Population structure in a common Caribbean coral-reef fish: implications for larval dispersal and early life-history traits.

Genetic population structure throughout the Caribbean Basin for one of the most common and widespread reef fish species, the bicolour damselfish Stegastes partitus was examined using microsatellite DNA markers. Spatial autocorrelation analysis showed a significant positive correlation between genetic and geographic distance (isolation by distance) over distances <1000 km, suggesting that populations are connected genetically but probably not demographically, i.e. over shorter time scales. A difference in spatial patterns of populations in the eastern v. the western Caribbean also raises the probability of an important role for meso-scale oceanographic features and landscape complexity within the same species. A comparison of S. partitus population structure and life-history traits with those of two other species of Caribbean reef fish studied earlier showed the findings to be concordant with a common hypothesis that shorter pelagic larval dispersal periods are associated with smaller larval dispersal scales.

Small-scale demographic variation in the stoplight parrotfish Sparisoma viride.

Age-based analysis of the stoplight parrotfish Sparisoma viride was used to examine whether observed differences in their abundance and size structure among reefs in a cross-shelf portion of the upper Florida Keys could be explained by variation in demographic rates. Annual and daily sagittal otolith increments were enumerated for 176 individuals collected from replicates of reefs in two strata, inshore and offshore reefs (2-6 m depth). von Bertalanffy growth functions fitted to size-at-age plots for each site were similar between reefs within each stratum (inshore and offshore), but differed between strata. Sparisoma viride on offshore reefs attained greater average standard length (L(S)) at age, greater mean asymptotic size and were longer lived than fish from inshore reefs. Fish on inshore reefs attained only half the maximum age observed on offshore reefs (4 v. 8 years, respectively). No terminal phase fish >4 years of age were found on either reef type. Estimates of mortality rates from age-frequency data of collected fish revealed higher mortality on inshore reefs. Demographic variables obtained in this study were similar to published values for S. viride from Caribbean reefs but differed significantly from published values from reefs at a similar latitude (Bahamas), reflecting high demographic plasticity on both local and regional scales.

Scaling of connectivity in marine populations.

Defining the scale of connectivity, or exchange, among marine populations and determining the factors driving this exchange are pivotal to our understanding of the population dynamics, genetic structure, and biogeography of many coastal species. Using a high-resolution biophysical model for the Caribbean region, we report that typical larval dispersal distances of ecologically relevant magnitudes are on the scale of only 10 to 100 kilometers for a variety of reef fish species. We also show the importance of the early onset of active larval movement mediating the dispersal potential. In addition to self-recruitment, larval import from outside the local area is required to sustain most populations, although these population subsidies are very limited in particular systems. The results reveal distinct regions of population isolation based on larval dispersal that also correspond to genetic and morphological clines observed across a range of marine organisms.

Connectivity of marine populations: open or closed?

Most marine populations are thought to be well connected via long-distance dispersal of larval stages. Eulerian and Lagrangian flow models, coupled with linear mortality estimates, were used to examine this assumption. The findings show that when simple advection models are used, larval exchange rates may be overestimated; such simplistic models fail to account for a decrease of up to nine orders of magnitude in larval concentrations resulting from diffusion and mortality. The alternative process of larval retention near local populations is shown to exist and may be of great importance in the maintenance of marine population structure and management of coastal marine resources.

Connectivity of marine populations: open or closed?

Most marine populations are thought to be well connected via long-distance dispersal of larval stages. Eulerian and Lagrangian flow models, coupled with linear mortality estimates, were used to examine this assumption. The findings show that when simple advection models are used, larval exchange rates may be overestimated; such simplistic models fail to account for a decrease of up to nine orders of magnitude in larval concentrations resulting from diffusion and mortality. The alternative process of larval retention near local populations is shown to exist and may be of great importance in the maintenance of marine population structure and management of coastal marine resources.(Au)

Ichthyological enthusiasm.

Coral Reef Fishes: Caribbean, Indian Ocean, and Pacific Ocean including the Red Sea by E. Lieske and R. Myers Princeton University Press, 1996. $35.00 hbk (400 pages) ISBN 0 691 02659 9 Air-Breathing Fishes: Evolution, Diversity, and Adaptation by J.B. Graham Academic Press, 1997. $79.95 hbk (xi+299 pages) ISBN 0 12 294860 2 The Diversity of Fishes by G.S. Helfman, B.B. Collette and D.E. Facey Blackwell, 1997. £55.00 hbk (xii+528 pages) ISBN 0 86542 256 7.

The effects of periodic eutrophication on parasitism and stock identification of Trematomus bernacchii (Pisces: Nototheniidae) in McMurdo Sound, Antarctica.

McMurdo Sound, Antarctica, is suited for the study of the effects of eutrophication on diet-related parasites of Trematomus bernacchii (Boulenger, 1902) (Pisces). It has been relatively well studied, the environment is predictable, and there are significant differences in primary productivity over small distances. The differences in parasitism for 5 helminth species can be attributed to the enrichment processes in the sound. The prevalences of the acanthocephalan Echinorhynchus sp., the nematode Ascarophis nototheniae, the digenean Dinosoma sp., and the cestode Phyllobothrium sp. are significantly higher on the east side of the sound than on the west. The prevalence of the digenean Lepidepedon garrardi was significantly higher on the west side. We believe that the differences in the prevalences of infection between the east and west sides suggest that at least the benthic, adult fish do not readily move from one side of the sound to the other. We report the following (new host records are marked by asterisks): Echinorhynchus sp., Corynosoma hamanni (Acanthocephala); Phyllobothrium sp., Diphyllobothrium sp., Trypanorhyncha (Cestoidea); Clavellopsis (Copepoda); Dinosoma sp., Lepidepedon garrardi (Digenea); Pseudobenedenoides brachicola, Polyopisthocotylea (Monogenea); Contracaecum sp., Ascarophis nototheniae (Nematoda); Myxoproteus sp., Henneguya sp., Ceratomyxa sp., and Zschokkella sp. (Protozoa).