Urbanisation and Fishing Alter the Body Size and Functional Traits of a Key Fisheries Species

Human pressures on ecosystems from landscape transformation and harvesting can result in changes to body size and functional traits of affected species. However, these effects remain very poorly understood in many settings. Here we examine whether and how fishing and the attributes of coastal seascapes can operate in concert to change the body size and functional traits of the giant mud crab, Scylla serrata; a prized fisheries species. We captured 65 legal sized (> 15 cm carapace width) male giant mud crabs from 13 estuaries in southeast Queensland, Australia. These estuaries span a wide range of fishing and catchment landscape transformation intensity. We made a total of 9000 external morphometric measurements in the study. There was a distinct effect of estuarine landscape context on body size, with the largest individuals captured from systems with bigger inlets and lower extent of intertidal flats. Variation in functional traits was most often associated with variation in fishing pressure and human population size in the catchment. Crabs from areas with less commercial fishing pressure and lower human populations in the catchment had the largest chelipeds. We also found effects of urbanisation (negative correlations), intertidal flats (inconsistent effects) and mangrove extent (positive correlations) on the size of some functional traits. Our results show that human pressures can have sublethal effects on animals in estuaries that alter body size and functional traits. These phenotypic responses might have consequences for the fitness and ecological roles of targeted species, and the yields of fisheries catches

Human actions alter tidal marsh seascapes and the provision of ecosystem services

Tidal marshes are a key component of coastal seascape mosaics that support a suite of socially and economically valuable ecosystem services, including recreational opportunities (e.g., fishing, birdwatching), habitat for fisheries species, improved water quality, and shoreline protection. The capacity for tidal marshes to support these services is, however, threatened by increasingly widespread human impacts that reduce the extent and condition of tidal marshes across multiple spatial scales and that vary substantially through time. Climate change causes species redistribution at continental scales, changes in weather patterns (e.g., rainfall), and a worsening of the effect of coastal squeeze through sea level rise. Simultaneously, the effects of urbanization such as habitat loss, eutrophication, fishing, and the spread of invasive species interact with each other, and with climate change, to fundamentally change the structure and functioning of tidal marshes and their food webs. These changes affect tidal marshes at local scales through changes in plant community composition, complexity, and condition and at regional scales through changes in habitat extent, configuration, and connectivity. However, research into the full effects of these multi-scaled, interactive stressors on ecosystem service provision in tidal marshes is in its infancy and is somewhat geographically restricted. This hinders our capacity to quickly and effectively curb loss and degradation of both tidal marshes and the services they deliver with targeted management actions. We highlight ten priority research questions seeking to quantify the consequences and scales of human impacts on tidal marshes that should be answered to improve management and restoration plans

Fisheries rely on threatened salt marshes

Salt marsh ecosystems and the seascapes in which they are embedded serve as critical habitats for species harvested by fisheries (1), which provide food and economic security for hundreds of millions of people (2). Historical marsh losses coupled with increasing pressures from coastal development and climate change place these intertidal ecosystems and surrounding uplands under growing threat (3). Preventing further losses of salt marshes and associated fisheries production will require greater public awareness and difficult choices in coastal policy and management, underpinned by greater understanding of marsh function