Reef fish assemblages in the Caribbean are under increasing pressure from human activities. Inadequate enforcement of legislation coupled with unreliable and ]]>
b. Most fish assemblages were dominated by small ]]>
Los ensamblajes de peces de arrecife en el Caribe están bajo una creciente presión de las actividades humanas. La ejecución inadecuada de la legislación, junto ]]>
W=aLb. La mayoría de las comunidades de peces son dominadas por pequeños herbívoros (<15cm), en particular Pomacentridae y Scaridae. Pocos depredadores grandes (>40cm), por ejemplo Serranidae, se observó, lo que es indicativo de la presión de pesca. El análisis de escala multidimensional identificó tres conjuntos distintos de peces indicados como i) ]]>
Palabras clave: trofismo, Tobago, peces de arrecife de coral, encuestas submarinas visuales.
Coral reef fishes are the most ]]>
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Reef fish communities around Tobago exist on the margin of coral reefs in the southern Caribbean, and play a critical role in maintaining reef integrity. However, declining reef fish (abundance and biomass) as told in the oral history of Tobago, threatens the mainstay of the local diet and dependent economies. Further, the recent invasion of the lionfish onto Tobago’s reefs poses a real threat to juvenile and small reef fish communities. The purpose of this study is to a) establish some baseline data on the abundance and species richness of reef fishes around Tobago and b) assess any ]]>
Materials and Methods
Study site: This study was conducted over an eighteen month period October 2011 to March 2013 on ]]>
Fig. 1), located 7km east off the Paria Peninsula. Study reefs (n=23) were of comparable size(~4ha) and represented the variability of the major reef systems. Tobago’s underwater topography is characterized by two distinct topographic regimes, a shallow limestone gently sloping shelf on the southwest side of the island, and a narrow, rocky, steeply sloping shelf on the northeastern side, upon which a variety of coral have been established (Snake, Rowe, Yule & Wadge, 1986). In this study, the southwest reefs are considered true ]]>
Montastraea faveolata, Siderastrea siderea, Diploria strigosa ]]>
Colpophyllia natans.
Reef fish census: Reef fish surveys were conducted to estimate abundance, richness and to determine spatial distribution. Surveys were conducted along three 25x5m belttransects along the outer reef slope between 10-15m depth. Along each transect the number of individuals of each species was estimated and the total length of each fish was visually estimated and classified into 10cm ]]>
2 (D) and species abundance (N), were determined for all reefs.
Fish biomass was ]]>
b. The most suitable “a” and “b” constants were acquired from Froese and Pauly (2013), and where no relationship was available for species, that of a closely related species as applied. Trophic guilds were classified according to Froese and Pauly (2013), however in many cases there was no definitive consensus as to the trophism of several species. As a result trophic groups were consolidated and presented as planktivores, primary consumers (herbivores and detritivores), secondary consumer (omnivores ]]>
Benthic cover and vertical relief was also measured along benthic transects. Benthic cover was estimated using six 10 x 1m belt transects at each site as described by (Hill & Wilkinson, 2004). Ten non-overlapping 1m2 photos were taken along ]]>
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Bray-Curtis similarity on fourth-root transformed abundance and biomass was calculated, and analysis of similarities (ANOSIM) was conducted to test for differences in similarity between reefs and reef types. The ANOSIM results in a global R statistic that reflects the differences in variability between groups and within groups, and checks for significance of R were performed using permutation tests (Clarke & Warwick, 2001). Two dimensional ordinations were created using non-metric multi-dimensional scaling (MDS), which was used to generate plots in which the distance ]]>
Results
A total of 15 576 fish, representing 96 species and 23 families were recorded around Tobago, with an average of 677.2±376.3 individuals/site. The most abundant species were Stegastes partitus, Chromis miltilineata and Clepticus parrae which ]]>
Balistes vetula, Mycteroperca bonaci, Bothus lunatus, Scarus coelestinus, Lutjanus cyanopterus, Lactophyrs quadricornis, M. tigris, Sphyraena barracuda and Abudefdub taurus, with each being only observed once.
