DOI: 10.3897/neobiota.108.186476

Authors: Sara Cabral, Frederico Carvalho, Joana P. C. Cruz, Joshua Heumüller, Jose M. F. Babarro, Luc A. Comeau, Paula Chainho, Ana C. Brito

Abstract: Despite the burgeoning number of non-indigenous species (NIS) in coastal ecosystems worldwide, the quantification of their direct impacts on native communities remains largely unexplored. This is particularly true for feeding competition among sympatric filter-feeding bivalves. This study aimed to fill a knowledge gap regarding potential trophic competition between native and non-indigenous bivalves by focusing on three species that co-occur in Portuguese estuarine systems: the native cockle (Cerastoderma edule) and the non-indigenous Portuguese oyster (Magallana angulata) and Manila clam (Ruditapes philippinarum). The specific objectives were to (i) estimate their capture efficiency (≈ particle retention efficiency; CE), (ii) assess their clearance rates (CR), and (iii) provide science-based support for suitable management measures regarding NIS. Experiments were conducted under both field and laboratory conditions using the natural seston present in seawater. CE was higher for the six larger particle-size classes (8–14 μm) measured (range: 4–14 μm; size resolution: 1 μm), regardless of species. Although individual CRs did not differ significantly among species, the CR per gram of ash-free dry body tissue weight was significantly higher for the native cockle, suggesting that NIS do not have a competitive advantage in clearing suspended particles. However, the Manila clam might limit food-source availability to the native species because their ecological niches overlap.

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DOI: 10.3897/neobiota.57.49196

Authors: Alexandra Markert

Abstract: Pacific oysters Crassostrea (Magallana) gigas have been successfully invading ecosystems worldwide. As an ecosystem engineer, they have the potential to substantially impact on other species and on functional processes of invaded ecosystems. Engineering strength depends on oyster density in space and time. Density has not yet been studied on the extent of reef structural dynamics. This study assessed abundance of naturalized Pacific oysters by shell length (SL) of live individuals and post-mortem shells at six sites over six consecutive years during post-establishment. Individual biomass, i.e. live wet mass (LWM), flesh mass (FM) and live shell mass (SM LIVE), were determined from a total of 1.935 live oysters in order to estimate areal biomass. The generic term density attribute was used for SL-related population categories and the biomass variables LWM, FM, SM LIVE and SM. As the oyster invasion modulated resident Mytilus edulis beds, the study was supplemented by contemporaneously assessed data of mussels and corresponding analyses. Interrelations of abundance and areal biomass revealed distinct linkages between specific density attributes. Most importantly, large individuals were identified as intrinsic drivers for the determination of areal biomass. Additionally, allometry of large oysters differed from small oysters by attenuated scaling relations. This effect was enhanced by oyster density as results showed that crowding forced large individuals into an increasing slender shape. The significant relationship between the density attributes large oyster and biomass enabled a classification of reef types by large oyster abundance. Reef type (simple or complex reef) and oyster size (small or large) were considered by implementing a novel concept of weighted twin functions (TF) for the relationship between SL and individual biomass. This study demonstrates that the interplay of scaling parameters (scalar, exponent) is highly sensitive to the estimation of individual biomass (shape) and that putative similar scaling parameters can exceedingly affect the estimation of areal biomass. For the first time, this study documents the crucial relevance of areal reference, i.e. cluster density (CD) or reef density (RD), when comparing density. RD considers reef areas devoid of oysters and results from CD reduced by reef coverage (RC) as the relative reef area occupied by oysters. A compilation of density attributes at simple and complex reefs shall serve as a density guide. Irrespective of areal reference, oyster structural density attributes were significantly higher at complex than at simple reefs. In contrast, areal reference was of vital importance when evaluating the impact of engineering strength at ecosystem-level. While mussel CD was similar at both reef types, RD at complex reefs supported significantly more large mussels and higher mussel biomass than at simple reefs. Although mussels dominated both reef types by abundance of large individuals, oysters were the keystone engineers by dominating biomass. The prominent status of large oysters for both allometric scaling and density, presumably characteristic for Pacific oyster populations worldwide, should be considered when conducting future investigations. The effort of monitoring will substantially be reduced as only large oysters have to be counted for an empirical characterization of Pacific oyster reefs. The large oyster concept is independent of sampling season, assessment method or ecosystem, and is also applicable to old data sets. Harmonization on the proposed density attributes with a clear specification of areal reference will allow trans-regional comparisons of Pacific oyster reefs and will facilitate evaluations of engineering strength, reef performance and invasional impacts at ecosystem-level.

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DOI: 10.3897/neobiota.48.35118

Authors: Elías D. Dana, Juan García-de-Lomas, Filip Verloove, Montserrat Vilà

Abstract: Despite the increasing number of invasive species, protocols devoted to assess the feasibility (i.e., probability of success or failure) of management actions in the field are scarce, yet success depends on a broad scope of issues beyond the biology of species and the ecosystem to be managed. In this paper we make a retrospective analysis of 90 actions and management proposals developed in Andalusia (southern Spain) in 2004 to 2018. Actions included 59 terrestrial and aquatic taxa. We identified items that in case of deficiency were responsible for either the rejection of action proposals (n = 44) or failure of implemented actions for which the goal was not achieved (n = 22). The most frequent deficiencies included the absence of funding during the necessary time to achieve the goals, the risk of reinvasion and an insufficient removal rate to achieve the specific objective. Based on the deficiencies found, we built a comprehensive, broad-scope compliance checklist to assist decision-makers to identify deficiencies before action. In addition, implemented actions for which the goal was achieved (n = 24) were used for validating the checklist. The checklist contains 40 items related to IAS features, administrative features, methodology effectiveness, efficiency and impacts of the action, and invaded ecosystem features. The checklist is valid across all taxa and habitats. The use of this checklist will help reduce the degree of arbitrariness and subjectivity of actions aimed at managing IAS, and a more efficient use of resources.

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