HABITAT PREFERENCES OF THE SYNGNATHIDAEIN THE RIA FORMOSA COASTAL LAGOON (SOUTH PORTUGAL)FREDERICO OLIVEIRA*, PEDRO MONTEIRO, LUIS BENTES, KARIM ERZINI AND JORGE M.S. GONÇALVES

Centre of Marine SCienCeS, UniverSidade do algarve-fCt CaMpUS de gaMbelaS, p-8005-139 faro, portUgal

*Corresponding author:fredoliveira@ualg.pt

RIa FORmOsa anD thE syngnathIDaE Ria Formosa is a large coastal barrier lagoon located in the South Portugal (Algarve). The Ria is 55 km long and 6 km at its widest point, with an average depth of 3 m. It includes 14522 ha of wetlands and 4000 ha of salt ponds, aquaculture ponds, salt marsh, sand and mud banks. There are further 2500 ha of sand dunes, farmland, forest and urban land. About 90% of the area is a Natural Park (Ria Formosa Natural Park). However this area is subject to strong pressure from a number of activities, such as fisheries and aquaculture, urban use and tourism, shipping and airport activity. Towns and localities located on the Ria (Faro, Olhão, Tavira and Fuzeta) are centers of tourism; contributing to human impacts and pressures on this ecosystem. Ria Formosa is a very productive

system, essencially because of high nutrient concentrations and insolation, as well as a good tidal water exchange. Several habitats are encountered in the lagoon ranging from bare sand, large deep canals, mud flats to shallow interconecting vegetated marsh streams (Fig.1). This extremely rich environment plays an important role as a nursery and habitat for many marine fauna including several commercially valuable fish species (Erzini et al., 2002). The project EU_DG XIV/C/1, carried out in 2001-2002 accounted for 112 fish species in this coastal lagoon including eight Syngnathidae species. Six of these species were a common component of the resident icthyofauna: Hippocampus guttulatus; Hippocampus hippocampus; Nerophis ophidion; Syngnathus abaster; Syngnathus acus and Syngnathus typhle. ObjECtIvEs Using the data collected in the project “Recruitment of sea breams (Sparidae) and other commercially important species in the Algarve (Southern Portugal)” (EU_DG XIV/C/1) we aimed to answer the following questions:

1.Do these six sympatric species occupy the same type of habitat? 2.Do they have preferences in the habitat selection such as vegetation cover, bottom type or depth?

A priori assumptions were that these species would prefer sheltered (i.e. shallower) densely vegetated areas, irrespective of the type of bottom substrate.

FIElD wORk & Data analIsys A total of 67 stations (Fig. 2) were sampled monthly over a seven month period (April to October 2001), using three sampling gears depending on the location of the sampling station: beam trawl (primary and secondary canals), beach seine (primary and secondary canal margins) and Riley’s pushnet (shallow, branched canals). The sampling stations were selected after the entire area had been classified into distinct zones based on a series of characteristics. Sampling took place at low tides and the captured fish were later sorted, identified, measured and weighed in the laboratory. At each station we recorded water depth, dominant seagrass cover and dominant type of

sediment. Habitat preference and occupation of the six most common sympatric species of the Syngnathidae was based on Ivlevs’ electivity index and density of individuals per habitat type. Habitat preferences were determined for each species and for three variables: seagrass cover (none, seagrass patches, dense seagrass); substrate (sand, mud, mixed sediment) and water depth (<2m, 2-4m, >4m). Differences in occupation (abundance of individuals in each type of habitat) were also tested for the three variables. Given the differences in the area sampled by each gear, density values calculated were standardized by area.

samplE ChaRaCtERIstICs A total of 3120 individuals belonging to the six Syngnathidae species were used to estimate habitat preference and occupation in Ria Formosa. The Broad-nosed pipefish (S. typhle) was the most abundant Syngnathidae during

this period (Fig. 3) with an average density of 13 fish/1000m2. For all species analysed, the majority of the specimens collected were either pre-adult or adult fish(Fig. 4).

habItat pREFEREnCE anD OCCupatIOn Both Hippocampus species did not show preferences or significant differences in occupation over the vegetation cover (Fig. 5), but demonstrated a slight preference for mud bottoms and moderate depths (2 to 4m). Syngnathus species and N. ophidion preferred vegetated areas and shallower depths (<2 m), occurring here in higher abundances. Among these latter species different substrate preferences were noted. While N. ophidion and S. typhle were more abundant over mixed sediment, S. abaster showed a minor preference for sand and S. acus for mud.

