Small Scale Genetic Population Structure of Coral Reef Organisms in Spermonde Archipelago, Indonesia

Abstract

Small island archipelagos with fringing and dispersed reef systems represent special marine ecosystems, providing a patchy habitat for many coral reef organisms. Although geographic distances may be short, it is still unclear if such environments are inhabited evenly with panmictic conditions or if limited connectivity between marine populations, even on small geographic scales, leads to genetic differentiation between areas within the archipelago or even single reef structures. To study diversity patterns and connectivity between reefs of the Spermonde Archipelago, Indonesia, population genetic analyses of two reef organisms were performed by using the mitochondrial control region and microsatellite markers. A vertebrate (clown anemonefish) and an invertebrate species (sea squirt) were studied in parallel to investigate if there are general patterns of connectivity in Spermonde for sessile or site attached marine species, which can be extrapolated to a larger group. The genetic population structures revealed restrictions in gene flow in the clown anemone fish (Amphiprion ocellaris), especially between near-shore reefs in the South of the archipelago. This indicates very localized genetic exchange and may also reflect the high self-recruitment typical for these fish. The northern reefs show higher connectivity despite geographic distances being larger. The filter-feeding sessile sea squirt, Polycarpa aurata, features similar population patterns, especially in the southern area. However, connectivity is generally higher in the middle and shelf edge areas of Spermonde for this species. The results underline that there are restrictions to gene flow even on very small geographic scales in the studied organisms, with many barriers to gene flow in the southern shallower shelf area. Weaker currents in this area may lead to more influence of biological factors for dispersal, such as larval behavior, motility and competition for suitable habitat. The results are discussed in the context of conservation and MPA planning in the Spermonde Archipelago.

Reduced Genetic Diversity in the Clown Anemonefish Amphiprion ocellaris in Exploited Reefs of Spermonde Archipelago, Indonesia

“…Inbreeding in a population could cause a reduction in the heterozygosity and an increase in the homozygosity, as shown in overharvested populations (Pinsky and Palumbi, 2014). Despite dispersing larvae, A. ocellaris showed a significant genetic differentiation between the two island populations (F ST 536 = 0.065 ± 0.048, p = 0.01), which was also shown in a previous study (Timm et al, 2017). In a study on the anemonefish species A. clarkii significant F ST -values (=0.028) were found between sites on a similarly small scale in the Philippines (Pinsky and Palumbi, 2014).…”

“…This strategy prevents the loss of rare alleles from older and bigger individuals. Second, the implementation of marine protected areas (MPAs), which take into account high self-recruitment in A. ocellaris (Madduppa et al, 2014b) and the limited connectivity of populations (Timm and Kochzius, 2008;Timm et al, 2012Timm et al, , 2017. High selfrecruitment implies that the populations are more vulnerable to fishing activity (Thorrold et al, 2001).…”

High genetic connectivity in a scleractinian coral (Lobophyllia corymbosa) around Sulawesi, Indonesia

“…However, it is possible that one reason for this apparent lack of structure and low differentiation is the limitation of the sampling design used in this study. The results of a study on clownfishes and sea squirts in the Spermonde Islands by Timm et al (2017) found fine-scale gene flow patterns which were limited to this small scale region.…”

“…Geographically, Indonesia is flanked by both the Pacific Ocean and the Indian Ocean, resulting in extremely complicated flow patterns within the Indonesian archipelago. In addition to the dynamics of the Indonesian Through Flow (ITF) that moves under the thermocline layer and carries biological material from the Pacific Ocean to the Indian Ocean (Timm et al 2017), complex surface flows also become a transportation medium for marine organisms whose dispersal and/or settlement phases take place in shallow waters.…”

Unexpected patterns of genetic connectivity in Lobophyllia corymbosa (Forskål, 1775) around Sulawesi, Indonesia

“…Many studies have used genetics to infer patterns of larval dispersal within Indonesia (Barber et al 2000(Barber et al , 2002(Barber et al , 2006Timm et al 2017;DeBoer and Barber 2010;Crandall et al 2010). These studies typically identify three unique regions: (i) Western Indonesia, including Sumatera, and Java, (ii) Central Indonesia including the Lesser of Sunda Islands, Sulawesi, and Sangihe-Talaud, and (iii) Eastern Indonesia, including Halmahera and West Papua Carpenter et al 2011).…”