E.M. Karasiova, V.M. Ivanovich

Transcription

1 ICES CM 27/ E:8 SEASONAL AND YEAR-TO-YEAR VARIABILITY OF ICHTHYOPLANKTON ASSEMBLAGE DIVERSITY INDICES IN THE COASTAL ZONE OF THE SOUTHEASTERN BALTIC UNDER THE INFLUENCE OF SPATIAL-TEMPORAL ENVIRONMENTAL DYNAMICS ABSTRACT E.M. Karasiova, V.M. Ivanovich Atlantic Research Institute of Marine Fisheries and Oceanography (AtlantNIRO), 5 Dm. Donskoy St., 23622, Kaliningrad, Russia [Tel: , fax: , karasiova@rambler.ru] The seasonal and year-to-year changes in ichthyoplankton assemblage abundance and species composition are demonstrated based on investigations carried out in the coastal zone of the SE Baltic in It was shown that depth gradient, bottom substratum variety and seasonal changeability of environment within the shallow-water zone provided higher ichthyoplankton diversity as compared with the open sea. The larvae of 15 fish species, the reproduction of which takes place by spawning of bottom eggs or carrying them in brood pouch, were the principal ichthyoplankton component. Pelagic eggs and fish larvae, from main spawning taking place in deepwater basins also occurred periodically. On average, the peak species richness and abundance were observed in July. The Shannon s indices of general diversity, Simpson s domination indices and Pielou s equitability indices were calculated to characterize the ichthyoplankton assemblage. It was shown that their values underwent significant inter-annual variability depending on the abundance of dominant species Pomatoschistus minutus. Three types of hydrographic situations that determined patterns of larval P. minutus spatial distribution and abundance were revealed: 1) prolonged upwelling and cold water penetration from intermediate layer to 1-15m depths, 2) alternation of upwelling and down-welling events, 3) prolonged development of down-welling at lack of cold water intrusions. Accordingly, phenomena observed were as: 1) low abundance, minimal species richness, and average values of diversity and domination indices, 2) average levels of abundance and species richness, high diversity index and low domination index, 3) outburst of P. minutus abundance, minimal diversity index and high domination index. Keywords: biodiversity, coastal zone, distribution patterns, ichthyoplankton assemblage. INTRODUCTION The coastal shallow zone of the south-eastern Baltic Sea is a biotope for reproduction of fishes with bottom eggs, as well as a feeding area both for their progeny and juvenile fish from spawning in the sea deeps. Ichthyoplankton assemblage of the coastal zone is characterized with the higher species diversity, however adapted mostly to considerably less stable environmental conditions as compared to the open-sea assemblages. Therefore results of ichthyoplankton biodiversity investigations demonstrate both similar and different traits by comparison with those observed in the Baltic proper.

2 2 MАTERIAL AND METHODS Ichthyoplankton sampling in the coastal zone was made at the depths from 5 to 5 m during the period from 1992 to 27 both at research vessels of AtlantNIRO and small fishing vessels by AtlantNIRO personnel. The study area covered the Russian economic zone in the South-Eastern Baltic Sea (Fig. 1). The net IKS-8 was used as the sampling gear. At each station vertical hauls were made in the layer from the bottom to the surface. In total, 732 stations were carried out from February to October (Table 1). Таble1 Number Мonth of Feb. Mar. Apr. May June July Aug. Sept. Nov. stations Total 732 stations Besides, during 4 surveys in July and 23 the vertical hauls at each station were accompanied by the surface sampling in the circulation. The surface haul duration was 5 minutes at the vessel speed about 3 knots. The total number of samples collected in the circulation amounted to 159. Besides several samples were collected with IKS-8 during 5-minute hauls in the sub-littoral zone at the depths from.5 to 1.2 m in the Curonian Spit area in July Ichthyoplankton abundance in the layer bottom-surface was assessed in sp./m 2. Ichthyoplankton abundance in the surface catches was assessed in sp./haul. The approach of the species diversity assessment in this study was based on the concept by Odum (1971). The total number of fish species eggs in ichthyoplankton was used as the species richness index S. Shannon's index was applied to characterized the general species diversity (Shannon, Weaver, 1963): Ĥ = - Σ (n ί / N ) log 2 (n ί / N ), where Ĥ index of the total diversity, nί number of individuals of each species, N total abundance. To describe the domination in ichthyoplankton assemblage the domination index C was used (Simpson, 1949): c = Σ(n ί / N) 2, where n ί number of each species individuals, N total abundance. Besides, the equitability index E (Pielou, 1969} was used: E = Ĥ/ log 2 S The data of ichthyoplankton vertical hauls were used to characterized seasonal variability of species diversity. Research of environmental factors impact on ichthyoplankton species diversity and abundance was made on the basis of the surface hauls during July surveys in and 24. In addition, the literature data on ichthyoplankton in Polish eastern coastal zone for were attracted to study the species composition (Mankowski, 1948, 195, 1955, 1959).

