Browsing by Author "Lappalainen, Juho"

The productivity and biodiversity of coastal areas, one of the most productive ecosystems on earth, are threatened by eutrophication and habitat loss which also drive deterioration of the macroalgal communities of shallow rocky bottoms and their perennial key species. The underwater light, being one of the most important factors determining the zonation and distribution of macroalgae, alternates in space and time. The water quality at the study area, Gulf of Finland, has deteriorated during the past hundred years which has lowered the amount of light at the bottom. Comprehensive studies on spatio-temporal changes at euphotic bottom and the their effects on macroalgae are yet to be done. This study investigates how the area of euphotic bottom at the Gulf of Finland has fluctuated during 2003 2011, and how the amount of light on the bottom determinates the zonation and distribution of macroalgae. Furthermore, the changes in the areas of euphotic bottom when the euphotic depth is altered and the effects on macroalgae are surveyed. One hypothesis is that in many areas macroalgae are not affected by too low light levels but the unsuitable bottom substrate that limits their distribution. The study material consists of euphotic depth GIS (Geographic Information System) layers derived from MERIS (MEdium Resolution Imaging Spectrometer) satellite images from May to September from 2003 2011, inventory data of the Finnish Inventory Programme for the Underwater Marine Environment (VELMU), water quality measurements and HIRLAM (High Resolution Limited Area Model) weather model. The distribution of euphotic bottom and its area were calculated for four parts of the Gulf of Finland. Changes in euphotic bottoms were evaluated in scenarios where euphotic depth changed -100 87,5 %. The effect of light on the zonation and distribution patterns of macroalgae were surveyed using distribution models. Boosted Regression Tree (BRT), Generalized Additive Model (GAM) and Climate Envelope Model (CEM) were utilized on bladderwrack (Fucus vesiculosus L.). In addition, scenarios of euphotic depth changing -50 50 % were modelled. The area of euphotic bottom varied seasonally and changed slightly between the study years. The area was larger in the inner archipelago compared to the outer arhcipelago and the difference was greater when the areas were normalized with local sea area. Always and occasionally euphotic bottoms were located near the shoreline and reefs. The altered euphotic depth affects euphotic bottoms the most in the outer archipelago. There were local differences in the performance of the distribution models. The change in euphotic depth affects the distribution of bladderwrack considerably: a deterioration of 25 % narrows off the distribution widely and a decline of 50 % suggests that the species is going to disappear from the Gulf of Finland. A decline in euphotic depth shifts the inner distribution limit towards the outer archipelago and narrows the macroalgae zone locally while even a small improvement expands the area significantly. However, the substrate of the newly exposed zone is only partially suitable for macroalgae and the portion of rocky substrate decreases as a function of euphotic depth. Changes in the optical properties of the sea affect the penetrance of light at the bottom and the area of euphotic bottom. Increasing turbidity of the sea is a remarkable threat to macroalgae. Vice versa, clarification of the water expands light-limited distribution and enlarges the macroalgal zones even though the growing amount of unsuitable soft substrate inhibits the distribution and zonation of macroalgae.