Over 80.0% of the ]]>
Table 1). Species from the families Pomacentridae, Labridae, Scaridae, Haemulidae, Acanthuridae and Serranidae were found at all locations, and together with Pomacentridae accounted for 90% of fish observed. Chaetontidae was observed in all but one site. Together, these seven families accounted for ~70.0% of the total biomass, with the highest biomass (21.0%) provided by Pomacentridae (56kg/100m2). Other major contributors to overall biomass included Scaridae (11.4%), Lutjanidae (8.2%), Acanthuridae (6.4%) and Haemulidae (6.2%), with all other noted families contributing <5% each to overall biomass (Table 2).
The most abundant trophic group was the primary consumer (herbivores and detritivores) which accounted for ]]>
Chromis multilineata (14.8%), Clepticus parrae (10.6%) and Thalassoma bifasciatum (9.1%). All other species each contributed <7% to overall fish biomass. ]]>
Fish assemblages at all locations were dominated by fish ≤10cm in size, probably as a result of the numerical abundance of the inherently small-sized pomacentrids. Fish ≤10cm in size accounted for 71.1% of all fish recorded. The 11-20 and 20-30cm size classes held 22.6% and 4.5% respectively.Very few fish were larger than 30cm. Those recorded larger than 30cm included Sparisoma viridae, Pomacanthus arcuatus, Scarus vetula and Hypoplectrus ]]>
MDS ordination identified three main assemblages of fish based on reef type (ANOSIM, R=0.281, P<0.001), with three outlier groups at LS, BI and MIE based on the numerical abundance of fish (Fig. 2). These assemblages were well separated from the other reefs in ordination space (Stress=0.2). Sites grouped into a northeast Tobago high relief assemblage (CR, STG, JG, ]]>
Fig 2).Species richness and diversity were generally higher at the northeastern Tobago reefs, particularly at BI (S=38, H’=2.989), STG (S=46, H’=2.95) and BJH (S=45, H’=2.72). The overall highest diversity was occurred at AR (3.003) in the southwest and the lowest H’ occurred at CO (H’=1.234) in the intermediate cluster (Table 2). ]]>
Similarly, there was also a significant difference in family composition with reef type (ANOSIM, R=0.263, P<0.002). The northeast assemblage accounted for 55.9% of the total fish biomass and 42.4% of the total fish abundance and the southwest assemblage accounted for 32.5% of total biomass and 36.2% of total abundance. The special interest area, Buccoo Reef Marine Park (BRMP) within the southwestern cluster accounted for 23% of total fish abundance but only 8.8% biomass. This separation in assemblages ]]>
With regards to fish biomass, while the general separation of clusters between northeastern and southwestern reefs was maintained in ordination space, there was no significantly relationship with reef type (ANOSIM, R=0.036, P=0.226). ]]>
Overall, the variation in abundance of Acanthuridae, Serranidae, Scaridae, Pomacentridae and Labridae was responsible for most of the dissimilarity among sites and assemblages. In particular, 16 species were responsible for most of the ]]>
Acanthurus bahianus),Serranidae (particularly Serranus tigrinus and Epinephelus adscensionis), Pomacentridae (particularly Chromis multilineata, Stegastes partitus, Microspathodon chrysurus) and Balistidae (particularly Melichthys ]]>
) were mostly found on the northeastern reef cluster, whereas Scaridae (particularlyScarus iseri, S. taeniopteus, Sparisoma viride, S. aurofrenatus) and Labridae (particularly Thalassoma bifasciatum, Clepticus parrae) were dominant in the southern and intermediate reef clusters.
