Diversity and time-series analyses of Caribbean deep-sea coral and sponge assemblages on the tropical island slope of Isla de Roatán, Honduras

Shore-based submersible operations, from 2006 to 2020, have allowed us to examine megabenthic assemblages along the island margin of Isla de Roatán from depths of about 150 to 750 m, including repeated observations of the same organisms. These dives were used to photo-document a diverse benthic assemblage and observe the health and condition of the sessile fauna in a well-explored but relatively undocumented area of the Mesoamerican Reef. Samples were collected by dip net, and some dives profiled the water column chemistry in the year 2011. The deep-sea coral assemblage observed off Roatan exhibits high abundance and diversity. The sessile habitat-forming taxa consist primarily of at least 20 different octocorals (e.g., Plexauridae, Primnoidae, Coralliidae, Isididae, and Ellisellidae) and 20 different sponges each (Demospongiae and Hexactinellida), with several known and unknown taxa of Zoantharia, Antipatharia (Bathypathes spp), and Scleractinia (e.g., Desmophyllum pertusum, Dendrophyllia alternata, Madracis myriaster, and solitary taxa). Crinoidea were also abundant and diverse, represented by at least nine species. Epifaunal assemblages associated with corals include at least 24 macroinvertebrate species dominated by Asteroschema laeve (Ophiuroidea) and Chirostylus spp. (Decapoda: Anomura). Repeated observations of a few large octocoral colonies over many years illustrate patterns of predation, recolonization, and epibiont host fidelity, including a 14-year record of decline in a plexaurid octocoral (putatively Paramuricea sp.) and loss of its resident ophiuroids. The shore-based submersible provides a practical and relatively inexpensive platform from which to study coral and sponge assemblages on a deep tropical island slope. The deep-sea coral gardens are likely to harbor new species and new discoveries if more samples can be acquired and made available for taxonomic research.

Structure and Trophic Niches in Mobile Epifauna Assemblages Associated With Seaweeds and Habitats of Syngnathid Fishes in Cíes Archipelago (Atlantic Islands Marine National Park, North West Iberia)

Syngnathids are vulnerable fishes closely associated with seaweeds and seagrass, which provide shelter and food resources. Even though most syngnathids commonly feed on small crustaceans, the feeding regimes may differ depending on the species and prey availability. This is the first monitoring study to explain syngnathid abundances and dietary regimes within macroalgal beds in Cíes Archipelago (Atlantic Islands Marine National Park, North West Iberian Peninsula). We sampled the epifaunal assemblages in seaweed communities dominated by the canopy-forming macroalgae Gongolaria baccata and Codium spp. seasonally during 2 years. The epifaunal structure was mostly represented by harpacticoid copepods, amphipods (especially gammarids) and gastropods. Epifauna exhibited low plant-host specificity and a higher dominance of amphipods on the more structurally complex macroalgae G. baccata. The epifaunal assemblages and syngnathid specimens were assessed for trophic structure using stable isotopes (δ13C and δ15N). The three syngnathids (Hippocampus guttulatus, Syngnathus acus, and Entelurus aequoreus) inhabiting Cíes Archipelago were sympatric. They occupied highly similar trophic positions (TPs), but differed in niche size, in such a way that the snake pipefish E. aequoreus would likely feed on smaller prey. The assessment of the feeding regime in the dominant great pipefish S. acus revealed that amphipods mostly contributed to bulk diet, followed by isopods, carideans, and copepods, whereas mysidaceans were not highly consumed. Seasonal changes in both epifaunal structure and syngnathids abundance confirmed that syngnathids are seasonal residents in Cíes Archipelago, migrating to other areas in autumn when the seaweed cover is drastically reduced and the epifaunal structure modified. This study showed the importance of Gongolaria assemblages in Cíes Archipelago, providing rich dietary sources and potentially contributing to higher abundances and diversity of syngnathids. Ongoing cover reduction in Gongolaria assemblages in certain regions (e.g., Mediterranean) should be considered a potential ecological concern for syngnathids and accompanying fauna, requiring further investigations.

The Invasive Seaweed Asparagopsis Taxiformis Erodes the Primary Productivity and Biodiversity of Native Algal Forests in the Mediterranean Sea

Invasive seaweeds are listed among the most relevant threats to marine ecosystems worldwide. Biodiversity hotspots, such as the Mediterranean Sea, are facing multiple invasions and are expected to be severely affected by the introduction of new non-native seaweeds in the near future. In this study, we evaluated the consequences of the shift from the native Ericaria brachycarpa to the invasive Asparagopsis taxiformis habitat at shallow rocky shores of Favignana Island (Egadi Islands, MPA, Sicily, Italy). We compared algal biomass and species composition and structure of the associated epifaunal assemblages in homogenous and mixed stands of E. brachycarpa and A. taxiformis. Results showed that the biomass of primary producers is reduced by 90% in the A. taxiformis invaded habitat compared to the E. brachycarpa native habitat. The structure of the epifaunal assemblages displayed significant variations among homogenous and mixed stands. The abundance, species richness and Shannon-Wiener diversity index of the epifaunal assemblages decreased by 89%, 78% and 40%, respectively from homogenous stands of the native E. brachycarpa to the invasive A. taxiformis. Seaweed biomass was the structural attribute better explaining the variation of epifaunal abundance, species richness and diversity. Overall, our results suggest that the shift from E. brachycarpa to A. taxiformis habitat would drastically erode the biomass of primary producers and the associated biodiversity. We hypothesize that a complete shift from native to invasive seaweeds can ultimately lead to bottom-up effects in rocky shore habitats, with negative consequences for the ecosystem structure, functioning and the services provided.

