An exercise in the comparison of pelagic and benthic macrofauna species diversity

Monika Kedra, PhD student

Institute of Oceanology PAS, Sopot 81-712, Powstancow Warszawy 55, Poland

Figure 1. Geographical location of investigated areas
Figure 2. Bay of Puck (Photograph: E. Andrulewicz)
Figure 3. Kongsfjorden (Photograph: M. Zajaczkowski)

Introduction

Among the number of biodiversity measures developed in recent years, Taxonomic Distinctness (Warwick & Clarke 1995) was highly recommended by international network BIOMARE (Feral et al. 2003). However there are still only a few examples where this index has been used for biodiversity comparisons. This was highlighted during the discussions at a recent MARBENA workshop, held in Sopot, April 2004. Participants agreed, that species check lists should where possible be made available from all the BIOMARE biodiversity sites on the internet, and from this a number of studies may be developed using this material. This article presents the results of a small exercise to use of Average Taxonomic Distinctness Index (ATDI) for analysing the basic check lists of selected macrofauna taxa, from three very different localities: an Arctic fjord (Kongsfjorden, Svalbard) with a relatively young glacial history, an Antarctic fjord (Admiralty Bay) with millions of years glacial history, and the brackish water of the southern Baltic site which is younger than 10.000 years of age. Data have been provided by IOPAS, the University of Gdansk, and the University of L�dz. Researchers from www.iopan.gda.pl provided data from Kongsfjorden and Puck Bay data and Admiralty Bay data was obtained from the published references of University of L�dz marine biologists. We were especially interested in the introducing the pelagic data into analysis, since so far the biodiversity is largely benthic inclined.

Research areas

Kongsfjorden is located on the west coast of Spitsbergen, in the Svalbard Archipelago at 79 N. An active tidal glacier, which is located at the head of the fjord, has the greatest influence on the environmental conditions. It causes gradients in salinity, temperature and sedimentation rates. The area is under influence of North Atlantic Current (Figure 1).

The Bay of Puck is situated in the inner part of Bay of Gdansk at 54 N. With its shallow sandy sea grass beds, no tides and low salinity (from 3 PSU to 6 PSU) it is considered representative for southern Baltic region (Figure 2).

Admiralty Bay is located on King George Island in South Shetlands Archipelago at 63 S. The size of the bay, presence of the glaciers, salinity, temperature, sedimentation are similar to the Arctic site however there is a high ratio of endemic species caused by hydrological isolation due to the Antarctic convergence (Figure 3).

Pelagic and benthic biodiversity comparison

Biodiversity measures that utilise higher taxa richness and evenness are of great importance (Warwick & Clarke 1995). To assess the species diversity for non-quantitative data (i.e. species lists, presence/absence data) ATDI + was calculated (Clark & Warwick 1998).

Firstly the macrofaunal lists of pelagic and benthic species at the three sites were compared. At Kongsfjorden and Admiralty Bay the number pelagic species is much lower than the number of benthic species; however the ATDI (Figure 2) is not. That suggests that in spite of lower species number, the taxonomic diversity among pelagic species is relatively high. Also striking is the small difference in diversity between both polar areas, the Antarctic was commonly regarded as the very diverse, old evolutionary, centre of species richness (Knox & Lowry 1977). For the Bay of Puck the index is also quite close to the species rich polar areas (Figure 4).

The same analyses were made for selected taxa. The biodiversity of benthic Mollusca and Polychaeta, measured with ATDI, was much higher than the pelagic diversity for these groups. For Crustacea the + index was similar in all cases but the Bay of Puck. The results for Amphipoda are presented in Figure 5 and even though the species number is much higher in the benthos the diversity is not, especially in case of Admiralty Bay. In Bay of Puck only one species of Amphipoda is observed in plankton.

Figure 4. Average Taxonomic Distinctness Index calculated for species recorded in Kongsfjorden, Bay of Puck and Admiralty Bay.

Figure 5. Average Taxonomic Distinctness Index calculated for Amphipoda species recorded in Kongsfjorden, Bay of Puck and Admiralty Bay

This exercise shows that the application of ATDI for the large scale comparisons (gamma diversity) of very different sites is useful but may need further research. The species rich (over 500 taxa) Antarctic site was classified as very similar to the Baltic brackish water temperate site of low species richness (approx. 50 species). However it is still likely that ATDI will serve well in comparisons of beta - diversity - among sites of the same area.