Elsevier

Marine Pollution Bulletin

Volume 105, Issue 2, 30 April 2016, Pages 546-552
Marine Pollution Bulletin

Note
Colony size-frequency distribution of pocilloporid juvenile corals along a natural environmental gradient in the Red Sea

https://doi.org/10.1016/j.marpolbul.2015.10.051Get rights and content

Highlights

  • Mean juvenile coral density varies along an environmental gradient in the Red Sea.

  • Coral size distributions were not sensitive to changes in the environmental conditions.

  • Algal cover and parrotfish density were higher in the southern Red Sea.

  • Fish density and algal cover appear not to be responsible for juvenile coral size distributions.

Abstract

Coral colony size-frequency distributions can be used to assess population responses to local environmental conditions and disturbances. In this study, we surveyed juvenile pocilloporids, herbivorous fish densities, and algal cover in the central and southern Saudi Arabian Red Sea. We sampled nine reefs with different disturbance histories along a north–south natural gradient of physicochemical conditions (higher salinity and wider temperature fluctuations in the north, and higher turbidity and productivity in the south). Since coral populations with negatively skewed size-frequency distributions have been associated with unfavorable environmental conditions, we expected to find more negative distributions in the southern Red Sea, where corals are potentially experiencing suboptimal conditions. Although juvenile coral and parrotfish densities differed significantly between the two regions, mean colony size and size-frequency distributions did not. Results suggest that pocilloporid colony size-frequency distribution may not be an accurate indicator of differences in biological or oceanographic conditions in the Red Sea.

Introduction

A key mechanism by which coral reef ecosystems are capable of recovering from natural or anthropogenic disturbances is their ability to replenish their populations through the successful recruitment of new individuals (Bak and Engel, 1979, Caley et al., 1996). The establishment and survival of juvenile corals are indicative of good conditions for the development and growth of corals, and consequently highlight the importance of studying demographic processes (Dunstan and Johnson, 1998, Babcock et al., 2003). Although many factors may influence recruitment and colonization patterns of reef organisms (Burt et al., 2009, Trapon et al., 2013a, Trapon et al., 2013b, Lozano-Cortés and Zapata, 2014a), there is little information about coral reproduction and demography in the Red Sea (Berumen et al., 2013). While there are a few accounts of inferred or observed spawning patterns from the Red Sea (Shlesinger and Loya, 1985, Shlesinger et al., 1998, Hanafy et al., 2010, Bouwmeester et al., 2011a, Bouwmeester et al., 2011b, Bouwmeester et al., 2015), published literature on coral recruitment in this region is restricted to the far northern area (Gulf of Aqaba) and is focused primarily on settlement in artificial plates (Glassom et al., 2004, Abelson et al., 2005, Glassom and Chadwick-Furman, 2006).

Bak and Meesters (1998); Meesters et al. (2001) and Vermeij and Bak (2002) used colony size-frequency data and a lognormal size distribution model of corals in the Caribbean Sea to quantify characteristics of the coral populations (e.g., coefficient of variation, mode, and skewness) and related these measurements to reef environment (e.g., degradation level). These authors used skewness to compare the proportion of small vs. large colonies as a proxy for the establishment of new juvenile corals in reefs with different degrees of pollution. They found differences in these size-frequency variables among- and within-species in different reef localities and suggested that these characters could provide a tool to more generally estimate the response of coral populations to changes in the environment. These studies reported a relationship between negative values of skewness and more degraded reefs. Similar results were found by Crabbe (2009) and Lozano-Cortés and Zapata (2014b) in other Caribbean coral reefs that had been impacted by bleaching events and tourism (Hawkins et al., 1999), as well as by Bauman et al. (2013) in reefs under extreme environmental conditions (high temperature and salinity) in the Arabian Gulf.

