Interactions of larval dynamics and substrate preference have ecological significance for benthic biodiversity and Ostrea edulis Linnaeus, 1758 in the presence of Crepidula fornicata

Abstract

1. Populations of the European flat oyster Ostrea edulis have experienced catastrophic declines across Europe and subsequent spread of the non-native species Crepidula fornicata has led to its occurrence in exceptionally high densities in some areas previously dominated by O. edulis. 2. Spatial and temporal concurrence of C. fornicata larvae within the zooplankton community occurs throughout the O. edulis spawning season. A C. fornicata larval peak density of 374.7 ± 96.5 larvae/ml (mean ± SD) was observed in Langston Harbour sympatrically with O. edulis density of 45.7 ± 20.1 larvae/ml in early August. Overall oyster larvae contribution to the zooplankton community was higher in Portsmouth Harbour (12%) than C. fornicata contribution (9.6%), whilst the opposite occurred in Langstone (oysters, 11.7%; C. fornicata, 12%). 3. Larval abundance is not reflected in recruitment on the seabed, owing to the conspecific substrate preference of O. edulis. Settlement of O. edulis spat was significantly greater on settlement discs covered with recently deceased oyster shells; 6.7 ± 1.2 (mean ± SE) spat/disc vs old smooth oyster shells, 2.7 ± 1.3, C. fornicata shell 1.7 ± 0.3, cemented discs 2 ± 1 or the plastic control disc 0.7 ± 0.7. 4. Settlement substrate type matters in the presence of high benthic and larval densities of C. fornicata. The Solent has become a substrate-limited system for O. edulis; substrate management or reef deployment is required to restore a selfrecruiting population. 5. Finally, although C. fornicata may provide functional equivalence in terms of filtering services, it supports a significantly different and less biodiverse faunal community from that of O. edulis. Therefore C. fornicata does not provide equivalence as an ecosystem engineer and mechanisms of ecological phase shift are occurring within areas dominated by this invasive species.

A small step or a giant leap: Accounting for settlement delay and dispersal in restoration planning

“…edulis larvae are specialist settlers [ cf . 61 ], finely-tuned to target conspecifics and their own habitats [ 31 , 44 ]. Specialist settlers metamorphose at low rates on surfaces which provide a habitat that is neither optimal nor deleterious for juveniles [ 63 ].…”

“…O . edulis larvae appear to be selective settlers, finely-tuned to settle in response to specific substrates [ 43 – 45 ] and cues which are indicative of their adult habitat requirements, such as conspecifics or habitat-associated biofilms [ 31 , 44 ]. Evidence suggest that O .…”

Forty questions of importance to the policy and practice of native oyster reef restoration in Europe

“…In the case of O. edulis in Europe, reference sites that may provide a baseline for assessing the progress of restoration efforts are absent from much of the range. Moreover, sites that still contain populations are generally modified as a result of a history of oyster production, dredging and other fishing activities, or modified via shifts in the dominant biotic community (Allison, Hardy, Hayward, Cameron, & Underwood, 2019;Helmer et al, 2019;Preston et al, 2020). As such, establishing reasonable baselines to inform adaptive management of restoration efforts where O. edulis habitats are currently absent is a key priority.…”

Life cycle informed restoration: Engineering settlement substrate material characteristics and structural complexity for reef formation

“…O. edulis , where fertilization occurs internally in the females), after several weeks, settle as spat on the seafloor. Oyster spat preferentially settle on hard, stable substrates on which they cement themselves in place, such as oyster shells or concrete (Bersoza Hernández et al., 2018; Christianen et al., 2018; Preston et al., 2020; Rodriguez‐Perez et al., 2019). After this, they are sessile filter feeders and highly dependent on the quality of the local environment for their survival, growth and reproduction (Burreson & Ragone, 1996; Peyre et al., 2016; Pogoda et al., 2019).…”