Forecasting intensifying disturbance effects on coral reefs

Anticipating future changes of an ecosystem's dynamics requires knowledge of how its key communities respond to current environmental regimes. The Great Barrier Reef (GBR) is under threat, with rapid changes of its reef‐building hard coral (HC) community structure already evident across broad spatial scales. While several underlying relationships between HC and multiple disturbances have been documented, responses of other benthic communities to disturbances are not well understood. Here we used statistical modelling to explore the effects of broad‐scale climate‐related disturbances on benthic communities to predict their structure under scenarios of increasing disturbance frequency. We parameterized a multivariate model using the composition of benthic communities estimated by 145,000 observations from the northern GBR between 2012 and 2017. During this time, surveyed reefs were variously impacted by two tropical cyclones and two heat stress events that resulted in extensive HC mortality. This unprecedented sequence of disturbances was used to estimate the effects of discrete versus interacting disturbances on the compositional structure of HC, soft corals (SC) and algae. Discrete disturbances increased the prevalence of algae relative to HC while the interaction between cyclones and heat stress was the main driver of the increase in SC relative to algae and HC. Predictions from disturbance scenarios included relative increases in algae versus SC that varied by the frequency and types of disturbance interactions. However, high uncertainty of compositional changes in the presence of several disturbances shows that responses of algae and SC to the decline in HC needs further research. Better understanding of the effects of multiple disturbances on benthic communities as a whole is essential for predicting the future status of coral reefs and managing them in the light of new environmental regimes. The approach we develop here opens new opportunities for reaching this goal.     

The importance of Quaternary records in reducing risk from tropical cyclones

Numerous late Holocene records of tropical cyclones have been collected from north-east Queensland, Australia. They are in the form of multiple sedimentary ridges paralleling the shore. The ridges are composed of coral fragments, or shell and sand or pure sand. A method to determine the intensity of the tropical cyclone responsible for deposition of the ridges at each site has been applied and the results suggest that in the majority of cases these features were deposited by very high magnitude events. The results suggest that extrapolations of long-term cyclone magnitude and frequencies from the 30- to 40-year-long instrumental record, which is the method commonly used to assess risk from this hazard, substantially underestimate the risk from this hazard. This is confirmed for the Cairns region by an 800-year-long high-resolution isotope record of tropical cyclones preserved in a limestone stalagmite. Together the sedimentary and isotope records suggest that tropical cyclone activity in north-east Queensland has been in a phase of quiescence since before European settlement of the region in approximately AD 1870. It is suggested that the incorporation of the palaeo record into risk assessments will provide a more realistic guide to the magnitude frequency relationship of tropical cyclones and help reduce risk from this hazard as a consequence.     

Seasonal differences and response to a tropical storm reflected in diatom assemblage changes in a southwest Florida watershed

Because estuaries are dynamic on many temporal scales, it is difficult to differentiate long-term shifts from those resulting from erratic pulse events like severe storms. Diatoms are abundant and diverse in estuaries, and may characterize these dynamics across relevant time scales. The climate of south Florida is subtropical, with dry winters and wet summers that may also harbor tropical storms and cyclones. We investigated whether these repeated seasonal drivers of change in estuaries differ from the influence of tropical cyclones on planktonic and benthic diatom assemblages. Diatom assemblages and environmental parameters were measured in the Charlotte Harbor watershed of southwest Florida to identify differences between the wet and dry seasons and changes that occurred following Tropical Storm Debby in 2012. Indicator taxa that were significantly affiliated with each season and post-storm conditions were identified. Diatom assemblages across the watershed were similar in wet and dry seasons, but differences increased following the tropical storm. The reduction in community dispersion following the storm was pronounced in each of the major drainages of the estuary. There were spatially-distinct responses of diatoms to environmental changes driven by the storm. These results suggest that past storm activity could be detected using diatoms preserved in estuarine sediments using both single indicator-species as well as community approaches.     

A decrease in the abundance and strategic sophistication of cleaner fish after environmental perturbations

Coral reef ecosystems are declining worldwide and under foreseeable threat due to climate change, resulting in significant changes in reef communities. It is unknown, however, how such community changes impact interspecific interactions. Recent extreme weather events affecting the Great Barrier Reef, that is, consecutive cyclones and the 2016 El Niño event, allowed us to explore potential consequences in the mutualistic interactions involving cleaner fish Labroides dimidiatus (hereafter “cleaner”). After the perturbations, cleaner densities were reduced by 80%, disproportionally compared to the variety of reef fish clients from which cleaners remove ectoparasites. Consequently, shifts in supply and demand yielded an increase in the clients’ demand for cleaning. Therefore, clients became less selective toward cleaners, whereas cleaners were able to choose from a multitude of partners. In parallel, we found a significant decline in the ability of cleaners to manage their reputation and to learn to prioritize ephemeral food sources to maximize food intake in laboratory experiments. In other words, cleaners failed to display the previously documented strategic sophistication that made this species a prime example for fish intelligence. In conclusion, low population densities may cause various effects on individual behavior, and as a consequence, interspecific interactions. At the same time, our data suggest that a recovery of population densities would cause a recovery of previously described interaction patterns and cleaner strategic sophistication within the lifetime of individuals.     

