Habitat fragmentation has some impacts on aspects of ecosystem functioning in a sub-tropical seagrass bed

Navigating biodiversity patterns in fragmented seagrass mosaics

Human-driven fragmentation of natural habitats increasingly threatens biodiversity, particularly in coastal ecosystems like seagrass meadows. Fragmentation breaks continuous habitats into smaller, isolated patches, amplifying edge effects and disrupting community structures and ecosystem functions. This study examines the effects of habitat fragmentation on large (> 1 mm) and small (0.2-1 mm) epifauna, as well as infauna, within eelgrass (Zostera marina) meadows along the Skagerrak coast in western Sweden. We assessed faunal responses across three fragmentation levels (low, medium, and high) and patch zones (Edge, Near-Edge and Center), providing a novel multi-assemblage analysis of these dynamics. Field surveys and statistical modeling revealed distinct community responses: large epifauna, especially amphipods, dominated low and moderately fragmented meadows, whereas highly fragmented areas showed more even species distributions. In contrast, small epifauna exhibited consistent abundance across zones and fragmentation levels. Infaunal communities varied most, with high fragmentation linked to increased evenness and shifts in species composition. These findings underscore the importance of conserving less fragmented meadows and highlight the need for targeted restoration efforts to enhance biodiversity and ecological resilience in degraded areas. By addressing both patch- and seascape-level fragmentation effects, this study offers critical insights into the ecological impacts of habitat fragmentation, supporting the development of targeted conservation strategies for coastal ecosystems.

Habitat Stability Modulates Temporal β-Diversity Patterns of Seagrass-Associated Amphipods Across a Temperate-Subtropical Transition Zone

Identifying drivers that shape biodiversity across biogeographical regions is important to predict ecosystem responses to environmental changes. While β-diversity has been widely used to describe biodiversity patterns across space, the dynamic assembly of species over time has been comparatively overlooked. Insights from terrestrial and marine studies on temporal β-diversity has mostly considered environmental drivers, while the role of biotic mechanisms has been largely ignored. Here, we investigated patterns of temporal variation in β-diversity of seagrass-associated amphipods. We conducted a study in three biogeographical regions across a temperate to subtropical latitudinal gradient (approximately 2000 km, 13° of latitude in total). In each region, we randomly selected three Cymodocea nodosa meadows, totaling nine meadows sampled seasonally (i.e., four times per year) from 2016 to 2018. We partitioned temporal β-diversity into its turnover (i.e., species replacement) and nestedness (i.e., differences in species composition caused by species losses) components and addressed the relative influence of both temporal variation in habitat structure (i.e., biotic driver) and environmental conditions on the observed β-diversity patterns. Our study revealed high temporal β-diversity of amphipod assemblages across the three biogeographical regions, denoting significant fluctuations in species composition over time. We identified species turnover as the primary driver of temporal β-diversity, strongly linked to temporal variability in local habitat structure rather than to regional climatic drivers. Subtropical Atlantic meadows with high structural stability over time exhibited the largest turnover rates compared with temperate Mediterranean meadows, under lower structural stability, where nestedness was a more relevant component of temporal β-diversity. Our results highlight the crucial role of habitat stability in modulating temporal β-diversity patterns on animals associated with seagrasses, stressing the importance of monitoring variations in habitat structure over time for developing management plans and restoration actions in the context of diversity loss and fragmentation of ecosystems.

Spatial sedimentation and plant captured sediment within seagrass patches

Habitat degradation in coastal ecosystems has resulted in the fragmentation of coastal aquatic vegetation and compromised their role in supplying essential ecological services such as trapping sediment or sequestering carbon. Fragmentation has changed seagrass architecture by decreasing the density of the canopy or engendering small patches of vegetated areas. This study aims to quantify the role different patch sizes of vegetation with different canopy densities have in the spatial distribution of sediment within a patch. To this aim, two canopy densities, four different patch lengths, and two wave frequencies were considered. The amounts of sediment deposited onto the bed, captured by plant leaves, remaining in suspension within the canopy, and remaining in suspension above the canopy were used to understand the impact hydrodynamics has on sediment distribution patterns within seagrass patches. In all the cases studied, patches reduced the suspended sediment concentrations, increased the capture of particles in the leaves, and increased the sedimentation rates to the bed. For the lowest wave frequency studied (0.5 Hz), the sediment deposited to the bottom was enhanced at canopy edges, resulting in spatial heterogeneous sedimentation patterns. Therefore, restoration and preservation of coastal aquatic vegetation landscapes can help face future climate change scenarios where an increase in sedimentation can help mitigate predicted sea level rise in coastal areas.

