Marine Biology

The Chilean scallop (Argopecten purpuratus) fishery has been closed for many years, but natural scallop beds are still in jeopardy because illegal harvesting continues. Overexploitation has resulted in decreased productivity, which in many areas of Chile has caused the decline or complete elimination of natural scallop populations. Moreover, illegal harvesting is of particular concern as it threatens efforts to establish self-sustaining scallop beds along Chile's northern coastline.This paper reports on the status of the scallop bed in Puerto Aldea, located in Tongoy Bay, Chile, which was responsible for 97.5% of Chile's scallops produced in cultures in 1991. Mean scallop densities in this area were calculated to be as low as 1.64 ind m−2. Growth rates (estimated using ELEFAN) were faster than previously estimated, with scallops taking 18 months to reach commercial size (> 90 mm). Growth parameters were Loo = 125 mm and K= 0.84. The ratio was calculated at 2.08 and current productivity was estimated at 0.5 kg m−2 yr−1 total fresh weight. A restocking programme is suggested to achieve a target population density of 10 ind m−2, which would result in a potential production of 32 tons ha−1 of whole scallops. Recommendations are also made for setting a maximum exploitation rate of 10% in an effort to promote sustainable use of the resource.

Some of the many mining operations that exist in northern Chile dispose their mine tailings directly into the sea.  Little is known about the effects of these tailings on shallow rocky subtidal communities. This study reports these effects for an iron ore pelletization plant that has discharged for ca. 23 years in the intertidal of a cove on the exposed rocky coast of northern Chile, generating high turbidity in the water column and deposit of sediments on the bottom. A nonparametric multidimensional scaling (nMDS) ordination analysis for the species of the rocky subtidal communities, based on the Bray-Curtis dissimilarity index, showed great differences, the affected communities being dominated by incrusting invertebrates, whereas the unaffected areas at the same depth had kelp beds. The effects where observed only close to the discharge, and were not observed in the more shallow water communities, which in affected and unaffected areas consisted of barren grounds dominated by calcareous algae and sea urchins. The effect on the community zonation pattern did not produce differences in the effective diversity, which turned out to be similar among impacted and control sites.  This occurred because of the replacement, more than the elimination of species on impacted sites.  This type of studies, whose information is generally maintained in reports only seen by the industry and governments, needs to be published in order to contribute to a more comprehensive database regarding impacts of human activities on coastal subtidal rocky communities, necessary for the improvement of the decision-making processes regarding coastal subtidal rocky communities of human activities on these environments.

The beetle Phaleria maculata is a common inhabitant of the upper intertidal fringe of Chilean beaches. Anthropogenic intervention in coastal areas has increased intensely, leading to changes in the flora and fauna of sandy beaches. To examine the impact of human activities on P. maculata, we studied several beaches along the northern Chilean coast. Beaches were characterized based on morphodynamics and the level of intervention, leading to the estimation of an "Urbanization Index" based on various indicators. The analysis showed a significant inverse correlation between the rate of urbanization and night sky quality. Larval and adult beetles were almost absent on beaches with high levels of urbanization. The results of simple and multiple correlations based on nMDS ordination showed an inverse relationship between increases in urbanization and the abundance of beetles. Because darkling beetles are very sensitive to human interventions on sandy beaches, we suggest that they are ideal indicator organisms for the health of these environments.

Through a systematic study of a stretch of coast in north central Chile, the variety and vertical zonation patterns of the rocky subtidal communities are described, thereby revising apparent uniformity and lack of vertical zonation of the rocky subtidal of southeastern Pacific shores previously reported in the literature. Over the 600 km of coast studied, the following pattern of depth-zonation is described: an upper fringe (lower part of the sublittoral fringe) characterized by barren grounds dominated by calcareous encrusting algae and the sea urchin Tetrapygus niger; an intermediate fringe (upper Infralittoral sub-zone) characterized either by deep barren grounds similar to the former, or kelp beds of Lessonia trabeculata, or an assemblage of suspension feeding organisms, as the big barnacle Austromegabalanus psittacus and/or the tunicate Pyura chilensis; and a deep fringe (Circalittoral sub- zone) dominated by small encrusting or mobile invertebrates. This basic vertical zonation pattern of the shallow rocky subtidal communities seems to be common to most of the temperate coasts of the world. The analysis, first of the occurrence of the general zonation pattern and second of the species composition within the assemblages corresponding to each sub-zone, offers a useful framework for the assessment of the eventual impacts and changes within the shallow rocky subtidal habitat, for example within environmental monitoring programs.

Landings of Concholepas concholepas, a carnivorous gastropod and valuable fishery resource, appear disproportionately high compared with herbivorous or suspension feeding mussels.  The species has been previously described as feeding on a great variety of prey, the most important being barnacles, mussels, and tunicates. To quantitative evaluate published information on the diet of C. concholepas, an analysis of the stomach contents of 925 individuals was performed, representing a wide side-range, broad geographical distribution (29°30´S to 32°08´S), and different community types (variety potential prey choices).  The diet was based principally on suspension feeders, such as barnacles (Balanus laevis and Austromegabalanus psittacus) (75%) and the ascidian Pyura chilensis (16%).  An additional sampling, in wich abundance prey in the habitat and microhabitats occupied by the gastropod was determined, showed that the gastropod positively selects these preys species, the ascidian being the most preferred.  The rest of the diet was made up of Calyptraea trochiformis and the mytilid bivalves.  According the literature, intertidal individuals of this species only feed at night.  To confirm this behavior for subtidal populations, two 24-h samplings (analyzing digestive tract contents) was performed at a single location.  No Distinct circadian cycle of feeding for subtidal populations was found, most animals feeding most the time.  This, together with the characteristics of diet, made mainly by suspension feeders, which transfer energy from primary productivity in the water column which varies along the coast, to benthic carnivores, help to explain the high productivity of the gastropod and its variability along the coast of Chile.

More than two million scallops (Argopecten purpuratus Lamarck) were stranded on the beach at Tongoy Bay, northern Chile (30°20′S) in March 1999 during a period of unusually strong wave action. The scallops, which were stranded in living condition, had frondose algae attached, principally Ulva lactuca Linneaus, to the upper valve. Settlement and growth of the algae on the scallop shells facilitated the stranding due to the large surface area thus exposed to water movement. A preponderance of larger size classes of scallops fouled with algae were stranded, suggesting that the epibionts decreased the chance of "escape" from the effects of water movement in relation to the size of the individuals.The stranding represented about 20% of the population of the bed. It is suggested that nearshore areas were mainly affected, where light conditions promoted the rapid growth of the epiphytic seaweeds.

A new area populated by Heterozostera tasmanica (Martens ex Aschers.) den Hartog was discovered in Caleta Chascos, Salado Bay (27° 40′ SL), Chile. This discovery extends the present distribution of H. tasmanica from Puerto Aldea, Tongoy Bay (30° 16′ SL) to Caleta Chascos. H. tasmanica forms a 1–4-m-deep subtidal bed having a local, patchy distribution. Plants collected were up to 0.9 m in height; biomass in the patches was on average 1506 g dry weight (DW) m−2. No reproductive structures were observed.

This work describes individuals of Achelia assimilis (Haswell) collected in a bed of Heterozostera tasmanica (Martens ex Aschers.) den Hartog from Puerto Aldea (Coquimbo, Chile), extending its geographical range from Chiloe north to Coquimbo. Latitudinal variations in size and A. assimilis body proportions are suggested. The distribution and dispersal of A. assimilis along the southeast Pacific is briefly discussed.