3 3 The data on the water temperature and salinity in the Gdansk Deep and coastal zone were obtained from AtlantNIRO database and published sources (Zezera, 22). The data on the air temperature in Kaliningrad region, the surface water temperature at Baltiysk meteo-station and on the wind regime were presented by Kaliningrad Meteoagency. Frequency of the northeasterlies (W, %) during a month prior to the survey was used as the characteristic of the wind regime. In the years when surveys were carried out during the first days of July ( ), the mean W for June were used, while for the survey carried out in the last days of July (in 24), the mean W for July were used. RESULTS Species composition According to retrospective Polish data and current data from AtlantNIRO, ichthyoplankton species composition in the considered area included larvae of 15 fish species reproducing only in shallow sea areas (the coastal zone, banks) (Table 2). As a rule, these fish species spawn bottom eggs, and 2 species of Syngnatidae carry eggs in the brood pouch. Among them only one species - Clupea harengus is characterized by a high abundance and is distributing outside the shallow zone during the most part of its life cycle. Besides, such species as garfish Belone belone and turbot Psetta maxima belong to migratory species. The fist species is spawning eggs in algae, where eggs are fixed by shell filaments. In our samples garfish eggs were found at the depths from.8 to 1 m in July 1999 during fishing in the sub-littoral zone. Turbot eggs being pelagic at the sea salinity, are descending to the bottom at 6-8 in the Baltic banks areas. Nevertheless, some number of turbot eggs were caught with IKS-8 over the depths from 1 to 25 m in July Besides, ichthyoplankton included larvae of fishes spawned pelagic eggs in the deep-water sea areas (sprat, flounder, rockling, plaice). Eggs of the first two species also occurred over the depths less than 5m. In particular this is typical to sprat due to its transition to reproduction in the surface layer in the late spring. Therefore, in the coastal zone two ichthyoplankton complexes may be specified: near-shore one consisting of 15 species, and offshore one including 4 species of fish larvae. Brief description of abiotic environment One of the features of the coastal zone hydrological regime is a sharply pronounced seasonal variability of the water temperature (Fig. 2а). According to the data for 2 24 the mean water temperature in the coastal zone during summer could approach С, while in February the temperature could reduce to C. At the same time, even in the warmest months of the year, the water intrusions from the cold intermediate layer under the impact of upwelling are able to reduce the near-bottom water temperature (Fig. 3). Taking in account the effect of upwelling downwelling alternations and wind-induced waving, the near-shore shallow areas provide much more diversified but less stable conditions as compared to the deepwater sea areas. The coastal zone is characterized by the halocline absence and low salinity, which varies depending on the river discharge. Seasonal fluctuations of salinity are much less pronounced as compared to the temperature fluctuations (Fig. 2b). The mean ling-term salinity at the stations of Baltiysk and Klaipeda constituted 5.6 and 5.4, while inter-annual fluctuations were 1.5 and 1.7 respectively. In the inter-annual aspect the dynamics of mean-annual temperature of the water temperature in Baltiysk for demonstrated the growing trend (Fig. 4). The similar

