Stranding events of drift organisms (Arribadas) in southern Brazil and the spread of invasive bryozoan in South America.

The accumulation of drift organisms (Arribadas, constituted by benthic microalgae, macroalgae and bryozoans) on Central Beach in Balneário Camboriú (SC) has drawn attention since the early 2000s. However, historical surveys suggest an ancient phenomenon that has been increasing in intensity, promoted by urbanization and the eutrophication of the bay in recent years, leading to changes in the taxonomic composition. Previously, these Arribadas were comprised of two species of benthic microalgae (Amphitetras antediluviana and Biddulphia biddulphiana) and the bryozoan Arbocuspis ramosa. However, since 2019, a substantial increase in biomass has been observed on the beach and the dominance of the macroalgae Bryopsis plumosa strongly suggests an increase in the load of organic matter and nutrients in the bay. Recently (2022) the presence of a new invasive bryozoan species (Amathia alternata) was detected, highlighting the need to continue investigating the Arribadas to monitor the ecological evolution of this process.

Consumer Responses to Experimental Pulsed Subsidies in Isolated versus Connected Habitats.

AbstractIncreases in consumer abundance following a resource pulse can be driven by diet shifts, aggregation, and reproductive responses, with combined responses expected to result in faster response times and larger numerical increases. Previous work in plots on large Bahamian islands has shown that lizards (Anolis sagrei) increased in abundance following pulses of seaweed deposition, which provide additional prey (i.e., seaweed detritivores). Numerical responses were associated with rapid diet shifts and aggregation, followed by increased reproduction. These dynamics are likely different on isolated small islands, where lizards cannot readily immigrate or emigrate. To test this, we manipulated the frequency and magnitude of seaweed resource pulses on whole small islands and in plots within large islands, and we monitored lizard diet and numerical responses over 4 years. We found that seaweed addition caused persistent increases in lizard abundance on small islands regardless of pulse frequency or magnitude. Increased abundance may have occurred because the initial pulse facilitated population establishment, possibly via enhanced overwinter survival. In contrast with a previous experiment, we did not detect numerical responses in plots on large islands, despite lizards consuming more marine resources in subsidized plots. This lack of a numerical response may be due to rapid aggregation followed by disaggregation or to stronger suppression of A. sagrei by their predators on the large islands in this study. Our results highlight the importance of habitat connectivity in governing ecological responses to resource pulses and suggest that disaggregation and changes in survivorship may be underappreciated drivers of pulse-associated dynamics.

Assessment the short-term effects of wrack removal on supralittoral arthropods using the M-BACI design on Atlantic sandy beaches of Brazil and Spain.

Wrack removal has been adopted indiscriminately, with no previous assessment of the ecological implications for sandy beach ecosystem. This study evaluated, through an M-BACI design, the effect of wrack removal on supralittoral arthropods on Atlantic sandy beaches receiving different types of wrack: mangrove propagules (Brazil), seagrasses and macroalgae (Spain). Impacted plots were contrasted with controls in 8 successive periods before and after experimental wrack removal. After the disturbance, drastic decreases in the densities of the amphipod Platorchestia monodi, coleopterans Cleridae, Nitidulidae and Phaleria testacea (Brazilian beaches) and amphipod Talitrus saltator (Spanish beaches) were detected in the impacted plots. The recovery patterns of arthropods might be related to wrack features (amount, composition, and degradation) combined with density and species-specific strategies (e.g. mobility, feeding preferences) in each Atlantic region. The temporary suppression of wrack and its associated fauna can have potential effects on the wrack-derived process and food-web structure on sandy beaches.