Most top ]]>
Ocyurus chrysurus and Lutjanus cyanopterus. The only site where no piscivores were observed was MJ. LS, the northeastern and intermediate assemblages accounted for 24.9%, 19.3% ]]>
Chromis multilineata and Thalassoma bifasciatum. Primary consumers were most dominant within the northeast cluster and secondary consumers were most dominant within the southwest cluster (Table 1). ]]>
Few fish >40cm were recorded, and where they were noted densities were quite low. The highest densities of large fish occurred at AV (3.5 individuals/100m2), ER (2.7 individuals/100m2) and BP (1.6 individuals/100m2). Overall most fish (93.7%) were <20cm in size. Fish <10cm were similarly distributed among reefs, with the highest densities occurring at LS (7.4 individuals/100m2) in the northeast and KR (7.3 individuals/100m2) in ]]>
Scarus spp, Sparisoma spp, Pomacanthus paru, Mulloidichtys martinicus, Acanthurus spp and Stegastes spp. Whereas, the northeast ]]>
Thalassoma spp, Halichores spp, Chromis spp, Clepticus sp., Haemulon spp, Mycteroperca tigris, Cephalopholis cruentata, Cephalopholis fulva, Ocyurus chrysurus,
Aulostomus maculates and s Scarus spp.
Within the 23 reefs, live coral cover ranged from 4.6% at CO to 42.8% at STG. Macroalgae (including erect coralline algae, turf algae and fleshy macroalgae) was the dominant feature on most reefs, with only four reefs (KW, KR, BJH and JG) having <30% algal cover. Sponge cover ranged from 0.3%28.0%, and ]]>
Table 2). Overall, the northeastern reefs were mostly high relief ]]>
Discussion
This study examined variation in ]]>
m2 and were dominated by small-bodied fishes of low commercial value (such as pomacentrids and labrids) and few highly valuable commercial species such as serranids and lutjanids. This is similar to other reefs in the Caribbean that have been overfished or highly impacted (Hughes, 1994; Mallela, Roberts, Harrod & Goldspink, 2007; Aguilar-Perera & Appledoorn, 2008). Reef fish biomass in Tobago was low compared to other islands in the region. Newman, Gustavo, Sala & Jackson, (2006) estimated fish biomass in a range of coral reef habitats in the Caribbean and found average biomass estimates to range between 15 and ]]>
m2, whereas in Tobago mean biomass 10.7±11.0g/m2.
MDS ordination separated fish populations in three distinct assemblages with three outlier groups. ]]>
Structurally complex habitats fragment the area, resulting in numerous microhabitats being formed and ]]>
The differences in spatial variability of piscivores (Table 1) could be due to spatial differences ]]>
Table 1) in the northeastern reefs could be a direct result of the food availability and an indirect result of habitat availability for prey items (Stewart & Jones, 2011). Serranids and lutjanids are roving predators that feed mostly on fish and are associated with coral reefs (Ferreira, Floeter, Gasparini, Ferreira & Joyeux, 2004). ]]>
Marine protected areas enclosing coral reefs have had a broad range of positive effects such as ]]>
m2) was almost twice the scarid biomass of nearby reefs (~6.8g/100m2) (Table 1). When compared to other well protected MPA in the region such Los Roques (scarid biomass 60.7g/m2) and Flower Garden Banks (scarid biomass 35.8g/m2) (Posada, Villamizar & Alvarado, 2003), the MPA’s scarid biomass is quite low. On the non-protected fishes reefs of Curacao scarid biomass is approximately 15.2g/m2 and as low as 4.6 on the overfished Montego Bay reefs (J. Jackson et al., ]]>
This study represents a comprehensive baseline assessment of the reef fish fauna of Tobago and is instructive as to where efforts should be prioritised to conserve reef fish populations from human threats (fishing) and alien invasive threats (Pterois sp.). Additionally, future research on the reef fishery, particularly spears fishing, to determine impacts by these ]]>
Acknowledgments
I would like to thank Stefan Lue Chin, Sherron Barker, Jonathan Gomez and Addison Titus who assisted in ]]>
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1. Institute of Marine Affairs, Hilltop Lane, Chaguaramas, Trinidad and Tobago, W.I., Tel: +1 868 678 3718, Fax: +1 868 634-4433; jalemu@ima.gov.tt
Received 22-VIII-2013 Corrected 18-II-2014 Accepted 24-III-2014