4 4 trend is revealed on the basis of the air temperature in Kaliningrad region during winter-spring (Fig.5). Seasonal variability of species composition and diversity indices Considerable seasonal variability of the temperature regime creates preconditions for so-called spawning chain according to Rass es terminology (Rass, 1987), i.e. sequential replacement of ichthyoplankton eggs and larvae of species with different spawning terms (Таble 3). In the seasonal aspect the earliest winter-spring spawning has been found in gunnel Ph. gunnellus and, probably, in snakefish L. lampretiformes. Mainly spring reproduction period is characteristic to sculpins, snailfish, spring-spawning herring. Larvae of garfish, turbot and two species of pipefishes occurred in ichthyoplankton in summer only. The longest period of larvae occurrence was observed in sand eel (May-October) and goby P. minutus (May-November). The latest spawning period, and hence the occurrence, was observed in autumn-spawning herring. The maximum number of species in ichthyoplankton was recorded in July, and the minimum one in February-March and October. Comparison of the species richness in different periods indicated that the main difference is related to the more frequent occurrence of larvae of fishes reproducing at the beginning and the very end of the spawning period during as compared to the current period. These species include Ph. gunnellus, L. lampretiformis and the glacial relic Myoxocephalus (Triglopsis) scorpius, as well as autumn-spawning herring. The quantitative estimates for and indicated that the maximum abundance, as well as the species richness, occurred in July (Fig.6). Larvae of P. minutus (sand goby) became the dominating species in July-August ichthyoplankton, constituting above 7% and 9% of the total abundance. Abundant indices of other larvae of Gobiidae family were at a low level. The seasonal peak of species richness did not coincide with the peak of Shannon s diversity index, approaching its maximum in May (Fig.7а). This lack of coincidence was caused by the fact that Shannon s index was defined by not only species number, but also by their numeric ratio. As a result, seasonal variability of Shannon s index occurred in counter-phase with Simpson s domination index (Fig. 7b). The maximum of Shannon s index in May was likely related to the optimal combination of relatively high species richness and low domination index. Impact of environment factors on spatial distribution and diversity indices The spatial distribution of ichthyoplankton assemblage in July, i.e. in the season of maximum abundance, was characterized with considerable seasonal variability, which can be traced at the study area transects along the depths gradient during July surveys (Fig. 8). In July 1999 with very low abundance and species richness, the most number of Gobiidae larvae concentrated near the shore at the depths from 8 to 1 m, while sprat larvae occurred only along the external boundary of the study area at the depths more than 4 m. In July 2 with high abundance and species richness, the maximum number of Gobiidae larvae was found at the depths from 2 to 25 m. Sprat larvae occurred in the whole depths range from 1 to 5 m. At the depth of 2 m rockling larva was caught, while adult fish of this species are able to reproduce only in the nearbottom layer of open sea areas. In July 22 with average levels of abundance and species richness, low numbers of gobiids larvae were caught much farther offshore as compared to the previous years at the depths from 3 to 5 m. Sprat larvae penetrated to the coastal zone only to the depth of 2 m.

