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. 2024 May 16;14(1):11203.
doi: 10.1038/s41598-024-62012-3.

Seasonal fish larvae abundance and composition in seagrass habitats of coastal East Africa

Noah Ngisiange  1   2 , Barnabas Tarimo  3 , Lillian Daudi  4 , Stephen Mwangi  4 , Fadhili Malesa  5 , Rushingisha George  6 , Margareth S Kyewalyanga  3 , Martin Gullström  7 , Melckzedeck Osore  4 , James Mwaluma  4 , Monika Winder  8
Affiliations

Seasonal fish larvae abundance and composition in seagrass habitats of coastal East Africa

Noah Ngisiange et al. Sci Rep. .

Abstract

Seagrass habitats play a major role in fisheries productivity through nursery functions and feeding grounds for diverse fish species. However, little is known about the seasonal distribution of fish larvae at large spatial scales in coastal East Africa. We investigated drivers of the seasonal fish larvae abundance and composition in seagrass habitats in Kenya and Tanzania. We found a high diversity of fish larvae (54 families) inhabiting seagrass habitats that differed between sites and seasons. Fish larvae abundance were highest in Kenya, particularly during the northeast monsoon season. Overall, total larval abundances per site were low, reaching less than 190 individuals/100 m3 in Kenya and less than 40 individuals/100 m3 in Tanzania, likely related to the low productivity and strong hydrodynamic processes in this region. Our data suggests that most of the fish spawn year-round in these tropical waters as we did not find strong seasonal patterns. All sites had a high relative abundance of larvae from demersal spawning fishes, indicating that many fish species move to coastal sites for spawning. Primary productivity and dissolved oxygen, driven by hydrodynamics conditions are positively related to fish larvae productivity both in Kenya and Tanzania. These findings indicate that the occurrence of both resident and transient fish larvae in seagrass meadows is driven by strong hydrodynamic and tidal processes that transport fish larvae across adjacent habitats.

Keywords: Abundance; Coastal East Africa; Community composition; Fish larvae; Seagrass habitat; Seasonality.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Map of the sampling area and dominating oceanic currents. The insert plot shows the study area along the East African coast and symbols the sampling locations. Sampling sites in Kenya are Watamu and Diani, and in Tanzania Tanga (mainland) and Zanzibar Island (Unguja, herein referred to as Zanzibar). Arrows indicate the dominating flow of the currents between different seasons i.e. SEM and NEM, i.e. the Somali Current (SC), South Equatorial Counter Current (SECC) and East African Coastal Current (EACC). The map was developed and generated using ArcGIS Desktop version 10.5.
Figure 2
Figure 2
Seagrass species cover. Mean percentage cover of the seagrass species at each sampling site across the two monsoon seasons.
Figure 3
Figure 3
Fish larvae abundance. Abundance of (A) total fish larvae and (B) mean by familyacross the four study sites during the two monsoon seasons. Families that contributed > 2% of the total abundance are included. NEM = northeast monsoon, SEM = southeast monsoon.
Figure 4
Figure 4
Abundance of fish larvae families. Bubble plots showing the mean abundance of fish larvae families for each sampling site over the season. NEM = northeast monsoon, SEM = southeast monsoon.
Figure 5
Figure 5
Non-parametric multidimensional scaling (nMDS) ordination of community composition of fish larvae families. Community composition across (A) season and (B) sites recorded over the entire sampling period. The stress value is 0.21. NEM = northeast monsoon, SEM = southeast monsoon.
Figure 6
Figure 6
Fish larvae development stage and spawning mode. Percentage of fish larvae (A) developmental stage and adult (B) spawning mode in the different sampling sites during the NEM (northeast monsoon) and SEM (southeast monsoon) seasons.
Figure 7
Figure 7
Fish larvae size. Distribution of fish larvae size at the different sampling sites during the NEM (northeast monsoon) and SEM (southeast monsoon) seasons.
Figure 8
Figure 8
Environmental variables recorded at all sampling sites over the season. The measured environmental variables include Northward current velocity (Nvel), Eastward current velocity (Evel), sea surface temperature (SST), salinity, pH, dissolved oxygen (DO) and chlorophyll a (chl a).
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