The Red Sea is characterized by a latitudinal gradient in physicochemical variables such as salinity (42–37 psu), temperature (20–32 °C), turbidity and primary productivity (low–high), creating distinct habitats in the north-central region from the southern region (Raitsos et al., 2011, Raitsos et al., 2013, Nanninga et al., 2014). The separation between these zones occurs around 20°N where there is a notable shift in both reef development patterns and oceanographic conditions (i.e., such as a shift from clear and oligotrophic waters in the north-central region to more turbid, warmer, nutrient-rich waters with less reef development in the south [Roberts et al., 1992]). This north–south latitudinal gradient is also strongly seasonal. For example, the water temperature changes from 26 to 20 °C (summer–winter) in the north and from 32 to 28 °C in the south. Similarly, Raitsos et al. (2013) documented a seasonal pattern for Chl-a with the highest concentrations during the winter and lowest during the summer. These authors attributed this seasonality to processes of vertical mixing (north) and high-nutrient water intrusion (south) during winter months, and the occurrence of strong water stratification in summer time. This marked environmental shift has also been associated with changes in biological factors of reef organisms such as abundance, community composition, and richness, as well as restrictions in gene flow between regions (Roberts et al., 1992, Froukh and Kochzius, 2007, Nanninga et al., 2014, Sawall et al., 2014a, Giles et al., 2015 but see Robitzch et al., 2015). More recently, differences in zooplankton diversity and zooxanthellae density in corals have been documented along the aforementioned gradient (Pearman et al., 2014, Sawall et al., 2014b). Finally, directly inverse relationships have been reported elsewhere between juvenile coral density and fish density or algal cover (Box and Mumby, 2007, Mumby et al., 2007, Trapon et al., 2013a). Although herbivory and grazing are generally considered to be beneficial for reef health (Mumby et al., 2006, Mumby, 2009), grazing fishes may be a major source of juvenile coral mortality via incidental removal or predation while feeding (Penin et al., 2010, Doropoulos et al., 2012). On the other hand, negative interactions between algal cover and coral juvenile density are expected due to competition for space. As such, high algal cover is typically associated with low coral recruitment (Hughes et al., 2007, Mumby et al., 2007, Hoey et al., 2011).

In this study, we quantified the abundance and size of pocilloporid juvenile corals in nine coral reefs in the central and southern regions of the Saudi Arabian Red Sea. The studied reefs experience different oceanographic regimes and levels of disturbances, including biological variables such as density of grazing fishes and algal cover. By assessing the size-frequency distributions of juvenile populations, we aimed to explore the relationship, if any, between these demographic variables and reef conditions. As negatively skewed populations have been previously associated with less favorable environmental conditions, we expected to find more negative values in the southern Red Sea in comparison with the central region where coral populations are potentially under suboptimal conditions for development (e.g., reduced somatic growth and less successful reproduction). The Red Sea's natural environmental gradient represents an excellent opportunity to study the variation of juvenile colony size-frequency and its relationship with the reef environment.

Section snippets

Study sites and species

A total of nine coral reefs (central and southern regions) were surveyed in the Saudi Arabian Red Sea spanning 670 km of coastline (Fig. 1, Table 1). In the central region, six reefs (one inshore, three mid-shelf, and two offshore) near Thuwal and Al Lith were surveyed between October 2013 and May 2014. Both sampling months in our study can be considered to be in the Red Sea summer season (May is early summer while October is late summer). Published studies on coral recruitment in the Red Sea

Juvenile corals

Juvenile corals (N = 454) ranged in size from 0.5 to 50 mm maximum diameter with an overall mean diameter of 29.43 mm (SD ± 10.24 mm; Table 1). Statistical differences were detected in the size of juvenile corals among reefs (K–W, H(8, N = 454) = 19.067, p = 0.0145), with smaller colonies in the offshore central reefs (Abu Madafi and Shib Kabir, M–W, U = 14,169.50, p = 0.000973; Table 1), but not between regions (M–W, U = 18,847.00, p = 0.146). Juvenile coral density (mean ± SD) differed significantly among reefs (W,

Discussion

We found that the pocilloporid juvenile coral size-frequency distribution, independent of the region, was more negatively skewed for reefs under unfavorable environmental conditions (i.e., recently bleached) or under ongoing biological stress (i.e., high parrotfish density and algal cover). Coral size-frequency distribution has been used as a proxy for reef conditions and past disturbances (Bak and Meesters, 1998, Meesters et al., 2001, Vermeij and Bak, 2002 Crabbe, 2009, Bauman et al., 2013,

Submission declaration and verification

The authors have declared that the work described in this paper has not been published previously and it is not under consideration for publication elsewhere. All the authors approved the final version of this paper and its submission to Marine Environmental Research.

Contributors

Conceived and designed the experiments: DLC MLB. Performed the experiments: DLC. Analyzed the data: DLC. Contributed reagents/materials/analysis tools: MLB DLC. Wrote the paper: DLC MLB.

Conflict of interest

The authors have declared that no competing interests exist.

