Spatial and temporal variation in subtidal molluscan diversity amongst temperate estuarine habitats

Abstract

Effective management of marine ecosystems is enhanced when detailed information on biodiversity is available. Key information to underpin management actions and conservation planning includes relationships between species assemblages and environmental gradients, and information on species distributions. We conducted a subtidal biodiversity assessment of surface‐dwelling subtidal molluscs in eight a priori defined habitat types using underwater visual censuses to quantitatively explore relationships between molluscan assemblages, and their correlation with benthic habitats and abiotic variables. In addition, variations in diversity were examined for two key habitat types (areas dominated by Dendronephthya australis and by filter feeders) over a period of 15 months to examine temporal change. We found that molluscs form distinct assemblages within subtidal habitats, but that assemblages within key habitats show inherent temporal variability. Regional (gamma) diversity of molluscs was found to result from a combination of: (i) within habitat alpha diversity, which increased with habitat complexity; (ii) between habitat beta diversity, with significant differences in molluscan assemblages amongst habitats with differing benthic growth, substrate type, and depth; and (iii) temporal beta diversity, with significant changes detected in molluscan assemblages over time. The results demonstrate how habitats and abiotic variables (principally depth and substrate type) combine to contribute to molluscan biodiversity in temperate estuaries, and illustrate the value of these factors as surrogates for surface‐dwelling subtidal molluscs in conservation planning.

A Hotspot in the Romanian Black Sea: Eelgrass Beds Drive Local Biodiversity in Surrounding Bare Sediments

“…Seagrasses provide food resources, add live surface for colonization, attenuate currents, stabilize shorelines, buffer the negative effect of eutrophication, and help with carbon sequestration (Bos et al, 2007;Baeta et al, 2009;Bouma et al, 2009;Duarte et al, 2010;Marin-Diaz et al, 2020). Most studies on seagrass meadows show that they sustain and enhance localscale diversity of communities (Attrill et al, 2000;Włodarska-Kowalczuk et al, 2014;Davis et al, 2017;Hyman et al, 2019;Rodil et al, 2021), or conspicuous groups of epifaunal organisms (Sánchez-Jerez et al, 1999;Hovel and Lipcius, 2002), polychaetes (Somaschini et al, 1994;Gambi et al, 1998) or fish (Guidetti and Bussotti, 2002). However, these meadows are not always recognized as hotspots of diversity and we argue that this is likely due to two main reasons: (1) there are well-known exceptions in which species composition or diversity measures within and outside seagrass beds do not differ (Den Hartog, 1983;Asmus and Asmus, 2000;Polte et al, 2005;Barnes, 2014;Barnes and Barnes, 2014) and (2) where striking between-habitat diversity differences occur, sometimes we have failed to highlight their potential influence on surrounding marine sediments (Hyman et al, 2019).…”

Sea Slugs—“Rare in Space and Time”—But Not Always

“…The majority of studies of sea slug diversity are based on short-term or sporadic data [7,10,17], or data collected in widely-spaced surveys [6,25], with the consequent risk that species may be identified as rare due to data insufficiency [2]. Long-term data are necessary to assess patterns of rarity and to determine if this is due to: temporal variability linked to normal seasonal fluctuations [26]; persistent presence but numerical rarity; or vagrancy. Climate-change-driven poleward range extensions of several species of sea slug [27][28][29] is also resulting in designation of rarity for species occurring at novel locations [30], or as single observations [28].…”

Long-term persistence of structured habitats: seagrass meadows as enduring hotspots of biodiversity and faunal stability

“…In marine ecosystems, empirical studies of coral reefs, seagrass meadows and other structurally complex habitats yielded multi-pronged support for this hypothesis. First, structured marine habitats represent well-known hotspots of α-diversity [2,6]. Second, increased biodiversity frequently correlates with increased structural complexity [1,7].…”