Archipelago Zone Research Articles

Latitudinal and archipelago effect on the composition, distribution, and abundance of zooplanktonic organisms in the Gulf of California

The upper Gulf of California is one of the most energetic regions owing to its tidal range and strong tidal currents, making the upper gulf and the archipelago zone highly turbulent regions; the abundance of zooplankton should be associated with mixing phenomena. We aimed to determine the latitudinal distribution of zooplanktonic organisms in this region and the influence of the islands on their distribution and abundance using historical data. Distribution of abundance followed the current patterns, the archipelago influences abundance favorably but does not affect diversity. Latitudinal zooplankton richness had a quasi-parabolic shape. A decrease in richness was observed at 27.5°N, in the archipelago region, with maximum richness at 26.5°N and 28.5°N. The distribution of latitudinal ranges is consistent with geometric constraints models; taxa with wide ranges are in the central area, while those with narrow ranges are near the boundaries and the Upper Gulf. Zooplankton responds in some way to the existence of the southern boundary as shown by the decrease of richness in this region. At the whole scale of the Gulf, the distribution of richness followed geometric constraints model, while at smaller scales, distribution and abundance are conditioned by the hydrodynamics of the Gulf. We compared zooplankton spatial distribution with Sea Level Anomaly, Sea Surface Temperature, and Chlorophyll-a concentrations from Copernicus to establish relationships between these factors. We performed Cluster and Redundancy Analysis to characterize similarities between stations in terms of biomass and taxon composition and to assess the importance of environmental variables on the distribution of zooplankton.

Half-century trends in alpha and beta diversity of phytoplankton summer communities in the Helsinki Archipelago, the Baltic Sea.

We analyzed phytoplankton biodiversity trends in a 52year (1967-2018) monitoring time-series from the archipelago of Helsinki, Gulf of Finland, the Baltic Sea. The community ordination revealed strong ordering of samples along the time axis (generalized additive model-gam fit: R 2 = 0.9). Species richness increased in time and was the most influential alpha diversity descriptor related to the community structure (gam fit: R 2 = 0.56-0.70). Changes in species richness accounted for 35-36% of the mean between-sample beta diversity. The remaining 64-65% was due to species turnover-the dominant component of the biodiversity trend. The temporal beta diversity trend reflected the eutrophication history of the geographically confined region, with a turning point in mid-1990s demarking the adaptation and recovery phases of the phytoplankton community. Trends in spatial beta diversity revealed homogenization of the communities in the outer archipelago zone, but not in the inner bays. The temporal decay of community similarity revealed high turnover rate, with 23.6years halving time in the outer archipelago and 11.3years in the inner bays, revealing the differences in eutrophication strength. The observed phytoplankton trends manifest the regional eutrophication history, and dispersal of new species to the unsaturated brackish species pool.

Heavy metals Cd and Cr found in sponges (porifera) at spermonde archipelago Zone II

Samalona and Barrang Lompo Islands are located in zone II of Spermonde Archipelago with the nearest distance is about 5 km from Makassar city beach. The close distance causes heavy metals as pollutants produced from activities in Makassar city and it surroundings to be carried out to zone II of Spermonde Archipelago waters. Marine biotas used as a bioindicator of heavy metals (Cd and Cr) pollution were sponges (Porifera). Analysis results by ICP-OES indicated that the largest quantities of the heavy metals (Cd and Cr) were found in sponge Xestospongia, i.e 1.250 mg/kg and 5.400 mg/kg dry weight, respectively.

