Scartella cristata - Amazon S3

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Scartella cristata is a wide-ranging species occurring on nearshore reefs and rocky shores
throughout the tropical Atlantic, Caribbean, Gulf of Mexico, and Mediterranean. The Texas Gulf coast
likely represented a gap in the distribution of this species due to a lack of suitable habitat. With initiation
of jetty construction in Texas during the 1880’s, S. cristata larvae that historically would pass the Texas
coast found new habitat to colonize in state waters. The genetic structure of local populations on Texas
jetties reflects the history of this colonization. Haplotype diversity (h) of S. cristata across Florida,
Galveston, Port Aransas, and South Padre Island was high; however, nucleotide diversity (π) was low to
moderate. While these results indicate a large number of different haplotypes exist in the S. cristata
population, low nucleotide diversity suggests they are closely related and effective population size is
relatively small. This relationship between h and π is consistent with findings by Muss et al. (2001) for
another wide ranging blenniid, Ophioblennius atlanticus, and appears to be a common theme among many
marine fishes (Palumbi 1994, Grant and Bowen 1998).
Both haplotype and nucleotide diversity were greater for conspecifics from the middle and lower
Texas coast than that for their upper coast and Florida cohorts. This suggests that the source population of
Scartella cristata for Port Aransas and South Padre Island is more diverse and possibly older or larger than
that for Galveston and Florida. Whether or not Florida is the source population for Galveston cannot be
answered definitively based on the limited number of sample sites and small number of individuals from
the former. It is clear that if Florida is not the source population for Galveston then the two share the same
origins. Similarities in haplotype distribution and among group component of variation (Φ ST ), low genetic
distances between sites (0.005), and high level of gene flow per generation link the two sites despite the
large geographic distance (689 km) and the Mississippi River plume that separates them. This linkage is
accomplished through predominant nearshore currents in the Gulf, which would tend to carry larvae from
east to west throughout the year (Fig. 26).
Transport of Scartella cristata larvae to Texas jetties from either Mexico or Florida is plausible.
Although not known for S. cristata, the larval duration of Hypsoblennius ionthas lasts from 6 to 8 weeks
(Clarke 1979). Longshore currents along the Texas coast range in velocity from 12 (Fox and Davis 1976)
to 21.5 cm/s (Smith 1975) under typical conditions, while larvae entrained in a boundary current such as