To assess distributional shifts of species in response to recent warming, historical distribution records are the most requisite information. The surface seawater temperature (SST) of Kochi Prefecture, southwestern Japan on the western North Pacific, has significantly risen, being warmed by the Kuroshio Current. Past distributional records of subtidal canopy-forming seaweeds (Laminariales and Fucales) exist at about 10-year intervals from the 1970s, along with detailed SST datasets at several sites along Kochi's >700 km coastline. In order to provide a clear picture of distributional shifts of coastal marine organisms in response to warming SST, we observed the present distribution of seaweeds and analyzed the SST datasets to estimate spatiotemporal SST trends in this coastal region. We present a large increase of 0.3°C/decade in the annual mean SST of this area over the past 40 years. Furthermore, a comparison of the previous and present distributions clearly showed the contraction of temperate species' distributional ranges and expansion of tropical species' distributional ranges in the seaweeds. Although the main temperate kelp Ecklonia (Laminariales) had expanded their distribution during periods of cooler SST, they subsequently declined as the SST warmed. Notably, the warmest SST of the 1997–98 El Niño Southern Oscillation event was the most likely cause of a widespread destruction of the kelp populations; no recovery was found even in the present survey at the formerly habitable sites where warm SSTs have been maintained. Temperate Sargassum spp. (Fucales) that dominated widely in the 1970s also declined in accordance with recent warming SSTs. In contrast, the tropical species, S. ilicifolium, has gradually expanded its distribution to become the most conspicuously dominant among the present observations. Thermal gradients, mainly driven by the warming Kuroshio Current, are presented as an explanation for the successive changes in both temperate and tropical species' distributions.

Marine organisms have evolved defence mechanisms to prevent epibiosis. This study investigated the anti-settlement properties of natural periostracal microtopographies of two mytilid species, Mytilus edulis (from North, Baltic and White Seas) and Perna perna (from the SW Atlantic). Resin replicas of shells were exposed to cyprids of the barnacle Semibalanus balanoides. Replicas with intact isotropic microtopographies and smooth controls were much less fouled than roughened anisotropic surfaces. This indicates that in both M. edulis and P. perna the periostracum possesses a generic anti-settlement property, at least against S. balanoides cyprids, which is not regionally adapted. Such a potential globally effective antisettlement mechanism possibly contributes to the invasive success of Mytilidae.

Many marine invertebrate larvae respond behaviourally to environmental settlement cues, yet behaviours are often only inferred from settlement patterns or are limited to laboratory studies. The behaviour of wild cypris larvae of Semibalanus balanoides L. was filmed on settlement tiles in the field. Tiles were of five different textures with a nested treatment of crude conspecific adult extract (AE). The effects of texture and AE on eleven defined behaviours were analysed. Texture affected the gross and net exploratory distances, velocity, acceleration and time spent exploring. AE attracted more cyprids during the first minute of immersion and increased the time spent on surfaces. Relatively few arrivals that either travel far and fast, or exit the surface rapidly, may indicate a lower chance of settlement. An increase in time spent on a surface may increase the probability of being in contact with the surface when the sign stimulus to settle occurs.

This chapter defines the term settlement, as it applies to marine biofouling, and outlines the stages and levels of complexity involved in the process. It is beyond the scope of this work to present an exhaustive review of the literature, instead the work aims to outline some broad patterns and provide examples from the wealth of research that exists. The processes of surface encounter and attachment are given particular attention, as well as the role of environmental cues and passive and behavioural responses to them, whilst highlighting the pitfalls associated with inferences made without direct observation. Finally, there is a substantial resource table, summarising the species studied, the cue or influence on settlement, and a brief summary of the findings. IntroductionMany fouling species naturally occur in distinct zones (Plate I C), and three possible hypotheses were originally proposed to explain this phenomenon, namely (i) larvae settle randomly and those that do not encounter a suitable site die, (ii) species with a motile adult stage settle randomly then migrate to or are confined to an area based on species-specific biotic or abiotic factors and (iii) larvae may congregate at a particular depth in the water column when they are ready to settle. Since then it has been realised that larvae of many species are capable of sophisticated site-selection behaviours during settlement, as adaptations that maximise the likelihood that a site with an appropriate combination of biotic and abiotic factors (niche) will be arrived at.Species settlement is not the same phenomenon as recruitment. For the purposes of this chapter, settlement is defined as the process that follows the planktonic phase and precedes metamorphosis, and at the most basic level it involves surface encounter and attachment. Once settlement and metamorphosis has occurred, marine macrofouling organisms are immobile species that grow attached to artificial structures. The most notable of these belong to both algal and invertebrate groups: Algae, Mollusca (e.g. mussels), Crustacea (e.g. barnacles), Bryozoa, Annelida (e.g. tubeworms), Tunicata (colonial and solitary forms), Cnidaria (corals, anemones and hydroids) and Porifera (sponges). As settlement marks the transition from the planktonic to the sessile phase, it has logically become a focus of intense research. From a biofouling perspective, it is of major importance to understand the processes that influence settlement, as 30 Biofouling Edited by Simone Dürr and Jeremy C. Thomason

Barnacle cypris larvae respond to many cues when selecting a settlement site. The settlement of over a million larvae on tiles of different textures, orientations and densities of incumbent settlers was measured on the rocky intertidal at Great Cumbrae, Scotland. Half of the tiles were replaced every tide whereas the others simultaneously accumulated settlers. Factor effects varied on each tide, and converged in the accumulating deployment. Increasing incumbent density led to net loss of settlement, which was less probable on the textures on which fastest settlment occurred ('very fine'), and more probable on those on which settlement was slowest ('smooth'). More settlement occurred on down-facing orientations during daylight and vice versa. Cue ranks were non-linear, so a path analysis model quantified the relative influence of each factor. Gregariousness was the most influential cue measured, although unmeasured factors had greater effects, highlighting the complexity of settlement influences in this species.