Environmental stress and parasitism as drivers of population dynamics of Mesodesma donacium at its northern biogeographic range

Abstract Riascos, J. M., Heilmayer, O., Oliva, M. E., and Laudien, J. 2011. Environmental stress and parasitism as drivers of population dynamics of Mesodesma donacium at its northern biogeographic range. – ICES Journal of Marine Science, 68: 823–833. Mesodesma donacium is a commercially important bivalve in Chile and Peru. During strong El Niño events, populations at the northern end of its geographic distribution are wiped out, so to understand its threshold responses to biotic and abiotic factors, the population dynamics of one of the northernmost population remnants was analysed between 2005 and 2007. Strong interannual differences were found in abundance, body mass, growth rate, somatic production, and the prevalence of the parasite Polydora bioccipitalis. A Spearman rank correlation analysis showed that changes in beach slope, seemingly linked to repeated storm surges, negatively affected the clam's abundance and seemingly also affected growth, mortality, body mass somatic production, and parasite prevalence. Infestation by P. bioccipitalis was restricted to adult clams. Juvenile clams suffered high mortality because they inhabit the intertidal zone, where wave action is strong. Larger clams also showed high mortality, which seemed best explained by a synergistic effect of parasite load and environmental stress. This parasite-climate-driven mortality of larger clams had a strong impact on somatic production and implied a dramatic loss of fecundity (82%), which may significantly affect the ability of the species to recover its former abundance and distribution.</jats:p

In situ growth evaluation of scleractinian corals using underwater photography and 3D modeling applications

In order to gain accurate information on coral growth increments, the buoyant weight technique (BWT) is a commonly employed technique. However, this method is not readily applicable for in situ studies, as individual coral fragments need to be retrieved regularly to be measured in the lab. The use of 3D photogrammetry on the basis of underwater photography eliminates both of these issues. The pictures as a source for the data can be directly taken from the in situ setup with underwater photography. Consequentially, no transfer of specimen to the lab is required, stress is limited for the coral specimen. This new digital tool further enables data acquisition in remote places without laboratory access. The process turning underwater pictures into 3D models involves three steps, including the creation of a 3D model, and the subsequent calculation of its respective volume. Potential pitfalls of this application are discussed. This non-invasive method is beneficial not only for coral reef research but also applicable for projects with other sessile animals

Complex, Dynamic Combination of Physical, Chemical and Nutritional Variables Controls Spatio-Temporal Variation of Sandy Beach Community Structure

Sandy beach ecological theory states that physical features of the beach control macrobenthic community structure on all but the most dissipative beaches. However, few studies have simultaneously evaluated the relative importance of physical, chemical and biological factors as potential explanatory variables for meso-scale spatio-temporal patterns of intertidal community structure in these systems. Here, we investigate macroinfaunal community structure of a micro-tidal sandy beach that is located on an oligotrophic subtropical coast and is influenced by seasonal estuarine input. We repeatedly sampled biological and environmental variables at a series of beach transects arranged at increasing distances from the estuary mouth. Sampling took place over a period of five months, corresponding with the transition between the dry and wet season. This allowed assessment of biological-physical relationships across chemical and nutritional gradients associated with a range of estuarine inputs. Physical, chemical, and biological response variables, as well as measures of community structure, showed significant spatio-temporal patterns. In general, bivariate relationships between biological and environmental variables were rare and weak. However, multivariate correlation approaches identified a variety of environmental variables (i.e., sampling session, the C:N ratio of particulate organic matter, dissolved inorganic nutrient concentrations, various size fractions of photopigment concentrations, salinity and, to a lesser extent, beach width and sediment kurtosis) that either alone or combined provided significant explanatory power for spatio-temporal patterns of macroinfaunal community structure. Overall, these results showed that the macrobenthic community on Mtunzini Beach was not structured primarily by physical factors, but instead by a complex and dynamic blend of nutritional, chemical and physical drivers. This emphasises the need to recognise ocean-exposed sandy beaches as functional ecosystems in their own right

Genetic variability of Chilean and Peruvian surfclams (Donax marincovichi and Donax obesulus)

Exposed intertidal sandy beaches are commonly dominated by surf clams of the genus Donax. In Peru and Chile these bivalves play an important role for artisanal fisheries. Beside that, little is known about the taxonomy, biology, and the clams susceptibility to climatically induced changes. The taxonomic status of the two Donax species Donax marincovichi and Donax obesulus, distributed along the Peruvian coastline, is controversially discussed. As morphometric comparisons reveal no significant differences we possibly deal with a single rather than with two species. Furthermore, our knowledge on larval dispersal allowing gene flow among populations is scarce. Therefore, both putative Donax species were sampled at ten beaches along the coastline from northern Chile to northern Peru. Partial cytochrome oxidase I sequences were analysed in order to estimate the genetic distances between both putative species and to estimate the intraspecific gene flow along the coastline. Region specific patterns and the dependence on recruitment of local stocks are discussed

El Niño induced changes of the coastal fish fauna off northern Chile and implications for ichthyogeography (Cambios de la fauna íctica del norte de Chile inducidos por El Niño y sus implicancias en la ictiogeografía)

The coastal fringe off northern Chile (18º-23ºS) is inhabited by numerous neritic fish species of which 249 are commonly observed during normal and cold La Niña (LN) conditions. During El Niño (EN) the ichthyofauna of northern Chile changes significantly due to about 100 invading fish species normally inhabiting lower latitudes, named “septentrional invaders” and “tropic-equatorial fishes”. This results in a composition including 15 fish families and 86 genera. Analyses showed that species affected by EN were not the same between the last three EN events revealing that only the epipelagic species Anchoa naso, Albula vulpes, Atherinella nocturna and Scomberesox saurus stolatus behaved consistently. Off northern Chile, EN 1982/83, 1986/87, 1991/92, 1997/98, 2002/2003 and the not clearly EN defined 2004/2005 period with their aligned thermal abnormalities of each particular event were directly related to the number of invading/affected species. Most of the alien species (>50%) were epipelagic, 25% were typical for sandy beaches and 14.6% for rocky shores. The shore fish community did not show major changes during and after EN events, as only a few invading species were recorded; just Umbrina xantii was found during all events considered. In order to understand the response of the fish community to ENSO events a biogeographical analyses of 721 fish species reported for neritic habitats (coastal epipelagic and benthic) distributed between 0°-57°S (Gulf of Guayaquil to Cape Horn) was made. Their distribution ranges for normal oceanic conditions were taken from the very numereous existing literature. It is concluded that the north/south migration of Panamic and Peruvian warm water fishes during EN/LN events along the north Chilean coast between 18º-23ºS, indicates that it represents a wide transition zone between the Peruvian and the Chilean ichthyogeographic provinces