A functional analysis reveals extremely low redundancy in global mangrove invertebrate fauna

Abstract

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.

A DNA barcode library for mangrove gastropods and crabs of Hong Kong and the Greater Bay Area reveals an unexpected faunal diversity associated with the intertidal forests of Southern China

“…In terms of fauna, the invasive apple snail, Pomacea canaliculata, is abundant in Hong Kong freshwater wetlands and can impact these habitats by outcompeting native snails [56] and predating on amphibian eggs [57]. In this local context, the lack of non-native invertebrate species in mangrove forests confirms the current hypothesis postulating that mangroves are a uniquely harsh environment where only well adapted and specialised fauna can deal with the ecological and physiological challenges posed by these forests [7,19,58].…”

“…This study is the first attempt to provide a reference barcode library for mangrove-associated macrobenthic fauna of Hong Kong and the whole Greater Bay Area and represents a reliable tool to assist researchers and managers in their conservation efforts. Macrobenthos diversity is in fact a recognised indicator of the state, functionality, and health of mangrove forests [7]. Mangrove-associated macrobenthic fauna perform crucial ecosystem functions, such as their bio-engineering activities on the sediment that ultimately influence nutrient cycling and sequestration [6,87].…”

“…Despite accounting for only 0.7% of the total tropical forests of the world [1], mangroves play a critical role in the protection of coastal areas, act as nurseries for many species, sequestrate carbon, recycle nutrients, and provide benefits to people through the direct exploitation of their resources [2][3][4][5]. Such ecosystem services are provided by a unique biome represented by a floral community of terrestrial origin and the specialised marine and intertidal macroinvertebrate assemblages thriving in these forests [2,[6][7][8].…”

“…Although it is now well understood that a rich and functionally redundant fauna is the key to ensure full mangrove functionality [7], taxonomic surveys and species identification have proved to be challenging for mangrove associated macrofauna, mainly due to the cryptic behaviour of many species, inaccessibility to some areas, and the presence of a high number of morphologically very similar, and phylogenetically related, species. Recent studies have circumvented the identification issues by using DNA barcodes to identify the presence of species in mangrove forests [20,[22][23][24].…”

The Mangrove Periwinkle Littoraria angulifera (Mollusca: Littorinidae) in the Urabá Gulf (Colombian Caribbean): Finding Ways in an Urbanizing Coast?

“…From a functional point of view, specialists are more sensitive to ongoing human impacts and are being rapidly replaced by generalist species in diverse systems, prompting a global functional homogenization that could alter ecosystem functioning (Clavel et al, 2011;Dharmarajan et al, 2021;Filgueiras et al, 2021). This is critically important in ecosystems where functional redundancy is extremely low, as tropical mangrove forests (see Cannicci et al, 2021) because eliminating specialists may also imply loosing key ecosystem functions.…”