Drivers of variation in seagrass-associated amphipods across biogeographical areas

Amphipods are one of the dominant epifaunal groups in seagrass meadows. However, our understanding of the biogeographical patterns in the distribution of these small crustaceans is limited. In this study, we investigated such patterns and the potential drivers in twelve Cymodocea nodosa meadows within four distinctive biogeographical areas across 2000 Km and 13° of latitude in two ocean basins (Mediterranean Sea and Atlantic Ocean). We found that species abundances in the assemblage of seagrass-associated amphipods differed among areas following a pattern largely explained by seagrass leaf area and epiphyte biomass, while the variation pattern in species presence/absence was determined by seagrass density and epiphyte biomass. Seagrass leaf area was also the most important determinant of greater amphipod total density and species richness, while amphipod density also increased with algal cover. Overall, our results evidenced that biogeographical patterns of variation in amphipod assemblages are mainly influenced by components of the habitat structure, which covary with environmental conditions, finding that structurally more complex meadows harboring higher abundance and richness of amphipods associated.

Economic mapping and assessment of Cymodocea nodosa meadows as nursery grounds for commercially important fish species. A case study in the Canary Islands

Cymodocea nodosa seagrass meadows provide several socio-economically ecosystem services, including nurseries for numerous species of commercial interest. These seagrasses are experiencing a worldwide decline, with global loss rates approaching 5% per year, mainly related to coastal human activities. Cymodocea nodosa, the predominant seagrass in the Canary Archipelago (Spain), is also exposed to these threats, which could lead to habitat loss or even local disappearance. In this case study, we estimated the potential economic value of Cymodocea nodosa seagrass meadows for local fisheries at an archipelago scale. Habitat suitability maps were constructed using MAXENT 3.4.1, a software for modelling species distributions by applying a maximum entropy machine-learning method, from a set of environmental variables and presence and background records extracted from historical cartographies. This model allows characterising and assessing the C. nodosa habitat suitability, overcoming the implicit complexity derived from seasonal changes in this species highly dynamic meadows and using it as a first step for the mapping and assessment of ecosystem services. In a second step, value transfer methodologies were used, along with published economic valuations of commercially-interesting fish species related to C. nodosa meadows. We estimate that the potential monetary value of these species can add up to more than 3 million euros per year for the entire Archipelago. The simplicity of the proposed methodology facilitates its repeatability in other similar regions, using freely available data and hence, being suitable for data-scarce scenarios.

The role of seagrass vegetation and local environmental conditions in shaping benthic bacterial and macroinvertebrate communities in a tropical coastal lagoon

We investigated the influence of seagrass canopies on the benthic biodiversity of bacteria and macroinvertebrates in a Red Sea tropical lagoon. Changes in abundance, number of taxa and assemblage structure were analyzed in response to seagrass densities (low, SLD; high, SHD; seagrasses with algae, SA), and compared with unvegetated sediments. Biological and environmental variables were examined in these four habitats (hereafter called treatments), both in the underlaying sediments and overlaying waters, at three randomly picked locations in March 2017. Differences between treatments were more apparent in the benthic habitat than in the overlaying waters. The presence of vegetation (more than its cover) and changes in sedimentary features (grain size and metals) at local scales influenced the observed biological patterns, particularly for macroinvertebrates. Of note, the highest percentage of exclusive macroinvertebrate taxa (18% of the gamma diversity) was observed in the SHD treatment peaking in the SA for bacteria. Benthic macroinvertebrates and bacteria shared a generally low number of taxa across treatments and locations; approximately, 25% of the gamma diversity was shared among all treatments and locations for macrofauna, dropping to 11% for bacteria. Given the low overlap in the species distribution across the lagoon, sustaining the connectivity among heterogeneous soft sediment habitats appears to be essential for maintaining regional biodiversity. This study addresses a current scientific gap related to the relative contributions of vegetated and unvegetated habitats to biodiversity in tropical regions.