On the role of sedimentological processes controlling phosphorus burial in the coastal zone of the Baltic Sea

On the role of sedimentological processes controlling phosphorus burial in the coastal zone of the Baltic Sea

Coastal Hypoxia and the Importance of Benthic Macrofauna Communities for Ecosystem Functioning

Coastal ecosystems are important because of the vital ecosystem functions and services they provide, but many are threatened by eutrophication and hypoxia. This results in loss of biodiversity and subsequent changes in ecosystem functioning. Consequently, the need for empirical field studies regarding biodiversity-ecosystem functioning in coastal areas has been emphasized. The present field study quantified the links between benthic macrofaunal communities (abundance, biomass, and species richness), sediment oxygen consumption, and solute fluxes (NO3 − + NO2 −, NH4 +, PO4 3−, SiO4, Fe, Mn) along a 7.5-km natural gradient of seasonal hypoxia in the coastal northern Baltic Sea. Sampling was done in late August 2010 in the middle archipelago zone of the Hanko peninsula, Finland. As predicted, the macrofaunal communities were decimated with increasing hypoxia, and the nutrient transformation processes were changed at the sediment-water interface, with notably higher effluxes of phosphate and ammonium from the sediment. Solute fluxes varied even during normoxia, which implies a high context-dependency, and could be explained by even small variations in environmental variables such as organic matter and C/N ratios. Importantly, the low diversity benthic macrofaunal communities, which were dominated by Macoma balthica and the invasive Marenzelleria spp., had a large influence on the solute fluxes, especially under normoxia, but also under hypoxia.

Long-term progression and drivers of coastal zoobenthos in a changing system

Coastal zones are facing climate-driven change coupled with escalating eutrophica- tion. With increasing shifts in hydrographic conditions during the past few decades, a focal task is to understand how environmental drivers affect zoobenthic communities, which play a crucial role in ecosystem functioning. By using long-term data, spanning 40 yr (1973 to 2013) in the northern Baltic Sea, we showed a disparity in zoobenthic responses with pronounced changes in commu- nity composition and a trend towards decreased biomass in sheltered areas, while biomasses increased in exposed areas of the coastal zone. We used generalized additive modeling to show that bottom oxygen saturation, sea surface temperature and organic load of the sediments were the main environmental drivers behind contrasting patterns in biomass progression. Oxygen sat- uration alone explained over one third of the deviation in the biomass developments in sheltered areas, while exposed areas were mainly limited by organic content of the sediments. We analyzed high-resolution climate-scenario simulations, following the Intergovernmental Panel on Climate Change scenarios for the Baltic Sea region in combination with different nutrient load scenarios, for the end of the 21st century. The scenario outcomes showed negative trends in bottom oxygen concentrations throughout the coastal and archipelago zone along with overall increasing temper- atures and primary production, and decreasing salinity. Our results suggest that these projected future conditions will strengthen the observed pattern in decreasing zoobenthic production in the immediate coastal zones. Moreover, the potential intensification of unfavorable conditions ex - panding seaward may lead to an expansion of biomass loss to more exposed sites.

Turbidity characterizes the reproduction areas of pikeperch ( Sander lucioperca (L.)) in the northern Baltic Sea

The pikeperch ( Sander lucioperca (L.)) is an economically important fish species occurring in the fresh and brackish waters of Europe. To evaluate the distribution and extent of the reproduction areas in the northern Baltic Sea, a field survey was carried out in two separate coastal areas. Presence/absence data were used to develop a geographic information system (GIS)-based predictive spatial distribution model, where high resolution raster maps of the focal environmental variables and a logistic regression equation were used to predict the probability of larval occurrence. The results indicated that the pikeperch reproduction areas are located in the innermost archipelago zone where high water turbidity best explained their presence. Turbidity was related to several other variables such as fetch and depth. Contrary to our preliminary hypothesis, surface water temperatures measured during the survey had no significant effect in the model due to the low spatial variation in the measured values. Since turbidity is possible to determine by remote sensing methods, the probability maps can be cost-effectively extended to more extensive coastal areas with proper validation.

