The influence of colony size and coral health on the occupation of coral-associated gobies (Pisces: Gobiidae)

Pygmy seahorses are a group of little-known miniature hippocampid fish that differ considerably in biology and ecology from their larger congeners. We estimated the population density, sex ratio and habitat of 2 sympatric, obligate gorgonian-associated pygmy seahorses, Hippocampus bargibanti and H. denise, in a 20 km long coastal marine protected area in southeast Sulawesi, Indonesia. Belt transects covering 200 m 2 each were surveyed at 7 sites and 5 depth contours to record the density of seahorses and their host gorgonians. The population density (± SE) was 1.17 (± 0.27) per 200 m 2 for H. denise and 0.34 (± 0.20) per 200 m 2 for H. bargibanti, some of the lowest densities for unexploited seahorse populations studied thus far. Male−female pairs (43.9%) were the most common group composition for H. denise, with single, 3 or 4 individuals found on 19.5, 7.3 and 29.3% of inhabited gorgonians, respectively. H. denise inhabited 7.8% of Annella reticulata gorgonians within the survey area but were recorded from a total of 8 gorgonian genera during extensive opportunistic ad hoc searches. Annella spp. density was 10.7 times higher than that of Muricella spp. (the sole host of H. bargibanti), of which 20.0% were inhabited. The small population size, occurrence of pygmy seahorses in groups on their hosts with the resulting skew in sex ratios, and habitat specialisation likely all impact the species' population dynamics, and hence these need to be considered in conservation management strategies.KEY WORDS: Habitat specialist · Miniature species · Abundance · Rare species · Hippocampus · Syngnathidae · Pygmy seahorse · Gorgonian 444: 195-206, 2012 Many organisms that live on coral reefs rely directly on architectural species for their existence (Jones et al. 2004). An association with gorgonians can be beneficial to other organisms due to the gorgonians' temporal stability as hosts, their unpalatability, thus acting as a chemical refuge, and their provision of access to rich food resources via their position in high water flow (Goh et al. 1999, Puglisi et al. 2000, Kumagai 2008. Two of the 7 described species of pygmy seahorses are obligate associates of gorgonian corals and form small groups of individuals that appear to spend their entire post-pelagic life on a single host (Smith 2011). The associations of these miniature seahorses with gorgonian hosts have been documented for Hippocampus bargibanti, which lives exclusively with Muricella plectana and M. paraplectana (Gomon 1997), and H. denise, which has a wider range of hosts including Annella reticulata, Muricella sp. and unconfirmed associations with Echinogorgia sp. and Acanthogorgia sp. (Gomon 1997, Lourie & Randall 2003, Lourie & Kuiter 2008. Despite a paucity of knowledge regarding the biology and ecology of gorgonian-associated pygmy seahorses, their host specialisation is a factor potentially placing them at an increased risk due to habitat disturbance , Munday 2004, Feary 2007. Resale or republication not permitted without written consent of th...

Section: Introductionmentioning

confidence: 99%

Extreme habitat specialisation and population structure of two gorgonian-associated pygmy seahorses

Smith

Grutter²,

Tibbetts³

2012

“…Previous studies have shown that branch space increases with colony size (Kuwamura et al 1994, Schiemer et al 2008, Kane et al 2009). To account for this, colony size was kept constant for the different treatments (largest diameter range 21 to 28 cm).…”

Section: Effect Of Host Structure and Health On Survivorship And Condmentioning

confidence: 99%

“…Variable patch size, coral health and physical structure have all been shown to influence population dynamics of coral-associated reef fishes (Tolimieri 1995, Holbrook et al 2000, Holbrook & Schmitt 2003, Aburto-Oropeza et al 2007, Thompson et al 2007, Schiemer et al 2008, Bonin et al 2012. To date a range of responses have been observed for different habitat attributes.…”