Forest edges affect ectoparasite infestation patterns of small mammalian hosts in fragmented forests in Madagascar

Habitat loss and fragmentation drive the worldwide depletion of biodiversity. Although it is known that anthropogenic disturbances severely affect host and ecosystem integrity, effects on parasites are largely understudied. This study aims to investigate if and how habitat fragmentation affects the composition of ectoparasite communities on small mammalian hosts in two networks of dry deciduous forest fragments in northwestern Madagascar. Forest sites differing in size, proportion of edge habitat and host density were studied in the Ankarafantsika National Park and in the Mariarano region. A total of 924 individuals of two mouse lemur species, Microcebus murinus (n = 200) and Microcebus ravelobensis (n = 426), and two rodent species, endemic Eliurus myoxinus (n = 114) and introduced Rattus rattus (n = 184), were captured to assess ectoparasite infestations. Ectoparasite prevalence and ectoparasite species richness were statistically related to nine ecological variables applying generalized linear mixed models. Hosts harbored ticks (Haemaphysalis microcebi), mites (Schoutedenichia microcebi, Listrophoroides spp., Laelaptidae gen. spp.) and sucking lice (Lemurpediculus spp., Polyplax sp., Hoplopleuridae gen. sp.). Parasite prevalence differed significantly between host species for all detected parasite taxa. Proximity to the forest edge led to a significant reduction in ectoparasites. Parasite-specific edge effects were observed up to a distance of 750 m from the forest edge. The obtained results imply that habitat fragmentation impacts ectoparasite communities, in particular by negatively affecting temporary parasite species. The results are best explained by an interplay of parasite life cycles, responses to changes in abiotic factors induced by edges and host-specific responses to habitat fragmentation. The negative responses of most studied ectoparasite taxa to forest edges and habitat fragmentation demonstrate their ecological vulnerability that may eventually threaten the integrity of ecosystems and potentially impact ectoparasite biodiversity worldwide.

Sargassum blooms in the Caribbean alter the trophic structure of the sea urchin Diadema antillarum

The arrival of large masses of drifting Sargassum since 2011 has caused changes in the natural dynamics of Caribbean coastal ecosystems. In the summer of 2015, unprecedented and massive mats of S. fluitans and S. natans have been observed throughout the Mexican Caribbean including exceptional accumulations ashore. This study uses stable isotopes to assess the impact of Sargassum blooms on the trophic dynamics of the Diadema antillarum sea urchin, a keystone herbivore on many Caribbean reefs. Bayesian models were used to estimate the variations in the relative proportions of carbon and nitrogen of assimilated algal resources. At three lagoon reef sites, the niche breadth of D. antillarum was analysed and compared under massive influx of drifting Sargassum spp. vs. no influx of Sargassum blooms. The effects of the leachates generated by the decomposition of Sargassum led to hypoxic conditions on these reefs and reduced the taxonomic diversity of macroalgal food sources available to D. antillarum. Our trophic data support the hypothesis that processes of assimilation of carbon and nitrogen were modified under Sargassum effect. Isotopic signatures of macroalgae associated with the reef sites exhibited significantly lower values of δ¹⁵N altering the natural herbivory of D. antillarum. The Stable Isotopes Analysis in R (SIAR) indicated that, under the influence of Sargassum blooms, certain algal resources (Dictyota, Halimeda and Udotea) were more assimilated due to a reduction in available algal resources. Despite being an abundant available resource, pelagic Sargassum was a negligible contributor to sea urchin diet. The Stable Isotope Bayesian Ellipses in R (SIBER) analysis displayed differences between sites, and suggests a reduction in trophic niche breadth, particularly in a protected reef lagoon. Our findings reveal that Sargassum blooms caused changes in trophic characteristics of D. antillarum with a negative impact by hypoxic conditions. These dynamics, coupled with the increase in organic matter in an oligotrophic system could lead to reduce coral reef ecosystem function.