A Climate for Change

(^158) The Fishing and Mariculture Industries Human Development Report - Croatia 2008
vides more favourable conditions for species from the
southern areas. The northward spread and increase
in abundance of southern species occurs in several
phases. At first, only a single adult individual appears.
Subsequently, more adult individuals are observed.
Reproduction then begins and larval and juvenile
stages occur in the area. Finally the southern species
achieves the status of a new settler. It can be conclud-
ed with certainty that in the Adriatic Sea, warm-water
species are extending their range northward. Two fac-
tors may be causing this migration:

1. Demographic expansions, which affect individual
   species; and


2. Climatic fluctuations, which shift the bio-geo-
   graphical boundaries.

Historical temperature data and hydrological infor-

mation favour the second factor. Examples of inva-

sive species in the Adriatic include the following:

the common dolphinfish,XV the grey triggerfish,XVI

bluefish,XVII parrotfish,XVIII round sardinella,XIX the At-

lantic lizardfish,XX the Atlantic pomfret,XXI and the Eu-

ropean barracuda.XXII Some species, such as the blue-

fish, could affect local fisheries due to their significant

impact on the food chain. In the Adriatic, the bluefish

feeds mainly on mullets, anchovy, and atherinids.

However, bluefish could become an alternative spe-

cies in local fisheries. There are four categories of bio-

logical response to climatic change:

• The appearance of indicator species,


• The appearance of new populations,


• The increase or decrease in fish stocks, and


• Structural changes in the ecosystem – including
  demographics of fish populations and interac-
  tions inside the food chains.

Species introductions into the Adriatic Sea have yet to

be studied systematically, although existing data im-

ply the existence of new species. The settling of new

species in the environment has caused a progressive

decline in biodiversity in general, but at present there

are no studies regarding the impact on the diversity

of fish species. Most occurrences of new species were

recorded during two recent warm periods - 1985-1987

and 1990-1995, for which there were positive tem-

perature anomalies of 0.15ºC and 0.30ºC, respectively

• demonstrating that when the water is warmer, fish
  migrate and new species invade the Adriatic.^24
  Extensive research has been undertaken on the phe-
  nomenon of species migration in neighbouring eco-
  systems. After the construction of the waterway be-
  tween the eastern Mediterranean and the Gulf of Suez


• the Suez Canal – in 1869, hundreds of Erythrean
  species traversed the channel and settled in the Medi-
  terranean. This process is called Lessepsian migration
  and is considered to have been an important factor
  in the increase of Mediterranean fish diversity. Twelve
  Lessepsian fish species were recently recorded in the
  Adriatic Sea. Temperature again is the most important
  non-biological factor in determining the dispersal of
  Lessepsian fish. Although the impact of the Lessep-
  sian migrants on the Adriatic environment is still not
  known in detail, some of the newcomers could poten-
  tially affect the environment, since data shows that
  some have established populations in the Adriatic.
  Their quick spread in the Adriatic followed by rapid
  population booms in the invaded areas could impact
  the local fish populations.^25

Existing invasive species: threats and opportunities

The introduction of new species into the Adriatic Sea

is environmentally problematic, since these new spe-

cies threaten indigenous species. However, economi-

cally the impact can be both positive and negative as,

despite the decrease in indigenous species, new spe-

cies can become commercially viable in the market.

XV Coryphaena hippurus

XVI Balistes capriscus

XVII Pomatomus saltatrix

XVIII Sparisoma cretense

XIX Sardinella aurita

XX Synodus saurus

XXI Brama brama

XXII Sphyraena sphyraena

The introduction

of new species

into the

Adriatic Sea is

environmentally

problematic,

since these new

species threaten

indigenous

species