Reproduction areas of roach (Rutilus rutilus) in the northern Baltic Sea: potential effects of climate change

The roach ( Rutilus rutilus ) is a common freshwater fish species in the brackish coastal areas of the northern Baltic Sea. In this study, surveys of roach larvae were carried out at reed-belt shores encompassing the entire archipelago zone in the northwestern Gulf of Finland. A logistic regression model was constructed and then used to spatially predict and map potential roach reproduction areas using a geographic information system (GIS). The results indicate that low spring salinity (<4‰) is the most important factor determining the success of roach reproduction. Reed-belt shores in the inner archipelago with large freshwater inputs in the spring constitute the key reproduction areas. Spring runoff peaks caused by melting snow together with the effects of ice cover on the spreading of freshwater runoff enable roach to reproduce relatively far from river mouths. Nevertheless, 68% of the reed-belt shores in the study area are presently beyond the 4‰ salinity limit and thus unsuitable for reproduction. In the future, climate change is predicted to reduce the salinity of the Baltic Sea, but the potential climate change impacts on roach are partly contradictory. The most likely outcome, however, is a spatial increase in the extent of roach reproduction areas in the northern Baltic Sea.

Effects of spring bloom phytoplankton dynamics and hydrography on the composition of settling material in the coastal northern Baltic Sea

The phytoplankton species succession and sedimentation characteristics were studied on a sheltered and an open coastal station during a spring bloom in the northern Baltic Sea. Biomass (phytoplankton carbon and chlorophyll a), inorganic nutrients and particulate organic carbon and nitrogen (POC and PON) were determined in the suspended material. Sediment traps moored at different depths were used to determine the vertical flux of total particulate material (TPM), POC and PON, chlorophyll a, phaeopigments and phytoplankton carbon. The spring phytoplankton biomass was dominated by dinoflagellates that formed a dense bloom of short duration, whereas diatoms were present in the water column throughout the spring period in more moderate biomasses. The vertical flux of phytoplankton carbon was however dominated by diatoms at all times. The formation of resting stages increased the sedimentation of dinoflagellates, but compared to the suspended biomass of vegetative cells, their sinking rates were low. The ambient silicate concentration did probably not limit diatom growth; these were rather removed from the surface layer through sinking, a situation beneficial for dinoflagellates capable to exploit deep nutrient reserves through vertical migration. Due to rapid sinking soon after bloom formation and high specific loss rates, diatoms can be considered important contributors to the vertical flux of autochtonous material. Dinoflagellates mostly disintegrate in the water column and may settle as phytodetritus, except for the fraction of the populations that form rapidly sinking cysts. In addition to vertical export, advection of water from the stations seems to have been an important loss factor in the phytoplankton community. The two stations differed in that resuspension and input from littoral sources to the vertical flux were more important in the inner and shallower archipelago zone. This was also reflected in the C/N ratio of the settling material and in the bottom surface layer. In our study area, both the hydrographical regime and the species composition of the phytoplankton community were found to affect sedimentation characteristics and the composition of the settling material during the spring period.

Coastal-Fish Communities along the Northern Coast of the Gulf of Finland, Baltic Sea: Responses to Salinity and Eutrophication

The Gulf of Finland is an elongated estuarine sea receiving a large freshwater input and nutrient load, especially in the east from the River Neva. The surface water salinity of the gulf increases from < 1 to 6‰ from east to west, and the less haline eastern areas of the gulf are the most eutrophied. Five study areas in the archipelago zone were surveyed with multimesh gill nets in summer 1998. Our results confirmed that salinity is an important factor influencing species richness in the northern coastal waters of the Gulf of Finland, as marine species gradually disappeared towards the less haline eastern areas. However, the conventional indicators of eutrophication derived from lakes (high total catches, high catches of cyprinids) did not show logical differences between more and less eutrophic coastal areas. The higher productivity in the eastern part of the gulf has not led to higher fish biomasses in the archipelago zone. A potential factor affecting fish communities seems to be the high fishing pressure in some coastal areas.

