Evaluation of the full set of habitat suitability models for vulnerable marine ecosystem indicator taxa in the South Pacific high seas

\ua9 2024 The Authors. Fisheries Management and Ecology published by John Wiley & Sons Ltd. In the high seas, regional fishery management organisations are required to implement measures to prevent significant adverse impacts on vulnerable marine ecosystems (VMEs). Our objectives were to develop habitat suitability models for use in the spatial management of bottom fisheries in the South Pacific and to evaluate these and existing models using independent data from high-quality seafloor imagery. Presence-only models for seven VME indictor taxa were developed to complement previous modelling. Evaluation of habitat suitability models using withheld data indicated high mean True Skill Statistic scores of 0.44–0.64. Most habitat suitability models performed adequately when assessed with independent data on taxon presence and absence but were poor surrogates for abundance. We therefore advocate caution when using presence-only models for spatial management and call for more systematically collected data to develop abundance models

Independent statistical validation of the New Zealand Seafloor Community Classification

\ua9 2024 The Authors. Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley & Sons Ltd. The New Zealand Seafloor Community Classification (NZSCC) is a national-scale numerical community classification which depicts compositional turnover of 1716 taxa (demersal fish, reef fish, benthic invertebrates and macroalgae) classified into 75 groups representing seafloor communities. To ensure the continual use of the NZSCC for spatial planning and reporting, a robust maintenance framework must be set in place; key to this is being able to assess the ability of the classification to represent (discriminate between) different seafloor communities. Here we describe an approach for validating the NZSCC using temporally independent evaluation data for demersal fish and benthic invertebrates (the latter sampled via a different method), which identifies whether the NZSCC represents different seafloor communities (i.e., assesses classification strength), evaluates the underlying statistical model, and considers heterogeneity in environmental coverage and statistical uncertainty. Additionally, the availability of abundance estimates for these evaluation datasets provides an opportunity to test whether the NZSCC—which was developed using presence-absence data—can reflect abundance-weighted seafloor communities. The ANOSIM global R values (measuring classification strength) were 0.53 and 0.46 (and significant at the 1% level) for demersal fish and benthic invertebrates, respectively, indicating that the NZSCC groups define biologically distinctive environments. The proportion of significant inter-group differences were very high (95% and 97% for demersal fish and benthic invertebrates, respectively) suggesting NZSCC groups were distinct from each other in their taxonomic composition. There were positive relationships between the evaluation datasets and the underlying statistical model. There was no evidence of these relationships being affected by the statistical uncertainty of the NZSCC. NZSCC model validation metrics using abundance evaluation data were also moderately high (albeit lower than for presence-absence for invertebrates) suggesting that the NZSCC, can at least in part, represent variation in abundance-weighted communities. Results presented here suggest that the existing NZSCC is currently fit-for-purpose for informing management decisions

Optimal siting, sizing, and enforcement of marine protected areas

The design of protected areas, whether marine or terrestrial, rarely considers how people respond to the imposition of no-take sites with complete or incomplete enforcement. Consequently, these protected areas may fail to achieve their intended goal. We present and solve a spatial bio-economic model in which a manager chooses the optimal location, size, and enforcement level of a marine protected area (MPA). This manager acts as a Stackelberg leader, and her choices consider villagers’ best response to the MPA in a spatial Nash equilibrium of fishing site and effort decisions. Relevant to lower income country settings but general to other settings, we incorporate limited enforcement budgets, distance costs of traveling to fishing sites, and labor allocation to onshore wage opportunities. The optimal MPA varies markedly across alternative manager goals and budget sizes, but always induce changes in villagers’ decisions as a function of distance, dispersal, and wage. We consider MPA managers with ecological conservation goals and with economic goals, and identify the shortcomings of several common manager decision rules, including those focused on: (1) fishery outcomes rather than broader economic goals, (2) fish stocks at MPA sites rather than across the full marinescape, (3) absolute levels rather than additional values, and (4) costless enforcement. Our results demonstrate that such naïve or overly narrow decision rules can lead to inefficient MPA designs that miss economic and conservation opportunities

Patchiness and Co-Existence of Indigenous and Invasive Mussels at Small Spatial Scales: The Interaction of Facilitation and Competition

Ecological theory predicts that two species with similar requirements will fail to show long-term co-existence in situations where shared resources are limiting, especially at spatial scales that are small relative to the size of the organisms. Two species of intertidal mussels, the indigenous Perna perna and the invasive Mytilus galloprovincialis, form mixed beds on the south coast of South Africa in a situation that has been stable for several generations of these species, even though these populations are often limited by the availability of space. We examined the spatial structure of these species where they co-exist at small spatial scales in the absence of apparent environmental heterogeneity at two sites, testing: whether conspecific aggregation of mussels can occur (using spatial Monte-Carlo tests); the degree of patchiness (using Korcak B patchiness exponent), and whether there was a relationship between percent cover and patchiness. We found that under certain circumstances there is non-random conspecific aggregation, but that in other circumstances there may be random distribution (i.e. the two species are mixed), so that spatial patterns are context-dependent. The relative cover of the species differed between sites, and within each site, the species with higher cover showed low Korcak B values (indicating low patchiness, i.e. the existence of fewer, larger patches), while the less abundant species showed the reverse, i.e. high patchiness. This relationship did not hold for either species within sites. We conclude that co-existence between these mussels is possible, even at small spatial scales because each species is an ecological engineer and, while they have been shown to compete for space, this is preceded by initial facilitation. We suggest that a patchy pattern of co-existence is possible because of a balance between direct (competitive) and indirect (facilitative) interactions

Biogeographic comparisons of the traits and abundance of an invasive crab throughout its native and invasive ranges

High abundances of non-native species in the invaded range may be linked to changes in fitness related traits. However, few studies have compared differences in both life-history traits and abundances of introduced species between their native and invaded ranges. We determined differences in 12 morphological traits, an important fitness related trait (body size), and the abundance of the porcelain crab, Petrolisthes elongatus, in its native (New Zealand) and invasive (Tasmania, Australia) ranges. P. elongatus was more abundant in the introduced range; however, changes in abundance depended on tidal height, with higher abundances only at mid and low tidal zones. The biomass of male crabs was higher in the invaded range compared to the native range, but there was no difference in female biomass between ranges. Despite increases in male biomass, sex ratios between native and invasive populations did not differ. In addition, principal components analysis showed no differences in overall morphology between Tasmania and New Zealand. Our study indicates that increased abundance in the invaded range of P. elongatus may be linked to high values of an important trait (greater biomass) in the invaded range. Importantly, changes in biomass and abundance may be due to P. elongatus being able to utilise mid/low zones more in the invaded range. Furthermore, our findings indicate that understanding how sex specific changes in biomass interact with the recipient environment (biotic and abiotic) in the introduced range will be important for determining the mechanisms underpinning the establishment and spread of P. elongatus. © 2013 Springer Science+Business Media Dordrecht