5 5 Therefore, inter-annual differences in the spatial distribution manifested themselves in different extent of the near-shore fish larvae spreading to the offshore direction, and of the offshore fish larvae spreading to the onshore direction. Such variability was determined by different hydrographic situations, in particular: 1) a long period of upwelling development during the previous survey period in 1999, 2) a long period of downwelling development in 2, 3) alternation of upwelling and downwelling events in 22. According to each hydrographic situation mentioned above, the near-bottom water temperature distribution along the depths gradient was characterized either a sharp reduction from 19 С to 4 С (in 1999), or almost total absence of the temperature gradient at the mean near-bottom temperature of 15 С (in 2) (Fig.9). In 21 the intermediate situation was observed, characterizing with a weak temperature gradient within the depths range from 1 to 3 m and a more pronounced gradient at the depths 3-5 m. Depending on the extent of the cold near-bottom water penetration into the coastal zone, the depth of 1 С-isotherm and abundance of gobiids larvae changed (Fig. 1), while the latter increased at the higher near-bottom temperature. In general during the observation period (July , 24) the negative relationship between Gobiidae larvae abundance and frequency of north-easterlies, causing upwelling near the Baltic eastern coast was observed (Fig.11). Inter-annual variability of Shannon s index and Pielou s equitability index was positively related to abundance of the dominant species P. minutus, but was oppositely related to the Simpson s domination index (Fig. 12). This was explained by the fact that Shannon s index increased at more uniform quantitative c distribution of species in the ichthyoplankton assemblage, and decreased with dominance increase, i.e. with increase of the dominant species abundance. DISCUSSION Owing to a variety of bottom substrata (sands, pebbles, shells, underwater plants), the coastal zone provides a mosaic of different habitats for species with bottom eggs. P. minutus (sand goby) is spawning on the shell folds and its spawning biotope associates with the mussel biocenosis (Каlinina, 1976). P. microps (common goby) is spawning on the sand-shell ground usually at the depths less than 1 m (Каlinina, 1976). Sand-eel and turbot are spawning on sand grounds, however, at different depths ranges (Svetovidov, 1964, Kaendler, 1944). Round goby, Ponto-Caspian invader, is spawning eggs on the bottom and side surfaces of rocks and submerged objects (Svetovidov, 1964). Herring, garfish, sculpins and partially black goby G. niger use underwater plants as a substratum (Каzanova, 1954) Considerable seasonal variability of the water temperature in the shallow areas facilitates differentiation of spawning biotopes and thus provides more complete utilization of resources in the coastal zone as the habitat environment. In general, three basic factors diversity of the bottom substrate, depths gradient and seasonal variability of the temperature regime provide the higher diversity of ichthyoplankton as compared to the open sea areas.

6 6 Evidently, long-term fluctuations of the water temperature affect the proportional abundance of relatively psychrophilic species with winter-spring and spring spawning peaks and thermophilic species with a summer spawning peak, which has been reflected in reduction of larvae occurrence of such species as gunnel Ph. gunnellus and glacial relic bullrout M. scorpius in the current period as compared to the middle of the last century. The dynamics of taxonomic composition and diversity index demonstrated the pronounced seasonal cycle. However, maximum diversity indices by Shannon (May) did not coincide with the maximum species richness (July) due to the dominance extent increase in the summer ichthyoplankton. At present, P. minutus is the most abundant species in summer ichthyoplankton of the Baltic Sea coastal zone (Karasiova et al, 22, Ivanovich, 24). This species domination relatively to other Gobiidae species seems to be caused by the high migratory activity of adult fish linked to searching for the most suitable habitats and development of migratory behavior (trophic migration) in post-larvae (Bouchereau, 1996). It should be noted that in the latest years Gobiidae diversity in the Baltic Sea has increased due to unintentional introduction of round goby. This species, unlike gobies of Atlantic-boreal origin (for example, Pomatoschistus ), is a brackish-water Ponto-Caspian relic (Каlinina, 1976). Inter-annual abundance fluctuations of P. minutus larvae as the dominating species, were negatively related to variability of diversity and equitability indices, and positively related to the domination index variability. In general, inter-annual variability of all considered ichthyoplankton assemblage characteristics in the summer season were determined by the environment fluctuations, in particular, by duration and intensity of upwelling and downwelling, depending in turn on the inter-annual fluctuations of the north-easterlies frequency. The long development of upwelling in the period preceding July peak causes the cold water intrusion from the intermediate layer at the coastal zone bottom up to 1-m isobath. As a result, sharp decrease of the near-bottom water temperature, blockage of adult specimens maturation and reproduction, inhibition of already spawned eggs development occurred. Under the impact of downwelling in the layer from the surface to 3 m the temperature regime appeared close to homothermy with the temperature from 15 to 17 С favourable to thermophilic fish species reproduction. Phytoplankton and zooplankton organisms and fish larvae of the sea complex are introduced into the coastal zone with the onshore surface water pile-up With the change of different hydrographic situations the alternation occurs of the periods favorable to Gobiidae bottom eggs development and larvae hatching (downwelling), and periods facilitating fish larvae spread in the coastal zone within a wider depths range (upwelling). However, the transport of grown-up larvae of Gobiidae into the deep-water sea areas seems to be unfavorable to this species population. In general, it can be stated that the basic characteristics of ichthyoplankton assemblage may vary depending on the observed type of hydrographic situation. In the case of prolonged upwelling the low abundance of both ichthyoplankton and dominating species occurs, as well as the minimum species richness, average values of diversity and domination indices; in the case of upwelling and downwelling alternation the average level of abundance and species richness, high diversity index and low domination index are observed; in the case of prolonged downwelling