Spatial distribution patterns of newly settled plaice ( Pleuronectes platessa L.) along the Swedish Skagerrak archipelago

Spatial distribution patterns of newly settled plaice ( Pleuronectes platessa) were investigated along a 200 km coastline of the Swedish Skagerrak archipelago. Juvenile plaice were sampled quantitatively with a drop-trap in 32 small (0.02–0.04 km 2) nursery bays over a 13-day period in mid-May 1998. The investigated area was divided into four geographical regions along the coast, each with an inner and an outer archipelago zone. In each of the resulting eight sub-areas two randomly allocated pairs of closely situated (500–1000 m) bays were sampled, so that variation in post-settlement densities of plaice could be tested over different scales from hundreds of metres to tens of kilometres. Plaice density varied significantly on a regional scale, with order-of-magnitude higher densities in the northern (22.3 ind. m −2) than southern (2.3 ind. m −2) bays. Further, bays situated in the outer archipelago had significantly higher densities of juvenile plaice than bays in the inner archipelago. However, considerable variation was also found on a smaller spatial scale, with significant differences in plaice density within pairs of bays. The seasonal development in growth and mortality of juvenile plaice was studied in a sub-sample of bays characterised by high, medium and low post-settlement densities in May. Three bays from each group were revisited in July and August. Growth rates showed negative, and mortality rates positive, density-dependent relationships with plaice density. The observed patterns in settlement densities of plaice reflected the potential for variation in larval supply, local habitat characteristics and predation, over the spatial scales investigated. In addition, we outline the processes likely to produce density-dependent relationships in growth and mortality rates of juvenile plaice.

Trends and Gradients in Nutrient Concentrations and Loading in the Archipelago Sea, Northern Baltic, in 1970–1997

Eutrophication has been a major environmental change affecting the water quality both in the coastal and open sea areas of the Baltic Sea since the 1960s. Although the total nutrient loading to open sea and also to the Finnish coastal waters is rather well known, the relative importance of various loading sources in different areas is still obscure. We found in the Archipelago Sea, SW Finland, that the great majority of nutrients come as non-point-source loading with the river discharges in the innermost archipelago zone. Fish farming in the middle archipelago zone exerts a remarkable influence on water quality there. The outer archipelago facing the Gulf of Finland and the Baltic proper is influenced by both depending on the season. In a time series study after the initial general rise since the 1970s the increase of nutrient concentrations culminated and levelled off or even turned to a decline in most of the locations studied. It is difficult to single out the cause of this culmination. A reasonable explanation is the general economical decline in Finland. However, same kind of culmination has been found in some other coastal areas of the Baltic Sea, too. The development of the N:P-ratio indicates that during the last two decades nitrogen has developed towards the limiting nutrient in the area studied. The general conclusion is that environmental care should be directed at different targets depending on the archipelago area in question.

Distributions, life cycles and hybridization of two Mysis relicta group species (Crustacea: Mysida) in the northern Baltic Sea and Lake Båven

We used electrophoretically identified material to assess the geographical distributions, life cycles and interspecific hybridization of two sibling species of the Mysis relicta species group (sp. I and sp. II) in the northern Baltic region. In the Gulf of Finland, sp. I prevails in inshore waters and sp. II in the open sea; the distributions overlap in the outer archipelago zone. In the Gulf of Bothnia, only sp. II was found in the southern part (Bothnian Sea), whereas the two species coexist throughout the northerly Bothnian Bay. Both the local and large-scale distributions are salinity-related, but salinity alone does not explain the differences. The two species exhibit different patterns of geographical variation in their life histories. In strict sympatry in the north they have identical two-year life cycles with winter breeding. Further south (Gulf of Finland), sp. I exhibits a predominantly one-year winter-breeding cycle, whereas sp. II breeds throughout the year. The patterns comply with the concept of a great phenotypic flexibility and environmental control of life history characteristics in the Mysis relicta group, and make a contrast to the stable life cycle of the congeneric M. mixta. F1 hybrids between the two M. relicta group species were found at a low frequency (0.6%) in the Bothnian Bay, but not in other areas of sympatry.