Multi-Scale Sampling to Evaluate Assemblage Dynamics in an Oceanic Marine Reserve

To resolve the capacity of Marine Protected Areas (MPA) to enhance fish productivity it is first necessary to understand how environmental conditions affect the distribution and abundance of fishes independent of potential reserve effects. Baseline fish production was examined from 2002–2004 through ichthyoplankton sampling in a large (10,878 km2) Southern Californian oceanic marine reserve, the Cowcod Conservation Area (CCA) that was established in 2001, and the Southern California Bight as a whole (238,000 km2 CalCOFI sampling domain). The CCA assemblage changed through time as the importance of oceanic-pelagic species decreased between 2002 (La Niña) and 2003 (El Niño) and then increased in 2004 (El Niño), while oceanic species and rockfishes displayed the opposite pattern. By contrast, the CalCOFI assemblage was relatively stable through time. Depth, temperature, and zooplankton explained more of the variability in assemblage structure at the CalCOFI scale than they did at the CCA scale. CalCOFI sampling revealed that oceanic species impinged upon the CCA between 2002 and 2003 in association with warmer offshore waters, thus explaining the increased influence of these species in the CCA during the El Nino years. Multi-scale, spatially explicit sampling and analysis was necessary to interpret assemblage dynamics in the CCA and likely will be needed to evaluate other focal oceanic marine reserves throughout the world

Holoplanktonic polychaetes from the Gulf of Tehuantepec, Mexico

Composition, abundance, and main assemblages of holoplanktonic polychaetes were analysed in the Gulf of Tehuantepec. This Gulf, in Mexican waters of the eastern tropical Pacific, is a very productive system due to an upwelling during the winter. Zooplankton samples were taken over a station grid covering neritic and oceanic waters during March and November 1978. Most species showed their highest densities in the oceanic region. In the western Gulf, the area sampled in both seasons, mean polychaete abundance was higher in November (549.2 ind.1000 m(-3)) than in March (143.8 ind.1000 m(-3)). A regression tree analysis showed that pH and dissolved oxygen were the main factors affecting the total polychaete abundance over the study area during March. Identified families were: Lopadorhynchidae (88.8%), Alciopidae (6.6%), Iospilidae (2.8%), Tomopteridae (1. 1%) and Typhloscolecidae (0.7%). The dominant species, Pelagobia longicirrata, accounted for 86.5% of the total polychaete abundance. A Bray-Curtis analysis identified two main polychaete assemblages during March: "oceanic" and "neritic". Species richness and mean polychaete abundance were higher in the "oceanic" assemblage, and P. longicirrata, Plotohelmis capitata, Rhynchonerella gracilis and Lopadorhynchus henseni were the most frequent and abundant species in this assemblage. In the "neritic" assemblage, the iospilids Phalacrophorus uniformis and Iospilus phalacroides registered the highest relative abundance. It is suggested that the structure of holoplanktonic polychaete assemblages could be determined by the feeding habits of the species and their tolerance to the variability in environmental conditions

Chaetognath assemblages in Bahia de Banderas, Mexico

The composition, distribution, and main assemblages of chaetognath species were examined throughout an annual cycle in Bahia de Banderas, Mexico. Zooplankton sampling was carried out during five seasons (1989 and 1991), using a 50 cm diameter and 1.5 m long conical net with a 505 pm mesh size. The abundance of chaetognaths in each season was subjected to a Factor Correspondence Analysis (FCA) in order to identify the main assemblages. A total of 4142 individuals was sorted out from samples, and seven species were identified: Sagitta euneritica (Alvarino, 1961), Sagitta neglecta Aida, 1897, Sagitta inflata Grassi, 1881, Sagitta bedoti Beraneck, 1895, Sagitta pacifica (Tokioka, 1940), Sagitta minima Grassi, 1881, and Krohnitta pacifica (Aida, 1897). Sagitta euneritica was the most abundant and widely distributed species throughout the study area. The FCA defined two chaetognath groups, the "euneritic assemblage" and the "mixed assemblage," whose differences were established mainly by relative species abundance, rather than composition. For most of the year, the "euneritic assemblage" occupied the area over the shelf, possibly reflecting an area of high secondary production

Morphometry and sexual dimorphism of the coastal spotted dolphin, Stenella attenuata graffmani, from Bahia de Banderas, Mexico

External measurements and size differences between the sexes were examined in the coastal spotted dolphin, Stenella attenuata graffmani, in Bahia de Banderas, on the Mexican Pacific coast. The dolphins were collected by local fishermen and 29 external characteristics were measured by members of the Marine Mammals Laboratory, University of Mexico. The length of each characteristic with respect to total length was analysed through adjustment of the data to a power equation. A stepwise discriminant analysis was applied to the absolute values and to those expressed as proportions to analyse the differences between the sexes. Results indicate that growth in these dolphins is generally negatively allometric, and most of the characteristics measured were, in both absolute and proportional terms, greater in male dolphins than in female dolphins. As found in many species of odontocetes, the discriminant analysis showed that the main differences between the sexes for this coastal subspecies include the relative positions of the umbilicus, the genital aperture and the anus. The morphometric data provided by this study, corresponding to 29 specimens of S. a. graffmani collected in a restricted locality of the Mexican Pacific coast, are particularly interesting to studies documenting latitudinal morphological differences in the coastal spotted dolphin

Copepod assemblages in the Gulf of Tehuantepec, Mexico

The Gulf of Tehuantepec, in the Mexican waters of the eastern tropical Pacific, is a very productive area with a high biological complexity, as the result of a wind-induced upwelling that occurs from November to February. The main assemblages of pelagic copepods in this region were identified and analysed in this study, during the final stage of the upwelling process. Samples were collected in oblique plankton hauls using a station grid that covered neritic and oceanic waters. Copepods were separated taking 10 mi aliquots from each sample. Data of copepod abundance were expressed as ind. m(-3) and subjected to a Factor Correspondence Analysis, in order to determine the main copepod assemblages. Results indicate the presence of two main assemblages: neritic and oceanic. The neritic assemblage is located on shelf waters. Its characteristic species are Microsetella norvergica, Macrasetella gracilis, Nannocalanus mino

Species effects on ecosystem processes are modified by faunal responses to habitat composition.

Heterogeneity is a well-recognized feature of natural environments, and the spatial distribution and movement of individual species is primarily driven by resource requirements. In laboratory experiments designed to explore how different species drive ecosystem processes, such as nutrient release, habitat heterogeneity is often seen as something which must be rigorously controlled for. Most small experimental systems are therefore spatially homogeneous, and the link between environmental heterogeneity and its effects on the redistribution of individuals and species, and on ecosystem processes, has not been fully explored. In this paper, we used a mesocosm system to investigate the relationship between habitat composition, species movement and sediment nutrient release for each of four functionally contrasting species of marine benthic invertebrate macrofauna. For each species, various habitat configurations were generated by selectively enriching patches of sediment with macroalgae, a natural source of spatial variability in intertidal mudflats. We found that the direction and extent of faunal movement between patches differs with species identity, density and habitat composition. Combinations of these factors lead to concomitant changes in nutrient release, such that habitat composition effects are modified by species identity (in the case of NH4-N) and by species density (in the case of PO4-P). It is clear that failure to accommodate natural patterns of spatial heterogeneity in such studies may result in an incomplete understanding of system behaviour. This will be particularly important for future experiments designed to explore the effects of species richness on ecosystem processes, where the complex interactions reported here for single species may be compounded when species are brought together in multi-species combinations