7 7 the outburst of P. minutus abundance, minimum diversity index and high domination index are recorded. Therefore, analysis of inter-annual variability of abundance and species diversity in ichthyoplankton zone seems to confirm the conclusion, that the coastal part of large Baltic ecosystem as well as the Baltic proper are controlled mainly by the limiting hydrophysical environmental factors. REFERENCES Bouchereau J.-L Bioecology of three teleostean Gobiidae fishes: Pomatoschistus minutus (Pallas, 177), P. microps( Kroeyer, 1838), Gobius niger Linnaeus, 1758: tactics for surviving in an environment of the north Mediterranean lagoon. In: Functioning of coastal ecosystems in various geographical regions. Second Int. Symp., Sopot, Poland, September 5-7, P.2. Ivanovich. V.M. 24. Distribution and abundance of larvae of Pomatoschistus minutus ( fam. Gobiidae, Bonaparte, 1832) in coastal waters of south-eastern Baltic in July In: Fish. biol.. researches by AtlantNIRO in the Baltic Sea.Kaliningrad. 2: (in Russian). Kaendler R Uber den Steinbutt der Ostsee. Berichte d. Deutsch. Wissenschaftl. Kommission f. Meeresforschung. Neue Folge. Band XI, Heft 2: Kalinina E.M The reproduction and development of gobiids of the Asov and Black Seas. Kiev. Naukova dumka. 12pp. (in Russian). Karasiova E.M.. Gribov E.A., V.M. Andreeva. 22. Fish larvae assemblages in the coastal shallow zone of the south-eastern Baltic Sea: environmental factors driving inter-annual variability. ICES CM 22/O:11. Kazanova I.I Guide to fish eggs and larvae of the Baltic Sea and lagoons. VNIRO proceedings. Vol. XXVI: (in Russian). Mankowski W Macroplankton Investigations in the Gulf of Gdansk in June July period Biul. Morsk. Lab. Ryb. w Gdyni., 4: (in Polish). Mankowski W.195. Macroplankton of the Gulf of Gdansk in Biuletyn Morsk. Inst Ryb. 5: (in Polish). Mankowski W.195. Badania planktonowe w Baltyku poludniowym w r BiuletynMorsk Inst. W Macroplankton Baltyku poludniowego w r Prace MIR, 6 :83-94 (in Polish). Mankowski W Badania planktonowe na poludniowym Baltiku w roku 1951// Prace MIR w Gdyni., 8 : (in Polish). Mankowski W Badania makroplanktonu poludniowego Baltiku w latach // Prace MIR w Gdyni, 1/A : (in Polish). Odum E.P Fundamentals of ecology. Philadelphia - London-Toronto. 74pp. Pielou E.C An Introduction to Mathematical Ecology. New York. 286pp.

8 8 Shannon C., Weaver W The mathematical theory of communication. University of Illinois Press. Urbana. 117 pp. Simpson E. H Measurement of diversity. Nature pp. Svetovidov A.N Fishes of the Black Sea. M. Nauka. 552pp. (in Russian). Zezera А. S. Long-term changes of the hydrographic characteristics in the deep waters of the South-East Baltic Sea ( 198-2). In: Fisheries and biological research by AtlantNIRO in 2-21, vol. 2: 7-12

