Temporal and spatial variability of blenny (Perciformes:Labrisomidae and Blenniidae) assemblages on Texas jetties

Abstract

Structured, hard-bottom habitats and associated cryptic fish species were effectively absent from the northwestern Gulf of Mexico coast prior to jetty construction 120 years ago. Fishes in the Families Labrisomidae and Blenniidae now distributed across the northwest Gulf may have been influenced by jetty construction. Little is known about the species composition, population dynamics, or origin(s) of blenny assemblages on Texas jetties. In this study, blennies were dipnetted monthly from jetty habitats at Galveston, Port Aransas, and South Padre Island, Texas, during May 2000 through August 2001; and in Florida, once during December 2001 to characterize assemblage structure. All specimens (n=4555) were identified, enumerated, and measured and a subsample taken for otolith microstructure analysis (n=99) and mtDNA sequencing (n=67). Four blenniid species (Hypleurochilus geminatus, Hypsoblennius hentz, Hypsoblennius ionthas, and Scartella cristata) and one labrisomid (Labrisomus nuchipinnis) contributed to spatially distinct assemblages differing significantly in species composition, diversity and evenness across sampling sites. Galveston exhibited the highest diversity index values while Port Aransas yielded the most species (4). Temperature appears to be the driving factor behind species composition over time at each sampling site. Scartella cristata dominated blenny assemblages on Texas jetties regardless of local environmental conditions and was found to be a short-lived species with an extended spawning period. The Galveston population of S. cristata exhibited the statistically highest mean total length and age and demonstrated a close affinity to Florida conspecifics, thus indicating the eastern Gulf to be a likely source. Scartella cristata on the lower and middle Texas coast originated from at least two sources, suggesting two genetically distinct populations may exist in the Gulf. Jetty construction on the Texas coast has allowed these two populations to mix.