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Temporal and spatial isotopic variability of marine prey species in south-eastern Australia: Potential implications for predator diet studies.

ABSTRACT: Stable isotope analyses, particularly of carbon (δ13C) and nitrogen (δ15N), are used to investigate ecological relationships among species. For marine predators, research has shown the main factors influencing their intra-specific and intra-individual isotopic variation are geographical movements and changes in the composition of diet over time. However, as the differences seen may be the result of changes in the prey items consumed, a change in feeding location or the combination of both, knowledge of the temporal and spatial consistency in the isotopic values of prey becomes crucial for making accurate inferences about predator diets. This study used an abundant marine predator, the Australasian gannet (Morus serrator), as prey sampler to investigate the annual variation in fish and squid prey isotope values over a four-year period (2012-2015) and the geographic variation between two sites with contrasting oceanographic conditions. Significant inter-annual variation was observed in δ13C and/or δ15N values of five of the eight prey species analysed. The strongest inter-annual variation in both δ13C and δ15N values occurred in 2015, which coincided with a strong El Niño-Southern Oscillation (ENSO). This may suggest a temporal fluctuation in the geographic source of prey or the origin of their nutrients. These results suggest that it is important to consider the potential significant differences in isotopic values within the prey assemblages that predators consume. This is important to improve the interpretation of marine predator isotope results when determining the influence of environmental variability on their diets.

SUBMITTER: Rodriguez-Malagon MA

PROVIDER: S-EPMC8631622 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Despite increases in the frequency and intensity of disturbances on coral reefs over the past few decades, the response of subtropical coral assemblages to climate change is poorly understood. To address this knowledge gap on Australian reefs and provide a baseline for future comparisons, we quantified spatial (10-100's of kilometres) and temporal (decadal) patterns of benthic assemblages across a latitudinal gradient along the east Australian coastline (23.5° S to 31.5° S). Benthic community composition was quantified at six locations from the southern Great Barrier Reef, Queensland (Heron Reef, 23.5° S, 152° E) to northern New South Wales (31° S, 153.1° E) and at Lord Howe Island (31.5° S, 159.1° E). Our results indicate significant latitudinal differences in benthic assemblages, while community composition at some sites was more similar to those hundreds of kilometres away than to that of neighbouring reefs. A general trend was observed with decreasing cover of Acroporidae with increasing latitude, corresponding with an increasing cover of Pocilloporidae and Dendrophylliidae. Heron Reef comprised a high proportion of Acropora corals (43% total coral cover) and coralline algae (44%). In contrast, high-latitude reefs were dominated by mixed coral assemblages (0-52%) and high macroalgal cover (16-27%). Decadal comparisons of high-latitude reefs showed regional stability of benthic assemblages (9 out of 11 assemblages remained stable at > 75% similarity), during a period of warming oceans (0.15-0.24°C per decade). Such temporal stability suggests that eastern Australian subtropical communities may be more resistant than tropical reef communities that have experienced assembly shifts caused by perturbations associated with recent global climate change. Despite the clear differences in the structure of coral assemblages evident in our spatial surveys, we suggest that the temporal stability of high-latitude reefs may provide a limited refuge for tropical coral populations in an increasingly uncertain future.

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Temporal and spatial isotopic variability of marine prey species in south-eastern Australia: Potential implications for predator diet studies.

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