9 9 Table 2. Species composition of fish larvae in the coastal zone of the South-Eastern Baltic Sea Spawning area and hatching characteristics Coastal zone; hatching from bottom eggs Coastal zone; hatching from eggs in brood-pouch Deep-sea area and partially the coastal zone; hatching from pelagic eggs Deep-sea area; hatching from pelagic eggs Species 1. Pholis gunnellus (L., 1758) 2. Lumpenus lampretiformis ( Walbaub, 1792) 3. Myoxocephalus scorpius (L., 1758) 4. Clupea harengus membras (L., 1758) 5. Liparis liparis (L., 1758) 6. Taurulus bubalis (Euphrasen, 1786) 7. Ammodytes tobianus (L., 1758) 8. Belone belone (L., 1758) 9. Рomatoschistus minutus (Pallas, 177) 1. Pomatoschistus microps (Kroyer, 1938) 11. Gobius niger (L., 1758) 12. Neogobius melanostomus (Pallas, 1814) 13. Psetta maxima * (L., 1758) 14. Nerophis ophidion ophidion (L., 1758) 15. Syngnatus typhle (L., 1758) 16. Sprattus sprattus balticus (Schneider, 194) 17. Platichtys flesus trachurus (Duncker, 1829) 18. Encheleopus cimbrius (L., 1758) 19. Pleuronectes platessa balticus (Nilsson, 1855) * Eggs of Psetta maxima are pelagic at the North Sea salinity

10 1 Table 3. The seasonal occurrence of fish larvae from spawning in the coastal zone of the Gdansk Deep in ( ) and ( ). Species I II III IV V VI VII VIII IX X XI XII Pholis gunnellus Lumpenus lampretiformes Myoxocephalus scorpius Liparis liparis Clupea harengus(spring) Parenophris bubalis Psetta maxima Ammodytes tobianus Belone belone Nerophis ophidion Syngnatus typhle Pomatoschistus minutus Pomatoschistus microps Gobius niger Neogobius melanostomus Clupea harengus (autumn)

11 м Curonian spit 55. Kaliningrad Vistula spit - stations 54.5 Fig.1. Ichthyoplankton study area in the coastal zone of RF in the Baltic Sea (South-Eastern Baltic) during

12 T C a 12 2m 9m II V VIII X Years S, psu 11 b 9 7 2m 9m 5 II V VIII X Years Fig.2. Seasonal fluctuations of the water temperature (a) and salinity (b) at the depth levels 2 and 9 m in the Gdansk Deep ( )

13 -1 а 1999 b а 2 b 18,6 С 2,33 С 14,65 С 15,25 С Depth (м) thermocline layer w arm layer (t>4 C) cold layer (t<4 C) Fig. 3. Location of a thermocline and a cold intermediate layer on offshore (а, N; 19 12'E) and inshore (b, N; E) stations in early July 1999 and 2. T C Years Fig. 4. Inter-annual variability of the surface water temperature in the Baltic Sea during

14 winter-spring summer.5 Anomalies Years -1.5 Fig.5. Anomalies of the air temperature in Kaliningrad region during spring-winter and summer seasons of

15 12 S a II III IV V VI VII VIII X Months 6 N.% b II III IV V VI VII VIII X Months Fig.6. Seasonal variability of: a) species richness S, b) abundance N, % in ichthyoplankton assemblage of the coastal zone.

16 2,5 H 2 a 1,5 1, III IV V VI VII VIII Months 1 C,8,6 b ,4,2 III IV V VI VII VIII Months Fig. 7. Seasonal variability of: а) Shannon's diversity index, b) Simpson's domination index in ichthyoplankton assemblage of the coastal zone.

17 N, sp/haul 15 1 Goby Sprat H, m H,m Stations N, sp/haul Goby Sprat Sand eel Turbot Rockling H,m H,m Stations N, sp/haul Goby Sand eel Sprat H H, m Stations Fig. 8. Ichthyoplankton distribution (N) by depths at transects across the coastal zone in July 1999, 2, 22.

18 T C H,m Fig.9. The bottom temperature T C variability by the coastal zone depths in early July 1999, 2, N 2 1 sp/haul Hm 3 H,m Years Fig.1. The mean abundance of goby larvae (N, sp/haul) in 1-5 m depth range according to 1 C isotherm location( H, m)

19 N 12 9 N W,% 5 W, % Years Fig.11. Abundance of (N, sp/m 2 ) goby larvae in July and frequency (W, %) of north-easterlies during the previous month

20 12 N 1 a 1,4 H,bit 8 6,7 4 2 N H Years 12 N 1 8 b,9 C, N C ,3 Years 12 N 1 c N E,6 E 8,4 6 4, Years Fig.12. Inter-annual variability of Shannon's (а), Simpson's ( b), Pielou's ( c) indices in ichthyoplankton assemblage during July