Deforestation results in habitat fragmentation, decreasing diversity, and functional degradation. For mangroves, no data are available on the impact of deforestation on the diversity and functionality of the specialized invertebrate fauna, critical for their functioning. We compiled a global dataset of mangrove invertebrate fauna comprising 364 species from 16 locations, classified into 64 functional entities (FEs). For each location, we calculated taxonomic distinctness (Δ+), functional richness (FRi), functional redundancy (FRe), and functional vulnerability (FVu) to assess functional integrity. Δ+ and FRi were significantly related to air temperature but not to geomorphic characteristics, mirroring the global biodiversity anomaly of mangrove trees. Neither of those two indices was linked to forest area, but both sharply decreased in human-impacted mangroves. About 60% of the locations showed an average FRe < 2, indicating that most of the FEs comprised one species only. Notable exceptions were the Eastern Indian Ocean and west Pacific Ocean locations, but also in this region, 57% of the FEs had no redundancy, placing mangroves among the most vulnerable ecosystems on the planet. Our study shows that despite low redundancy, even small mangrove patches host truly multifunctional faunal assemblages, ultimately underpinning their services. However, our analyses also suggest that even a modest local loss of invertebrate diversity could have significant negative consequences for many mangroves and cascading effects for adjacent ecosystems. This pattern of faunal-mediated ecosystem functionality is crucial for assessing the vulnerability of mangrove forests to anthropogenic impact and provides an approach to planning their effective conservation and restoration.

Coral reefs are home to the greatest diversity of marine life, and many species on reefs live in symbiotic associations. Studying the historical biogeography of symbiotic species is key to unravelling (potential) coevolutionary processes and explaining species richness patterns. Coral-dwelling gall crabs (Cryptochiridae) live in obligate symbiosis with a scleractinian host, and are ideally suited to study the evolutionary history between heterogeneous taxa involved in a symbiotic relationship. The genus Opecarcinus Kropp and Manning, 1987, like its host coral family Agariciidae, occurs in both Indo-Pacific and Caribbean seas, and is the only cryptochirid genus with a circumtropical distribution. Here, we use mitochondrial and nuclear DNA gene fragments of Opecarcinus specimens sampled from 21 Indo-Pacific localities and one Atlantic (Caribbean) locality. We applied several species delimitation tests to characterise species diversity, inferred a Bayesian molecular-clock time-calibrated phylogeny to estimate divergence times and performed an ancestral area reconstruction. Time to the most recent common ancestor (tMRCA) of Opecarcinus is estimated at 15−6 Mya (middle Miocene—late Miocene). The genus harbours ~ 15 undescribed species as well as several potential species complexes. There are indications of strict host-specificity patterns in certain Opecarcinus species in the Indo-Pacific and Atlantic, however, a robust phylogeny reconstruction of Agariciidae corals—needed to test this further—is currently lacking. The Indo-West Pacific was inferred to be the most probable ancestral area, from where the Opecarcinus lineage colonised the Western Atlantic and subsequently speciated into O. hypostegus. Opecarcinus likely invaded from the Indo-West Pacific across the East Pacific Barrier to the Atlantic, before the full closure of the Isthmus of Panama. The subsequent speciation of O. hypostegus, is possibly associated with newly available niches in the Caribbean, in combination with genetic isolation following the closure of the Panama Isthmus.

Increasing temperatures on a global scale and locally deteriorating water quality affect coral distribution and health. Mechanisms that convey environmental robustness are poorly understood and have been attributed to the coral host, algal symbionts, and prokaryotic associates. Flexibility of the host’s (bacterial) microbiome has been suggested to contribute to environmental robustness, but the underlying mechanisms are unclear. We therefore utilised the vastly contrasting water quality gradient present along Hong Kong’s highly urbanised coastline to explore whether flexibility in the microbiome of Oulastrea crispata relates to spatial variations in temperature, salinity, dissolved oxygen, pH, nitrate, nitrite, ammonia, total nitrogen, phosphorus, turbidity, and chlorophyll a. We identified differences in the coral microbiomes between sites, but the measured environmental variables only explained ~ 23% of the variation suggesting other factors are contributing substantially. The observed structural complexity of the microbiome (based on alpha diversity indices) appears to be relatively conserved across the environmental gradient even at sites where no other hard coral can survive. Therefore, we conclude that, at least in O. crispata, flexibility in the microbiome does not appear to underpin the robustness of this broadly distributed coral.

Background Mangroves are tropical and subtropical intertidal forests colonising sheltered coasts across the world. They host a unique faunal community, dominated by brachyuran crabs and gastropods. These invertebrates strongly contribute to the functionality of the entire forest. The reliable assessment of mangrove faunal diversity is, thus, a crucial step for efficient management and conservation plans, but it is hindered by difficulties in species identification. Here we provide a verified DNA barcode library for brachyuran crabs and gastropods inhabiting the mangroves of the Greater Bay Area, Southern China. In particular, we collected and morphologically identified 1100 specimens of mangrove associated brachyuran crabs and gastropods. The partial sequences of the mtDNA cytochrome oxidase subunit I gene were obtained from 275 specimens. Barcode sequences were then used to delineate Molecular Operational Taxonomic Units (MOTUs), employing three different delimitation methods: the automatic barcode gap discovery (ABGD) method, the general mixed Yule coalescent (GMYC) model and a Bayesian implementation of the Poisson tree processes (bPTP) model. Results By integrating DNA barcodes with morphology, we identified 44 gastropod species and 58 brachyuran species associated with Hong Kong mangroves, with five and seven new records, for gastropods and crabs, respectively, for the Greater Bay Area. The delineation of MOTUs based on barcode sequences revealed a strong congruence between morphological and molecular identification for both taxa, showing the high reliability of the barcode library. Conclusions This study provides the first reference barcode library for mangrove-associated macrobenthic fauna in the Greater Bay Area and represents a reliable tool to management and conservation plans. Our molecular analyses resolved long lasting taxonomic misidentifications and inconsistencies and updated the knowledge on the geographical distribution of Asian mangrove associated fauna, ultimately highlighting a level of biodiversity higher than previously thought for Southern China.

No abstract

Following an incidental observation of captive Clibanarius corallinus (H. Milne Edwards, 1848) supposedly removing algae from each other’s shells, we conducted a feeding experiment over 72 hours to understand its potential role as a mesograzer in coral reef ecosystems. Epiphyte-covered, coral rubble fragments of Acropora spp. were exposed to hermit crab (N = 41) activity for 72 h in a flow-through seawater aquarium system at Heron Island, southern Great Barrier Reef, Australia to understand whether hermit crabs could remove epilithic algae and if so, to what extent. Coral fragments exposed to the hermit crabs had 9.1% less chlorophyll at the end of the experiment. The detritus generated in the experimental set-up had 2.4 times more chlorophyll and 33.4% less organic biomass than the detritus generated in the control environment. The crabs did on average lose 0.11 g of their initial weight, which could have been a consequence of the experimental set-up. These results suggest that C. corallinus has the potential to contribute to the control of epilithic algae in coral reefs, with such effect having hitherto been overlooked as a result of the cryptic behaviour of this hermit crab species.

No abstract

No abstract