Acknowledgments

This work was supported in part by baseline funding from King Abdullah University of Science and Technology (KAUST) to MLB, with logistical support from the KAUST Coastal and Marine Resources Core Lab and the crew of the R/V Thuwal. We thank the members of the Reef Ecology Lab at KAUST, especially Jessica Bouwmeester, Remy Gatins, Maha Khalil, Alex Kattan, May Roberts, and Marcela Herrera-Sarrias, as well as Eva Salas (University of California Santa Cruz) and Océane Salles (Université de

References (60)

  • J. Bouwmeester et al.

    Daytime broadcast spawning of Pocillopora verrucosa on coral reefs of the central Red Sea

    Galaxea: J. Coral Reef Stud.

    (2011)
  • J. Bouwmeester et al.

    Synchronous spawning of Acropora in the Red Sea

    Coral Reefs

    (2011)
  • J. Bouwmeester et al.

    Multi-species spawning synchrony within scleractinian coral assemblages in the Red Sea

    Coral Reefs

    (2015)
  • S.J. Box et al.

    The effect of macroalgal competition on the growth and survival of juvenile Caribbean corals

    Mar. Ecol. Prog. Ser.

    (2007)
  • M.J. Caley et al.

    Recruitment and the local dynamics of open marine populations

    Annu. Rev. Ecol. Evol. Syst.

    (1996)
  • C. Doropoulos et al.

    Interactions among chronic and acute impacts on coral recruits: the importance of size-escape thresholds

    Ecology

    (2012)
  • W.C. Dullo

    Coral growth and reef growth: a brief review

    Facies

    (2005)
  • P.K. Dunstan et al.

    Spatio-temporal variation in coral recruitment at different scales on Heron Reef, southern Great Barrier Reef

    Coral Reefs

    (1998)
  • M. Fine et al.

    A coral reef refuge in the Red Sea

    Glob. Chang. Biol.

    (2013)
  • T. Froukh et al.

    Genetic population structure of the endemic fourline wrasse (Larabicus quadrilineatus) suggests limited larval dispersal distances in the Red Sea

    Mol. Ecol.

    (2007)
  • K.A. Furby et al.

    Susceptibility of central Red Sea corals during a major bleaching event

    Coral Reefs

    (2013)
  • E.C. Giles et al.

    Exploring seascape genetics and kinship in the reef sponge Stylissa carteri in the Red Sea

    Ecol. Evol

    (2015)
  • D. Glassom et al.

    Recruitment, growth and mortality of juvenile corals at Eilat, Northern Red Sea

    Mar. Ecol. Prog. Ser.

    (2006)
  • D. Glassom et al.

    Coral recruitment: a spatio-temporal analysis along the coastline of Eilat, northern Red Sea

    Mar. Biol.

    (2004)
  • P.W. Glynn et al.

    Reef coral reproduction in the eastern Pacific: Costa Rica, Panama, and Galapagos Islands (Ecuador). Agariciidae (Pavona gigantea and Gardineroseris planulata)

    Mar. Biol.

    (1996)
  • M.H. Hanafy et al.

    Synchronous reproduction of corals in the Red Sea

    Coral Reefs

    (2010)
  • J.P. Hawkins et al.

    Effects of recreational scuba diving on Caribbean coral and fish communities

    Conserv. Biol.

    (1999)
  • A.S. Hoey et al.

    High macroalgal cover and low coral recruitment undermines the potential resilience of the world's southernmost coral reef assemblages

    PLoS One

    (2011)
  • T.P. Hughes et al.

    Phase shifts, herbivory, and the resilience of coral reefs to climate change

    Curr. Biol.

    (2007)
  • C. Jessen et al.

    In-situ effects of simulated overfishing and eutrophication on benthic coral reef algae growth, succession, and composition in the Central Red Sea

    PLoS One

    (2013)
  • Cited by (6)

    • Productivity and sea surface temperature are correlated with the pelagic larval duration of damselfishes in the Red Sea

      2016, Marine Pollution Bulletin
      Citation Excerpt :

      Due to its shape, location, and only a single shallow and narrow connection to the Indian Ocean, it displays a unique environmental gradient of temperature, salinity, productivity, turbidity, and essentially reef-scape (Racault et al., 2015; Raitsos et al., 2013). These physical and environmental characteristics have made the Red Sea a natural location to assess the environmental impact on several coral reef organisms (e.g., Froukh and Kochzius, 2007; Giles et al., 2015; Lozano-Cortés and Berumen, 2015; Nanninga et al., 2014; Ngugi et al., 2012; Roberts et al., 1992; Robitzch et al., 2015; Sawall et al., 2014a, 2014b). Here, we focus on the two seemingly major parameters that may drive PLD variations in the environmental gradient of the Red Sea: temperature and food availability.

    View full text