Fish nursery value of algae habitats in temperate coastal reefs

Fish nursery value of algae habitats in temperate coastal reefs Hilmar Hinz1 ,2 , Olga Reñones2 , Adam Gouraguine3 , Andrew F. Johnson4 and Joan Moranta2 1 Instituto Mediterraneo de Estudios Avanzados (IMEDEA; CSIC-UIB), Esporles, Illes Balears, Spain Instituto Español de Oceanografía (IEO), Centre Oceanográfic de les Balears, Ecosystem Oceanography Group (GRECO), Palma, Illes Balears, Spain 3 School of Biological Sciences, University of Essex, Colchester, United Kingdom 4 MarFishEco, Portland, OR, United States of America 2 ABSTRACT Submitted 7 November 2018 Accepted 17 March 2019 Published 15 May 2019 Corresponding author Hilmar Hinz, Academic editor Isabel Sousa Pinto Additional Information and Declarations can be found on page 20 DOI 10.7717/peerj.6797 Copyright 2019 Hinz et al. Distributed under Creative Commons CC-BY 4.0 The nursery function of coastal habitats is one of the most frequently mentioned and recognized ecosystem services in the valuation of coastal ecosystems. Despite its importance our understanding of the precise habitat parameters and mechanisms that make a habitat important as a nursery area is still limited for many species. The study aimed to establish the importance of different algae morphotypes in providing shelter and food for juvenile coastal fish during the main settlement peaks, in early spring and late summer, in littoral rocky reef systems in the Northwestern Mediterranean. The results of our study showed strong seasonal differences in algae cover, composition and height between the two sampling periods. Overall, during spring the algae were well developed, while in late summer, both density and height, of most algae decreased considerably. Equally, prey biomass, in form of suitable sized invertebrate fauna associated to the algae, decreased. Accordingly, the shelter and food for the fish settling in this habitat during late summer were less abundant, indicating a mismatch between the observed presence of juvenile fish and optimal habitat conditions. Differences in prey densities were detected between algae morphotypes, with structurally more complex algae, such as Cystoseira spp. and Halopteris spp. consistently containing more prey, independent of season, compared to simpler structured morphotypes such as Dictoytales. The study furthermore related juvenile fish density to habitats dominated by different algae morphotypes. Out of the three-study species (Diplodus vulgaris, Symphodus ocellatus, Coris julis) only S. ocellatus showed a significant association with an algae habitat. S. ocellatus related positively to habitats dominated by Dictoytales which provided the highest cover during late summer but had the lowest prey densities. A strong association of this species with Cystoseira, as reported by other studies, could not be confirmed. Cystoseira was abundant within the study area but in a state of dieback, showing loss and reduced height of foliage, typical for the time of year within the study area. It is therefore likely that algae-fish associations are context-dependent and that several algae species may fulfil similar functions. We also discovered that prey biomass did not appear to have an important effect on juvenile abundances. Nevertheless, the availability of prey may influence juvenile fish condition, growth performance and ultimately long-term survival. We therefore suggest that future studies on habitat quality should also include, besides abundance, indicators related to the condition and growth of juveniles. OPEN ACCESS How to cite this article Hinz H, Reñones O, Gouraguine A, Johnson AF, Moranta J. 2019. Fish nursery value of algae habitats in temperate coastal reefs. PeerJ 7:e6797 http://doi.org/10.7717/peerj.6797 Subjects Conservation Biology, Ecology, Marine Biology Keywords Juvenile fish, Match/mismatch theory, Benthic prey, Habitat complexity, Cystoseira, Macroalgae, Labridae, Nursery areas, Dictoytales, Rocky reefs INTRODUCTION The provision and value of nursery habitats by the coastal zone is one of the most frequently mentioned and recognized ecosystem services in the valuation of coastal marine ecosystems (Duarte, 2000; Jackson et al., 2001; Jackson et al., 2015). As many coastal habitats are under increasing human pressures from urbanisation, fishing, climatic change and the introduction of alien species (Sala et al., 2011; Sala et al., 2012; Vergés et al., 2014a; Vergés et al., 2014b), the provisioning of this ecosystem service is progressively also under threat. While the large-scale importance of nursery habitats for ecosystem functioning, food production and integrity of ecosystems is recognized, a detailed understanding over which habitat types constitute to this function is still lacking (Beck et al., 2001). Seagrass meadows and estuarine systems have been the focus of marine nursery habitat research (e.g., Heck, Hays & Orth, 2003; Seitz et al., 2013; Woodland et al., 2012; Ruiz-Frau et al., 2017), while studies that focus on littoral rocky reef systems appear less frequently in the literature (but see Cheminée et al., 2017; Guidetti, 2000; Harmelin-Vivien, Harmelin & Leboulleux, 1995). Although spatially less extensive compared to seagrass meadows, littoral rocky reef systems harbour a wide variety of different algae species, providing shelter and food, in the form of associated fauna, to juvenile fish (Harmelin-Vivien, Harmelin & Leboulleux, 1995; Cheminée et al., 2013; Félix-Hackradt et al., 2014). In the Mediterranean, littoral rocky reef habitats are used by a variety of commercial and non-commercial species for part, or their entire life cycle (Harmelin-Vivien, Harmelin & Leboulleux, 1995; Guidetti, 2000; La Mesa et al., 2011; Félix-Hackradt et al., 2014; Cheminée et al., 2017). In general, coastal species with smaller body sizes, such as many Labridae, Blenniidae and Gobiidae, complete their entire life cycle within this habitat. Several other, larger, commercial species, such as various Sparid species e.g., Pagelus spp or Dentex dentex, often only use it as a nursery habitat, with the larger juvenile and adult life stages moving further offshore. Settlement of juvenile fishes in rocky littoral habitats occurs throughout the year but most species have a settlement peak between early spring and late summer (García-Rubies & Macpherson, 1995; Biagi, Gambaccini & Zazzetta, 1998; Bussotti & Guidetti, 2011). The survival of recently settled juveniles within a habitat, through to their recruitment to the adult population, depends to a large extent on the environmental conditions encountered at the site of settlement (Beck et al., 2001). Intolerance to physical extremes, starvation and predation are among the major causes of juvenile mortality in these habitats (Sogard, 1997; Guidetti, 2001; Thiriet et al., 2016; Cuadros et al., 2018). High nursery value is thus conferred through a combination of factors that provide adequate physical conditions, refuge space and a sufficient food supply. (...truncated)