0 2 4 6 8 10 12 14 16 18

Hippocampus guttulatus

Hippocampus hippocampus

Nerophis ophidion

Syngnathus abaster

Syngnathus acus

Syngnathus typhle

Density (individuals/1000m2)

Figure 3. Mean density of fish (individuals/1000m2) estimated for the six Syngnathidae in the sampled area during the study period (error bars represent 95% Confidence Interval of mean).

Figure 2. The study area and the location of the sampling stations according to the sampling gear used.

Figure 4. Per cent frequency distribution of total lenght of the six Singnathidae species collected during the study period (dashed red lines represent the lenght at first maturity available in literature).

%

Fish size (cm)

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

Hippocampus guttulatus

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

Nerophis ophidion

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

3 5 7 9 11 13 15 17 19 21 23 25 27 29 >30

Syngnathus acus

Hippocampus hippocampus

Syngnathus abaster

3 5 7 9 11 13 15 17 19 21 23 25 27 29 >30

Syngnathus typhle

%

%

Fish size (cm)

Beach SeineBeam Trawl

Riley’s Pushnet

N

DIsCussIOn In general, both Hippocampus species had similar preferences in bottom type and depth of the habitat, but showed no preference regarding vegetation cover. The prehensile tail of this genus allows them to explore different habitats besides submerged seagrass, as long as holdfasts are available, such as submerged branches, sessile fauna (e.g. tunicates, briozoans or sponges) or coraligenous algae. N. ophidion and S. typhle preferences for habitat were almost identical and their habitats probably overlap. However, different life strategies may allow them to share the same space. In laboratory experiments Malavasi et al. (2007) noticed that N. ophidion spends most of the time at the lower portion of the seagrass leaves while S. typhle prefers the intermediate and canopy portion. These microhabitat choices are highly related to the feeding strategy of both species. S. abaster showed a preference for shallow,

vegetated sand habitats. Despite the higher preference for dense seagrass, this species had a higher mean density over patchy vegetation where the remaining species were almost absent. This might be a strategy to avoid competition for resources with other Synganthidae. S. acus is the larger species of the Family occurring in Ria Formosa and probably the most mobile, often found in adjacent coastal waters at greater depths. Nevertheless this species also showed a minor preference for dense seagrass at medium and shallow depths over mud bottoms. S. abaster, S. typhle and N. ophidion were apparentely more selective in the habitat and depended more on submerged vegetation than the other Syngnathidae in Ria Formosa. Habitat preferences may also vary according to ontogeny or season, because of different requirements such as type of prey availability or breeding activity.

Figure 5. Ivlev’s electivity Index (D) of the six Syngnathidae species (Black columns) and their respective mean densities (Grey columns; error bars represent 95% Confidence Interval of mean; P values for Kruskal–Wallis one way ANOVA on ranks) according to the habitat variables studied.

D of 0 indicates that habitat is used in proportion to its availability, >0 that habitat is used more than expected relative to its availability (preference) and <0 that habitat is used less than expected relative to its availability (avoidance).

-1,0

-0,5

0,0

0,5

1,0 Hippocampus guttulatus

0

20

40

60

-1,0

-0,5

0,0

0,5

1,0 Hippocampus hippocampus

0

20

40

60

-1,0

-0,5

0,0

0,5

1,0 Nerophis ophidion

0

20

40

60

-1,0

-0,5

0,0

0,5

1,0 Syngnathus abaster

0

20

40

60

-1,0

-0,5

0,0

0,5

1,0 Syngnathus acus

0

20

40

60

-1,0

-0,5

0,0

0,5

1,0

None Patch Dense Mixed Mud Sand <2m 2-4m >4m

Vegetation Bottom Depth

Syngnathus typhle

0

20

40

60

None Patch Dense Mixed Mud Sand <2m 2-4m >4m

Vegetation Bottom Depth

D

Dens

ity (i

ndiv

idua

ls/1

000m

2 )

P=0.553 P<0.001 P<0.001

P=0.657 P<0.001 P=0.004

P<0.001 P<0.001 P<0.001

P<0.001 P=0.002 P<0.001

P<0.001 P<0.001 P=0.007

P<0.001 P<0.001 P<0.001

Figure 1. Canals, mud flats and shallow marsh streams are some of the tipical habitats of Ria Formosa

References: Malavasi, S. et al. Habitat selection and spatial segregation in three pipefish species. Estuarine, Coastal and Shelf Science 75, 143–150 (2007). Erzini, K. et al. Recruitment of sea breams (Sparidae) and other commercially important species in the Algarve (Southern Portugal). Final Report, DG XIV/C/1, Ref. 99/061, Universidade do Algarve, Faro, 178 p (2002).

FARO

OLHÃO

Acknowledgements: