D ATA A NALYSIS

Reserve and connectivity effects were evaluated using a modified Control-Impact design. Analysis examined the interactive effects of connectivity and ecosystem protection through comparison of the three reserves and three control locations. Replicates were grouped into five sites at each of the six locations, three of these were on coral reef (close to seagrass, close to mangroves, and isolated from both), and one in each of seagrass and mangroves located close to reef. Fish density data were log transformed to reduce heterogeneity of variances and analysed with analysis of variance (ANOVA). Post hoc Student–Newman–

Keuls tests were used to differentiate significant means. Assemblage data was examined using permutational multivariate analysis of variance (PERMANOVA) (Anderson 2001) applied to Bray-Curtis similarity matrices, calculated on fourth-root transformed data. A posteriori pair-wise tests were applied to significant factors following PERMANOVA. Three-factor analyses were conducted for reef fish variables, and two-factor analyses were performed for mangrove and seagrass fish variables. The factors were: protection (a fixed orthogonal factor), location (a random orthogonal factor) and connectivity (a fixed orthogonal factor used in reef analyses only). Patterns of similarity in the composition of fish assemblages were displayed visually using non-metric multidimensional scaling (nMDS) (Clarke 1993). The size of individual species with distributions on reefs that correlated with connectivity to mangroves or seagrass was compared between reefs and either adjacent habitat using T-tests.

R

ESULTS

R

ESERVE AND

C

ONNECTIVITY

E

FFECTS ON

F

ISH

A

SSEMBLAGES

Habitat connectivity mediated the effect of marine reserves on the composition of reef fish assemblages.

Reserve reefs adjacent to seagrass and mangroves supported different assemblages to unprotected reefs, irrespective of location (near mangroves: t = 3.94, p = 0.001; near seagrass: t = 4.16, p = 0.001) (Figure 112).

In contrast, the composition of fish assemblages did not differ between reserve and unprotected reefs that were isolated from both seagrass and mangroves (t = 1.38, p > 0.05). Reserve seagrass adjacent to reefs contained different assemblages to unprotected seagrass, irrespective of location (F = 8.15, p = 0.001), and assemblage composition varied among locations (F = 9.14, p = 0.001), but did not influence the effect of protection (Figure 112). Reserve mangroves adjacent to reefs supported different assemblages to unprotected mangroves, regardless of location (F = 7.26, p = 0.001) (Figure 112). Assemblage composition also varied among locations (F = 8.05, p = 0.001), but not between reserve mangroves at Kida and Olive (t = 0.50, p = 0.884).

R

ESERVE AND

C

ONNECTIVITY

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FFECTS ON

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ISH

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ENSITIES

Connectivity improved the performance of marine reserves in promoting the abundance of three fish families (haemulidae, lutjanidae and siganidae) and 18 fish species (Figure 113, Table 34). The responses of

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Chapter 6 Connectivity

between coral reefs and seagrass, six by connectivity between reefs and mangroves, and three by connectivity among reefs, seagrass and mangroves (Table 34).

Protection of neighbouring reef and seagrass from fishing enhanced the abundance of three species (bumphead parrotfish, maori wrasse [Cheilinus undulatus] and thumbprint emperor [Lethrinus harak]) on adjacent reefs and seagrass, four species (paddletail snapper [Lutjanus gibbosus], manyspotted sweetlip [Plectorhinchus chaetodonoides], lined sweetlip [Plectorhinchus lineatus] and bluebarred parrotfish [Scarus ghobban]) on reefs near seagrass, and two species (grass emperor [Lethrinus laticaudis] and whitespotted rabbitfish [Siganus canaliculatus]) on seagrass near reefs (Fig. 4, Table 1). In contrast, it had a negative effect on the abundance of ornate emperor (Lethrinus ornatus) and dashdot goatfish (Parapeneus barberinus).

Protection of adjacent reef and mangroves enhanced the abundance of three species (mangrove jack [Lutjanus argentimaculatus], giant sweetlip [Plectorhinchus albovittatus] and brown sweetlip [Plectorhinchus gibbosus]) on close reefs and mangroves, blackspot snapper (Lutjanus fulviflamma) on reefs near mangroves, and two species (redfin emperor [Lethrinus erythropterus] and blacktail snapper [Lutjanus fulvus]) on mangroves near reefs (Figure 113, Table 1). It also had a negative effect on the abundance of monocle bream (Scoliopsis spp.).

Closure to fishing increased the abundance of anchor tuskfish (Choerodon anchorago), barred rabbitfish (Siganus doliatus) and lined rabbitfish (Siganus lineatus) in adjacent mangrove, reef and seagrass habitats (Figure 113, Table 34). It also enhanced the abundance of lined bristletooth (Ctenochaetus striatus) and white-ringed surgeonfish (Acanthurus spp.) on coral reefs, regardless of their proximity to seagrass and mangrove habitats (Figure 113, Table 34).

Seventeen of the species that were influenced by habitat connectivity were larger on reefs than in adjacent habitats (Table 35). Differences in the sizes of fish: between seagrass and reef (nine species), mangroves and reef (five species), and among all three habitats (three species), suggest that the importance of connectivity for these species may relate to changes in habitat usage and a migration to coral reefs with increasing size (Table 35).

Chapter 6 Building social and ecological resilience to climate change in Roviana, Solomon Islands

Figure 112 Multidimensional scaling (MDS) ordinations comparing relationships among: (1) fish assemblages on reserve and unprotected coral reefs at each level of connectivity with mangroves and seagrass, and fish assemblages in reserve and unprotected (2) seagrass, and (3) mangroves at each location.

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Figure 113 Density of selected fish species (mean ± SE) on reserve and unprotected mangrove, coral reef and seagrass habitats. * represent significant differences between reserve and unprotected locations (identified by SNK post hoc analyses). Bumphead parrotfish represent species with responses to protection that were enhanced by seagrass connectivity. Mangrove jack signify species for which protection effects were mediated by reef-mangrove connectivity. Goldlined rabbitfish denote species with protection responses that were improved by both reef-mangrove and reef-seagrass connectivity. Ringtail surgeonfish epitomize species for which protection effects were not influenced by connectivity. Monocle bream and dashdot goatfish represent species that were more common in unprotected then reserve habitats (fish illustrations sourced from www.efishalbum.com).

Several taxa exhibited location specific responses to reserve protection and habitat connectivity. At Nusa Hope, reserve mangroves supported more pygmy snapper (Lutjanus maxweberi), rabbitfish (siganidae), parrotfish (scaridae) and roving herbivorous fish than unprotected mangroves. Reserve reefs also contained more snappers (lujanidae) and parrotfish (scaridae), and more roving herbivores and benthic invertevores when close to seagrass and mangroves. At Olive, reserve seagrass supported more orange-striped emperor (Lethrinus obsoletus), emperors (lethrinidae), parrotfish (scaridae), roving herbivores and benthic invertevores. Reserve mangroves contained more pygmy snapper and reserve reefs supported more onespot snappers (Lutjanus monostigma), emperors (lethrinidae) and parrotfish (scaridae) when close to seagrass, and more roving herbivores and benthic invertevores when close to seagrass and mangroves.

Chapter 6 Building social and ecological resilience to climate change in Roviana, Solomon Islands

Table 34 Mean density of taxa in reserve (R) and unprotected (NR) mangroves, coral reef and seagrass. Only means that differed (ANOVA, p < 0.05) between reserve and unprotected locations for each habitat are reported. NM, coral near mangroves; I, isolated coral reef; NS, coral near seagrass; ns, non-significant.

Scientific Name Rovianan name English name Mangrove Coral (NM) Coral (I) Coral (NS) Seagrass

R NR R NR R NR R NR R NR

Chapter 6 Horticulture & agroforestry vulnerability assessment

Table 35 Mean size of fish in mangroves, coral reef and seagrass habitats. Only means that differed (T Test, p < 0.05) between reef and mangrove or reef and seagrass habitats are reported. ‘nc’: no comparison of fish sizes was made between seagrass-reefs for species with densities influenced by mangroves or between mangroves-reefs for species with densities influenced by seagrass.

Scientific name Roviana name English name Mangroves Coral reef Seagrass

Seagrass influence

Bolbometapon muricatum Topa Bumphead parrotfish nc 37.88 5.36

Cheilinus undulatus Habili Maori wrasse nc 29.63 5.68

Lethrinus harak Osanga Thumbprint emperor nc 24.83 12.27

Lethrinus laticaudis Osanga Grass emperor nc 21.55 8.99

Lethrinus ornatus Osanga Ornate emperor nc 19.00 8.78

Lutjanus gibbosus Heheoku Paddletail snapper nc 27.70 9.97

Parapeneus barberinus Pakao Dashdot goatfish nc 23.40 10.65

Plectorhinchus lineatus Pipirikoho Lined sweetlip nc 59.25 7.40

Scarus ghobban Bobogo Bluebarred parrotfish nc 27.27 10.55

Mangrove influence

Lutjanus argentimaculatus Kakaha Mangrove snapper 28.82 48.75 nc

Lutjanus fulviflamma Kida kale Blackspot snapper 20.01 29.06 nc

Lutjanus fulvus Odongo Blacktail snapper 21.42 31.76 nc

Plectorhinchus albovittatus Pehu Giant sweetlip 40.71 74.33 nc

Plectorhinchus gibbosus Pehu Brown sweetlip 40.00 48.48 nc

Mangroves and seagrass influence

Choerodon anchorago Pakopako Anchor tuskfish 17.31 23.73 10.90

Siganus doliatus Mendo mendo Barred rabbitfish 11.74 21.99 6.30

Siganus lineatus Tetego Lined rabbitfish 19.44 27.17 10.59

D

ISCUSSION

The approach to conservation planning in Roviana and Vonavona lagoons incorporated local indigenous ecological knowledge, existing sea tenure and conservation science to design marine reserves with the primary objective of conserving exploited bumphead parrotfish (Aswani and Hamilton 2004a). Our results demonstrate that habitat connectivity between reefs and seagrass improved the performance of these reserves in promoting fish abundance including the iconic bumphead parrotfish. Given the large size, mobility and the diversity of habitats utilized by this species (Aswani and Hamilton 2004a, Hamilton et al.

2009, Bellwood and Choat 2011), the design of these reserves necessitated protection of habitat diversity and connectivity across heterogenous tropical seascapes that support reefs, seagrass and mangroves. Many other fish species are also exploited as they move among these habitats over tidal, diel and ontogenetic cycles, and in addition to effects on bumphead parrotfish abundance, habitat connectivity mediated the affect of protection on the composition of reef fish assemblages and the abundance of 17 fish species.

Reef-seagrass connectivity improved the performance of reserves in promoting the abundance of an additional eight species, reef-mangrove connectivity enhanced reserve performance for six species and connectivity among all three habitats elevated reserve performance for another three species. These findings indicate that the approach adopted for marine conservation in Roviana and Vonavona lagoons has been successful, and suggest that bumphead parrotfish are an important umbrella species (sensu Simberloff 1998, Branton and Richardson 2010) for the conservation of local reef fish assemblages. That is, the protection of heterogeneous seascapes with high habitat connectivity and diversity to conserve bumphead parrotfish has also inadvertently conserved many other fish species. This has significant implications for local communities because the overwhelming majority of these species are harvested in local subsistence fisheries, and they contribute substantial protein to people’s diets (Brewer et al. 2009, Aswani and Sabetian 2010). These results corroborate the findings of studies that have shown the potential for habitat connectivity, diversity and heterogeneity to improve the performance of marine reserves (Edwards et al. 2010, Huntington et al. 2010, Olds et al. 2012a). Furthermore, they support the idea that we may further improve coral reef resilience by managing both reefs and their adjacent habitats together as functional seascape units (Bellwood et al. 2011, Olds et al. 2012b). This is important because many of these

Chapter 6

Building social and ecological resilience to climate change in Roviana, Solomon Islands

habitats (e.g. mangroves) appear to be threatened to a greater extent by coastal clearing and development than climate change, and can benefit greatly from improved local management (Adam et al. 2011).

Two species that occurred in greater abundance in reserves where reef and seagrass were located in close proximity (i.e. bumphead parrotfish and maori wrasse) are considered threatened globally (Donaldson and Sadovy 2001, Donaldson and Dulvy 2004). These are the world’s largest parrotfish and wrasse species, they are heavily harvested throughout their ranges, but quantitative studies that examine their use of habitats as juveniles and changes in habitat use through ontogeny are lacking (Dorenbosch et al. 2006, Bellwood and Choat 2011). We recorded small juveniles of both species in shallow water coral reef and seagrass habitats, juvenile bumphead parrotfish were also recorded in mangroves, but abundance was greatest in areas of contiguous seagrass and coral patches. Differences in the size of these fish (and 15 other species) among habitats suggest the importance of habitat connectivity may reflect migration to coral reefs with increasing fish size. That being said, many of these species (including members of the haemulidae, labridae, lethrinidae, lutjanidae, scaridae, serranidae and siganidae) are known to migrate tidally or diurnally between reefs and adjacent seagrass and mangroves (Heck et al. 2008, Grober-Dunsmore et al. 2009, Sheaves 2009). Indeed, the abundance of larger individuals from each of these families in seagrass and mangrove habitats indicates that they may also be important foraging areas for fish in Roviana and Vonavona lagoons. Never-the-less, the movement of these species between lagoon habitats may in turn be followed by the migration of larger adults to passage and outer barrier reefs to spawn, or with changing resource requirements (Aswani and Hamilton 2004b). Such migrations would take fish across the boundaries of existing marine reserves in the lagoon to areas where they could be captured by local fishers.

The potential for this spillover highlights the importance of establishing lagoon reserves close to passages and river channels to both facilitate the offshore movement of adults, and to improve their potential for capturing the inshore recruitment of juveniles into nursery habitats (sensu Nagelkerken 2009b). Our results suggest that both functions will be enhanced where new reserves are established near passages in heterogeneous seascapes that include reefs, seagrass and mangroves. They also indicate that the performance of existing small reserves may be improved by extending their boundaries to increase habitat connectivity, diversity and heterogeneity. Aggregations of large adult fish on passage and outer barrier reefs are also vulnerable to exploitation, for this reason bans on the spearfishing of bumphead parrotfish have been introduced for passage habitats (Aswani and Hamilton 2004a) and reserves have been established to protect spawning aggregations of groupers and maori wrasse (Aswani and Hamilton 2004b).

This provides little protection, however, for other fish species that aggregate on these reefs and additional offshore reserves may need to be established in the future to maintain the recruitment of juveniles into lagoon reserves.

Our findings indicate that the approach adopted for marine conservation in Roviana and Vonavona lagoons has been successful. They demonstrate that connectivity can improve the performance of marine reserves in promoting the abundance of iconic bumphead parrotfish (a local conservation priority), and suggest that the large size, mobility and the diversity of habitats utilized by this species make it an important umbrella species for the conservation of local reef fish assemblages. In addition to the influence on bumphead parrotfish abundance, connectivity among reef, seagrass and mangroves enhanced the effects of protection on the abundance of 17 harvested fish species. These results support the assertion that habitat connectivity, diversity and heterogeneity can improve the performance of marine reserves and indicate that we may further improve coral reef resilience by managing both reefs and their adjacent habitats together as functional seascape units. We suggest that the performance and resilience of marine reserves in Roviana and Vonavona will be enhanced where they incorporate high connectivity among reefs, seagrass and mangroves and are positioned to facilitate the offshore movement of adult fish and the inshore

Chapter 6 Connectivity

Figure 114 Typical seagrass, mangrove and seagrass habitat adjacent to small lagoon islands

Figure 115 High fish biomass within mangrove habitats of Roviana

Chapter 6

Building social and ecological resilience to climate change in Roviana, Solomon Islands

G ^ENETIC C ONNECTIVITY

Im Dokument Building social and ecological resilience to climate change in Roviana, Solomon Islands (Seite 152-160)