Section: Introductionmentioning

confidence: 99%

“…The use of different coral species makes it difficult to isolate the effects of differences in structure from other potential differences between coral species. Many coral species exhibit substantial intraspecific morphological variation (Veron & Pichon 1976, Vytopil & Willis 2001, Schiemer et al 2008, Kane et al 2009) that may have a dramatic influence on the quality of the shelter they provide to fishes.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Coral size, health and structural complexity: effects on the ecology of a coral reef damselfish

Noonan¹,

Jones²,

Pratchett³

2012

The structure and dynamics of animal populations are strongly influenced by the physical and biotic characteristics of their habitats. However, in complex habitats such as coral reefs, the particular habitat features that are important and the mechanisms that impact on populations are poorly understood. This study investigates the influence of coral colony size, health and branching structure of the host coral Seriatopora hystrix on the ecology of the resident damselfish Chromis retrofasciata. Field observations indicated C. retrofasciata preferentially occupied larger S. hystrix colonies, but among occupied corals, group size was greatest on colonies of an intermediate size and with wider branch spacing. Healthy corals were observed to support higher abundances. The effects of both coral health (live vs. dead) and coral complexity (fine, medium and coarse branching) on survivorship of stocked juvenile C. retrofasciata were examined in a patch reef experiment. Survival was 20% higher in living colonies compared to dead ones, and fish in medium complexity coral exhibited approximately 10 and 20% greater survival than those in both the low and high complexity categories, respectively. These factors had an additive effect with the highest survival observed on healthy colonies with intermediate complexity (95%) and the lowest on highly complex, dead corals (55%). Body size distributions were also reduced on corals with the narrowest branch spacing. During habitat selection trials, juveniles were observed to preferentially occupy colonies with intermediate branch spacing. Prey may prefer corals of intermediate spacing and survive better as such habitats provide shelter that obstructs predator access. This study provides evidence that suggests small reef fish species will be sensitive to disturbances that result in the loss of live coral and alter preferred structural complexity of habitats.

“…In similar-sized colonies, branches are longer than in A. gemmifera while IBDs are similar. These 2 factors combined offer better protection against predation, also explaining the high occupation rate (up to 86%) of A. digitifera colonies in the investigation area (Schiemer et al 2009). Untersteggaber et al (2014) discovered that the mean BLs of corals occupied by adult fishes was greater (> 5 cm) than in unoccupied colonies.…”

Section: Growth Patterns and Shape Differences In Corals And Fishesmentioning

confidence: 89%

Microhabitat characteristics influence shape and size of coral-associated fishes

Wehrberger¹,

Herler²

2014

Coral reefs provide a high diversity of habitats, including the often complex structure of reef-building corals themselves. Since these coral microhabitats are constrained spatially, specific phenotypic adaptations of associated species to the geometric structure of corals are expected. In the northern Red Sea, we investigated how the physical structure of 2 Acropora corals influences the size, shape and growth of fishes that live in these corals. Branch length and interbranch distance increased strongly and differentially with colony size in both coral species, making large colonies more suitable for larger fishes. We used traditional and geometric morphometrics to demonstrate that the 2 coral-dwelling gobies Gobiodon histrio (Valenciennes) and G. rivulatus (Rueppell) follow different ontogenetic growth patterns. Adult G. histrio show a dorsoventrally expanded body combined with a lateral compression, while the wider-bodied G. rivulatus has a smaller maximum body length. The lateral compression enables G. histrio to pass smaller interbranch distances than G. rivulatus of the same body length, as demonstrated in an experiment testing their ability to pass narrow interbranch distances. Measurements of G. histrio revealed a greater increase of body length and mass with coral colony size in Acropora digitifera than in A. gemmifera or other coral species. Outliers in growth rates of the fishes demonstrated that moving to larger corals and/or associating with a larger breeding partner benefits fish growth. Shape-related lateral body size differences provide an explanation why those fishes that are better adapted to certain host corals compete more successfully for these microhabitats. The evolution of different shapes in coral-associated fishes indicates differences in habitat specialization to reef-building corals with different geometries.