Epifaunal invertebrate assemblages associated with branching Pocilloporids in Moorea, French Polynesia

Reef-building corals can harbour high abundances of diverse invertebrate epifauna. Coral characteristics and environmental conditions are important drivers of community structure of coral-associated invertebrates; however, our current understanding of drivers of epifaunal distributions is still unclear. This study tests the relative importance of the physical environment (current flow speed) and host quality (e.g., colony height, surface area, distance between branches, penetration depth among branches, and background partial mortality) in structuring epifaunal communities living within branching Pocillopora colonies on a back reef in Moorea, French Polynesia. A total of 470 individuals belonging to four phyla, 16 families and 39 genera were extracted from 36 Pocillopora spp. colonies. Decapods were the most abundant epifaunal organisms (accounting for 84% of individuals) found living in Pocillopora spp. While coral host characteristics and flow regime are very important, these parameters were not correlated with epifaunal assemblages at the time of the study. Epifaunal assemblages associated with Pocillopora spp. were consistent and minimally affected by differences in host characteristics and flow regime. The consistency in abundance and taxon richness among colonies (regardless of habitat characteristics) highlighted the importance of total habitat availability. With escalating effects of climate change and other localized disturbances, it is critical to preserve branching corals to support epifaunal communities.

Sabella spallanzanii and Seafloor Biodiversity Enhancement in a Marine Soft-Sediment System

Predicting and managing the potential economic, social, and ecological impacts of bioinvasions is a key goal of non-indigenous species (NIS) research worldwide. The marine fan worm, Sabella spallanzanii, is an ecosystem engineering NIS that forms dense filter-feeding canopies on hard substrata and large clumps of individuals in soft sediment habitats. In this study, we investigated the epifaunal assemblages associated with Sabella clumps of increasing size and complexity from soft-sediment benthic ecosystems in Auckland Harbour, New Zealand. The diversity and abundance of epifaunal taxa increased with clump size. Species accumulation curves suggest that with further increases in Sabella clump size, diversity will continue to increase. There were no differential effects on taxa related to feeding mode or motility despite the potential for Sabella to reduce food to suspension feeders (through competition) and increase food supply to deposit feeders (through biodeposition). Our results provide an example of local biodiversity enhancement by an NIS, though some of the species benefitting from Sabella were themselves non-indigenous or of uncertain origin (cryptogenic/indeterminate). Longer term studies of the impacts of Sabella on native biodiversity and ecosystem functioning, including on food webs, are important next steps.

Taxonomic composition of mobile epifaunal invertebrate assemblages on diverse benthic microhabitats from temperate to tropical reefs

Anthropogenic drivers are flattening reef structure from 3-dimensional habitats composed of macroalgae and live branching corals towards low-profile turfing algae. Our current understanding of the consequences of widespread reef degradation currently fails to consider the responses of small mobile invertebrates (‘epifauna’) to patterns of change amongst reef structural elements (‘microhabitats’). Here, the taxonomic composition of 152 epifaunal assemblages was compared among 21 structurally diverse benthic microhabitats across an Australian temperate to tropical climatic gradient, spanning 28.6 degrees in latitude from Tasmania to the northern Great Barrier Reef. Epifauna varied consistently with different microhabitat types, and to a much lesser extent with latitude. Macroalgae, live branching coral and turfing algae represented 3 extremes for epifaunal community structure, with most microhabitats possessing epifaunal assemblages intermediate between these endpoints. Amongst structural characteristics, epifauna related primarily to the degree of branching and hardness of microhabitats. Mobile invertebrate communities are likely to transform in predictable ways with the collapse of large erect macroalgae and live coral towards low-lying turf-associated communities.

Spatiotemporal dynamics of the molluscan community associated with seagrass on the western equatorial Atlantic

This study aimed to qualitatively and quantitatively analyse the molluscan assemblages associated with a Halodule wrightii seagrass bed in a rarely studied area within a conservation unit in north-eastern Brazil. Seasonal and spatial changes in several seagrass meadow characteristics, including sediment, were evaluated to explain temporal and spatial variations in the molluscs found there. The molluscan community differed in its structure among periods and meadows, as well as in the composition of its infaunal and epifaunal assemblages. The results of this study indicated that molluscs are affected by the particular characteristics of a seagrass meadow, especially by its location in the intertidal zone, more than by the area of the meadow. Molluscs were also affected by other characteristics of the seagrass meadow, such as above-ground biomass and shoot density. Changes in all molluscan assemblages were also mediated by differences among months and seasons in this region of the western equatorial Atlantic, but not by seasonal changes of the meadow. The studied meadow was found to be one of the densest in Brazil, which has considerable importance to its associated fauna.