We compare the value of using habitat categories and species assemblages as surrogates for marine biological diversity in the context of choosing a set of representative areas for a marine reserve network. Habitat categories were based on interpretation of aerial photographs and maps, and on local knowledge. Species assemblages were created from comprehensive survey data on 977 taxa (mainly species), derived from an intensive threeyear study of a temperate marine embayment, and classified into plant, fish, and invertebrate assemblages. Reserves were selected using a heuristic iterative algorithm to simulate a marine reserve network based on 10-80% representation of each surrogate. The effectiveness of each surrogate was evaluated by comparing the number of taxa that would be coincidentally included in each simulated reserve for the bay. Areas selected to represent 10% or 20% of the surrogates were best chosen using fish or invertebrate assemblages, because by spatial coincidence, they included 60-80% of all available taxa. However, areas selected to represent Ն40% of the surrogates were generally best derived from habitat categories, because they included Ն93% of all available taxa. Plant assemblages were generally poor surrogates for overall species richness. These findings suggest that habitatlevel surrogates may be a highly cost-effective method for initial identification of highpriority areas to manage marine diversity of coastal ecosystems.

We compare the value of using habitat categories and species assemblages as surrogates for marine biological diversity in the context of choosing a set of representative areas for a marine reserve network. Habitat categories were based on interpretation of aerial photographs and maps, and on local knowledge. Species assemblages were created from comprehensive survey data on 977 taxa (mainly species), derived from an intensive three‐year study of a temperate marine embayment, and classified into plant, fish, and invertebrate assemblages. Reserves were selected using a heuristic iterative algorithm to simulate a marine reserve network based on 10–80% representation of each surrogate. The effectiveness of each surrogate was evaluated by comparing the number of taxa that would be coincidentally included in each simulated reserve for the bay. Areas selected to represent 10% or 20% of the surrogates were best chosen using fish or invertebrate assemblages, because by spatial coincidence, they included 60–80% of all available taxa. However, areas selected to represent ≥40% of the surrogates were generally best derived from habitat categories, because they included ≥93% of all available taxa. Plant assemblages were generally poor surrogates for overall species richness. These findings suggest that habitat‐level surrogates may be a highly cost‐effective method for initial identification of high‐priority areas to manage marine diversity of coastal ecosystems.

No abstract

Seagrasses are important habitat-formers and ecosystem engineers that are under threat from bloom-forming seaweeds. These seaweeds have been suggested to outcompete the seagrasses, particularly when facilitated by eutrophication, causing regime shifts where green meadows and clear waters are replaced with unstable sediments, turbid waters, hypoxia, and poor habitat conditions for fishes and invertebrates. Understanding the situations under which seaweeds impact seagrasses on local patch scales can help proactive management and prevent losses at greater scales. Here, we provide a quantitative review of available published manipulative experiments (all conducted at the patch-scale), to test which attributes of seaweeds and seagrasses (e.g., their abundances, sizes, morphology, taxonomy, attachment type, or origin) influence impacts. Weighted and unweighted meta-analyses (Hedges d metric) of 59 experiments showed generally high variability in attribute-impact relationships. Our main significant findings were that (a) abundant seaweeds had stronger negative impacts on seagrasses than sparse seaweeds, (b) unattached and epiphytic seaweeds had stronger impacts than ‘rooted’ seaweeds, and (c) small seagrass species were more susceptible than larger species. Findings (a) and (c) were rather intuitive. It was more surprising that ‘rooted’ seaweeds had comparatively small impacts, particularly given that this category included the infamous invasive Caulerpa species. This result may reflect that seaweed biomass and/or shading and metabolic by-products like anoxia and sulphides could be lower for rooted seaweeds. In conclusion, our results represent simple and robust first-order generalities about seaweed impacts on seagrasses. This review also documented a limited number of primary studies. We therefore identified major knowledge gaps that need to be addressed before general predictive models on seaweed-seagrass interactions can be build, in order to effectively protect seagrass habitats from detrimental competition from seaweeds.