to diminish their abundance. Using ship surveys we examined the abundance, composition and distribution of FMD during the years 2002-2005 in the fjords, gulfs and channels of southern Chile. Abundances of FMD were relatively high compared with other studies, ranging from 1 to 250 items km(-2). The majority (approximately 80%) of FMD was composed of styrofoam (expanded polystyrene), plastic bags and plastic fragments. Styrofoam, which is intensively used as flotation device by mussel farms, was very abundant in the northern region but rarely occurred in the southern region of the study area. Food sacks from salmon farms were also most common in the northern region, where approximately 85% of the total Chilean mussel and salmon harvest is produced. Plastic bags, which could be from land- or sea-based sources, were found throughout the entire study area. Our results indicate that sea-based activities (mussel farming and salmon aquaculture) are responsible for most FMD in the study area. In order to reduce FMDs in the environment, in addition to stronger legislation and identification of potential sources, we suggest environmental education programs and we encourage public participation (e.g. in beach surveys and clean-ups).

EFFECT OF TEMPERATURE AND GRAZING ON GROWTH AND REPRODUCTION OF FLOATING MACROCYSTIS SPP. (PHAEOPHYCEAE) ALONG A LATITUDINAL GRADIENT(1).

Macroalgal rafts frequently occur floating in coastal waters of temperate regions of the world's oceans. These rafts are considered important dispersal vehicles for associated organisms with direct development. However, environmental factors may limit the floating potential of kelp and thereby the dispersal of associated organisms. To examine the effect of water temperature and grazing on growth, reproductive output, and survival of floating Macrocystis spp., experiments were conducted in outdoor tanks during austral summer 2006/2007 at three sites along the Chilean Pacific coast (20° S, 30° S, 40° S). At each site, Macrocystis spp. was maintained individually at three different water temperatures (ambient, ambient - 4°C, ambient + 4°C) and in the presence or absence of the amphipod grazer Peramphithoe femorata for 14 d. High water temperatures (>20°C) provoked rapid degradation of Macrocystis spp. rafts. At moderate temperatures (15°C-20°C), algal survival depended on the presence of associated grazers. In the absence of grazers, algal rafts gained in biomass while grazing caused considerable losses of algal biomass. Algal survival was the highest under cooler conditions (<15°C), where raft degradation was slow and grazer-induced biomass losses were compensated by continuing algal growth. Our results indicate that floating kelp rafts can survive for long time periods at the sea surface, but survival depends on the interaction between temperature and grazing. We suggest that these processes limiting the survival of kelp rafts in warmer temperatures may act as a dispersal barrier for kelp and its associated passengers.