Abstract The exploited mangrove crab Ucides cordatus, an important ecosystem engineer in South American mangroves, has a biphasic lifecycle with pelagic larvae developing offshore. Megalopae return to the mangrove forest to settle, i.e., metamorphose into benthic juveniles but its environmental drivers remain poorly understood. We postulate that conspecific crabs facilitate recruitment. In the field, we investigated whether the number of recruits is higher near conspecific burrows than in areas without conspecific bioturbation. Recruit sampling was conducted monthly from April 2008 to May 2009 along an environmental gradient. First, U. cordatus recruits of that year emerged from March to July. Intraspecific facilitation was indicated by significantly higher recruit numbers in bioturbated than in non-bioturbated substrates. Recruits were most abundant in zones with intermediate conditions of inundation, leaf litter standing stock, sediment consistency, luminosity, temperature, salinity, and pH. Avoidance of more inundated zones likely reduces predation by fishes and of less inundated zones helps individuals escape more stressful, drier environmental conditions. The observed habitat-specific recruitment pattern must be considered when designing field assessments of the population structure of U. cordatus (which should include sampling recruits) and enhancing stocks by releasing laboratory-cultivated larvae and first juveniles into the wild.

Resumo Esta é uma síntese enquadrada na Rede de Monitoramento de Habitats Bentônicos Costeiros (ReBentos, GT4: Manguezais e Marismas), embasada em literatura científica que examina interações entre clima e biodiversidade, assim como fatores antrópicos, incluindo aqueles responsáveis pela diminuição da resiliência sistêmica. O objetivo deste trabalho é determinar as dificuldades quanto à detecção de sinais precoces e alertas de mudanças climáticas com dados de monitoramento. No presente trabalho, também foram exploradas formas de contornar os diversos obstáculos identificados. A exposição e a sensitividade de espécies de mangue e de marisma, bem como dos ecossistemas dos quais fazem parte, os tornam extremamente vulneráveis e potenciais indicadores ambientais de mudanças de nível do mar e outras respostas às variações do clima. Entretanto, a interpretação de mudanças em manguezais e marismas e em seus atributos sistêmicos deve ser meticulosa, considerando assinatura energética, regime de distúrbios e pressões ambientais em cada local de estudo. Os potenciais de adaptação e de sobrevivência, em resposta a tais mudanças, dependem da fisiologia de cada espécie e dos processos contextuais onde reside a resiliência e a capacidade de persistir (em níveis local, de paisagem e regionais). A zona costeira deve ser alvo de medidas antecipatórias para redução de riscos por quaisquer impactos, uma vez que nela há intensa convergência de processos sociais e ecológicos. Os ecossistemas dessa zona devem ser integrados em estratégias de adaptação. O manejo costeiro deve ser embasado em mitigação pró-ativa e colaborativa de longo-termo, sempre com base em estudos ecossistêmicos e em programas de monitoramento que possam 1) prover sistema de alerta precoce; 2) preencher lacunas entre correlações simplistas que proveem inferências fracas, e abordagens baseadas em processos que levem a atribuições mais confiáveis e a melhores níveis de antecipação.

Abstract This synthesis is framed within the scope of the Brazilian Benthic Coastal Habitat Monitoring Network (ReBentos WG 4: Mangroves and Salt Marshes), focusing on papers that examine biodiversity-climate interactions as well as human-induced factors including those that decrease systemic resilience. The goal is to assess difficulties related to the detection of climate and early warning signals from monitoring data. We also explored ways to circumvent some of the obstacles identified. Exposure and sensitivity of mangrove and salt marsh species and ecosystems make them extremely vulnerable to environmental impacts and potential indicators of sea level and climate-driven environmental change. However, the interpretation of shifts in mangroves and salt marsh species and systemic attributes must be scrutinized considering local and setting-level energy signature changes; including disturbance regime and local stressors, since these vary widely on a regional scale. The potential for adaptation and survival in response to climate change depends, in addition to the inherent properties of species, on contextual processes at the local, landscape, and regional levels that support resilience. Regardless of stressor type, because of the convergence of social and ecological processes, coastal zones should be targeted for anticipatory action to reduce risks and to integrate these ecosystems into adaptation strategies. Management must be grounded on proactive mitigation and collaborative action based on long-term ecosystem-based studies and well-designed monitoring programs that can 1) provide real-time early warning and 2) close the gap between simple correlations that provide weak inferences and process-based approaches that can yield increasingly reliable attribution and improved levels of anticipation.

Recruits of the mangrove crab Ucides cordatus (Linnaeus, 1763), rarely encountered in the field were found co-inhabiting burrows of larger male and female conspecifics in the mangrove forest. They were located in the sediment of the inner walls and burrow plugs. Average carapace width (CW) of the hosting and co-inhabiting crabs was 3.8 ± 0.20 and 0.9 ± 0.03, respectively. As shown by the size-frequency distribution, while most recruits leave the conspecific burrows after reaching 1.0 cm CW, some stay until they reach a size of 2.5 cm CW. The results of this study contribute to a better understanding of recruitment patterns in this ecologically and economically important mangrove crab species. Follow-up studies are however needed to fully determine the role of conspecific burrows for juvenile habitat choice and survivorship in U. cordatus.