“Too low” δO of paleo-meteoric, low latitude, water; do paleo-tropical cyclones explain it?

Isotopic analysis of rock samples showed anomalously ¹⁸O-depleted reconstructed isotopic composition of paleo-meteoric water over southern Israel between the Late Cretaceous and the Early Miocene, with δ¹⁸O_W as low as −14‰ [SMOW]. This range is significantly “lighter” than the expected values for rain at the relevant paleo-latitudes (~ 8^°N to 25^°N). It is similar or lighter than areas with meteoric water at the present climate, in which rainfall contribution from tropical cyclone (TC) is significant. Rainfall from TCs is ¹⁸O-depleted because of the recirculation of the vapor into repeated precipitation or distillation cycles. A paleo-geographic reconstruction of the region shows that throughout the period there was a warm ocean to the east and southeast of the relevant area. Thus, TCs formed over the ocean and made landfall on the coastline at a distance of 300 to 400 km to the east. The reconstructed composition of the rainwater implies dominance of TCs at these times. Furthermore, the combination of warmer seas and lighter rainwater than at present suggests that the TCs were more dominant than in the most TC-prone coastal areas at the present climate. The results of the present study suggest that climate during the relevant time periods was very different from the present, with TC activity similar or exceeding the most TC prone locations in the world at the present climate. This might also hint that warmer sea waters in the geological past were conducive to greater TC activity than in the present climate. Answering this question requires additional research.     

Assessing the impact of extreme adverse weather on the biological traits of a European storm petrel colony

Climate change affects the climatic disturbance patterns and regimes and is altering the frequency and intensity of subtropical cyclones. These events can affect population dynamics of seabirds (e.g., survival, reproduction). In this work we tested the effect of adverse weather on a colony of European storm petrels (Hydrobates pelagicus) located in a small islet (Aketx) in northern Spain. Over a long-term monitoring period (1993–2014) we ringed 3728 petrels. From 2003 onwards we also monitored breeding success, the percentage of immature individuals and moult scores. We used Cormack-Jolly-Seber models and Underhill and Zucchini models to analyze the effects of climatic conditions on a number of biological traits (survival, breeding parameters, moulting patterns). Our analyses revealed a constant value of adult survival over the 26-year monitoring period. Recapture probability, however, tended to be positively influenced by NAO conditions in spring, and negatively influenced by NAO conditions in winter (although this would only affect to a fraction of first-captured birds). Moreover, the impact of adverse weather, especially in 2011 and 2014, resulted in an increasing proportion of yearlings in the breeding population, a lower breeding success and a delayed onset of moult. These effects were similar to those observed during the Prestige oil spill catastrophe.     

Tropical Rain Forest Recovery from Cyclone Damage and Fire in Samoa1

In 1990 and 1991, Samoa was struck by two cyclones, Ofa and Val. In the Tafua Rain Forest Preserve on the island of Savai'i, one part of the forest also burned after the first cyclone. Here we report on patterns of regeneration and changes in tree species composition in the Tafua lowland rain forest after five years of recovery from cyclone and fire disturbance. In the unburned area, tree canopy cover increased from 27 percent after the last cyclone to 58 percent, and in the burned area from below 12 to 49 percent. Nine of the ten most common tree species decreased in relative abundance in the entire forest after the last cyclone. One fast growing pioneer species, Macaranga harveyana now makes up 42 percent of the total number of trees (>5 cm DBH) in the unburned area and 86 percent in the burned area. Large interspecific differences occur in size distribution and there are at least four distinguishable regeneration patterns, which may be related to shade tolerance. Mean number of species per plot was generally higher in the unburned area than in the burned area, while the Shannon evenness index was higher in the unburned than in the burned area only for trees above 1 cm DBH. Species with fruits known to be fed upon by birds and/or bats generally made up a larger proportion of all trees in the burned than in the unburned area. In contrast to other studies of post‐cyclone regeneration, in which recovery is often rapid due to resprouting of trees, recovery in the Tafua forest was a slow process with regeneration more dependent on vertebrate seed dispersal than on resprouting.     

Australian tropical forest canopy crane: New tools for new frontiers

Abstract An industrial crane was installed in the Daintree lowland rainforest in 1998 to provide a new means of accessing the canopy. Approximately 0.95 ha of forest, including 680 trees of 82 species with a diameter at breast height of greater than 10 cm, are accessible using the crane. The site was hit by a Category 3 Cyclone in 1999 and has shown a remarkable rate of recovery. The crane has been used for a very wide range of research including tree physiology and ecology, interactions with vertebrate and invertebrate biodiversity and studies of carbon and water fluxes. Results from studies on this crane and 11 other cranes around the world are changing views of the importance of the rainforest canopy.